Reply
 
Thread Tools Display Modes
  #1   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay.
Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem.
Customer took the unit to a tech who carried out the mod as described in an email from the company.
Only now the unit is something like 12dB down in level than before.

I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct.

Original Pultec schematic he
http://www.gyraf.dk/gy_pd/pultec/pultech.gif


The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary.

The pultec schematic shows a 1k resistor in series with a capacitor on the output, the unit is question has a factory fitted 2k2 resistor across the output, but no cap.

I am not having much joy from the company on this matter, but it seems to me that putting 100 ohms across the output transformer is going to reduce the output level rather drastically.
This transformer is directly connected to pins 2 & 3 of the output XLR, so essentialy there is 100 ohms across pins 2 & 3.
Transformer secondary measures 113 ohms DC disconnected.

I have been trying to suggest that either this 100 ohms is incorrect, or the 100 ohms in parallel with the 0.1uF capacitor is not intended to be put across the output, but should in fact be installed somewhere else.
Maybe on the grounding circuit to prevent the motorboating under certain conditions I can't create on the bench.


Any thoughts on this? I'm getting rather frustrated.


Cheers.



  #2   Report Post  
Posted to rec.audio.pro
Don Pearce[_3_] Don Pearce[_3_] is offline
external usenet poster
 
Posts: 2,417
Default Pultec EQP clone problem

On Tue, 2 Feb 2021 13:42:49 -0800 (PST), gareth magennis
wrote:

Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay.
Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem.
Customer took the unit to a tech who carried out the mod as described in an email from the company.
Only now the unit is something like 12dB down in level than before.

I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct.

Original Pultec schematic he
http://www.gyraf.dk/gy_pd/pultec/pultech.gif


The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary.

The pultec schematic shows a 1k resistor in series with a capacitor on the output, the unit is question has a factory fitted 2k2 resistor across the output, but no cap.

I am not having much joy from the company on this matter, but it seems to me that putting 100 ohms across the output transformer is going to reduce the output level rather drastically.
This transformer is directly connected to pins 2 & 3 of the output XLR, so essentialy there is 100 ohms across pins 2 & 3.
Transformer secondary measures 113 ohms DC disconnected.

I have been trying to suggest that either this 100 ohms is incorrect, or the 100 ohms in parallel with the 0.1uF capacitor is not intended to be put across the output, but should in fact be installed somewhere else.
Maybe on the grounding circuit to prevent the motorboating under certain conditions I can't create on the bench.


Any thoughts on this? I'm getting rather frustrated.


Cheers.


Motor boating is normally caused by taking negative feedback from the
secondary of the output transformer. It is the low frequency phase
shift as the transformer runs out of puff that causes it. But this
circuit appears to have no feedback of any kind so it is hard to see
what could motorboat. They already have a Zobel network on the output
to keep things tame at the top end.

If you are losing 12dB when you add the 100 ohms, this thing has a
seriously high output impedance (caused by the lack of feedback). I
think the approach here is to see how high a resistor value you can
get away with before motorboating starts. Then perhaps drop that by
one value and stick with that. Valves are very variable, so it is very
unlikely that every unit will need so drastic a fix as 100 ohms.

d

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

  #3   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Tuesday, 2 February 2021 at 22:01:06 UTC, Don Pearce wrote:
On Tue, 2 Feb 2021 13:42:49 -0800 (PST), gareth magennis
wrote:

Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay.
Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem.
Customer took the unit to a tech who carried out the mod as described in an email from the company.
Only now the unit is something like 12dB down in level than before.

I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct.

Original Pultec schematic he
http://www.gyraf.dk/gy_pd/pultec/pultech.gif


The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary.

The pultec schematic shows a 1k resistor in series with a capacitor on the output, the unit is question has a factory fitted 2k2 resistor across the output, but no cap.

I am not having much joy from the company on this matter, but it seems to me that putting 100 ohms across the output transformer is going to reduce the output level rather drastically.
This transformer is directly connected to pins 2 & 3 of the output XLR, so essentialy there is 100 ohms across pins 2 & 3.
Transformer secondary measures 113 ohms DC disconnected.

I have been trying to suggest that either this 100 ohms is incorrect, or the 100 ohms in parallel with the 0.1uF capacitor is not intended to be put across the output, but should in fact be installed somewhere else.
Maybe on the grounding circuit to prevent the motorboating under certain conditions I can't create on the bench.


Any thoughts on this? I'm getting rather frustrated.


Cheers.


Motor boating is normally caused by taking negative feedback from the
secondary of the output transformer. It is the low frequency phase
shift as the transformer runs out of puff that causes it. But this
circuit appears to have no feedback of any kind so it is hard to see
what could motorboat. They already have a Zobel network on the output
to keep things tame at the top end.

If you are losing 12dB when you add the 100 ohms, this thing has a
seriously high output impedance (caused by the lack of feedback). I
think the approach here is to see how high a resistor value you can
get away with before motorboating starts. Then perhaps drop that by
one value and stick with that. Valves are very variable, so it is very
unlikely that every unit will need so drastic a fix as 100 ohms.

d

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus



Ok, thanks.

I haven't experienced this motorboating because apparently it only happens in certain known production units, and only when connected to a patchbay.
Presumably all those long cables and earth loops are a factor.

I doubt I will be able to make it motorboat on the bench, it appears to be fine.


Also the schematic I posted is of the original Pultec, I don't have the schematic of this clone, which is not exactly the same.
They don't have a zobel network on the output, just a 2k2 resistor across the output, no capacitor.
And obviously they use different transformers so most componet values are going to be different.


I will experiment with different resistor values to see when things start to go bad.


The problem is, the customer has a pair of these, only one of which exhibited the motorboating, and thus only one had the mod done.
Now he has one unit 12 db lower than the other.
Not good.

  #4   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

gareth magennis wrote:
===================

Any thoughts on this? I'm getting rather frustrated.


** Motorboating in audio stages that do not use NFB is caused by supply rail coupling of imposed signal from the later stages back to the first stage - usually at a sub sonic frequency.

The inter-stage coupling caps are way too large at 270nF - try 22nF instead for each.

This shifts the -3dB point up to to 7 Hz.

Increasing the PSU filter caps - by paralleling with a 47uF - will also help reduce LF coupling.


...... Phil



  #5   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Tuesday, 2 February 2021 at 23:13:16 UTC, wrote:
gareth magennis wrote:
===================

Any thoughts on this? I'm getting rather frustrated.

** Motorboating in audio stages that do not use NFB is caused by supply rail coupling of imposed signal from the later stages back to the first stage - usually at a sub sonic frequency.

The inter-stage coupling caps are way too large at 270nF - try 22nF instead for each.

This shifts the -3dB point up to to 7 Hz.

Increasing the PSU filter caps - by paralleling with a 47uF - will also help reduce LF coupling.


..... Phil




Yes, customer was reporting a "tick" every couple of seconds.


  #6   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Tuesday, 2 February 2021 at 23:15:30 UTC, gareth magennis wrote:
On Tuesday, 2 February 2021 at 23:13:16 UTC, wrote:
gareth magennis wrote:
===================

Any thoughts on this? I'm getting rather frustrated.

** Motorboating in audio stages that do not use NFB is caused by supply rail coupling of imposed signal from the later stages back to the first stage - usually at a sub sonic frequency.

The inter-stage coupling caps are way too large at 270nF - try 22nF instead for each.

This shifts the -3dB point up to to 7 Hz.

Increasing the PSU filter caps - by paralleling with a 47uF - will also help reduce LF coupling.


..... Phil

Yes, customer was reporting a "tick" every couple of seconds.



How can I force this motorboating to happen on my bench, so I can deal with it?
I've not seen it yet.





  #7   Report Post  
Posted to rec.audio.pro
Mike Rivers[_2_] Mike Rivers[_2_] is offline
external usenet poster
 
Posts: 2,190
Default Pultec EQP clone problem

On 2/2/2021 6:35 PM, gareth magennis wrote:
How can I force this motorboating to happen on my bench, so I can deal with it?
I've not seen it yet.


If it only happens when connected to a patchbay, it's likely due to the
cable capacitance hanging across the output.

You should ask the owner with the problem a couple of questions:

1. How long are the cables between the EQ and the patchbay? If it's
going to a normalled jack, add the length of the cable between the
normalled jack of the pair to wherever it goes.

2. If it's going to a normalled jack, what's that jack going to?

or

Does it motorboat if the normalled connection is broken (stick a cable
in the "destination" patchbay jack)

You could experiment with loading the output with a capacitor. Start
with 500 pF and go up in value to about 0.01 uF to see if you can make
it take off.

I agree than 100 ohms sounds like a pretty hefty load, but you can see
what the source impedance really is by putting in a tone and measuring
the open circuit voltage at the output. Then hang resistance across it
until the voltage drops in half (6 dB if you're using a meter calibrated
in dB). The resistance value that gives you the 6 dB drop will be
representative of the output impedance of the unit.



--
For a good time, call http://mikeriversaudio.wordpress.com
  #8   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

gareth magennis is soooo annoying :

==============================
Any thoughts on this? I'm getting rather frustrated.


** The feeling is mutual - pal.


** Motorboating in audio stages that do not use NFB is caused by supply rail coupling of imposed signal from the later stages back to the first stage - usually at a sub sonic frequency.


Yes, customer was reporting a "tick" every couple of seconds.


** How the hell is a tick = sub sonic oscillation?

The term "motor-boating" is kinda obvious.
Got any idea what "hiss", "hum" and buzz" actually sound like ?
Know why they have those names ?


....... Phil
  #9   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

gareth magennis is super annoying :

=========================

How can I force this motorboating to happen on my bench, so I can deal with it?
I've not seen it yet.



** FFS !!!

How will you ever know if you have fixed it ?????

Rule one of troubleshooting: " Observe the Fault "



...... Phil
  #10   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Wednesday, 3 February 2021 at 01:48:00 UTC, wrote:
gareth magennis is super annoying :

=========================

How can I force this motorboating to happen on my bench, so I can deal with it?
I've not seen it yet.

** FFS !!!

How will you ever know if you have fixed it ?????

Rule one of troubleshooting: " Observe the Fault "



..... Phil





Ok, I think I may have got to the bottom of this.

I found this, which I believe is the issue and its solution.
https://www.gearslutz.com/board/so-m...fications.html


There, it states the mod is a 25pf in series with 100 ohms, which makes much more sense.
I fitted it and, of course, it doesn't drop the level by 12dB.

I did measure things before finding this, and the output inpedence of the circuit is around 360 ohms, in the method described by Mike.
Thanks MIke.
I also tried to measure the low frequency rolloff, which was way below 10 Hz.
Thanks, Phil.

Maybe there never was any "motorboating", this notion came from the customer in his email to the company.
I never found any, despite adding caps on the output like Mike suggested.



  #11   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

gareth magennis wrote:

===================


Maybe there never was any "motorboating", this notion came from the customer in his email to the company.


** So you OP here was an entire pile of bull crap.

I never found any, despite adding caps on the output like Mike suggested.


** So what the **** were you trying to *fix* ?????

Dear Mr Magennis,

your total lack of insight & professionalism is appalling.
If I were your employer, I would hand you broom and tell you sweep the floor.


......... Phil
  #12   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Wednesday, 3 February 2021 at 12:06:07 UTC, wrote:
gareth magennis wrote:

===================


Maybe there never was any "motorboating", this notion came from the customer in his email to the company.

** So you OP here was an entire pile of bull crap.
I never found any, despite adding caps on the output like Mike suggested.

** So what the **** were you trying to *fix* ?????

Dear Mr Magennis,

your total lack of insight & professionalism is appalling.
If I were your employer, I would hand you broom and tell you sweep the floor.


........ Phil



I think it is obvious I fixed an incorrect modification instruction from the company.

I felt strongly enough that this instruction was just not right, that I felt the need to post my concerns here, where I might get some vaulable insight into whether these concerns bore any weight, or perhaps I was missing something.

As usual, it turned out worthwhile.

Both Don and yourself explained the motorboating phenomenon in a system without negative feedback.
Thanks, that is valuable education indeed, and I appreciate that.

It doesn't really matter that the alleged motorboating may have turned out to be a red herring, I think we all learned something from that.
I said from the outset I was unable to recreate it, it was reported as such by the customer.



My only concern now is that I return the unit to the customer with the proper mod in place, to find it really does have a motorboating problem I can't recreate on the bench, as the mod actually seems to be a low pass filter to stop hf oscillations, not to stop a motorboating issue.







  #13   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

gareth magennis wrote a pile of self serving drivel:

===========================================
My only concern now is that I return the unit to the customer with the proper mod in place,


** Which does next to nothing.

to find it really does have a motorboating problem I can't recreate on the bench,


** There is another way a piece of audio gear can be made to " motor boat " at a low frequency.

You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level.

Bet your dopey customer has done that by missconnecting the patch bay.

Try it and see if what YOU get matches with their story.


...... Phil










  #14   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Wednesday, 3 February 2021 at 22:36:33 UTC, wrote:
gareth magennis wrote a pile of self serving drivel:

===========================================
My only concern now is that I return the unit to the customer with the proper mod in place,

** Which does next to nothing.
to find it really does have a motorboating problem I can't recreate on the bench,

** There is another way a piece of audio gear can be made to " motor boat " at a low frequency.

You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level.

Bet your dopey customer has done that by missconnecting the patch bay.

Try it and see if what YOU get matches with their story.


..... Phil





Funny, that's what I just said, but in a different language.
  #15   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Wednesday, 3 February 2021 at 23:09:36 UTC, gareth magennis wrote:
On Wednesday, 3 February 2021 at 22:36:33 UTC, wrote:
gareth magennis wrote a pile of self serving drivel:

===========================================
My only concern now is that I return the unit to the customer with the proper mod in place,

** Which does next to nothing.
to find it really does have a motorboating problem I can't recreate on the bench,

** There is another way a piece of audio gear can be made to " motor boat " at a low frequency.

You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level.

Bet your dopey customer has done that by missconnecting the patch bay.

Try it and see if what YOU get matches with their story.


..... Phil

Funny, that's what I just said, but in a different language.



I think we are actually on the same page here.




  #16   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

gareth magennis is a massive narcissist :

------------------------------------------------------------------------
You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level.

Bet your dopey customer has done that by missconnecting the patch bay.

Try it and see if what YOU get matches with their story.


Funny, that's what I just said, but in a different language.



** You said *nothing of the sort* - you pathetic bull**** artist.

Got a broom handy - know how to use it?

....... Phil
  #17   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Wednesday, 3 February 2021 at 23:20:53 UTC, wrote:
gareth magennis is a massive narcissist :

------------------------------------------------------------------------
You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level.

Bet your dopey customer has done that by missconnecting the patch bay.

Try it and see if what YOU get matches with their story.


Funny, that's what I just said, but in a different language.

** You said *nothing of the sort* - you pathetic bull**** artist.

Got a broom handy - know how to use it?

...... Phil




Oh well, I tried.




  #18   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

gareth magennis wrote:

=====================

------------------------------------------------------------------------
You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level.

Bet your dopey customer has done that by missconnecting the patch bay.

Try it and see if what YOU get matches with their story.


Funny, that's what I just said, but in a different language.


** You said *nothing of the sort* - you pathetic bull**** artist.

Got a broom handy - know how to use it?


Oh well, I tried.


** ROTFL !!!!

The only thing this tedious prick " tried " was to bull**** his way out of admitting his massive incompetency.




...... Phil




  #19   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Thursday, 4 February 2021 at 00:21:30 UTC, wrote:
gareth magennis wrote:

=====================

------------------------------------------------------------------------
You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level.

Bet your dopey customer has done that by missconnecting the patch bay.

Try it and see if what YOU get matches with their story.


Funny, that's what I just said, but in a different language.

** You said *nothing of the sort* - you pathetic bull**** artist.

Got a broom handy - know how to use it?


Oh well, I tried.


** ROTFL !!!!

The only thing this tedious prick " tried " was to bull**** his way out of admitting his massive incompetency.




..... Phil



OK, briefly,

I talked at length to the customer today.
His experience of this "motorboating" was an oscillation around 90 Hz.

I had an email converation with the company today.
They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay.
They designed this mod to combat this occasional 90Hz problem, and made circuit revisions thereafter.

I was incorrect in assuming this mod was to guard against HF oscillations.



If you refer back to the Gearslutz thread I referred to, you will find this problem described thus:

2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables.

link to thread again he
https://www.gearslutz.com/board/so-m...fications.html
  #20   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Thursday, 4 February 2021 at 23:17:09 UTC, gareth magennis wrote:
On Thursday, 4 February 2021 at 00:21:30 UTC, wrote:
gareth magennis wrote:

=====================

------------------------------------------------------------------------
You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level.

Bet your dopey customer has done that by missconnecting the patch bay.

Try it and see if what YOU get matches with their story.


Funny, that's what I just said, but in a different language.

** You said *nothing of the sort* - you pathetic bull**** artist.

Got a broom handy - know how to use it?


Oh well, I tried.


** ROTFL !!!!

The only thing this tedious prick " tried " was to bull**** his way out of admitting his massive incompetency.




..... Phil

OK, briefly,

I talked at length to the customer today.
His experience of this "motorboating" was an oscillation around 90 Hz.

I had an email converation with the company today.
They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay.
They designed this mod to combat this occasional 90Hz problem, and made circuit revisions thereafter.

I was incorrect in assuming this mod was to guard against HF oscillations.



If you refer back to the Gearslutz thread I referred to, you will find this problem described thus:

2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables.

link to thread again he
https://www.gearslutz.com/board/so-m...fications.html



I haven't been able to experience this problem, but it is starting to look like it is not a full blown oscillation at full volume, but rather some background noise problem, where a 90Hz tone gets added to the audio.
Dunno, this is work in progress I guess.


  #21   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

gareth magennis is a total IDIOT wrote:

==================================

** You said *nothing of the sort* - you pathetic bull**** artist.

Got a broom handy - know how to use it?


Oh well, I tried.


** ROTFL !!!!

The only thing this tedious prick " tried " was to bull**** his way out of admitting his massive incompetency.


OK, briefly,

I talked at length to the customer today.
His experience of this "motorboating" was an oscillation around 90 Hz.


** Jesus ****ing Christ - STOP using the wrong names for things. !!

Does a motorboat sound like a 90 Hz tone to you ???


I had an email converation with the company today.
They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay.


** Absolute ******** !!!


I was incorrect in assuming this mod was to guard against HF oscillations.


** That may be the one thing you got correct.


2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables.


** So it is now a "buzz" - not a motorboat sound.

Sounds *hell of a lot* like " parasitic oscillations " which can be discontinuous.

If so, despite being in the supersonic range may generate an audible buzz at some rate.

FFS leave audio alone, your broom awaits.


....... Phil

  #22   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Thursday, 4 February 2021 at 23:29:41 UTC, wrote:
gareth magennis is a total IDIOT wrote:

==================================

** You said *nothing of the sort* - you pathetic bull**** artist.

Got a broom handy - know how to use it?


Oh well, I tried.

** ROTFL !!!!

The only thing this tedious prick " tried " was to bull**** his way out of admitting his massive incompetency.


OK, briefly,

I talked at length to the customer today.
His experience of this "motorboating" was an oscillation around 90 Hz.

** Jesus ****ing Christ - STOP using the wrong names for things. !!

Does a motorboat sound like a 90 Hz tone to you ???
I had an email converation with the company today.
They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay.

** Absolute ******** !!!
I was incorrect in assuming this mod was to guard against HF oscillations.

** That may be the one thing you got correct.
2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables.

** So it is now a "buzz" - not a motorboat sound.

Sounds *hell of a lot* like " parasitic oscillations " which can be discontinuous.

If so, despite being in the supersonic range may generate an audible buzz at some rate.

FFS leave audio alone, your broom awaits.


...... Phil



Phil,
read this carefully, this is what I said.

I talked at length to the customer today.
His experience of this "motorboating" was an oscillation around 90 Hz.



Do you see the quote marks around motorboating?

I haven't experienced any such oscillations, all I have done is to quote the customer who has claimed "motorboating".

Today I learned that this "motorboating" he experienced was in fact a 90 Hz oscillation.


Your reply to this information was:


** Jesus ****ing Christ - STOP using the wrong names for things. !!

Does a motorboat sound like a 90 Hz tone to you ???



Arguing semantics here is not very helpful, is it.
I know you're better than that.
  #23   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem


**** off Nut Case TROLL !!

=====================
I talked at length to the customer today.
His experience of this "motorboating" was an oscillation around 90 Hz.

** Jesus ****ing Christ - STOP using the wrong names for things. !!

Does a motorboat sound like a 90 Hz tone to you ???
I had an email converation with the company today.
They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay.

** Absolute ******** !!!
I was incorrect in assuming this mod was to guard against HF oscillations.

** That may be the one thing you got correct.
2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables.

** So it is now a "buzz" - not a motorboat sound.

Sounds *hell of a lot* like " parasitic oscillations " which can be discontinuous.

If so, despite being in the supersonic range may generate an audible buzz at some rate.

FFS leave audio alone, your broom awaits.

il
Phil,
read this carefully, this is what I said.


** Get ****ed you smug pile of ****.


Do you see the quote marks around motorboating?



** Means nothing to me.

Cos a customer uses a totally wrong name does not excuse you doing it.

So far, YOU have NOT ONCE used the right name !!!!!!!!!!!!!!!!!!!!!!!!!!!!!


I haven't experienced any such oscillations, all I have done is to quote the customer who has claimed "motorboating".


** Quoting bull**** on usenet is not a good idea - ****head.

Why did you *never* ask them to *explain* what the noise sounded like ???

Because you are an ASD ****ed idiot - that's why.


** Jesus ****ing Christ - STOP using the wrong names for things. !!

Does a motorboat sound like a 90 Hz tone to you ???


Arguing semantics here is not very helpful,


** This has not one tiny thing to do with ****ing "semantics" !!!!!!!!!

Get a BIG dictionary and shove it you your stupid fat arse !!!


....... Phil
  #24   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Friday, 5 February 2021 at 00:19:50 UTC, wrote:
**** off Nut Case TROLL !!

=====================
I talked at length to the customer today.
His experience of this "motorboating" was an oscillation around 90 Hz.

** Jesus ****ing Christ - STOP using the wrong names for things. !!

Does a motorboat sound like a 90 Hz tone to you ???
I had an email converation with the company today.
They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay.
** Absolute ******** !!!
I was incorrect in assuming this mod was to guard against HF oscillations.
** That may be the one thing you got correct.
2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables.
** So it is now a "buzz" - not a motorboat sound.

Sounds *hell of a lot* like " parasitic oscillations " which can be discontinuous.

If so, despite being in the supersonic range may generate an audible buzz at some rate.

FFS leave audio alone, your broom awaits.

il
Phil,
read this carefully, this is what I said.

** Get ****ed you smug pile of ****.
Do you see the quote marks around motorboating?

** Means nothing to me.

Cos a customer uses a totally wrong name does not excuse you doing it.

So far, YOU have NOT ONCE used the right name !!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I haven't experienced any such oscillations, all I have done is to quote the customer who has claimed "motorboating".

** Quoting bull**** on usenet is not a good idea - ****head.

Why did you *never* ask them to *explain* what the noise sounded like ???

Because you are an ASD ****ed idiot - that's why.
** Jesus ****ing Christ - STOP using the wrong names for things. !!

Does a motorboat sound like a 90 Hz tone to you ???


Arguing semantics here is not very helpful,

** This has not one tiny thing to do with ****ing "semantics" !!!!!!!!!

Get a BIG dictionary and shove it you your stupid fat arse !!!


...... Phil




Here's a thought.

90Hz equates to 5400 rpm.

That sounds like a small outboard motor to me.


Night.
  #25   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

gareth magennis ned shooting :
------------------------------------------

** This has not one tiny thing to do with ****ing "semantics" !!!!!!!!!

Get a BIG dictionary and shove it you your stupid fat arse !!!


...... Phil



Here's a thought.


** You do not have any cos you' re a mental retard.



90Hz equates to 5400 rpm.

That sounds like a small outboard motor to me.



** But the sound is ****ing BUZZ not a tone of any kind !!!!!

FOAD moron.


..... Phil




  #26   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Friday, 5 February 2021 at 01:30:29 UTC, wrote:
gareth magennis ned shooting :
------------------------------------------
** This has not one tiny thing to do with ****ing "semantics" !!!!!!!!!

Get a BIG dictionary and shove it you your stupid fat arse !!!


...... Phil



Here's a thought.

** You do not have any cos you' re a mental retard.
90Hz equates to 5400 rpm.

That sounds like a small outboard motor to me.

** But the sound is ****ing BUZZ not a tone of any kind !!!!!

FOAD moron.


..... Phil




Phil,

the original problem was putting a 100 ohm resistor across the output transformer and dropping the output level by 12 db.

Remember that?


I don't remember any input from you to indicate this might actually be something of concern.
  #27   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

gareth magennis total **** wrote:

==========================

** You have a very punchable face.

What out what I can do to you on SED.


....... Phil


  #28   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Saturday, 6 February 2021 at 00:23:40 UTC, wrote:
gareth magennis total **** wrote:

==========================

** You have a very punchable face.

What out what I can do to you on SED.


...... Phil



Is that a threat?
  #29   Report Post  
Posted to rec.audio.pro
Scott Dorsey Scott Dorsey is offline
external usenet poster
 
Posts: 16,853
Default Pultec EQP clone problem

gareth magennis wrote:
Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay.
Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem.
Customer took the unit to a tech who carried out the mod as described in an email from the company.
Only now the unit is something like 12dB down in level than before.

I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct.

Original Pultec schematic he
http://www.gyraf.dk/gy_pd/pultec/pultech.gif


The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary.


You sure they aren't in series? If they were in series, that would sound like
a normal zobel network designed to keep the transformer from ringing or to add
a stabilization pole for something else. In parallel they would just swamp
the transformer which is designed for a 600 ohm load.

I bet, given the description, that the thing works perfectly fine with a
600 ohm load, and only motorboats when connected to modern high-z
transformerless inputs. I bet the transformer sounds better with the
600 ohm load too. The Pultec design is intended for a 600 ohm load.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #30   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Thursday, 11 February 2021 at 12:53:54 UTC, Scott Dorsey wrote:
gareth magennis wrote:
Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay.
Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem.
Customer took the unit to a tech who carried out the mod as described in an email from the company.
Only now the unit is something like 12dB down in level than before.

I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct.

Original Pultec schematic he
http://www.gyraf.dk/gy_pd/pultec/pultech.gif


The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary.


You sure they aren't in series? If they were in series, that would sound like
a normal zobel network designed to keep the transformer from ringing or to add
a stabilization pole for something else. In parallel they would just swamp
the transformer which is designed for a 600 ohm load.

I bet, given the description, that the thing works perfectly fine with a
600 ohm load, and only motorboats when connected to modern high-z
transformerless inputs. I bet the transformer sounds better with the
600 ohm load too. The Pultec design is intended for a 600 ohm load.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."



One of the first things I did was to try them in series, in case this was the error.
This produced a significant rolloff at 10 KHz, so I guessed that wasn't the error.

The Gearslutz post says 100 Ohms in series with 25pf, which I thought made a lot more sense.
I'm reluctant to accept that without comfirmation from the company, though, which I still haven't received.

Is that a typo? should it be 22pF, or even 22nF? I struggled to find a 25pF cap.
Hence my reluctance.


  #31   Report Post  
Posted to rec.audio.pro
Scott Dorsey Scott Dorsey is offline
external usenet poster
 
Posts: 16,853
Default Pultec EQP clone problem

gareth magennis wrote:
The Gearslutz post says 100 Ohms in series with 25pf, which I thought made a lot more sense.
I'm reluctant to accept that without comfirmation from the company, though, which I still haven't received.

Is that a typo? should it be 22pF, or even 22nF? I struggled to find a 25pF cap.
Hence my reluctance.


Put a 1 KHz square wave through. Does it look nice and square at the output or
does it ring?

Mild ringing: http://www.panix.com/~kludge/xformers/DSC00263.JPG

Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG

If you add a 600 ohm termination resistor (which everybody should be using
running a Pultec into a modern output anyway) does it get better or worse?

If the square wave looks good, things are good.

You can use the calibration output from a Tek scope as a 1kc square wave
generator. It's convenient and comes free with the scope.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #32   Report Post  
Posted to rec.audio.pro
gray_wolf gray_wolf is offline
external usenet poster
 
Posts: 38
Default Pultec EQP clone problem

On 25/02/2021 7:01 pm, Scott Dorsey wrote:
gareth magennis wrote:
The Gearslutz post says 100 Ohms in series with 25pf, which I thought made a lot more sense.
I'm reluctant to accept that without comfirmation from the company, though, which I still haven't received.

Is that a typo? should it be 22pF, or even 22nF? I struggled to find a 25pF cap.
Hence my reluctance.


Put a 1 KHz square wave through. Does it look nice and square at the output or
does it ring?

Mild ringing: http://www.panix.com/~kludge/xformers/DSC00263.JPG

Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG

If you add a 600 ohm termination resistor (which everybody should be using
running a Pultec into a modern output anyway) does it get better or worse?

If the square wave looks good, things are good.

You can use the calibration output from a Tek scope as a 1kc square wave
generator. It's convenient and comes free with the scope.
--scott


Any idea what the catastrophic ringing harmonics would look like on a spectrum
analyzer.
  #33   Report Post  
Posted to rec.audio.pro
Don Pearce[_3_] Don Pearce[_3_] is offline
external usenet poster
 
Posts: 2,417
Default Pultec EQP clone problem

On Fri, 26 Feb 2021 02:29:37 -0600, gray_wolf
wrote:

On 25/02/2021 7:01 pm, Scott Dorsey wrote:
gareth magennis wrote:
The Gearslutz post says 100 Ohms in series with 25pf, which I thought made a lot more sense.
I'm reluctant to accept that without comfirmation from the company, though, which I still haven't received.

Is that a typo? should it be 22pF, or even 22nF? I struggled to find a 25pF cap.
Hence my reluctance.


Put a 1 KHz square wave through. Does it look nice and square at the output or
does it ring?

Mild ringing: http://www.panix.com/~kludge/xformers/DSC00263.JPG

Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG

If you add a 600 ohm termination resistor (which everybody should be using
running a Pultec into a modern output anyway) does it get better or worse?

If the square wave looks good, things are good.

You can use the calibration output from a Tek scope as a 1kc square wave
generator. It's convenient and comes free with the scope.
--scott


Any idea what the catastrophic ringing harmonics would look like on a spectrum
analyzer.


The same is non-catastrophic but bigger. That is just a judgement
call. The way you judge it to be actual ringing is that one harmonic
is much bigger than any other. That is the ringing frequency.

d

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

  #34   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

Don Pearce wrote:

-----------------------------
gray_wolf


Any idea what the catastrophic ringing harmonics would look like on a spectrum
analyzer.


The same is non-catastrophic but bigger. That is just a judgement
call. The way you judge it to be actual ringing is that one harmonic
is much bigger than any other. That is the ringing frequency.


** You sure about "any" ?

Square waves have cascading, odd numbered harmonics.
The ringing one would merely be out of step with the others.

FYI:

I like to test 31 band graphics using just a few square wave frequencies.
40, 300 and 3000Hz for example.
Then move each slider through its full travel and watch the result on my scope.
Malfunction or wiper noise is VERY obvious.


....... Phil

  #35   Report Post  
Posted to rec.audio.pro
Don Pearce[_3_] Don Pearce[_3_] is offline
external usenet poster
 
Posts: 2,417
Default Pultec EQP clone problem

On Fri, 26 Feb 2021 01:57:59 -0800 (PST), "
wrote:

** You sure about "any" ?

Square waves have cascading, odd numbered harmonics.
The ringing one would merely be out of step with the others.


Ringing and how it works was brought home to me when I had to set up a
CNC mill. Part of the setup was automatic, and was for the movement
servos to characterize themselves. When they come to a fast stop, the
heavy stuff attached rings (wobbles), and that has to be prevented. So
the servos use feedback to find the frequency of that ring. Then they
use a convolution algorithm to notch that frequency out of the
transient edge. Result - fast stops and no ringing or oscillation.
In linear systems frequencies can't be created out of nothing. All
frequencies are present in a fast edge, and this is where the energy
for the ring comes from. Remove that frequency from the edge and you
will not see any ringing. Note - this is not the same as harmonics of
the square wave. It is a continuous sinc curve of energy associated
with each edge.
This is super non-intuitive but provided there is no non-linearity, it
works.

d

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus



  #36   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Friday, 26 February 2021 at 13:23:46 UTC, Don Pearce wrote:
On Fri, 26 Feb 2021 01:57:59 -0800 (PST), "
wrote:

** You sure about "any" ?

Square waves have cascading, odd numbered harmonics.
The ringing one would merely be out of step with the others.

Ringing and how it works was brought home to me when I had to set up a
CNC mill. Part of the setup was automatic, and was for the movement
servos to characterize themselves. When they come to a fast stop, the
heavy stuff attached rings (wobbles), and that has to be prevented. So
the servos use feedback to find the frequency of that ring. Then they
use a convolution algorithm to notch that frequency out of the
transient edge. Result - fast stops and no ringing or oscillation.
In linear systems frequencies can't be created out of nothing. All
frequencies are present in a fast edge, and this is where the energy
for the ring comes from. Remove that frequency from the edge and you
will not see any ringing. Note - this is not the same as harmonics of
the square wave. It is a continuous sinc curve of energy associated
with each edge.
This is super non-intuitive but provided there is no non-linearity, it
works.
d

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus




This Pultech clone has "catastophic ringing" with a 1kHz square wave, almost identical to the example posted.

A 600 ohm resistor alone reduces level by almost half, but the ringing remains at the same proportion of the square wave amplitude.
A 100ohm resistor in series with 10nF reduces the catastophing ringing initial spikes hugely, but nowhere near to "mild ringing", and has a slight rolloff on a sine wave at 10 and 20 kHz but not 1kHz.
A 100ohm resistor with 68 nF has way too much hf rolloff, but the ringing is eliminated entirely with a sloping squarewave wavefront showing the hf cut.
A 100 ohm resistor with 4.4nF to 1nF causes full amplitude oscillation, very bad.

The 10nF seems to be the most useful. Anything higher does eventually elliminate the ringing, but with unacceptable rolloff.

Thanks,

Gareth.
  #37   Report Post  
Posted to rec.audio.pro
Scott Dorsey Scott Dorsey is offline
external usenet poster
 
Posts: 16,853
Default Pultec EQP clone problem

gray_wolf wrote:
kludge wrote:

Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG


Any idea what the catastrophic ringing harmonics would look like on a spectrum
analyzer.


They aren't harmonics!

They are the result of parasitic LC networks caused by the series inductance
of the transformer winding and the capacitance between turns. In the case
of simply-wound transformers (like the one in that picture), the result is
one big narrowband resonance somewhere. Any signal anywhere near that
resonance excites it, even the harmonics of the 1kc. And once it gets excited,
it will continue bouncing back and forth at its resonant frequency until
the energy is gone and that capacitor is discharged.

So on a spectrum analyzer that would likely be one single narrow spike.

Now... there are better ways to wind transformers in order to distribute
that across a wider area, so that you get more smaller resonances instead
of one big one. Those can result in multiple smaller spikes.

If the transformer is designed well, the spike is well above the audible
region where it can be eaten by a zobel network.

That severely ringing transformer was designed for communications applications
where having a very high ratio was more important than bandwidth or low
distortion, so that resonance is much more extreme and much lower than anyone
would tolerate for a pro audio transformer. But, this is a 200:80k ohm
transformer.... the fact that it works at all is a miracle.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #38   Report Post  
Posted to rec.audio.pro
gareth magennis gareth magennis is offline
external usenet poster
 
Posts: 73
Default Pultec EQP clone problem

On Friday, 26 February 2021 at 15:45:36 UTC, Scott Dorsey wrote:
gray_wolf wrote:
kludge wrote:

Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG


Any idea what the catastrophic ringing harmonics would look like on a spectrum
analyzer.

They aren't harmonics!

They are the result of parasitic LC networks caused by the series inductance
of the transformer winding and the capacitance between turns. In the case
of simply-wound transformers (like the one in that picture), the result is
one big narrowband resonance somewhere. Any signal anywhere near that
resonance excites it, even the harmonics of the 1kc. And once it gets excited,
it will continue bouncing back and forth at its resonant frequency until
the energy is gone and that capacitor is discharged.

So on a spectrum analyzer that would likely be one single narrow spike.

Now... there are better ways to wind transformers in order to distribute
that across a wider area, so that you get more smaller resonances instead
of one big one. Those can result in multiple smaller spikes.

If the transformer is designed well, the spike is well above the audible
region where it can be eaten by a zobel network.

That severely ringing transformer was designed for communications applications
where having a very high ratio was more important than bandwidth or low
distortion, so that resonance is much more extreme and much lower than anyone
would tolerate for a pro audio transformer. But, this is a 200:80k ohm
transformer.... the fact that it works at all is a miracle.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."



So it might be possible that the company's mod advice of 100 ohms in parallel with 0.1uF should really be 100 ohms in series with 0.01uF?


Gareth.


  #39   Report Post  
Posted to rec.audio.pro
[email protected] palli...@gmail.com is offline
external usenet poster
 
Posts: 125
Default Pultec EQP clone problem

Scott Dorsey wrote:
---------------------------------

Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG


Any idea what the catastrophic ringing harmonics would look like on a spectrum
analyzer.


They aren't harmonics!


** The ringing frequency is excited by *one* of the harmonics in the square wave.
Can be the fundamental too.

So on a spectrum analyzer that would likely be one single narrow spike.


** Now, the input is a square wave with odd numbered harmonics.

Plus resonances *cannot * create any new frequencies !!!

So the effect on an analyser display is that *one* harmonics is boosted.


....... Phil

  #40   Report Post  
Posted to rec.audio.pro
Don Pearce[_3_] Don Pearce[_3_] is offline
external usenet poster
 
Posts: 2,417
Default Pultec EQP clone problem

On Fri, 26 Feb 2021 01:57:59 -0800 (PST), "
wrote:

** You sure about "any" ?

Square waves have cascading, odd numbered harmonics.
The ringing one would merely be out of step with the others.


Nothing to do with the frequency of the wave or its harmonics. Each
ringing event is separate and is triggered by the broadband energy of
the rising or falling edge. The frequency of the ring is determined by
the LC circuit that is being struck by that edge. The ringing will be
restarted at twice the frequency of the square wave, but that is not
the same thing as the ringing frequency.

d

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

Reply
Thread Tools
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Dachman Audio U87 Clone Kit Paul Dorman Pro Audio 82 January 5th 21 02:50 AM
Good amps to clone Bret L Vacuum Tubes 0 April 25th 10 12:35 AM
WTB Waves Q-Clone License Haolemon Pro Audio 1 September 16th 07 08:26 AM
The clone marching on [email protected] Audio Opinions 5 August 23rd 07 05:23 AM
N72 1272 clone Studio Froombosch Pro Audio 0 March 31st 04 01:52 PM


All times are GMT +1. The time now is 02:34 AM.

Powered by: vBulletin
Copyright ©2000 - 2023, Jelsoft Enterprises Ltd.
Copyright 2004-2023 AudioBanter.com.
The comments are property of their posters.
 

About Us

"It's about Audio and hi-fi"