Reply
 
Thread Tools Display Modes
  #1   Report Post  
Posted to rec.audio.tubes
Paul D. Spiegel Paul D. Spiegel is offline
external usenet poster
 
Posts: 22
Default Using two taps of OT secondary

A common configuration for an output transformer secondary (a la Dynaco)
is C-4-8-16. The four ohm tap is roughly the mid-point of secondary.

If you connect one 4 ohm load from C-4 and then another 4 ohm load from
4-16, what would the overall load look like to the output stage? Would
it make a difference if you ground the 4 ohm tap instead of C?

This could be an interesting way to bi-wire a speaker.

What do RATs think?

- Paul
  #2   Report Post  
Posted to rec.audio.tubes
Patrick Turner Patrick Turner is offline
external usenet poster
 
Posts: 3,964
Default Using two taps of OT secondary

On Nov 16, 6:19*pm, "Paul D. Spiegel" wrote:
A common configuration for an output transformer secondary (a la Dynaco)
is C-4-8-16. *The four ohm tap is roughly the mid-point of secondary.

If you connect one 4 ohm load from C-4 and then another 4 ohm load from
4-16, what would the overall load look like to the output stage? *Would
it make a difference if you ground the 4 ohm tap instead of C?


Let me assume you have a pair of full range speakers, each 4 ohms.

The use of a full range 4 ohm speaker across C-4 gives the amp a 4 ohm
load. If anotherfull range 4 ohm speaker is connected across 4-16,
then you have 2 x 4 ohm speakers in parallel and the load is 2 ohms.
Maybe your Dynaco will smoke a bit.

But suppose you have ONE 4 ohm speaker but there is a 4 ohm bass and a
4 ohm treble with separate inputs. You could connect the bass C-4, and
the treble 4-16, and because the bandwidth of each speaker does not
include the bandwidth of the other, then the amp has a 4 ohm load and
is loaded identically to if you had one full range speaker C-4.

When connecting any speaker to C-4, only 1/2 of the secondary winding
is used to produce speaker current so secondary winding resistance
losses are high compared to using say 16 ohms across C-16 when losses
are at the minimum.
By using bass C-4 and treble 4-16, the losses will be reduced
slightly because treble energy is produced by a winding which is
otherwise not used to make power. Because the treble power above 1 kHz
is maybe only 20% of the bass power below 1kHz the use of all the
windings does not reduce winding losses very much, maybe -10% only -
and you will not hear the slightest improvement to the sound.

Patrick Turner.

This could be an interesting way to bi-wire a speaker.

What do RATs think?

*- Paul


  #3   Report Post  
Posted to rec.audio.tubes
Ian Iveson Ian Iveson is offline
external usenet poster
 
Posts: 960
Default Using two taps of OT secondary

Paul D. Spiegel wrote:

A common configuration for an output transformer secondary
(a la Dynaco)
is C-4-8-16. The four ohm tap is roughly the mid-point of
secondary.

If you connect one 4 ohm load from C-4 and then another 4
ohm load from
4-16, what would the overall load look like to the output
stage? Would
it make a difference if you ground the 4 ohm tap instead
of C?

This could be an interesting way to bi-wire a speaker.

What do RATs think?


Essentially you'd be connecting one amp to two speakers in
parallel. To retain the design load on the output stage, you
would need to use two 8ohm speakers.

Considering this group is not quite yet pro.test-tone.tubes,
remarks about using speakers with different frequency ranges
are spurious.

Here's a maths exercise. Let's say you have one speaker
that's 4ohms up to 2kHz and infinite impedance beyond, and
another speaker that's infinite impedance below 2kHz and
4ohms beyond. Connect these as you suggest. What is the
resulting impedance for a 1kHz tone? For a 3kHz tone? For a
signal that combines 1kHz and 3kHz equally? For music?

Answers on postcard marked "red herring".

Where's your feedback connected? Assuming you have global
feedback, it would be best connected to a point common to
both speakers. You can't do that with a centre tap
transformer whilst still utilizing all the windings. If the
two secondaries were separate, you could.

Ian


  #4   Report Post  
Posted to rec.audio.tubes
Big Bad Bob Big Bad Bob is offline
external usenet poster
 
Posts: 366
Default Using two taps of OT secondary

On 11/15/10 23:19, Paul D. Spiegel so witilly quipped:
A common configuration for an output transformer secondary (a la Dynaco)
is C-4-8-16. The four ohm tap is roughly the mid-point of secondary.

If you connect one 4 ohm load from C-4 and then another 4 ohm load from
4-16, what would the overall load look like to the output stage? Would
it make a difference if you ground the 4 ohm tap instead of C?

This could be an interesting way to bi-wire a speaker.

What do RATs think?


transformers and beam-power pentodes are expensive. I suggest NOT doing
that. Your total load will be twice that of a 4 ohm load on the 4 ohm
tap because you're loading it TWICE instead of once. The end result at
full power would be pink plates and possible burnt windings. The magic
blue smoke won't go back in, by the way. You'll have to get "a new one"
(whatever blows up first).

You could wire ONE of the speakers on 4-16 but I see no reason why you
would want to. Instead, wire the speakers in series and use the 8 ohm
tap, or (if whoofer/tweeter) use series crossover cap/coil and phase
invert the tweeter.

Or keep on hand a stock of tubes, transformers, filter chokes, and solder.

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
McCain Taps Palin Annika1980 Audio Opinions 5 August 31st 08 10:11 PM
what the heck! DC on secondary?? alfred Vacuum Tubes 3 December 12th 05 04:34 PM
Ground your secondary winding Adam Stouffer Vacuum Tubes 2 August 22nd 04 11:43 AM
PT HV secondary wsc Vacuum Tubes 1 April 30th 04 05:26 PM
ElectroPrint TM3KB (w/UL taps) output xforms for sale Randy Cook Marketplace 0 February 11th 04 02:30 AM


All times are GMT +1. The time now is 08:26 AM.

Powered by: vBulletin
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AudioBanter.com.
The comments are property of their posters.
 

About Us

"It's about Audio and hi-fi"