[rdx]

Question: How can I run the output from a tube amplifier head into a
line-level audio input?

Details:

I have a Peavey VTM-60 tube amplifier head, for guitar.

It has several outputs on the back, power amp output, for driving 4ohm,
8 ohm, or 16 ohm speakers. (3 seperate outputs). There is no
line-level output or headphone output or anything.

I also have a Presonus Firebox audio interface. This has both
line-level and mic level inputs with phantom power, etc.


So basically I want to run my guitar through the VTM-60 to get the
sonic characteristics, then run this straight into the firebox without
mic'ing the output of an external cabinet. I don't want to burn out the
firebox line inputs with this 60W speaker driving output. Any
suggestions on how to proceed? I was considering adding a line output
after the preamp stage (the 6 12AX7s), but I'd rather not modify my
amplifier if that could be avoided. Plus there are some cool features
that occur during the gain stage, notably the tube distortion through
the two 6L6s...


Cheers,
Alex

[Arny Krueger]

"rdx" wrote in message
ups.com
Question: How can I run the output from a tube amplifier
head into a line-level audio input?

Details:

I have a Peavey VTM-60 tube amplifier head, for guitar.

It has several outputs on the back, power amp output, for
driving 4ohm, 8 ohm, or 16 ohm speakers. (3 seperate
outputs). There is no line-level output or headphone
output or anything.

I also have a Presonus Firebox audio interface. This has
both line-level and mic level inputs with phantom power,
etc.


So basically I want to run my guitar through the VTM-60
to get the sonic characteristics, then run this straight
into the firebox without mic'ing the output of an
external cabinet. I don't want to burn out the firebox
line inputs with this 60W speaker driving output. Any
suggestions on how to proceed? I was considering adding
a line output after the preamp stage (the 6 12AX7s), but
I'd rather not modify my amplifier if that could be
avoided. Plus there are some cool features that occur
during the gain stage, notably the tube distortion
through the two 6L6s...


Cheers,
Alex

[Arny Krueger]

"rdx" wrote in message
ups.com
Question: How can I run the output from a tube amplifier
head into a line-level audio input?

Details:

I have a Peavey VTM-60 tube amplifier head, for guitar.

It has several outputs on the back, power amp output, for
driving 4ohm, 8 ohm, or 16 ohm speakers. (3 seperate
outputs). There is no line-level output or headphone
output or anything.

I also have a Presonus Firebox audio interface. This has
both line-level and mic level inputs with phantom power,
etc.

So basically I want to run my guitar through the VTM-60
to get the sonic characteristics, then run this straight
into the firebox without mic'ing the output of an
external cabinet. I don't want to burn out the firebox
line inputs with this 60W speaker driving output. Any
suggestions on how to proceed?


If you can solder and built small projects, then you want a resistive
divider. Figure you want about 1 volt of signal for a line-level input.
Figure that maximum output of the amp is 20-30 volts, so you want a 25-30 dB
attenuator with an output impedance of about 1K ohms.

If you can't, find a direct box and set the amplifier/instrument switch to
"amplifier".

I was considering adding
a line output after the preamp stage (the 6 12AX7s), but
I'd rather not modify my amplifier if that could be
avoided. Plus there are some cool features that occur
during the gain stage, notably the tube distortion
through the two 6L6s...

Here's a site with a lot of relevant resources:

http://amptone.com/

[Don Pearce]

On 15 Nov 2006 07:16:26 -0800, "rdx" wrote:

Question: How can I run the output from a tube amplifier head into a
line-level audio input?

Details:

I have a Peavey VTM-60 tube amplifier head, for guitar.

It has several outputs on the back, power amp output, for driving 4ohm,
8 ohm, or 16 ohm speakers. (3 seperate outputs). There is no
line-level output or headphone output or anything.

I also have a Presonus Firebox audio interface. This has both
line-level and mic level inputs with phantom power, etc.


So basically I want to run my guitar through the VTM-60 to get the
sonic characteristics, then run this straight into the firebox without
mic'ing the output of an external cabinet. I don't want to burn out the
firebox line inputs with this 60W speaker driving output. Any
suggestions on how to proceed? I was considering adding a line output
after the preamp stage (the 6 12AX7s), but I'd rather not modify my
amplifier if that could be avoided. Plus there are some cool features
that occur during the gain stage, notably the tube distortion through
the two 6L6s...


Cheers,
Alex

If you want to keep the sound of the entire amplifier, then you do
need to use the final output. Just drop the level of the signal with a
couple of resistors. Start with a 47k in series with the output,
followed by a 1k to ground - take the line signal from the junction of
the two. You can juggle the level up or down by decreasing or
increasing the 47k.

You still need to give the amplifier the right load, so if you don't
want to hear it while you are doing this, a suitable high power
resistor should substitute for the speaker.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Scott Dorsey]

rdx wrote:
Question: How can I run the output from a tube amplifier head into a
line-level audio input?

Details:

I have a Peavey VTM-60 tube amplifier head, for guitar.

It has several outputs on the back, power amp output, for driving 4ohm,
8 ohm, or 16 ohm speakers. (3 seperate outputs). There is no
line-level output or headphone output or anything.

You need a powersoak, or some other 8 ohm load. The load replaces the
speaker in the amplifier, and it's just a huge 8 ohm resistor that can
handle a hundred watts or so without burning up. Some fancier ones have
loads that attempt to match that of a real loudspeaker. Then you can just
bridge the output of the thing into a passive DI box like an IMP-2, and
you have a mike-to-line level signal for your recorder.

So basically I want to run my guitar through the VTM-60 to get the
sonic characteristics, then run this straight into the firebox without
mic'ing the output of an external cabinet.

You'll find, though, that 90% of the sonic characteristics come from the
external cabinet. Well, maybe 75% anyway. But try a dummy load or
power soak and see for yourself.
--scott

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

[Bill]

rdx wrote:
Question: How can I run the output from a tube amplifier head into a
line-level audio input?

Details:

I have a Peavey VTM-60 tube amplifier head, for guitar.

It has several outputs on the back, power amp output, for driving 4ohm,
8 ohm, or 16 ohm speakers. (3 seperate outputs). There is no
line-level output or headphone output or anything.

I also have a Presonus Firebox audio interface. This has both
line-level and mic level inputs with phantom power, etc.


So basically I want to run my guitar through the VTM-60 to get the
sonic characteristics, then run this straight into the firebox without
mic'ing the output of an external cabinet. I don't want to burn out the
firebox line inputs with this 60W speaker driving output. Any
suggestions on how to proceed? I was considering adding a line output
after the preamp stage (the 6 12AX7s), but I'd rather not modify my
amplifier if that could be avoided. Plus there are some cool features
that occur during the gain stage, notably the tube distortion through
the two 6L6s...


Cheers,
Alex

Too easy.
Just use a good step down transformer. The output impedance will be
about 0.0001 ohm but the level will be right.
A resistor divider would do it too, but any but metal film resistors
have some amount of thermal noise. Something I learned in low level
signal amplifier engineering.
Bill Baka

[Bill]

Don Pearce wrote:
On 15 Nov 2006 07:16:26 -0800, "rdx" wrote:

Question: How can I run the output from a tube amplifier head into a
line-level audio input?

Details:

I have a Peavey VTM-60 tube amplifier head, for guitar.

It has several outputs on the back, power amp output, for driving 4ohm,
8 ohm, or 16 ohm speakers. (3 seperate outputs). There is no
line-level output or headphone output or anything.

I also have a Presonus Firebox audio interface. This has both
line-level and mic level inputs with phantom power, etc.


So basically I want to run my guitar through the VTM-60 to get the
sonic characteristics, then run this straight into the firebox without
mic'ing the output of an external cabinet. I don't want to burn out the
firebox line inputs with this 60W speaker driving output. Any
suggestions on how to proceed? I was considering adding a line output
after the preamp stage (the 6 12AX7s), but I'd rather not modify my
amplifier if that could be avoided. Plus there are some cool features
that occur during the gain stage, notably the tube distortion through
the two 6L6s...


Cheers,
Alex

If you want to keep the sound of the entire amplifier, then you do
need to use the final output. Just drop the level of the signal with a
couple of resistors. Start with a 47k in series with the output,
followed by a 1k to ground - take the line signal from the junction of
the two. You can juggle the level up or down by decreasing or
increasing the 47k.

You still need to give the amplifier the right load, so if you don't
want to hear it while you are doing this, a suitable high power
resistor should substitute for the speaker.

d

Best answer so far, but they can't be just junk carbon or they will put
noise back into the low level input. Metal film is the way to go for
this approach, not Radio Shack resistors.
Bill Baka

[Scott Dorsey]

Bill bbaka@c-o-m-c-a-s-t-dot-n-e-t wrote:
You still need to give the amplifier the right load, so if you don't
want to hear it while you are doing this, a suitable high power
resistor should substitute for the speaker.

Best answer so far, but they can't be just junk carbon or they will put
noise back into the low level input. Metal film is the way to go for
this approach, not Radio Shack resistors.

Umm.... you need a load resistor of between 100W and 250W at eight
ohms. Your choices probably don't include any metal films, unless you
consider Vitrohms to be metal films (which I suppose they are, just with
18 gauge thick films...).

In a pinch, you can use heating elements from electric ranges for the
job, but you will need to mix and match to get the correct load resistance
and you need to worry about the fact that the resistance increases as they
heat up, so derate considerably and use a cooling fan.
--scott

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

[Zilog]

rdx wrote:
Question: How can I run the output from a tube amplifier head into a
line-level audio input?

Details:

I have a Peavey VTM-60 tube amplifier head, for guitar.

It has several outputs on the back, power amp output, for driving 4ohm,
8 ohm, or 16 ohm speakers. (3 seperate outputs). There is no
line-level output or headphone output or anything.

I also have a Presonus Firebox audio interface. This has both
line-level and mic level inputs with phantom power, etc.


So basically I want to run my guitar through the VTM-60 to get the
sonic characteristics, then run this straight into the firebox without
mic'ing the output of an external cabinet. I don't want to burn out the
firebox line inputs with this 60W speaker driving output. Any
suggestions on how to proceed? I was considering adding a line output
after the preamp stage (the 6 12AX7s), but I'd rather not modify my
amplifier if that could be avoided. Plus there are some cool features
that occur during the gain stage, notably the tube distortion through
the two 6L6s...


Cheers,
Alex

Hi Alex,
I assume you still like to hear the guitar through the amp?
Then as is described by others you have to make a resistive divider to
get the correct level for your interface.
I would suggest to place that resistive divider in a small box and plug
it in one of the remaining speaker outputs. Your main speaker is
connected to the correct outlet of course...
But and here it is; I don't know if you disconnect the connected
loudspeaker when you plug another jack in the other outputs.
That is to be checked before. Insert another cab in the second output
just to try.
The value of the divider network will not influence your tone or power
as the value is very high compared to the ohmic value of the speaker.
In this way you will have all the nice tones coming from your amp,
directed to your interface.

Success,
Zilog

[Bill]

Scott Dorsey wrote:
Bill bbaka@c-o-m-c-a-s-t-dot-n-e-t wrote:
You still need to give the amplifier the right load, so if you don't
want to hear it while you are doing this, a suitable high power
resistor should substitute for the speaker.

Best answer so far, but they can't be just junk carbon or they will put
noise back into the low level input. Metal film is the way to go for
this approach, not Radio Shack resistors.

Umm.... you need a load resistor of between 100W and 250W at eight
ohms. Your choices probably don't include any metal films, unless you
consider Vitrohms to be metal films (which I suppose they are, just with
18 gauge thick films...).

In a pinch, you can use heating elements from electric ranges for the
job, but you will need to mix and match to get the correct load resistance
and you need to worry about the fact that the resistance increases as they
heat up, so derate considerably and use a cooling fan.
--scott

I wasn't answering that post. The resistor divider might work unless the
amp output just has to have a load or lose all fidelity.
Bill Baka

[George Gleason]

"rdx" wrote in message
ups.com...
Question: How can I run the output from a tube amplifier head into a
line-level audio input?

I would use a direct box into a preamp or mixer
many directs offer speaker level compatibility
but this would be a LIVE sound approach, I am not sure how a recoring
session would approach this
George

[Scott Dorsey]

Bill bbaka@c-o-m-c-a-s-t-dot-n-e-t wrote:

I wasn't answering that post. The resistor divider might work unless the
amp output just has to have a load or lose all fidelity.

Yes, it's a guitar amp. It not only needs to have a load (some of them
will in fact break out into oscillation and blow up without a load), but
that load preferably should model the reactance of a speaker.
--scott

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

[Paul Stamler]

"Bill" wrote in message
m...

A resistor divider would do it too, but any but metal film resistors
have some amount of thermal noise. Something I learned in low level
signal amplifier engineering.

True, but given the typical signal-to-noise ratio of an electric guitar plus
amp, the noise difference between metal films and carbon comps will be
irrelevant.

Peace,
Paul

[Bill]

Scott Dorsey wrote:
Bill bbaka@c-o-m-c-a-s-t-dot-n-e-t wrote:
I wasn't answering that post. The resistor divider might work unless the
amp output just has to have a load or lose all fidelity.

Yes, it's a guitar amp. It not only needs to have a load (some of them
will in fact break out into oscillation and blow up without a load), but
that load preferably should model the reactance of a speaker.
--scott

If you can blow up a pair of 6L6's then you have accomplished something
I have not been able to do. Blow up a cap or resistor maybe.
Bill Baka

[GregS]

In article , "Paul Stamler" wrote:
"Bill" wrote in message
om...

A resistor divider would do it too, but any but metal film resistors
have some amount of thermal noise. Something I learned in low level
signal amplifier engineering.

True, but given the typical signal-to-noise ratio of an electric guitar plus
amp, the noise difference between metal films and carbon comps will be
irrelevant.

Typical headphone outputs of amplifiers just use a series resistor
arrangement, allthough the series parallel being preffered. Headphone
outputs are very close to line levels.

The load on the amp will affect the sound. A resistor might not
sound like a woofer load.

greg

[Scott Dorsey]

Bill bbaka@c-o-m-c-a-s-t-dot-n-e-t wrote:
Scott Dorsey wrote:
Bill bbaka@c-o-m-c-a-s-t-dot-n-e-t wrote:
I wasn't answering that post. The resistor divider might work unless the
amp output just has to have a load or lose all fidelity.

Yes, it's a guitar amp. It not only needs to have a load (some of them
will in fact break out into oscillation and blow up without a load), but
that load preferably should model the reactance of a speaker.

If you can blow up a pair of 6L6's then you have accomplished something
I have not been able to do. Blow up a cap or resistor maybe.

Or a $200 output transformer, yes.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Bill]

Scott Dorsey wrote:
Bill bbaka@c-o-m-c-a-s-t-dot-n-e-t wrote:
Scott Dorsey wrote:
Bill bbaka@c-o-m-c-a-s-t-dot-n-e-t wrote:
I wasn't answering that post. The resistor divider might work unless the
amp output just has to have a load or lose all fidelity.
Yes, it's a guitar amp. It not only needs to have a load (some of them
will in fact break out into oscillation and blow up without a load), but
that load preferably should model the reactance of a speaker.

If you can blow up a pair of 6L6's then you have accomplished something
I have not been able to do. Blow up a cap or resistor maybe.

Or a $200 output transformer, yes.
--scott
I wouldn't expect the transformer to go from oscillation unless the
tubes were somehow driving it into saturation and that doesn't usually
happen except for a very low frequency. Maybe high frequency hysteresis
losses, but I have never killed a transformer.
It will probably happen now that I said that.
Bill Baka

[Chris Hornbeck]

On Wed, 15 Nov 2006 23:00:38 GMT, Bill wrote:

I wouldn't expect the transformer to go from oscillation unless the
tubes were somehow driving it into saturation and that doesn't usually
happen except for a very low frequency. Maybe high frequency hysteresis
losses, but I have never killed a transformer.
It will probably happen now that I said that.

The danger is from insulation arc-over. Oscillation rapidly
runs the output tubes up into class C; dI/dT makes big
voltage spikes; like that.

But, FWIW, none of these schemes will sound like the amp
itself, because they don't include the speaker.

All good fortune,

Chris Hornbeck
"I hate to see that evening Sun go down"

[Paul Stamler]

"Bill" wrote in message
om...
Scott Dorsey wrote:
Bill bbaka@c-o-m-c-a-s-t-dot-n-e-t wrote:
I wasn't answering that post. The resistor divider might work unless
the
amp output just has to have a load or lose all fidelity.

Yes, it's a guitar amp. It not only needs to have a load (some of them
will in fact break out into oscillation and blow up without a load), but
that load preferably should model the reactance of a speaker.
--scott

If you can blow up a pair of 6L6's then you have accomplished something
I have not been able to do. Blow up a cap or resistor maybe.

What usually blows when you operate a tubed amp without a load is not a
tube, but the output transformer.

Peace,
Paul

[[email protected]]

(Scott Dorsey) writes:

Umm.... you need a load resistor of between 100W and 250W at eight
ohms. Your choices probably don't include any metal films, unless you
consider Vitrohms to be metal films (which I suppose they are, just with
18 gauge thick films...).

Use a bunch of Rs in a cylinder, parellel connected. Dump the lot in a
coffey can of corn oil, with a `suitable' connector in the centre of
the lid. 20W-50W rating or resistors should be good for 200-500W for 5
min. Don't forget to use non-inductive Rs.


--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

[Arny Krueger]

wrote in message

(Scott Dorsey) writes:

Umm.... you need a load resistor of between 100W and
250W at eight ohms. Your choices probably don't include
any metal films, unless you consider Vitrohms to be
metal films (which I suppose they are, just with 18
gauge thick films...).

Use a bunch of Rs in a cylinder, parellel connected. Dump
the lot in a coffey can of corn oil, with a `suitable'
connector in the centre of the lid. 20W-50W rating or
resistors should be good for 200-500W for 5 min. Don't
forget to use non-inductive Rs.

This is good-enough advice for non-precision use. However, everybody should
think twice about doing something like this should they ever want to do
serious equipment tests. Just about every commodity off-the-shelf wirewound
resistor has a massive positive temperature coefficient. People like Arco
have good NI power resistors that are stable as a rock, even when hot enough
to boil that corn oil hard enough to make french fries.

[Scott Dorsey]

wrote:
(Scott Dorsey) writes:

Umm.... you need a load resistor of between 100W and 250W at eight
ohms. Your choices probably don't include any metal films, unless you
consider Vitrohms to be metal films (which I suppose they are, just with
18 gauge thick films...).

Use a bunch of Rs in a cylinder, parellel connected. Dump the lot in a
coffey can of corn oil, with a `suitable' connector in the centre of
the lid. 20W-50W rating or resistors should be good for 200-500W for 5
min. Don't forget to use non-inductive Rs.

Corn oil? Sheesh, at least use motor oil!
Gallon paint cans are appropriate for the job, a la the Heathkit Cantenna.
--scott

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

[Bill]

Scott Dorsey wrote:
wrote:
(Scott Dorsey) writes:

Umm.... you need a load resistor of between 100W and 250W at eight
ohms. Your choices probably don't include any metal films, unless you
consider Vitrohms to be metal films (which I suppose they are, just with
18 gauge thick films...).
Use a bunch of Rs in a cylinder, parellel connected. Dump the lot in a
coffey can of corn oil, with a `suitable' connector in the centre of
the lid. 20W-50W rating or resistors should be good for 200-500W for 5
min. Don't forget to use non-inductive Rs.

Corn oil? Sheesh, at least use motor oil!
Gallon paint cans are appropriate for the job, a la the Heathkit Cantenna.
--scott

You guys all forgot the other thing about a speaker load. There is a
certain amount of inductance involved so unless you want to get real
creative with resistors and inductors only a speaker will simulate a
speaker.
Bill Baka

[Scott Dorsey]

Bill bbaka@c-o-m-c-a-s-t-dot-n-e-t wrote:
Scott Dorsey wrote:
wrote:
(Scott Dorsey) writes:

Umm.... you need a load resistor of between 100W and 250W at eight
ohms. Your choices probably don't include any metal films, unless you
consider Vitrohms to be metal films (which I suppose they are, just with
18 gauge thick films...).
Use a bunch of Rs in a cylinder, parellel connected. Dump the lot in a
coffey can of corn oil, with a `suitable' connector in the centre of
the lid. 20W-50W rating or resistors should be good for 200-500W for 5
min. Don't forget to use non-inductive Rs.

Corn oil? Sheesh, at least use motor oil!
Gallon paint cans are appropriate for the job, a la the Heathkit Cantenna.

You guys all forgot the other thing about a speaker load. There is a
certain amount of inductance involved so unless you want to get real
creative with resistors and inductors only a speaker will simulate a
speaker.

No, I mentioned that in my first reply. There ARE some power soak devices
out there that attempt to model the reactance and some of the nonlinearity
of a speaker. They more or less work, but I still think that anything that
doesn't include the cabinet and cone breakup effects is missing the whole
point.
--scott


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

[Bill]

Scott Dorsey wrote:
No, I mentioned that in my first reply. There ARE some power soak devices
out there that attempt to model the reactance and some of the nonlinearity
of a speaker. They more or less work, but I still think that anything that
doesn't include the cabinet and cone breakup effects is missing the whole
point.
--scott


Agreed.
Bill Baka