Attenuating Power Supply?

ghetto · 25th July 2003, 11:41 PM

I've read that an effective volume control that preserves sound quality is to attenuate the transformer. The EE student inside me is very curious ... can anyone provide example schematics, theory, etc? Have I misread, and it is not possible to attenuate a transformer? This is for a gainclone style amplifier by the way. I can't really think of how to do this, and I've had no luck searching.

Any help is appreciated...

ghetto · 29th July 2003, 04:54 AM

No help?

moamps · 29th July 2003, 07:53 AM

Quote:

Originally posted by ghetto
I've read that an effective volume control that preserves sound quality is to attenuate the transformer. The EE student inside me is very curious ... can anyone provide example schematics, theory, etc? Have I misread, and it is not possible to attenuate a transformer? This is for a gainclone style amplifier by the way. I can't really think of how to do this, and I've had no luck searching.

Any help is appreciated...

Hi,

This isn't good idea. I saw some poor quality audio clippers application with OP-amps and variable +/- rails, but this isn't HIFI definitely. (Analogue AM transmitters uses this approach in modulation circuitry)

Regards

dhaen · 29th July 2003, 08:56 AM

I think you mis-read...

khush · 29th July 2003, 10:23 AM

Hi there,
I think you may be getting confused with transformer volume controls TVC's. These are multi tapped signal transformers
used as volume controls. A search of the audio asylum archives www.audioasylum.com over the past couple of years should bring up lots of information.
regards
Khush

sam9 · 29th July 2003, 03:31 PM

You can test this simply by plugging any amp into a Variac. I think you will find that it has little if any effect on volume until you bring it down the point at which clipping sets in where upon distortion goes through the roof.

Either you misunderstodd the advice or you need to find a better source for advice.

ghetto · 29th July 2003, 03:57 PM

Thank you sirs, I will look for a better volume control method now

jackinnj · 29th July 2003, 07:13 PM

Quote:

Originally posted by sam9
You can test this simply by plugging any amp into a Variac. I think you will find that it has little if any effect on volume until you bring it down the point at which clipping sets in where upon distortion goes through the roof.

Actually, the waveform you get from a Variac may or may not be a perfectly symmetrical sinewave -- that is, the wave in the second quadrant may have a different shape from that of the first quadrant -- it may be somewhat distorted.

Thinking of voltage regulating circuits, the waveform you get from a ferroresonant transformer is also not symmetrical.

sam9 · 30th July 2003, 07:22 PM

"Actually, the waveform you get from a Variac may or may not be a perfectly symmetrical sinewave -- that is, the wave in the second quadrant may have a different shape from that of the first quadrant -- it may be somewhat distorted.

Thinking of voltage regulating circuits, the waveform you get from a ferroresonant transformer is also not symmetrical."

I was thinking in terns of clipping distortion at the amplifier output. The Variac was just a way to conviently control the DC at the rails. The effect, if any, of the waveform from the Variac would depend on the success of the power supply design in filtering ripple, noise and so on and on the PSRR of the amp itself. The orginal post, If I read it right, seemed to be talking about controlling volume by attenuating the tranformer output and hence the rails.

fdegrove · 31st July 2003, 01:05 AM

Hi,

Quote:

Thank you sirs, I will look for a better volume control method now

The better/best way to control volume was presented already...

Quote:

I think you may be getting confused with transformer volume controls TVC's. These are multi tapped signal transformers

Anything else was just pure speculation, no doubt well meant.

Quote:

I think you mis-read...

You're too polite and overly British, John...

Ciao,

25th July 2003, 11:41 PM	#1
ghetto diyAudio Member Join Date: Jul 2003 Location: Oklahoma	Attenuating Power Supply? I've read that an effective volume control that preserves sound quality is to attenuate the transformer. The EE student inside me is very curious ... can anyone provide example schematics, theory, etc? Have I misread, and it is not possible to attenuate a transformer? This is for a gainclone style amplifier by the way. I can't really think of how to do this, and I've had no luck searching. Any help is appreciated...

29th July 2003, 10:23 AM	#5
khush diyAudio Member Join Date: Feb 2002 Location: Bath UK	Transformer volume controls Hi there, I think you may be getting confused with transformer volume controls TVC's. These are multi tapped signal transformers used as volume controls. A search of the audio asylum archives www.audioasylum.com over the past couple of years should bring up lots of information. regards Khush

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29th July 2003, 04:54 AM	#2
ghetto diyAudio Member Join Date: Jul 2003 Location: Oklahoma	No help?

29th July 2003, 08:56 AM	#4
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	I think you mis-read...

29th July 2003, 03:31 PM	#6
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	You can test this simply by plugging any amp into a Variac. I think you will find that it has little if any effect on volume until you bring it down the point at which clipping sets in where upon distortion goes through the roof. Either you misunderstodd the advice or you need to find a better source for advice.

29th July 2003, 03:57 PM	#7
ghetto diyAudio Member Join Date: Jul 2003 Location: Oklahoma	Thank you sirs, I will look for a better volume control method now

30th July 2003, 07:22 PM	#9
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	"Actually, the waveform you get from a Variac may or may not be a perfectly symmetrical sinewave -- that is, the wave in the second quadrant may have a different shape from that of the first quadrant -- it may be somewhat distorted. Thinking of voltage regulating circuits, the waveform you get from a ferroresonant transformer is also not symmetrical." I was thinking in terns of clipping distortion at the amplifier output. The Variac was just a way to conviently control the DC at the rails. The effect, if any, of the waveform from the Variac would depend on the success of the power supply design in filtering ripple, noise and so on and on the PSRR of the amp itself. The orginal post, If I read it right, seemed to be talking about controlling volume by attenuating the tranformer output and hence the rails.