Variable power supply to control gainclone volume? - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 8th July 2004, 05:23 PM   #1
MWP is offline MWP  Australia
diyAudio Member
 
Join Date: Oct 2002
Location: Adelaide, South Australia
Default Variable power supply to control gainclone volume?

Hi all,

Im looking at making a 6 channel amp.
Its going to be difficult to make a volume control/preamp for such a beast.

With the talk on regulated gainclones latley im starting to think about using a variable voltage supply to the gainclone ICs using LM338s or similar.

Can you guys think of any problems i may have with setting up such a system?

Thanks.
  Reply With Quote
Old 8th July 2004, 05:29 PM   #2
mateo88 is offline mateo88  United States
diyAudio Member
 
Join Date: May 2004
Location: Argyle, Texas
In my opinion (take it with a grain of salt, I'm not an expert), if it does work, it seems to me that it would be very difficult to control the volume, especially at low outputs.
  Reply With Quote
Old 8th July 2004, 06:33 PM   #3
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
It will not work. The supply has no influence on the volume, until you get so low that the amp output hits the supply voltage, which is called clipping. It is like the tops of the sine waves are sheared off, and it sounds VERY unpleasantly.

The volume is set by the level from your source (say the CD player), the gain of the amp, and the sensitivity of the speakers. Assuming that you cannot change the output level of the CD player and the sensitivity of the speakers, that only leaves the amp gain.

By manipulation of the amp feedback factor, you can vary the gain, but only within small limits. The lower you make the gain (min is one), the more the amp becomes prone to oscillations. The higher you make the gain (although you wouldn't want that probably, it's too high as it is normally) you get more distortion, because at higher gains you have less feedback to linearize the amp.

So the only real possibility to control volume is to vary the attenuation of the signal. That's why everyone does it that way. Because it is easiest to vary a small signal, it is mostly done before the power amp. In theory, you could put a heavy power pot between power amp and speaker, but the waste of power and the (un)availability of good quality power pots makes that less attractive.

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W. S. Maugham
Check out Linear Audio!
  Reply With Quote
Old 8th July 2004, 06:38 PM   #4
Account Disabled
 
Join Date: Apr 2003
Location: US
you can use some solid state pots to adjust volume. Or alternatively, you can use a gain trim opamp (either digital or analog).

changing the rail voltage on the chip does not work.
  Reply With Quote
Old 8th July 2004, 07:20 PM   #5
diyAudio Member
 
mrlots2do's Avatar
 
Join Date: May 2004
Location: Philadelpia
Quote:
Originally posted by janneman

So the only real possibility to control volume is to vary the attenuation of the signal. That's why everyone does it that way. Because it is easiest to vary a small signal, it is mostly done before the power amp.
Jan Didden
Jan,
Using BrianGT's boards how would I attenuate the signal to control volume. Could you show a schematic?

Phil
  Reply With Quote
Old 8th July 2004, 11:17 PM   #6
diyAudio Member
 
Sandy H.'s Avatar
 
Join Date: Nov 2002
Location: Charlotte, NC - USA
Quote:
Originally posted by mrlots2do


Jan,
Using BrianGT's boards how would I attenuate the signal to control volume. Could you show a schematic?

Phil
Check the current revision of the manual on Brian's site. On page 22, the simple pot diagram is included and may do just what you want. You might also be able to configure 3 stereo pots (like the Noble pictured) with gearing (as Cowrang did) to use 3 controls for one knob.

Let me know if that is not clear a clear enugh explanation. I think people are using 100k audio taper pots, but you might want to search to be sure.

Sandy.
  Reply With Quote
Old 9th July 2004, 02:04 AM   #7
diyAudio Member
 
mrlots2do's Avatar
 
Join Date: May 2004
Location: Philadelpia
Quote:
Originally posted by Sandy H.

Check the current revision of the manual on Brian's site. On page 22, the simple pot diagram is included and may do just what you want.
Thanks for the heads up. Would you advise connecting R3 as an unmounted resistor to board (two leads from board to unmounted resistor), this would allow an easy modification should I decide to add volume control after board assembly?
Quote:
Originally posted by Sandy H.

You might also be able to configure 3 stereo pots (like the Noble pictured) with gearing (as Cowrang did) to use 3 controls for one knob.
What did Cowang do???
How do I use 3 controls for one knob?
Quote:
Originally posted by Sandy H.

Let me know if that is not clear a clear enugh explanation. I think people are using 100k audio taper pots, but you might want to search to be sure.
Could someone give me a digikey part# for 100K audio taper pot and Noble stereo potentiometer

Thanks Phil
  Reply With Quote
Old 9th July 2004, 03:53 AM   #8
MWP is offline MWP  Australia
diyAudio Member
 
Join Date: Oct 2002
Location: Adelaide, South Australia
Quote:
Originally posted by janneman
It will not work. The supply has no influence on the volume, until you get so low that the amp output hits the supply voltage, which is called clipping. It is like the tops of the sine waves are sheared off, and it sounds VERY unpleasantly.
Yeh, thanks.
A few hours after posting this i realised this would happen.
It shows ive been thinking about class D amps too much latley
  Reply With Quote
Old 9th July 2004, 12:41 PM   #9
diyAudio Member
 
Sandy H.'s Avatar
 
Join Date: Nov 2002
Location: Charlotte, NC - USA
Quote:
Originally posted by mrlots2do

Thanks for the heads up. Would you advise connecting R3 as an unmounted resistor to board (two leads from board to unmounted resistor), this would allow an easy modification should I decide to add volume control after board assembly?

What did Cowang do???
How do I use 3 controls for one knob?

Could someone give me a digikey part# for 100K audio taper pot and Noble stereo potentiometer

Thanks Phil
Sorry, I misspelled his ID, its Cowanrg and his site is here. Click on his BOSOZ link to get the volume control arrangement he used. http://cowanrg.mesanetworks.net/projects/

You should be able to mount everything to the board as is and just use the volume control prior to the board. Signal in from source -> pot -> signal in on board.

I got my cheap stereo pots from mouser and some Noble pots from a Bill Fitzpatrick in the trading post a while back. I think percy audio also has high end pots and there are probably other good vendors.

Good luck.

Sandy.
  Reply With Quote
Old 9th July 2004, 05:08 PM   #10
diyAudio Member
 
mrlots2do's Avatar
 
Join Date: May 2004
Location: Philadelpia
Quote:
Originally posted by Sandy H.

I think people are using 100k audio taper pots, but you might want to search to be sure.
Sandy,

Regarding the 100K audio taper pot....
R3 on BrianGT's board is 680 ohm, is there a reason I need the 100K pot. Seems too large, maybe should be 50K but than I don't know nothing. Besides I haven't found them with more than 47K taper pot.

If I find I need greater than 47K taper pot could I put a 50K resistor before the 47K taper pot.

BrianGT if you read this.... The manual Rev B (page 5) component names R3, Rf, and so on, doesn't match schematic (page 3).
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
variable capacitor volume control lochness Tubes / Valves 11 21st June 2008 09:39 AM
Variable Voltage Volume control jkeny Power Supplies 4 10th February 2008 09:13 PM
Adjustable power supply to replace volume control Leolabs Solid State 8 11th July 2007 04:43 PM
Volume control : - pot' or pot' variable feedback resistor (gain) ? ash_dac Solid State 5 1st August 2006 05:07 AM
Variable power supply for Gainclone development AR Chip Amps 13 14th November 2003 03:22 AM


New To Site? Need Help?

All times are GMT. The time now is 01:53 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2