Low cost PWM volume control. Could it work? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 1st July 2004, 09:18 PM   #1
diyAudio Member
 
Join Date: Jul 2004
Location: Bucharest
Default Low cost PWM volume control. Could it work?

Hello
I have once read in a book (which of course I can't find anymore) about a direct PWM volume controller.
The idea is that you simply take the audio and chop it with a high frequency, variable duty cycle signal. Then you use some type of low pass filter, to get rid of the high frequency component, and that's it: the output signal equals the input signal (theoretically no distortions), scaled by the PWM ratio.
The schematic could be something like the atachement.
The advantage is that you can add any number of channels on the same PWM signal (I need 5), and they are completely synchronized.
I would like to implement such a volume controller, do you think it could work? (if anyone knows a similar design, I would appreciate it, no point in reinventing the wheel.)
I was thinking of using a 555 for the PWM generator, but I don't think it's a good idea, because I don't have the full range 0-100%. Especially the lower limit, there must be a setting on the potentiometer that gives 0 V on the PWM output, no audio is getting through, silence.
Also, what do you think about the output filter? Choosing values that give no more than 3dB drop at 20 KHz, gives a 22 dB reduction of the 200 kHz signal. Strictly speaking, the 200 KHz signal is exactly 22 dB below the audio signal. If the 200 KHz signal gets into amps and speakers, is there any danger? Because then I would have to use a more complex filter, and i want a low cost solution.
Should I aply any bias on the 4066, to get low distortions?
Thank you.
Attached Images
File Type: gif schem.gif (2.5 KB, 208 views)
  Reply With Quote
Old 2nd July 2004, 08:32 AM   #2
diyAudio Member
 
Ouroboros's Avatar
 
Join Date: Dec 2003
Location: Nottingham UK
I'm pretty certain that John Linsley-Hood showed this in one of his books. I'll have a look for it.

It would be one way of getting a multi-gang volume control to go on the outputs of a Behringer 2496 digital crossover, so that all the analogue outputs had a common gain control. (You don't want to use the main volume control on the input of a DSP-based XO because you lose digital resolution as you turn the gain down).
  Reply With Quote
Old 2nd July 2004, 09:05 AM   #3
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
This principle has been proposed in the "active fliter cookbook" for the tuning of state-variable filters. So it should basically but I don't know what quality one might achieve.


Regards

Charles
  Reply With Quote
Old 2nd July 2004, 09:08 AM   #4
diyAudio Member
 
Ouroboros's Avatar
 
Join Date: Dec 2003
Location: Nottingham UK
I've just done some SPICE simulations, and the technique works well, but obviously as it's a sampled-data system, the usual problems occur with filtering out the switching frequency.

You'll need to use fast, and high quality FET switches. Perhaps the DG411 type of switch will be OK. I think I'll breadboard this and give it a try.
  Reply With Quote
Old 2nd July 2004, 09:43 AM   #5
djQUAN is offline djQUAN  Philippines
diyAudio Member
 
Join Date: May 2004
Location: manila
Send a message via MSN to djQUAN Send a message via Yahoo to djQUAN
I just looked at the TL494 datasheet and it can handle a max freq of 200kHz.

might be a good alternative for a PWM source.
although I think (I read somewhere) the 555 could go up to 1MHz.


I have a scrap DG211,

DG508

and four AD7510's


the specs for the AD7510's are

SPST 4ch Latch-up Proof, 75ohm on resistance, 10nA channel ON leakage,

might be a good candidate...........not sure if they're fast enough though. but they work with +/-15V supplies.
  Reply With Quote
Old 2nd July 2004, 09:54 AM   #6
diyAudio Member
 
Ouroboros's Avatar
 
Join Date: Dec 2003
Location: Nottingham UK
You really need a switch with fast (and symmetrical) ON/OFF times, and also with low charge injection. Perhaps a MAX4501?

Although I bet even a simple 74HC4316 might do the job adequately.
  Reply With Quote
Old 2nd July 2004, 09:56 AM   #7
mskeete is offline mskeete  United Kingdom
diyAudio Member
 
Join Date: Oct 2003
Location: London
JLH publsihed a fully working circuit in Electronics World

-----------------------------------------------
Attenuator, Low-distortion for hifi
John Linsley Hood

April 1995, p320

With a distortion figure of just
0.005% over most of the audio
range, this switch-mode attenuator
design removes the transistor
matching problems normally
associated with high-performance
attenuators.
-----------------------------------------------

You can obtain a copy from the following website
http://www.softcopy.co.uk/electronicsworld/


Mark
  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
Volume control on DVD player remote. Lose resolution at low volume? Circlotron Digital Source 2 10th June 2011 07:20 PM
How does this volume control work? Stuey Everything Else 7 15th November 2006 01:11 PM
possible volume and balance control - does this look like it will work well? photo_marc Tubes / Valves 2 25th January 2006 10:46 PM
remote control motorised control for volume pot/knob CharlesY Parts 0 25th July 2005 11:12 AM
Would this work as a volume control??? george a Solid State 6 17th December 2004 02:43 AM


New To Site? Need Help?

All times are GMT. The time now is 01:28 PM.


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