Is there a practical way to make power filter capacitance variable? - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

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 12th October 2013, 12:07 AM   #1
diyAudio Member
 
Join Date: Sep 2013
Location: USA
Default Is there a practical way to make power filter capacitance variable?

Is filtering reduced if a resistor is placed in series with the neg of a filter cap and ground? If so, could a correctly spec'ed pot be placed there to make it controllable for an intended swing ??



This may be another dumb question, but I'm just gonna ask it anyway
  Reply With Quote
Old 12th October 2013, 12:11 AM   #2
diyAudio Member
 
Join Date: May 2011
Location: Silicon Valley
Standard circuit done all the time in nosebleed high speed digital IC design: supply bypass caps with Nchannel MOSFET switches in series with the ground end.

Generalize that by putting an analog voltage on the gate such that the mosfet is biased (0 < Rds < infinity) and presto, we have your idea. 50 amp MOSFETs are cheap; 50 amp potentiometers are not.
  Reply With Quote
Old 12th October 2013, 12:17 AM   #3
diyAudio Member
 
Join Date: Sep 2013
Location: USA
Why 50A?
  Reply With Quote
Old 12th October 2013, 12:21 AM   #4
diyAudio Member
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Send a message via Skype™ to JonSnell Electronic
It is called Power Factor Correction.Another requirement by the EEC for stopping noise both in and out of electronic equipment that is in common use.
Fitting any sort of impedance in series with a filter capacitance will normally impede its usefulness.
__________________
www.flyingmole.co.uk For World Wide support for Flying Mole, Class D, Refurbishment and Repairs. www.jonsnell.co.uk
  Reply With Quote
Old 12th October 2013, 12:28 AM   #5
diyAudio Member
 
Join Date: Sep 2013
Location: USA
In a standard tube rectified guitar amp circuit, would swinging the filtering effect the output bias? I'm thinking that if it did, it would be very very minimal...
  Reply With Quote
Old 12th October 2013, 04:48 AM   #6
ChrisA is offline ChrisA  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by Sea Biscuit View Post
Is filtering reduced if a resistor is placed in series with the neg of a filter cap and ground? If so, could a correctly spec'ed pot be placed there to make it controllable for an intended swing ??



This may be another dumb question, but I'm just gonna ask it anyway
If you really want to do this. Simply use several small caps in parallel and wire a switch in series with each one. If you want very fine control make each cape twice the size of the next. Then by using binary combinations you can have 16 effective cap values with only four switches or 8 with three switches.

As was said above you can use mosfets in place of toggle switches. You then control the mosfets with anything you like.

I'd start the experiment with just plain old toggle switches and see what the effect sounds like.

Webber sells capacitor boxes that let you dial in an cap you like. Try one of these first.
  Reply With Quote
Old 20th October 2013, 11:40 PM   #7
diyAudio Member
 
Join Date: Nov 2011
Location: W Yorkshire
I have read this thread all the way through and am intrigued as to the possible use of the proposed scenario... purely out of curiosity. Most of what I do applies to either valve guitar amps or the complete opposite end of the spectrum in digital telecommunications (go figure)... so I don't mind asking a dumbass question now and again if I'm going to learn something
  Reply With Quote
Old 22nd October 2013, 02:26 AM   #8
diyAudio Member
 
Join Date: Oct 2004
Location: Adelaide South Oz
Yes,
Use a Capacitance Multiplier Circuit with a potentiometer in place of the resistor

Description at Elliot Sound Practices
Capacitance Multiplier Power Supply Filter

And Shoog's experience
My experience with a Capacitance Multiplier

Cheers,
Ian
  Reply With Quote
Old 22nd October 2013, 02:40 AM   #9
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

What advanced nonsense are we talking about ?

Varying the capacitance mainly affects the amount of
ripple of the supply not the voltage swing of a supply.
Transformer taps is the way to vary voltage swing.

rgds, sreten.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
  Reply With Quote
Old 22nd October 2013, 10:45 AM   #10
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Don't forget this is Instruments and Amps. Normal audio electronics design rules need not apply. Any craziness which gets the required 'sound' is OK even if there is a simpler and more reliable way of getting the same result.
  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
State Variable Filter kipman725 Multi-Way 1 29th July 2009 04:43 PM
Variable High pass filter? ayearofholidays Instruments and Amps 1 30th April 2009 02:53 AM
variable infrasonic filter djronbxs Solid State 0 20th November 2007 10:05 AM
How do you make an audio potentiometer into a variable resistor? Darren Nemeth Parts 1 10th February 2005 08:15 AM


New To Site? Need Help?

All times are GMT. The time now is 10:03 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