Volume control, Evil Mad Scientist style - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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 23rd November 2012, 10:03 AM   #1
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Lightbulb Volume control, Evil Mad Scientist style



Here is a new idea for volume control: it uses the principle of
variable magnetic coupling


The coils used are air-cored, meaning they introduce no distortion.

Obviously, there has to be a frequency correction, but this is pretty straightforward, it is essentially a first order compensation.

The prototype is a proof-of-concept demonstrator, bulky, open and unshielded, for real applications the coils should be made with proper wire, not PVC covered wiring cable, have sufficient turns, and the assembly should be enclosed in a shield.

The values on this prototype are preposterous for audio: the coils only have 35t and 25t, with correspondingly low inductances (I made them first, measured them and made calculations and design around them) .

The transmit L/R time constant results in a 13KHz corner frequency, meaning there has to be a huge correction and a hefty Tx side amplifier.

Even so, the prototype works exceedingly well, with a nice and smooth variation, a perfect null thanks to a small auxiliary coil and a perfect audio transparency. Very pleasant!

The overall gain is much larger than 0dB at the maximal volume, a resistive pad is included at the output to restore the level and reduce the noise.
Other strategies would be possible.

Have fun!!
Attached Images
File Type: jpg VariM1.jpg (256.4 KB, 584 views)
File Type: jpg VariM2.jpg (307.4 KB, 559 views)
File Type: jpg VariM0%.jpg (253.0 KB, 540 views)
File Type: jpg VariM50%.jpg (209.2 KB, 502 views)
File Type: jpg VariM100%.jpg (240.2 KB, 491 views)
File Type: png VariMfreq.png (120.2 KB, 278 views)
File Type: png VariMtran.png (160.3 KB, 253 views)
Attached Files
File Type: asc VariM.asc (5.4 KB, 11 views)
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 23rd November 2012, 11:08 AM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
When you get fed up with it as a volume control you can convert it into a crystal set or an LF ATU.
  Reply With Quote
Old 23rd November 2012, 11:22 AM   #3
diyAudio Member
 
freax's Avatar
 
Join Date: Sep 2007
Now that is reinventing the wheel!
  Reply With Quote
Old 23rd November 2012, 11:45 AM   #4
diyAudio Member
 
KaffiMann's Avatar
 
Join Date: Sep 2009
Just like Dr.Wily would, lacking some robotic arm controlled by remote to regulate the knob though, would also be neet if you made the same robotic arm change input by toggle switches.

Volume down, toggle cd left off, toggle cd right off, toggle lp left on, toggle lp right on, lp player start, volume up

Last edited by KaffiMann; 23rd November 2012 at 11:51 AM.
  Reply With Quote
Old 23rd November 2012, 12:04 PM   #5
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by freax View Post
Now that is reinventing the wheel!
I wasn't aware that particular wheel had been invented.

Can you provide an example of such a volume control? (I mean not the plain old autoformer type)
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 23rd November 2012, 12:06 PM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Very imaginative Elvee
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 23rd November 2012, 12:09 PM   #7
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Varying coupling between circuits by moving/rotating a coil was used in early TRF radio sets for adjusting reaction, I think. It may not have been used for volume because it is not a good way to do it. It is easy to be first to invent a bad idea!
  Reply With Quote
Old 23rd November 2012, 12:50 PM   #8
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by DF96 View Post
It may not have been used for volume because it is not a good way to do it. It is easy to be first to invent a bad idea!
Compared to some alternatives volume control schemes, of which a number have been presented here, this idea looks rather sound, dull and rational
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 23rd November 2012, 12:59 PM   #9
diyAudio Member
 
freax's Avatar
 
Join Date: Sep 2007
Well heres the problem that I have with it.

I'm actually in the market for a good quality volume control inorder to go between or after my recently built TDA1543 DAC and a tube preamplifier.

I have the rather excellent and easy to find/purchase/install option of the Resistor based selector switch style of volume control.

Or I could go for a pot, which I'm not going to because I want the best here.

I don't want my sound to be muddled, I don't want my sound to be touched in any way, I am afterall considering spending a hundred bucks or so on a bag of good resistors and a high quality copper double gang selector switch.

What does your rather interesting project have to offer? it might have perfect linearity in a simulation but it doesn't in real life, I assure you of that.

More to that point (linearity), I am as of monday of next week purchasing a $1,000 OTL tube amplifier kit from Transcendent Sound, OTL means that it has no output transformer.

An output transformer colours the sound, and some people have spent many tens of thousands of dollars on just 1, made out of pure silver wire and some of the finest hand ground japanese iron cores, which are then rested in-between the breasts of a lovely japanese schoolgirl for 3-5 weeks.

Now I don't know about you but where and why exactly would I want to use a magnetically coupled volume control? which could quite easily pickup the magnetic field of a transformer, or a wire in the wall behind it, or the television set SMPS power supply.

You sir have built a radio more than a volume control, a volume control is transparent and passive, this, conceivably with a diode in the right place, could make a fine radio.

And that is what I mean by reinventing the wheel. Enjoy your invention, it looks nice and could even do good in the right place, a tube radio.

Last edited by freax; 23rd November 2012 at 01:03 PM.
  Reply With Quote
Old 23rd November 2012, 01:07 PM   #10
diyAudio Member
 
freax's Avatar
 
Join Date: Sep 2007
Now if you want something to really build, build a vacuum tube volume control.

One that has the input going to the cathode, output going to the plate, and a grid inbetween which is energized by a DC voltage inorder to "steal" the flow of electrons flowing from the cathode to the plate.

Woops, already been done: 6BE6 volume control
  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 08:20 PM
Replacing broken volume control with digital volume control Gunawan W Solid State 19 15th December 2010 11:46 AM
Op Amp chips in the signal path - evil or not evil ? thylantyr Solid State 19 25th July 2008 06:43 PM
New Scientist Feb 23 2008 7n7is Everything Else 0 25th February 2008 02:00 AM
remote control motorised control for volume pot/knob CharlesY Parts 0 25th July 2005 12:12 PM


New To Site? Need Help?

All times are GMT. The time now is 05:53 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