Preamp Volume Controls - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 27th January 2012, 06:39 PM   #1
10west is offline 10west  New Zealand
diyAudio Member
 
Join Date: Jan 2012
Location: Auckland
Default Preamp Volume Controls

I've got a bit of a dunce question. I've been making the odd valve power amp since I was 13-14 (25 now). I realise that I've never made a valve pre-amp, I've got enough parts in the old parts drawer to make something I think, but I don't understand about fitting a volume control. I see alot of designs on the net for preamps that have tone controls but thats it. Am I right in thinking that I can pretty much just put a variable resistor on the line source prior to it going into a preamp circuit such as the one below?
Attached Images
File Type: gif ef86preamp.gif (22.3 KB, 257 views)
  Reply With Quote
Old 27th January 2012, 06:46 PM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
A volume control is not quite a variable resistor (that would be two connections) but a potentiometer (three connections) acting as a potential divider. Just look at what other people do - there are plenty of preamp circuits on the web. Even the bad circuits usually manage to get the volume control right.
  Reply With Quote
Old 27th January 2012, 07:09 PM   #3
10west is offline 10west  New Zealand
diyAudio Member
 
Join Date: Jan 2012
Location: Auckland
Hi! Thanks for your help,

So What I need to be doing (using the above circuit as an exampe) is to put my potentiometer ont he input side, so the wiper feeds the input and the other two connections are connected to ground and the source signal respectively. I suppose the next question is what value pot to use.

I seem to remember reading that the ballpark figures were something along the lines of 10k for SS input or from a valve device you would use around 100k. Is is this at all valid? Or are there any simple calculations or rules you can follow to choose the correct one?

Thanks again for your help!
  Reply With Quote
Old 27th January 2012, 07:36 PM   #4
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Yes, you've got it. The value is not too critical. It needs to be equal to or higher than the minimum load of the source. It also needs to be less than four times the maximum source inmpedance for the next stage. If in doubt, use 50k - a bit more for valves, a bit less for SS.

You normally need a log law pot, so that it roughly matches the way our ears respond to volume changes.
  Reply With Quote
Old 28th January 2012, 04:02 PM   #5
Hi_Q is offline Hi_Q  England
diyAudio Member
 
Hi_Q's Avatar
 
Join Date: Oct 2007
Interesting that your schematic of a Pentode strapped as a Triode shows both G3 and G2 connected to the plate. This is the way I always expected it to be done but appears to be frowned upon in output stages. I can only assume it is because of the higher currents expected and the more fragile G3 is returned to cathode instead. Just to keep on thread, I think that all that requires to be said on the volume control values has already been stated. I recently came across a Guitar amplifier that had 3 volume controls fed from a Tone Ladder Network and then summed together. All controls were 470k LOG which always was a standard value on older tube equipment, in fact most volume controls were either that or 1 Meg Ohm. Nowadays I find much lower values in use, more probably due to the scarcity of the higher value controls, especially in Tandem configuration. 50k LOG and up seems to be the more common.
  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 Controls KatieandDad Analogue Source 10 21st November 2011 08:38 PM
Tapped volume controls fooeywuffle Swap Meet 0 19th July 2011 05:51 PM
Volume Controls Glowin Plates Tubes / Valves 8 8th April 2011 02:42 AM
Has Anyone Tried The P&S Volume Controls? dantwomey Chip Amps 5 22nd January 2010 07:57 PM
New version volume controls polsol Parts 2 21st September 2004 12:16 PM


New To Site? Need Help?

All times are GMT. The time now is 12:44 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