Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Pass Labs This forum is dedicated to Pass Labs discussion.

Audio Virtues of JFET Transconductance Amplifiers
Audio Virtues of JFET Transconductance Amplifiers
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 15th May 2018, 03:51 PM   #21
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
This is a circuit that I think works.
But I have to try it when I get home some more transistors.
It takes 18 of BC560C and BC550C.

It is a VCA. Voltage Controlled Amplifier.

At the input is a divider that divides with roughly 44.
The small resulting voltage is put to input pair.
The current difference is transported to the output, and put across a 10k resistor.
At the output is a buffer transistor.

Max bias input is like 1mA and so is 0.5mA at each transistor.
P2 potentiometer is to regulate the volume with the bias current.
P1 is for adjust eventual output offset.

I might need to adjust some values when I test it at my experimentboard.
Attached Images
File Type: png ota-3-vca.png (91.8 KB, 221 views)
__________________
lineup
  Reply With Quote
Old 15th May 2018, 05:25 PM   #22
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
Lineup,

It has been ten years...................since this thread was active......good to have you back lineup................Mr.Pass probably thinks I am a wildman too.

Jam

Last edited by jam; 15th May 2018 at 05:52 PM.
  Reply With Quote
Old 15th May 2018, 05:34 PM   #23
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
Just for grins and giggles.......................
Attached Images
File Type: png 2010171812720939.png (109.6 KB, 210 views)

Last edited by jam; 15th May 2018 at 05:49 PM.
  Reply With Quote
Old 15th May 2018, 05:36 PM   #24
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Audio Virtues of JFET Transconductance Amplifiers
Quote:
Originally Posted by EUVL View Post
A question for Nelson :

Suppose one builds a balanced version, but the two halves are not 100.0000000% well matched.
i.e. the output of one phase is not exactly -1.000000000x of the other.
Since both current outputs are connected to a single load, where the hell of the difference in the two currents should go to ?
The are absorbed by the net value of impedances at the output:

1) intrinsic output Z of the open loop circuit (always less than infinite)

2) output z due to negative feedback

3) load impedance
  Reply With Quote
Old 15th May 2018, 06:29 PM   #25
Zen Mod is offline Zen Mod  Serbia
Official Court Jester
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Audio Virtues of JFET Transconductance Amplifiers
Quote:
Originally Posted by jam View Post
Just for grins and giggles.......................
current mirrors are for Sissies

__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 15th May 2018, 06:34 PM   #26
stocktrader200 is offline stocktrader200  Canada
diyAudio Member
 
Join Date: Jan 2008
Location: Calgary
match all transistors to have a Hfe of 200 to 250. Just make sure that all are the same, then the distortion will be lowest.
  Reply With Quote
Old 15th May 2018, 06:58 PM   #27
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
Zen Mod.

Guess that makes me one.......................
  Reply With Quote
Old 15th May 2018, 07:03 PM   #28
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Quote:
Originally Posted by stocktrader200 View Post
match all transistors to have a Hfe of 200 to 250. Just make sure that all are the same, then the distortion will be lowest.
Is the hFE more important than the b-e voltage?
In this case.
__________________
lineup
  Reply With Quote
Old 15th May 2018, 07:09 PM   #29
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
Everyone seems to forget about the Early Effect...............

Eliminating the Early effect in the... (PDF Download Available)

Jam
  Reply With Quote
Old 15th May 2018, 07:39 PM   #30
Zen Mod is offline Zen Mod  Serbia
Official Court Jester
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Audio Virtues of JFET Transconductance Amplifiers
not Moi , Bubba



F4 Beast Builders
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote

Reply


Audio Virtues of JFET Transconductance AmplifiersHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Can I use the 2N5484 jfet diff pair in an audio amplifier front end? carpenter Pass Labs 27 28th March 2009 12:55 AM
First Watt F3 / Tube Audio Design TAD-125 Hibachi JFET amps vizion Tubes / Valves 1 31st August 2008 03:08 AM
Bestow upon me the virtues of MM vs. MC eeka chu Analogue Source 17 16th November 2005 07:45 AM
pro amplifiers vs. home audio amplifiers bonsai171 Solid State 26 25th February 2004 08:24 PM
IC audio amplifiers jteef Solid State 8 21st July 2001 03:14 PM


New To Site? Need Help?

All times are GMT. The time now is 02:52 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki