A really simple buffer with fets. - 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 2nd September 2009, 06:23 PM   #1
diyAudio Member
 
Join Date: Sep 2009
Location: Stavanger (NORWAY)
Default A really simple buffer with fets.

Dear Sirs,

I sincerely hope Mr. Echowars will excuse me but with the aim of building a very simple but elegant fet buffer I have stolen the following attached piece of schematic from one of his 3D about a Stax preamp
What intrigues me is the simplicity of this piece of circuit.
But now the doubts: can the Q208 and 209 couple work as a unity gain buffer ?
I would like to eliminate the output caps, deeming that the actual offset should be low.
In front of the pair are a coupling cap or biasing resistors needed ?
I have already a nice stepped attenuator to put in front of it.
Any suggestion would be very welcome and appreciated.
And of course thank you so much Mr. Echowars !

Kind regards,
ginetto
Attached Images
File Type: jpg fet buffer.JPG (24.6 KB, 568 views)
  Reply With Quote
Old 2nd September 2009, 08:43 PM   #2
gk7 is offline gk7
diyAudio Member
 
Join Date: Oct 2007
Location: Vienna, Austria
Yes it will work as a unity gain buffer and do so very well. Download "Jfets The New Frontier, Part 2" from Erno Borbelys website (Part 1 is recommended too of course) and have a look at Page 18, Figure 16B and Table 3/collumn 4.
  Reply With Quote
Old 3rd September 2009, 03:40 PM   #3
diyAudio Member
 
Join Date: Sep 2009
Location: Stavanger (NORWAY)
Quote:
Originally Posted by gk7 View Post
Yes it will work as a unity gain buffer and do so very well. Download "Jfets The New Frontier, Part 2" from Erno Borbelys website (Part 1 is recommended too of course) and have a look at Page 18, Figure 16B and Table 3/collumn 4.
thanks a lot for the very kind reply.
Moreover I wonder if any other passive component is needed between the pot and this stage, like a biasing resistor and/or a coupling cap.
Any help would be very much appreciated again.
kind regards,

ginetto
  Reply With Quote
Old 10th September 2009, 03:56 PM   #4
gk7 is offline gk7
diyAudio Member
 
Join Date: Oct 2007
Location: Vienna, Austria
Sorry for the late reply I was on holidays. You would not need anything between the pot and the input of this stage, but there will be some offset at the output (depends how good the FETs are matched) and therefore an output coupling cap (can be omitted if the next stage has already an input cap) will be needed.
  Reply With Quote
Old 10th September 2009, 09:30 PM   #5
diyAudio Member
 
R-K Rønningstad's Avatar
 
Join Date: Jan 2006
Location: Oslo
The first time I saw this solution was the input buffer for the negative input of the Mark Levinson ML-2.
See attachement

Rolv-Karsten
Attached Images
File Type: jpg ML2 negative input.jpg (51.9 KB, 338 views)
  Reply With Quote
Old 15th September 2009, 11:02 AM   #6
diyAudio Member
 
Join Date: Sep 2009
Location: Stavanger (NORWAY)
Quote:
Originally Posted by gk7 View Post
Sorry for the late reply I was on holidays. You would not need anything between the pot and the input of this stage, but there will be some offset at the output (depends how good the FETs are matched) and therefore an output coupling cap (can be omitted if the next stage has already an input cap) will be needed.
Thank you so much !
Now this very simple schema is even more interesting
I will try it
thanks again and kind regards.
gb
  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
Simple Volume/Buffer! amplifierguru Solid State 37 6th September 2010 06:41 PM
Simple Input Buffer Adam M. Chip Amps 17 1st May 2010 12:37 AM
CFP diamond buffer output stage with vertical FETs, thermally stable? Russ White Solid State 5 1st January 2008 04:16 AM
What is better -> Buffer or simple pre azamkita Chip Amps 11 17th March 2005 02:03 AM
simple line buffer fscarpa58 Tubes / Valves 14 9th December 2003 08:30 AM


New To Site? Need Help?

All times are GMT. The time now is 05:18 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