Pedja Rogic's J-fet buffer for dummies. - 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 26th January 2007, 09:57 AM   #1
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Talking Pedja Rogic's J-fet buffer for dummies.

After my bad luck with the Les Sarge circuit, I decided to give Pedja Rogic's J-fet buffer a try....

Well it worked straight away, and is sounding very mature... It seems to hang with the music relentlessly, and there is none of the hash in transients, I could hear with my other preamp attempts, except for maybe the ECC88 buffer this is replaceing.



So, I thought I will add it here for the future, and other noobs struggleing to get a good preamp going.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

http://www.pedjarogic.com/gc/index.html

Thanks PEDJA, and NUUK, for pointing me in this direction with your site and layout...mine is a little diffirent, trying to reduce wire jumpers, putting power connection on output side, and accommodating diffirent size caps I had... you can see that it is easy to adapt the outut filter caps to whatever size you have...
  Reply With Quote
Old 26th January 2007, 04:53 PM   #2
mlloyd1 is offline mlloyd1  United States
diyAudio Member
 
mlloyd1's Avatar
 
Join Date: Feb 2001
Location: illinois
for folks looking into understanding the jfet parts of this kind of buffer design, this paper is pretty good reading:
http://www.analogzone.com/col_01302004.pdf
or see article and more info about the author here:
http://www.analogzone.com/col_012004d.htm

mlloyd1
  Reply With Quote
Old 26th January 2007, 08:42 PM   #3
diyAudio Member
 
Steve Eddy's Avatar
 
Join Date: Sep 2002
Location: Sacramento, CA
Why not use a dual matched JFET like the LSK/2SK-389? Also, a source resistor on the top JFET would let you null out the DC offset and you could eliminate the coupling capacitor.

For the cascode MOSFET, how 'bout something like the Supertex DN-2540, which is a depletion mode device which would make it self-biasing which would eliminate the need for the voltage divider?

For that matter, you could also use one on the current source and end up with no more parts than you're using now.

se
  Reply With Quote
Old 27th January 2007, 03:43 AM   #4
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Sorry Steve you are getting ahead of me there... offset is minimal about 6mv... allthough there is a 2V DC spike at power on.

From what I understood, the lowpass was a neccesary element to get the circuit to work well with a chipamp which is internaly frequency limited...


What I would like to know is, if one should add decoupling caps to the power rails?

Will try to understand what you said later when I'm awake...
  Reply With Quote
Old 27th January 2007, 04:13 PM   #5
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
How do I know when I have a groundloop?

I suspect so, as the circuit is quiet when using earphones but have a slight hum with my My_ref C.

Could this be because of the lack of bypass caps...? once again, didn't see any in the schematic.

WHat would be the easiest tests for groundloop problem?

Input and output sockets are isolated from chassis.. have exactly the same earth decoupling network in the preamp as in the main amp... both connected to mains ground... no problem with my valve buffer, using same arrangement.
  Reply With Quote
Old 28th January 2007, 06:36 AM   #6
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Bump!

You guys are so fast to look smarter than each other, so how about a little help then?
  Reply With Quote
Old 28th January 2007, 06:52 AM   #7
diyAudio Member
 
Steve Eddy's Avatar
 
Join Date: Sep 2002
Location: Sacramento, CA
Quote:
Originally posted by Nordic
You guys are so fast to look smarter than each other, so how about a little help then?
Oops. Sorry. Got sidetracked. I'm just calling it a night but I'll make a note to reply in the morning.

se
  Reply With Quote
Old 28th January 2007, 06:56 AM   #8
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Baaah, it is the morning over here... next time I'll give you guys helpfullness pills before I go to bed, so you can solve my problems while I sleep...

But, in the meantime I'l be waiting open mouthed in the heat.
  Reply With Quote
Old 28th January 2007, 05:08 PM   #9
diyAudio Member
 
Steve Eddy's Avatar
 
Join Date: Sep 2002
Location: Sacramento, CA
Quote:
Originally posted by Nordic
Baaah, it is the morning over here...
Not my fault. Move to a better time zone.

Anyway, don't think your hum is for lack of bypass caps. They're not really doing anything for you at power line frequencies anyway.

What happens if you remove the buffer's ground from the mains safety ground?

se
  Reply With Quote
Old 28th January 2007, 05:32 PM   #10
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
I was waiting for someone to give me the go-ahead... gotta wait for the wife to finish watching TV now...

Thanks for comming back ...
  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
Pedja Rogic buffer + pllxo joshuajoshua Chip Amps 0 31st January 2009 05:32 AM
Help a noob build Pedja Rogic's J-fet buffer mattjk Chip Amps 5 29th July 2008 04:10 AM
WTB: Pedja Rogic buffer board vizion Swap Meet 0 16th May 2008 03:49 PM
low voltage PSU for Pedja Rogic's buffer sith Chip Amps 5 1st February 2008 06:19 PM


New To Site? Need Help?

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


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