J Fet Buffer problem - help ! - 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 22nd October 2009, 07:33 PM   #1
diyAudio Member
 
Join Date: Jun 2008
Default J Fet Buffer problem - help !

Hi

Just put together a cheap J fet buffer with regulated +/- 15 v supply.
All off E Bay from the usual suspects in the far east and less than 30 for the lot - including traffo - great !
Lashed it together in a hurry - placed it between CD player and Alps Black Beauty and hey presto....much better in bass, extra mid info and slam department.

I then read about putting it between the pre and power amp and found that in doing so the protection relay in the power amp clicked in and out.
No hum, music in between clicks from both speakers but could not find the problem.
Reversed it back to original config and it was fine again !!

My power amp has input impedance of 1V / 50 Kohms and the black beauty is 50 K.

Don't know whether this is relevant but if it is what value should I ideally have
please?

What have I done ?

Andrew
  Reply With Quote
Old 22nd October 2009, 07:43 PM   #2
diyAudio Member
 
Steve Eddy's Avatar
 
Join Date: Sep 2002
Location: Sacramento, CA
Perhaps some DC offset on the output of the buffer?

Is the buffer cap coupled on the output?

se
  Reply With Quote
Old 22nd October 2009, 07:44 PM   #3
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
Did you put DC into the power amp input?
  Reply With Quote
Old 22nd October 2009, 08:21 PM   #4
diyAudio Member
 
Join Date: Jun 2008
Truth is I really don't know.

If I have put DC on the input why does it work after the CD player and not after the pot ?

I think I've attached a pic of the buffer - you'll have seen it before
no doubt.

Can you tell me what to do ?

Hey, maybe there'll be no difference having it before or after the passive but I want to find out if poss.

Really appreciate the help

Andrew
Attached Images
File Type: jpg fetbuffer2.jpg (124.4 KB, 105 views)
  Reply With Quote
Old 22nd October 2009, 08:42 PM   #5
grufti is offline grufti  United States
wombat
diyAudio Member
 
grufti's Avatar
 
Join Date: Jun 2004
Location: Hillside
disconnect your buffer from all the other pieces of equipment - short the buffer inputs - power up your buffer - measure DC on your outputs - anything more than a couple of mV is no good.
  Reply With Quote
Old 22nd October 2009, 09:32 PM   #6
diyAudio Member
 
Join Date: Jun 2008
Grufti, thanks.

I'll give it a try and see.
Any idea why it's OK after the CD ?
It really is good, much better than when passive.
Thanks to all who have thought about this for me.

Andrew
  Reply With Quote
Old 22nd October 2009, 10:14 PM   #7
diyAudio Member
 
Join Date: Jun 2009
Send a message via Yahoo to kannan_s
Quote:
Originally Posted by AndrewGM View Post
Grufti, thanks.

I'll give it a try and see.
Any idea why it's OK after the CD ?
It really is good, much better than when passive.
Thanks to all who have thought about this for me.

Andrew
Since it looks like a small circuit with few components - make the schematics ( or ask the Hong Kong seller for the schematics) - measure the DC voltages/post it here so- people can tell you what is wrong - if any?
it will also help you understand this in relation to many buffers
sk
  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
Diamond Buffer - Super Buffer peranders Solid State 34 16th May 2010 01:46 PM
problem with 12AE6A buffer ionomolo Tubes / Valves 2 29th March 2009 11:40 PM
buffer TUBESMAN Solid State 4 22nd October 2008 05:32 PM
op-amp buffer for non os DAC AudioGeek Digital Source 2 6th November 2005 01:00 PM
Opamp + buffer, how to bypass buffer at HF for unity gain? Christer Solid State 10 29th October 2003 06:50 AM


New To Site? Need Help?

All times are GMT. The time now is 08:13 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