Conrad Johnson PV-7 noise - 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 13th July 2003, 09:28 PM   #1
diyAudio Member
 
Join Date: Jul 2003
Location: WI
Default Conrad Johnson PV-7 noise

Hi all, I did a little research on this and couldn't find a satisfactory answer:

I have noise on my CJ PV-7 tube preamp that is well beyond what it should be, and much more than it used to be (it's volume is independent of the volume pot.) It is a hiss/crackle not a hum. Changing out every tube makes no difference. I e-mailed the CJ repair department a long time ago (long standing problem that I am getting around to fixing) and they suggested if switching out tubes makes no difference, it is probably a bad power transformer.

Is there any possibility that it might be something else? I'd like to know before I go off and replace the power transformer.
  Reply With Quote
Old 14th July 2003, 10:35 AM   #2
diyAudio Member
 
Join Date: Apr 2003
Location: West Yorkshire, UK.
Could be a bad ("cold") solder joint finally making its presence heard. Try wiggling resistors?capacitors on the circuit board (gently!) to see if one of them is loose.
  Reply With Quote
Old 14th July 2003, 02:39 PM   #3
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Quote:
Is there any possibility that it might be something else?
It could be a number of things, a zener diode, a HT regulator, a cap, flaky resistor etc.

The last thing I'd suspect would be the powerxformer.

Cheers,
__________________
Frank
  Reply With Quote
Old 14th July 2003, 03:01 PM   #4
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
See what the B+ rail and filament voltages are (if you don't know your way around high voltage gear, don't listen to me! Serious safety issue! ). If they're in the normal range, your power transformer is OK.

Could they have said "power transistor"? The ones in the regulator could certainly cause a problem like this.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 14th July 2003, 04:01 PM   #5
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
It may even be a bad tube socket.
  Reply With Quote
Old 28th July 2003, 03:22 AM   #6
diyAudio Member
 
Join Date: Jul 2003
Location: WI
Thanks for the ideas everyone. I contacted the CJ repair department and they suggested it might be a capacitor in the power supply. I tested every one of the supply caps and they looked ok (high dc resistance and proper capacitance). I guess it's on to other components (diodes maybe?)
  Reply With Quote
Old 28th July 2003, 07:36 AM   #7
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
This surely can't be so difficult. CJ preamps are very simple. I don't have a circuit for PV7 but looking at PV6 it should be easy to narrow the culprit down. Why do you think it's the PS? Is the noise equal in both channels? It should be possible to remove all tubes bar the output cathode follower. Is the noise still there?
Have you checked the bypassing cap on the zener array? Have you cleaned all tube sockets?

cheers
peter
  Reply With Quote
Old 29th July 2003, 03:24 AM   #8
diyAudio Member
 
Join Date: Jul 2003
Location: WI
The pv7 schematic is now posted on my webspace for your reference here. It's a little hard to read, but far better than not having it.

The cap that I think you mean by the bypassing capacitor on the zener array (c4 on the diagram) was one of the ones I checked, it was fine.

I took out all the tubes except for V5 which appears to be the output tube. (V1-3 are just the phono stage which I don't use anyway) The noise was present and a bit louder than with all tubes in, and somewhat more pronounced in the left channel. With V4 and V5 both in, the noise is a little lower, and basically balanced between channels.

I haven't cleaned the tube sockets, I suppose given that the noise was there even with only V5 in, if it is a socket it has to be that one, but I am too pessimistic to think that it is that simple. Any tips on cleaning sockets?
  Reply With Quote
Old 29th July 2003, 10:48 AM   #9
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Quote:
Any tips on cleaning sockets?
Just pulling the tube out and reinserting it a few times should have sufficient cleaning effect already.

BTW, don't use the preamp without all the tubes in place for that will reduce the load on the PSU making the B+ rise to probably unsafe values for the surroundig components.

Cheers,
__________________
Frank
  Reply With Quote
Old 29th July 2003, 01:29 PM   #10
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Quote:
BTW, don't use the preamp without all the tubes in place for that will reduce the load on the PSU making the B+ rise to probably unsafe values for the surroundig components.
Ehm, don't think so Frank, B+ is regulated...
  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
Conrad Johnson Premier 10 Freddie Tubes / Valves 2 19th March 2013 08:45 AM
Question Conrad Johnson reg. psu? KJ2005 Tubes / Valves 9 18th November 2008 07:25 PM
FS: Conrad Johnson Premier 11A amp Studley Swap Meet 0 18th January 2007 10:50 PM
Conrad-Johnson PV6 Preamp paulcurrie Tubes / Valves 3 17th April 2004 07:11 PM
conrad johnson help efoda Tubes / Valves 3 24th January 2002 03:23 AM


New To Site? Need Help?

All times are GMT. The time now is 02:53 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