Conrad Johnson PV-7 noise

Kid Charles · 13th July 2003, 09:28 PM

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.

barretter · 14th July 2003, 10:35 AM

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.

fdegrove · 14th July 2003, 02:39 PM

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,

SY · 14th July 2003, 03:01 PM

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.

analog_sa · 14th July 2003, 04:01 PM

It may even be a bad tube socket.

Kid Charles · 28th July 2003, 03:22 AM

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?)

analog_sa · 28th July 2003, 07:36 AM

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

Kid Charles · 29th July 2003, 03:24 AM

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?

fdegrove · 29th July 2003, 10:48 AM

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,

analog_sa · 29th July 2003, 01:29 PM

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...

13th July 2003, 09:28 PM	#1
Kid Charles diyAudio Member Join Date: Jul 2003 Location: WI	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.

14th July 2003, 03:01 PM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX 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. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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14th July 2003, 10:35 AM	#2
barretter 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.

14th July 2003, 04:01 PM	#5
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	It may even be a bad tube socket.

28th July 2003, 03:22 AM	#6
Kid Charles 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?)

28th July 2003, 07:36 AM	#7
analog_sa diyAudio Member 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

29th July 2003, 03:24 AM	#8
Kid Charles 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?

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