need help with with Conrad Johnson amp/preamp

[Mary Smiley]

Hi, I don't even know if what I have is an issue with either of these, but I have to start somewhere.
I have 1980's vintage Conrad Johnson Power amp MV75A1 and CJ preamp PV2Ar and AR turntable with Sumiko MMT tonearm and a Talisman moving coil cartridge. I've been playing records after getting a new head amp for my mc cartridge which is a retipped Talisman B cartridge, tipped with a ruby cantilever.

The problem I am having is, all of a sudden my right speaker isn't working.Both were working just fine for several days but now no right side. I can push the reverse switch on the preamp and the right speaker works and then the left speaker doesn't work. If I play on mono they both work. I've tried wiggling the interconnects but still, no right side. I'm wondering if the interconnects could have gone bad or if it is an issue with the preamp or what. What are some tests I can do to try and figure out what is causing the problem?

I've posted here many years ago and always got lots of very useful feedback. Thanks in advance for any help you can give.

 

[goodolpg]

Based on your "reverse" test the channel works, so something in switching is not working.
Try cleaning the controls. You may have to take the cover off to get at the controls. MAKE SURE THE POWER IS OFF/UNPLUGGED
All of them. Get cleaner inside the controls, find a little hole or slot to shoot the fluid into. Then work the control back and forth until your arm hurts. Then do it some more.

Helpful hints here...you don't have to read the whole thread..
https://audiokarma.org/forums/index.php?threads/the-idiots-guide-to-using-deoxit-revisited.207005/

 

[Blue Shadow]

Using the reverse on the preamp means that the amplifier and speakers are playing correctly, the channel works when it gets a good signal from the preamp.

you can evaluate the preamp and the connections INTO the preamp by swapping cables from left to right and see if the channel working changes. Do not change any of the preamp output and amplifier input cables as we have veryified that both of those work...mono works and reverse changes what is missing.

If the cable swap doesn't change anything then the issue is in the preamp. Whether that be a tube loose in a socket or dirt in the controls or whatever, it would need more troubleshooting to find the issue.

When the system is off...Turn off the system to do this, rotate all the controls full left to right on the preamp a few times and operate the switches, just in case there is some dirt that might want to move out of the way. This can be done instead of the full cleaning mentioned above while you seek out some DeoxiT and wait for it to show up.

Check all connections on the phono.

Do you have another source, CDP, phone or something to use as a second input to verify the preamp vs the phono input?

 

[Mary Smiley]

Well, swapping the cables from left to right did change which speaker works. I think there is an issue with the cable. They are old but they were quite expensive in the day. I guess the first step will be replacing the interconnect between preamp and power amp. Thank you!

 

[Blue Shadow]

From your description of what changed the pre-power cable is fine as both channels worked based on the Stereo-Rev-Mono switch position. Your issue is in the preamp or before it.

 

[Mary Smiley]

From your description of what changed the pre-power cable is fine as both channels worked based on the Stereo-Rev-Mono switch position. Your issue is in the preamp or before it.

The NAD head amp says to plug the turntable into the auxiliary ports on the preamp and turn the source to aux on the preamp. It won't work if plugged into the phono port. What does CDP mean? to use as a second input?

 

[Blue Shadow]

compact disc player.

Yes the NAD phono needs to go into an AUX input.

I would be reversing the wires from the TT to the NAD and test
I would then reverse the wires from the NAD to the PV and test.

If something changes, you have a wire issue.

 

[Leviasean15]

This may come off as a dumb question, but do you have any "rca plugs" inserted into one of your left inputs? I ask because I recently experienced a similar issue with a Luxman CL-350. I swapped cables, DACs, TTs, but no matter what, only 1 chanel would play.

After losing my mind for a few minutes, I decided to unplug and reconnect my entire system, including the small plugs inserted into the tape-outs. Voila! The plug was inserted into the left tape-out and would not allowing the signal to pass through to the amplifier. Its a long shot, but you never know!