Tube Pre Troubleshooting (VMP-2)

[Denus]

Hi all.

A few days ago Channel 1 of my VMP-2 suddenly stopped functioning properly. It was giving me extremely low volume with a lot of static/noise... I could barely hear a signal with the gain cranked all the way up, and this pre sends a HOT signal normally. Given my limited knowledge of electronics I swapped out Channel 1's tubes one at a time (Tube 1 for Tube 1, 2 for 2, etc... jfyi: each channel has 3 Sovtek 12ax7LPS's followed by a Phillips 12at7W) while trying to cause the same malfunction in Channel 2. Channel 2 never failed, so I'm not sure what could be wrong with the Pre. I did find this on the forums:

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Originally Posted by vince @ speck
Is there an insert jack on each channel?

If so, maybe the mic pre signal goes through the insert jack and the jacks' "normaling" terminals are not making proper contact.

Vince, that's a really good point. A lot of the cheaper desks route the mic pre out through a normal on the line in jack and that is certainly a weak point. Insert a 1/4" plug into the line in about 20 times while listening to the mic pre and see if it affects the level of the mic pre.

From this thread:

dead console preamp trouble shooting
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That sounds similar to my problem, but I don't know if the VMP-2 was designed in the manner described above.

If anyone suspects the above is my problem, I'd love a more detailed explanation of how to carry out the "1/4 inch x 20 inserts" test. If not, I'd like to hear any ideas as to what could be wrong and how to diagnose it before I throw money down to get her serviced.

Thanks, and please forgive my limited knowledge on the subject.

[Denus]

Problem resolved... bad jumper connection...