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Need Vox V9310 Schematic

1/27/2004 3:00 AM
Rick Erickson
Need Vox V9310 Schematic
Hi all,  
I need a schematic for a Vox Model 9310 "Cambridge 30 Reverb" amp. It's a SS amp with a single 12AX7 tube. I actually have two of these in my shop and both have similar intermittent distortion problems. There are some interesting differences in the preamp circuits that I would like to get a better view of. Can't tell if they're both factory or if one has been modified but both amps appear to have been altered. Can anyone help me with this one?  
1/27/2004 8:48 PM

Rick, i thought Enzo might have the SS info stuff.  
You might try here..  
And send them and e-mail,they should be able to send you one..  
They have quite a few SS amps there listed..just not the one your looking for..  
1/28/2004 2:03 AM

Check your email.  
By the way, I have serviced a good half dozen of these, and every single one of them had the same thing wrong. There is the opto for the tremolo, the part is LT9914 or something like that. It is bad. I do work for Elderly Instruments, and they ordered a few, and I had to fix all of them. Not one was good out of the box. A couple have ccome in with customers, and sam ething.  
The sound will be distorted and crappy, and the trem will be very weak or nonexistant.  
The opto has an LED end and a photocell end. The photocell is in series with the signal path. SHort across it with a clip lead and see if the sound cleans up and gets loud.  
Of course I may just have had a bad lot of them and you have some other malady. I have not found a simple sub for the part, and Korg wants something stupid like $12 each.
1/28/2004 3:55 AM
Rick Erickson

Thanks Enzo,  
You da' man!!!  
I just got the schematic you sent me. I hadn't been able to log on due to internet problems today so I had Korg fax me a copy. What a waste of time. The copy I got from them was all but unreadable. I was able to determine that the channel switch IC was not the problem and that the photocell was the most likely suspect. I pulled the cell out of one amp and ran some tests on it to get a resistance/current curve that may be helpful in finding/making a replacement.  
Strange thing is - after installing Vector T-42 Flea-Clips to the pc board & reinstalling the photocell the amp seems to be working fine. I'm certain it will act up again though.  
"The sound will be distorted and crappy, and the trem will be very weak or nonexistant."
Exactly! I have two of these right now with exactly the same problem. I can't see putting in the same photocell if they are all failing so I guess I'll have to try my luck at finding a substitute or rolling my own. The Trem. trim pots (VR11 & 12) seem awfully touchy also. Seems like breathing on them changes the signal level considerably. Not sure what I can do there except to maybe measure their values when the circuit is working correctly and subbing fixed resistors. Not a very stable design imo.  
Speaking of which - last night while testing the "other" C-30R I opened the load switch on my dummy load box and powered up the amp. The output swung full positive and stayed there. I closed the load switch which was set to 8 ohms and powered it up again and the output device, a TDA2050 released all its smoke! I'm still not sure why that would have happened. (I might have closed the load switch before I turned off the power switch, and then cycled the power - oops!) I guess I'll have to get some replacement TDA2050's and see if I can do it again. :)  
Thanks for the help with this one!  
1/29/2004 8:27 AM

Well, don't put much stock in touchy adjustments with the bad part in there.  
I have replaced them all with the factory part, and none has failed since, so... ALl warranty work. When I get one out of warranty I will spend more brain time on a replacement. Let me know what you come up with.
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