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HELP HELP - VENDETTA RESEARCH SCP2A FAULTY

I recently purchased a Vendetta Research SCP2a phono stage - before i go on I am 100% certain it was sold to me without any faults, and that it may have been something else that was the problem -
HOWEVER!!!
I have a major problem
I used a step down transformer as recommended by John Curl so that I could run it off UK voltage which is 230.
I got a great sound out of my right channel - as it happened I only wired the ground to the left channel.

I checked the fuses (1 Amp) - but to be sure I went and got some replacements and put them in.

Once back on again there was a very faint signal out of the left channel alone - I replaced the fuses with the originals - just in case - same thing.

I tried it this morning - absolutely no sound at all -
I got a decent step down transformer from Maplins so that there would be ample overload protection.

I have emailed John Curl and await a response - I have also furiously e-mailed a few audio electricians in the UK - does anyone have an idea what the problem may be?

Alternatively is there anyone you know who may be able to resolve this?

Thanks

Lohan
parrotbee
10 responses Add your response
zd542
5,339 posts
 
Try the power supply for the right channel on the left. Also, check the cables going to the left channel. You may have accidentally reversed the IC's.
rcprince
3,068 posts
 
Agree with Zd, reversing the power supplies (or switching the interconnect channels) might help isolate the problem. I also will assume that you have plugged both channels' power supplies into your step down transformer.
lewm
12,858 posts
 
I am a little unclear about the recent history. You say you originally heard no problem with the right channel, only the left channel was without signal. And incidentally, you mention that only the L channel was grounded. When you replaced the fuses, did things get worse, in that you lost the R channel as well? It seems so, based on what you wrote.

Have you opened the chassis, at least to see by visual inspection whether there are any loose wires? The fact that only the L channel was grounded should be neither here nor there, because if you're talking about chassis to chassis grounding, the grounds are probably common to each channel. I don't think there is a problem with your transformer, because you would have heard nothing at all or something more catastrophic might have occurred, if the AC voltage coming out of your transformer is seriously off the mark. BUT do you perchance have an AC voltmeter with which you can check it?
parrotbee OP
103 posts
 
Hi Lewm
You have read entirely correctly:
- I lost signal entirely when I went back.
I opened the amp up - no burning smells - not sure about loose wires
I am confused due to having heard something from the right channel initially.
Spoke to a guy called Ben Jalopy from Highend audio repairs in NYC and he thinks it is most likely a capacitor issue.
If this piece of kit wasn't so rare I would probably do the work on it myself, but I think I have roped a good technician into dong the work.
My real fear is losing the original fets if they are damaged - I am told they are the best thing about this phono stage...
finger crossed...
dnath's avatar
dnath
38 posts
 
The Vendetta does need extremely closely matched JFETs which are no longer made.

IMHO I would only let John Curl work on the unit.
bpwalsh
1,200 posts
 
Dnath is correct. These NOS JFETs from the 70s have been unobtainium for a long time, and John Curl is one of only two or three people who matched them by curve tracing them.
lewm
12,858 posts
 
There is a company on the West Coast, the name of which escapes me, that carries a lot of supposedly no longer available transistors, including FETs. I was able to buy the full complement of transistors needed for my 1980-vintage Beveridge amplifiers from them. I will look for the name later today, but you may find it by simply doing a google search on the needed FET, if indeed you need a FET.
parrotbee OP
103 posts
 
Hi Lewm - I think I have found the 'unobtanium' company. Trust me it was a flipping pain in the backside to find them - I felt like a stalker tracking posts by John Curl on another site. I spoke to a chap called Ben Jalopy - a pretty decent guy who reckons that it is most likely the old Panasonic electroytic caps that have gone bad. He reckons Elna replacements are the way forward.
lewm
12,858 posts
 
The company you found, is it in California? If so, they're a really good source.
I feel remiss in not thinking about the electrolytic capacitors. By all means, they need to be replaced if still OEM. One can only hope that damage has not already been done to one or more of the FETs.

Last year I bought a Klyne 6LX. I built a new outboard supply for it using an overkill toroid from Antec, and I replaced all the lytics on the audio chassis with ELNA Silmic IIs. I also upped the values of the PS filter caps. Lots of bang for the buck.
atmasphere's avatar
atmasphere
11,756 posts
 
You might try seeing if the tape monitor function has a dirty switch. That could make the unit act as you describe. Operate the switch a few times and see if the channel pops back in.

A dirty slector switch can cause this too.
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