[JHC]

I have a ST-70 with Curcio premium mods and a Van Alstine SuperPas Three preamp and a Squeezebox. I think the issue is the preamp. Following the troubleshooting guide from the Curcio web site and reading several threads on their forum, this is what I've found:
1. With my Squeezebox into the preamp and preamp to amp, I get a loud buzzing hum in the left channel and slightly less hum in the right.
2. Squeezebox direct to the amp is fine. IPod direct to amp is fine.
3. Using just RCA shorting plugs on the amp, there's no hum.
4. Put shorting plugs on the any line input of the preamp and preamp connected to the amp, I get the same hum.
5. In the preamp, I swapped the tubes around and the hum doesn't switch channels; pulled the rectifier tube and hum doesn't change. If I swap L/R inputs to the amp only, the buzz/hum follows. I swapped interconnects with another pair and the hum remained.
6. With the shorting plugs on the preamp and preamp connected to the amp, when I turn the volume up about a quarter turn, the loud buzzing hum in the left channel goes away - but there is a fairly loud hum in both channels. Just as I turn to near full volume there is a noticeble click and the right channel hum jumps in volume. Not as loud and buzzing, though. Turn it back down and the left channel hum returns.
7. I tried grounding the preamp chassis to the amp chassis with the only long piece of wire I had around - an FM attenna, and it made no diff.

I tried using the preamp on the line input of my Home Theater receiver and do not get any hum, but since it isn't a true preamp in, I don't know if that's useful.

My question is: does this sound like a connection/grounding/solder problem or a problem with electrical components? I don't read schematics or know anything about caps or resistors, but I could use my multimeter if I knew what I was doing. Thanks for any suggestions.

[Wayner]

Sounds like you should give Frank a call and he'll help you get to the bottom of it. Sounds like it may have to go to the shop.

Wayner

[rlee8394]

JHC,

Do you have the original selector switch, or was a new one installed when the update was done. The new selector switch automatically grounds all of the other inputs that aren't selected. With the preamp off, try setting the selector switch to a line input. Then remove the component connected to that input and install the shorting plugs at that input. Power up the preamp and then the amp. See if the problem still exists. If it disappears, then the source component was the culprit. Also make sure the tape monitor switch makes good electrical connection. Just something else to watch out for. If you have the original selector switch, I wold recommend replacing it with a new one from Frank.

Ron

[avahifi]

Please call me at 651-330-9871 regarding this issue.  I will try and talk you through troubleshooting it.  It sounds like an open ground connection somewhere to me.

Regards,

Frank Van Alstine

[JHC]

JHC,

Do you have the original selector switch, or was a new one installed when the update was done.... If you have the original selector switch, I wold recommend replacing it with a new one from Frank.

I bought the preamp new from Van Alstine in 1994. It worked for years with my CD player (and Squeezebox if I recall) until the tape selector switch seems to have gotten dirty and I'd get weird distortion. Frank suggested cleaning it with contact cleaner and that helped it. But by that time I had gotten used to using the Squeezebox directly because I had remote control. Then I decided to run the Squeezebox at full volume and use the preamp.