Question for ad50vt-xl users "screeching noise"

[mike w]

What's up Hyper. sorry it took me so long to respond, I havn't looked at this thread in awhile.

I looked at your you tube vid and yeah that sounds like it. Tap the strings, make any kind of background noise and it becomes a screech. Mine also screeched while doing nothing if I was at a band practice type level.

You sAID ON your youtube you had a strat. Try it on that guitar with just one single coil turned on. 2 single coiles cancels out hum so just use 1. When I did this the 60 cycle hum turned into a loud screech. You can dilute it down with lower gain and NR. But still, what the hell?

I took mine to my repair guy, replaced tube, a transister, and... something else. nothing worked. He said it sounded wrong, Korg said it met "factory specs" Long story short after several months,and alot of argueing with korg, I now have a VT 50. No more Xl's in stock

I know you said the noise started up suddenly, but I just get the feeling it's a design flaw, or cheap parts .....?

But I do feel your pain Bro, there were times I wished it would either work perfectly right, or just blow the hell up. But best of luck. Hope your still under warrenty. And i hope Korg does the right thing. Will mail you on your you tube account. Peace.

[Lythes]

Check the caps at the OP AMPS, the small caps help regulate the gain of the OP AMP, if the cap is loose (bad solder connection), shorted or not working correctly (out of value) it will change the gain of the circuit, which can cause it to squeal and make noise.

Hmmm, unless the laws of physics and electronics have changed, the gain of an Op Amp is determined by the ratio of the input and feedback resistance. Almost as cute a concept as spraying/cleaning input sockets as a universal cure-all

RP

[Voxman]

Almost as cute a concept as spraying/cleaning input sockets as a universal cure-all
RP

Not a cure-all, but it fixes about 90-95% of all Valvetronix problems - unfortunately its because Vox uses cheap jack sockets. I've been playing guitar over 35 yrs and Vox are the ONLY manufacturer that have this issue. Strange but true I'm afraid.

[retrobob]

You are correct the resistance sets the gain, however, caps are often used to stabilize the feedback circuit and will help minimize squeals.

While squealing was the original symptom, and perhaps I used poor phrasing, I said “the caps help regulate the gain”. Please rest assured it was not my intent to miss lead or set a course of action against the laws of physics, it was simply a suggestion to check the caps and solder connections around the Op Amps before giving up on the amp.

IMHO, jack and switch contacts do in fact oxidize (laws of nature) which can cause signal degradation, cleaning the jacks with contact cleaner has helped many.