# weird problem just arose



## gibsonguitarguy (Feb 17, 2010)

*all fixed up*

thanks for replies. A tech found a loose connection.


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## Wild Bill (May 3, 2006)

gibsonguitarguy said:


> my boutique amp is hissing at fairly low volumes.
> When i *unplug* the guitar, and turn up volume and gain, the amp will actually feedback!!.
> my other amps don't make a sound when i unplug the guitar. the amp seems to sound alright other than a little noisy when at fairly low volumes and worst of course when louder.
> someone suggested I replace the preamp tubes, which i did to no avail. I replaced the power tubes to experiment and no difference there either. Any ideas?


Without knowing even the model of the amp, let alone how the circuit is arranged, trying to help you is like trying to diagnose why a car won't start to a friend on the phone, when all he can tell you about his car is that it is a red one! lol

Is this a high gain design? It sounds like it. The hissing and feedback is probably the result of having so much gain in any one particular stage that signal can be coupled from the output of a stage into its own input, likely because of lead dress, or parts and/or wires being too close to each other. It is the electrical equivalent of putting a microphone in front of a PA speaker.

There is a tendency for designers to try to flog one tube stage for all the gain possible, instead of adding another tube with its socket and associated parts. The extra tube and stuff adds more to the manufacturing costs, reducing profit. The obvious downside is that you get an amp prone to high hiss and squealing when the volume is turned up.

You need a tech who knows what he's doing. If you are lucky, he will be able to move wires around to reduce the tendency to feed back. Usually if the design worked in the first place this sort of thing will fix the problem. Old HiWatts are very prone to this.

It can sometimes be an actual component problem. Again, you will need a good tech. 

If you are REALLY lucky, it will be something like an input jack that is not shorting itself when no cord is plugged in. Most amps are designed this way because not having the input tied to ground with no guitar cord means the input will "float" and act like an antenna, picking up all sorts of crap and again, wanting to feed back upon itself. The Marshall style of plastic form jacks are very prone to this problem.

Wild Bill/Busen Amps

Hopefully, it is not an actual design flaw, which can still be fixed but requires more knowledge on the part of the tech.


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## Adcandour (Apr 21, 2013)

I think I know the problem...


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## nonreverb (Sep 19, 2006)

I think I know as well.....get rid of the rose.


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