Express Clone With Howling Feedback - HELP!!!!

[bluesky636]

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[d95err]

A guess: bad solder joint. Redo all solder joints you've done recently.

[hans-jörg]

In fact, several signal wires are tacked down with silicone.

Check your cables comeing from treble pot. The silicone is not the best way to fix wires - especially when they are too close to other components or wires. The chassis/ground is kind a part of signal. If you have the wron cable fixed a lenght to chassis, this could cause problems. A chop stick would help, but when they are fixed ...
When there are crossings: only by 90°, not parallel.
Let`em breath

Or a weak solder point - as written above.

Best,
Hans-Jörg

[bluesky636]

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[Blackburn]

Obviously, if the amp was working fine prior to these changes you made and now is unstable, you should probably focus on the modified area. That, and just maybe you moved something where it doesn't want to be, possibly by accident. The problem you describe is probably affiliated with lead dress.

[geetarpicker]

When you mention the howl is on specific strings it makes me think there is absolutely nothing wrong with the amp. On a high gain amp such as this you are going to have immediate feedback from the strings themselves, and it is up to you to mute the strings you do or don't want to sustain. If it's different strings on different guitars that surely sounds like you have to adjust your playing and muting techniques to work with the amp. Also potted pickups are not all the same in regards to how much they resist feedback, and potting will have no effect at all on the strings themselves howling. At that point it's up to the player to control it. With my original Express amp I have had potted pickups that actually needed to be potted again and more thoroughly to be workable when playing cranked up at close range. Now if you can mute the stings and stop the feedback, it's not the amp. If muting the strings doesn't stop the howl you could have a pickup that isn't sufficiently potted. Typically if the amp alone is oscillating it will not be string specific but more at a fixed frequency that might change when you turn the amp knobs. Could it be that your changes to the circuit increased the gain by a noticeable amount?

I just noticed you mentioned at the top that your guitars howl with the guitar on your lap and the amp knobs all on 12pm. With my Express amps that would be perfectly normal! They key is learn how to control it with palm, thumb, and finger muting sometimes with both hands.

[bluesky636]

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[bluesky636]

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[cap217]

My experience with express amps are that they are noisy and there is a hiss and a howl is to be expected. I find it hard to believe that you are saying this amp was dead quiet. If nothing changed then try swapping tubes.

[M Fowler]

I'm think a problem with the volume pot in the amp or wiring around that pot.

[bluesky636]

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[bluesky636]

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[M Fowler]

It doesn't matter if things were addressed months ago, weeks ago or whenever, something happened inside the amp to cause the howling or feedback loop. Not having the amp in front of me I suspect solder joint went bad perhaps when inserting and removing the preamp tubes. Maybe the sockets just need a good cleaning?

[romberg]

Could you provide more details on how you know that it is specific strings? You can't stand ten feet in front of an express with everything set at noon (including the guitar) with unmuted strings and have it not feedback.

If your strings are muted then I'm guessing it is a pickup that needs potting or more potting. Just because the pickup was potted at the factory does not mean it can "hang" ten feet from 50 watts. I have several guitars where "you just can't do that".

Mike

[bluesky636]

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