Peavey e208 making strange distorted sound

[KCman]

The amp was getting a distorted sound. I traced it to U3 after the matter volume. It was getting correct power and the components around it tested good. I replaced it and it worked. I put it back together and tested again. I had an electric guitar handy, so tried it and it still worked.

Somehow, I happened to try it with the guitar volume down a bit and it sounded super distorted, like a blown amp or speaker. Full volume sounded good. I tried an acoustic w/fishman in it and worked fine. I tried a different electric and same thing.

Before I start working on this again, does anyone have an idea or have seen this?

Thanks

[TomCarlos]

I tried a different electric and same thing.

Does that mean is sounded "fine" or "distorted" with the second electric guitar?

[KCman]

I meant it acted the same as the first electric, so it's not in the guitar.

[KCman]

Oh yeah, both input channels do the same

[Jazz P Bass]

"I tried an acoustic w/fishman in it and worked fine"

It's an acoustic amplifier is it not?

[TomCarlos]

As JPB noted, this amp is designed for an Electric Acoustic guitar. A guitar that has a built in preamp system will produce a higher output compared to an electric guitar that has magnetic pickups. If you have the volume levels on the guitar at "low", you are then having to maximize the input controls for the two input channels to get "sound" at the output.

As you stated, with acoustic electric guitar, it sounded fine. I normally have my A/E guitars at 75% volume. That gives me the ability to cut the volume or add (if needed). On this type of amp, if the volume settings are anywhere from 0 to 5 (of halfway), the signal should sound clean. If it does, you're good to go.

[KCman]

I understand what you guys are saying. But, I don't even have the amp at half volume, the electric guitar was louder than I had the acoustic w/preamp. It's not a volume compensation/gain too high thing. I can have the gain at 2 or 3 and the electric sounds good with the guitar pot all the way up, but the tiniest bit of resistance and crazy bad distortion.

Electric guitar volume all the way up -stum chord - while chord is ringing turn guitar volume down ever so slightly and distortion as if the woofer is blown (I tried another speaker also)

I plug my mandolin with magnetic pickup into acoustic amps all the time. Never a problem. But This I've never heard. It's strange enough that I thought someone might have run into it before.

[Jazz P Bass]

"It's strange enough that I thought someone might have run into it before"

Nope.
Not I.

[TomCarlos]

The odd thing is that you say you tried another electric guitar and you get the same result?

So it is odd that you have a guitar, with the volume set wide open, you get a relatively clean sound, then turn the volume down on the guitar (ever so slightly) and you hear distortion in the amp. And while you are doing this, you do not touch the amp controls. And you would get the same result with both channels.

My first check would be to make sure the pots in the guitar are clean (all pots). I used DeoxIT F5 (the one with lube). If I have two volumes controls (one for each pickup), I would switch to the other pickup and see if you get the same result. I would also test the guitar on another amp to see what happens. This step would rule out the guitar as a source of the problem. I would also test using a different instrument cable.

And I would run the tests multiple times, many times, to make sure it isn't the amp that is crapping out.

By the way (and we are talking about a solid state amp), does this problem happen soon after the amp is turned on? After a certain amount of time? All the time regardless?

[g1]

Another thing to check would be if there is any DC from the amp input. Unplug the cord at the guitar and check at the cord for DC.

[KCman]

No DC on the inputs. Both channels are doing the same thing. I don't really see a common component that would put DC on both inputs, but I checked it out anyway.

I'm gonna have to get back in there and check a couple more things. Since U3 was bad, something else must be wrong related to why U3 , maybe

[g1]

Did the acoustic that you tried have a volume control that you could turn down and everything was still fine?

[KCman]

Acoustic does have a volume and it doesn't matter where it is set.

After playing the acoustic a few times through it, the original problem is there still. It will randomly have a little crackle, like a bad connection or damaged speaker (both channels do it, and I tried another speaker). Then it was working good, with the acoustic, I turned it off and back on the crackle was there right away.

When I first got the amp, it had an intermittent crackle. I put sound in the input and sent it to my tester amp from r48 and it worked good. I sent it from r26 and it was crackly. I replaced U3 and that's where I am now. I thought it was fixed, but it came back The crackle is way less, but came back. The electric guitar thing is a new find. I'm gonna check around u3 some more.

The chorus has a very high noise floor which increases as you turn up the chorus knob.(figured it was just a cheap circuit, but noticed it) I tried the switch in both positions, didn't change the crackle or electric guitar problem.

[TomCarlos]

Yes, it sounds like you may have a problem with a "physical" connection. Take some time to check the solder joints, especially those on the pots. Make sure any connectors are secure. Make sure the speaker connections are tight. When the crackle occurs, move the pots left to right - see if that impacts the crackle. If it does, it could mean a dirty pot.

Intermittent problems are the hardest to find.