Unwanted distortion from guitar amp

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Hairman
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Unwanted distortion from guitar amp

Post by Hairman » March 31st, 2015, 4:51 pm

I have a single channel combo amp. By turning the "volume" (preamp stage) up to about 5, I used to have a great clean tone with just a touch of distortion on the peaks.

One night at a show, somebody borrowed my amp and had everything cranked to 10 for an entire set. Now I'm getting really bad distortion (with the overdrive turned off) unless I turn that volume down to 1 or 2 and turn up the master volume. At first I thought the speaker was blown, because that's almost exactly what it sounds like, but that's not the case. My observations lead me to believe that the problem is with the preamp or somewhere in the preamp stage. Any ideas?

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s1120
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Re: Unwanted distortion from guitar amp

Post by s1120 » April 5th, 2015, 4:43 am

My amp I can control the distortion by turning the main vol DOWN, and adjusting the level with the normal vol knob. use the main as the rough level, then adjust with the normal seems to give me the control to choose the right bit of gain I want.
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Re: Unwanted distortion from guitar amp

Post by Hairman » April 9th, 2015, 9:01 am

s1120 wrote:My amp I can control the distortion by turning the main vol DOWN, and adjusting the level with the normal vol knob. use the main as the rough level, then adjust with the normal seems to give me the control to choose the right bit of gain I want.
I appreciate your effort to help me out, but I'm not sure you understand my situation. This is not a pre/post channel. I have a single knob named "overdrive." This distortion I'm talking about is new, and very nasty sounding. It's happening with the overdrive turned to 0; when it should be clean. What I'm saying is that I need to have the preamp volume a lot lower than before, and I still have a bit of that distortion, not to mention the lack of power that I used to have from the preamp. Something is definitely damaged from the abuse it took at the bar, and I'm trying to narrow down the possibilities down so I can know just what I need to do to repair it.

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Alan Green
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Re: Unwanted distortion from guitar amp

Post by Alan Green » April 9th, 2015, 10:09 am

Blown speaker?
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Re: Unwanted distortion from guitar amp

Post by Hairman » April 9th, 2015, 2:48 pm

Alan Green wrote:Blown speaker?
As I mentioned in the original post, that was my first guess, but the speaker is fine. I even tried it with a replacement speaker I had kicking around, and it was doing the same thing. It does it with headphones too.

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Alan Green
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Re: Unwanted distortion from guitar amp

Post by Alan Green » April 9th, 2015, 10:44 pm

Next option then - I can save settings in my Marshall either direct on the front panel or onto a footswitch. Has some numpty just pressed buttons on your rig without knowing exactly what does what and you need to restore the factory settings?
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Re: Unwanted distortion from guitar amp

Post by Hairman » April 10th, 2015, 12:36 pm

Alan Green wrote:Next option then - I can save settings in my Marshall either direct on the front panel or onto a footswitch. Has some numpty just pressed buttons on your rig without knowing exactly what does what and you need to restore the factory settings?
No, this is a pretty basic amp. No footswitch, no buttons. A 0-10 overdrive knob is the only distortion setting. I know enough about this to know that something is damaged. It has nothing to do with settings.

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Isom
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Re: Unwanted distortion from guitar amp

Post by Isom » April 10th, 2015, 5:17 pm

Maybe the person whom borrowed it was a little rough plugging and unplugging the cables, maybe cause a short or ground loop in the connection. Does it hum with nothing plugged into it, or just the cable and not the guitar?

PS: Even dirt, oil, or some type of grease can cause problems with electrical connections.

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Re: Unwanted distortion from guitar amp

Post by Hairman » April 11th, 2015, 9:49 am

Isom wrote:Maybe the person whom borrowed it was a little rough plugging and unplugging the cables, maybe cause a short or ground loop in the connection. Does it hum with nothing plugged into it, or just the cable and not the guitar?

PS: Even dirt, oil, or some type of grease can cause problems with electrical connections.

:roll:

There's no hum anytime. And when I opened it up to check it out, I sprayed contact cleaner on all the connections and in all the pots. Something I like to do every once in a while. Your suggestion seems to be the closest one I've had yet, but I really think it has something to do with the preamp itself.

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Re: Unwanted distortion from guitar amp

Post by Isom » April 11th, 2015, 12:57 pm

Did he/she handle the preamp or do you think he/she just pumped to much power through it? If it were handled it could be a preamp connection. :?: :idea: :?:
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Re: Unwanted distortion from guitar amp

Post by Hairman » April 12th, 2015, 9:12 am

Isom wrote:Did he/she handle the preamp or do you think he/she just pumped to much power through it? If it were handled it could be a preamp connection. :?: :idea: :?:
It wasn't opened up. If the issue is related to his use, he must have just cranked it too loud. It's not a very good amp so it's possible that he pushed it too hard.

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Re: Unwanted distortion from guitar amp

Post by Moonrider » June 25th, 2015, 4:23 am

Is it a tube amp? Start with replacing the tubes.
If it's a solid state amp, sounds like a bad capacitor or blown chip.

Without knowing the brand and model of the amp, there's not much anyone can do but make wild guesses.
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Re: Unwanted distortion from guitar amp

Post by Hairman » June 25th, 2015, 3:09 pm

Moonrider wrote:Is it a tube amp? Start with replacing the tubes.
If it's a solid state amp, sounds like a bad capacitor or blown chip.

Without knowing the brand and model of the amp, there's not much anyone can do but make wild guesses.
Thanks, I think you may be on the right path. I've decided, however, that the problem is out of my area of comprehension. Once my financial situation settles, I know a guy who can fix it.

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