betalead repair question

[betalead]

My betalead amp is making muddy, farty noises. If I plug in keyboard, it makes this noise at all times. If I plug in guitar, I have to turn it up to hear anything, and the note I strike plays almost clean for a split second, then decays immediately with that farty noise. I thought my speakers would need reconing but they look fine, and they play fine when I hook them up to my stereo (tho my stereo isn't putting out 300w). Any ideas?

[JoeArthur]

The first thing that comes to mind would be a bad connecting cord.  The cutting out sound you describe seems pretty typical of a bad cord.

You might want to provide a little more info.  Has it always done this, or did it just start?  Did you drop the head recently.  Does it continue to make pretty much the same sound no matter where the drive control is positioned.  Does he master volume controls (master as well as channel volumes) change the sound any?  Do you plug into the both channel input and have you tried the channels individually?

[Anonymous]

Here's some more info:
I have tried different cords & different instruments, both old & new. I'm reasonably certain the issue is in the amp or speakers somewhere. I should mention the 3-prong plug is missing the ground plug but I got it that way 14 years ago.

It has not always done this. I've run bass & guitar out of it for years. This started several weeks ago but long after I began plugging in the keyboard, which is a Yamaha PSR-210. I used the Headphone/Aux_Out 1/4" jack from the Yamaha directly into the amp. As I say that worked fine & I'm not sure the keyboard would cause it to blow or anything like that.

I've never dropped it or dropped anything on it. It makes pretty much the same sound no matter where any of the controls are positioned. I've tried every conceivable combination of drive, level, volume & tone settings, as well as channels A, B, and both. The sound doesn't change any. When volume or drive or level are down, I can hear crackling before I hear any instrument sound.

I found the service manual on this site recently (many thanks to the gracious contributor!) and the Troubleshooting page suggests that if
"Problem = popcorn noise at mid-tone, then Possible Cause = Noisy I.C. {I.C.109, I.C.111}, and Suggested Solution = Replace I.C. and check for noise".
I'm assuming I.C. means Integrated Cicrcuit.

Thanks for responding Joe. Any help is very much appreciated.

[betalead]

I have some more info, but first a heart-felt word of gratitude to all users who posted Q&As here for folks like me to peruse & ponder. If it weren't for you I wouldn't have come up with the following diagnostic.

So I read in this forum about testing preamp & such to a known good amp (I never thought of that one). I know my PA system is good. I unplug speaker patch cord from the head to the cabinet. I plug guitar into Channel A only, then out of Preamp-Line-Out Channel A on the rear side into my PA. Sounds lovely - God I miss that sound. I do the same for Channel B which also works fine but seems softer (lower volume) than Channel A (yes I had all the volume & drive settings at the same level :wink: ). Then I tried both Channels in the middle input and that's fine too.

Then I go from Speakers output on the rear side directly into the PA and there's that nasty sound again, except this time it doesn't die out or decay, it just stays there farting, popping & crackling as long as I strum. Does this mean the preamp is good? Can I rule out any problem with the speakers? What else could be causing this?

Thanks again for taking the time to help your sunns & daughters.