Distortion/farting in fender frontman 25r

[washburn085]

Hi, I've had this frontman 25r for 9 years now. about 5 or 6 years ago (not my main amplifier anymore) I noticed that there was a lot of distortion/farting when playing low notes on the clean channel. I am sure it does it on the drive channel as well, just less noticeable. I think this happened after my roommate hooked up a cd player to the input jack and had the bass thumping.

back then I purchased a replacement speaker but that did not change anything. I know it does the same thing through the headphone jack as well.

It gets worse as I turn up the treble, but is still there even when treble is at 0. I opened it up and nothing seemed noticeably burned out. I need to dig out my multimeter to check the values to see if any of the analog parts are bad.

Anyone have any suggestions or ideas? I am thinking its an op amp in the tone stack, but not 100% sure. Here is a link to the schematics: Fender Frontman 25R Guitar Amplifier Schematic

Thanks!

[jmaf]

Farting in the amplifier can definitely be a nuisance. Check all MOSFART opamps for the right inpeedance and always follow the feeling in your gut. I smell a problem here somewhere, so remember to flush the caps until fully drained. A choke may be of temporary relief but if the tension rises the distorted farting will resume even more intensely. You'll probably also need to replace the shitty pots. I know they're a pain, but as soon as you let one out the others will come naturally. Good luck there brother, please let me know how it went.

[Jam]

fender

I agree I would check your IC outputs and I alway like to pull the PCB to look for a cold or bad solder joints. Iam sure you know but becare full when checking the IC

[washburn085]

ya, sadly my testing resources are limited nowadays, so I will have to be extra careful. the op amps are 60cents on digikey, so i will start there.

[radtekvp]

Frontman grounds

Another thing to look at on the frontman (and others of the lower end of the cost spectrum) is that the grounding technique to the housing for the reverb is not so good. They use a brass rivet to make the ground connection from the phono connector board to the steel case. After some aging and a few bumps these can end up with bad connections - which leaves what the amp sees as a big huge antenna picking up whatever noise, hum and whatnot and injecting it into the amp output. I add a groundscrew and a separate ground wire routing it through the ferrite just like the IN and OUT leads.