horsewhip wrote:I have a Mig 60. It sounds great, but has given me trouble. It puts out bass, though. So much bass that I can't even keep it on the cabinet. It puts out a crackle on the low-frequency notes that only stops when you take it off of the cabinet and move it to a chair or something. No tech has been able to fix this. Great sounding amp, though.

I had the same problem. Many techs looked at it without success. A friend and I did the chopsitck test and found that it was a cold solder joint on the PCB. You might try that.

best,
Justin

justin millar said:
I had the same problem. Many techs looked at it without success. A friend and I did the chopsitck test and found that it was a cold solder joint on the PCB. You might try that.

And that friend was me. Boo Yeah!

ben adrian

Ha! You wanna fix my amp then?

...

horsewhip, sure I'll fix your amp if you're in the bay area.

marshall mods. I can just tell you here.

Before you begin, if you aren't familiar with working on amps, have someone else do these mods for you. Amps, even when unplugged, can hold voltages which can injure or kill you.

First off, you need to have a 6 knob JCM 800 2203 or 2204.
Now go to marshallschematics.com and get the 2203 preamp... that's what I'm looking at.

First off, get rid of the cap across tyhe gain knob c 5 in this schematic. This just lets extra high frequency through when the gain is not set at max. Ick. try your amp, hear what it did.

Second. C4 and C8. These capacators when placed with the 470k resistors act as high pass filters. Yake out one or both of these caps to reduse some more high end.

Third. Add a 25uF 25v capacitor across R9. Watch your polarity. This will give you a touch more gain from that stage and a touch more low end.

Fourth. C3 and C7, the .022 uf coupling caps. You can replace these with .047 or .1 uf to let a bit more low frequency through.

now get the 2203 power amp schematic.

Fifth. C9, c14, and C15 can all be upped in value to let more low end through. .047 or .1 uf.

Sixth. C18 can be changed to a higher value to tame high end. try 100pf or 470pf. maybe even 1000pf.

You can also change tone stack values in the preamp, but that can get more complicated, so I'm not gonna go into it here.

All these mods are subtle by themselves, but combine them and you can really start getting effective high end reduction/low end increase.

In general, I say do these in order and check the results after each mod.

ben adrian
san francisco