Fender M-80

[assasukasse]

Hi everyone
i am the owner of a nice M-80 amp for my guitar.
right now i unassembled it to change the pads from the transistors with mica ones and thermal paste.
I use it with a multi-effect from Zoom, a G2, which unfortunately has a too high output so i am obliged to keep the amp at a volume that is very close to 0.
Since i wish to have more room, and the amp is unassembled, i wish to modify one of the input jack in order to use with the effect..

I was thinking about adding a trimmer to work out a nice volume from one of the channels, i noticed that R4 and R5 are the same 33kOhm, but there is also an R1 of 2.2kOhm..

I don't have the schematics so i am afraid of damaging it, but if i remove one pin from R4 and add in serie a 63kOhm trimmer, i shouldn't break anything...

of course if someone has the circuit schematics could give me better hints!
mine is a M-80 from 1989

Thanks

[52 Bill]

I use it with a multi-effect from Zoom, a G2, which unfortunately has a too high output so i am obliged to keep the amp at a volume that is very close to 0.

The M-80 has 2 input jacks, one is high gain and the other is low gain. Have you tried using the low gain input? Or have you tried using the power amp input jack instead of the front inputs. You will lose the use of the preamp controls, but it should handle the Zoom output better this way.

of course if someone has the circuit schematics could give me better hints!
mine is a M-80 from 1989

If you send me your email address, I will send a copy to you.

[assasukasse]

yes i tried the lo gain input (which should be the one on the right)
i made some modifications..
removed the transistor and put mica pad under
changed the bias resistances from 1K to 2.2K in order to prevent overheating
and while it was still open:
i changed the two red led with white ones, this seems to have given me wider dinamic
and added a 100k resistor on the low gain input (which has already a 33k one)
now it sounds almost right, tomorrow i might try to put a 147K one and it should be perfect!

Thanks!

[Enzo]

You didn't respond to Bill's suggestion to try the power amp in jack. PLug your effect unit into that. That will bypass the preamp and all its gain.

Do you realize that adding a lot of resistance to the inout jack resistor is the same thing as turning down the output volume of the external unit?

Why are you remounting the power transistors? The mica insulator and heat grease have absolutely nothing to do with loudness and power. Or is that a separate matter?

[assasukasse]

hi
i already made those modwhen i got the answer...
anyway today i am gonna take them down since i noticed from the schematic that that is not the correct way to do.
I will try to plug in the power amp jack and see how it goes!

I remounted the transistor because my amp was sligtly overheating and i found this mod here:
http://archive.ampage.org/articles/6...er_M-80_s.html

my amp was exactly one mounting the sil pad instead of the mica.
what i did was mounting mica pads with thermal grease
disassemble the rod and assemble it with thermal grease..
in fact that was a separate matter...