I got one of these to repair, and i'd like some advice on modding the preamp to give it more gain for metal and stuff.
here's the factory schem (dont know if i can post it but here it is):
http://img132.imageshack.us/i/jammer21edit.jpg/ (http://img132.imageshack.us/i/jammer21edit.jpg/)
It's a bit hard to see the details, but you have 3 gain stages. I would suggest starting with the leftmost 1st stage and increase the value of the feedback resistor, to the left of the gain/drive pot. Maybe try a value that is twice or so and check the performance. Adjust to taste. Adding a bit more gain on the second stage is no problem by doing the same thing, but definitely not to the extent of the 1st stage.
thanks man, good idea, i did consider te idea of adding some simple distortion on a separate board, like the big bastard... i'll post some pictures here later, and reupload the schem
Quote from: VITOR_BAN on February 13, 2011, 12:07:36 PM
I got one of these to repair, and i'd like some advice on modding the preamp to give it more gain for metal and stuff.
here's the factory schem (dont know if i can post it but here it is):
http://img132.imageshack.us/i/jammer21edit.jpg/ (http://img132.imageshack.us/i/jammer21edit.jpg/)
uploaded the schem with the right size>> http://img843.imageshack.us/f/jammer21edit.jpg/ (http://img843.imageshack.us/f/jammer21edit.jpg/)
the energy coming from the transformer is rectified and filtrated by two zeners for +15 and -15v going to the 4558, and for the power section its 22v, maybe taking the energy directly from transformer to avoid too much stuff inside the chassis... tomorrow i get some guts posted here
i'm back... dos the dual supply of the IC(4558) affect the gain? i tried messing with the diodes and got nothing but a clean signal over the distortion and i dont know how to get it back how it was... any ideas?