Modded Marshall Jackhammer problems with Distortion

[srmoska]

Hi, I'm currently trying to mod a Marshall Jackhammer JH-1 pedal that I got used recently and I need suggestions as what could be causing a problem I'm having with it.

First I removed the IC's and put sockets, then I replaced IC1 with a NE3552 and IC2 and IC3 with a couple of JRC4558. I also Replaced one of the diodes (D5) with a 1n34 germanium diode , D4 stayed with a stock 1n4148 silicon diode. I didn't noticed that I placed IC1 upside down so it got fried, after this incident I placed a new TL072 toreplace to get it back to stock.

I proceded to test the pedal and I liked the sound of it, then after around 30-50 minutes the gain (it was at the highest setting from the beggining) lost a bit of presence and it also started to sound very muddy (trebble was also at highest setting).

I didn't paid much attention to that so I thought it was sounding that awful all the time, so I then removed the TL072 from IC1 and placed another JRC4558, also replaced the 1n34 diode on D5 with the stock 1n4158 diode. Went to test the latest modifications, at first I liked the result but again after 30-50 minutes it started to lose gain presence and sounded muddy.

A friend suggested me replacing C12 (1uf/50V hydrolytic capacitor)

here's a link for the schematic: http://diystompboxes.com/pedals/schems/JH-1.pdf

When the pedal arrived I tested it just a couple times and then started working on it so I can't tell if my problem was before I even attempted modding the pedal

I'm using a Bugera G20 amp to test my pedal and a Epiphone Les Paul Special II guitar

Thanks in advance for any suggestions.