Dominic Lampron
Member
- Joined
- Feb 2, 2020
- Messages
- 137
- Reaction score
- 3
Hey everyone! Here is my new project: JMP 2203 MKII 1976 master model. I bought this amp and cab earlier this summer that was, in my own opinion, in relatively good shape when i saw all pics and talk to the seller. When i've pick up the stack at the music store, i knew i'll have to restore it a bit as previous owner did some weird mods into the amp (change 1 bias cap for a radial 22uf 80v, the other was original ERIE one, the bias feed resistor was a 4.7k... and one of the 2 bias resistor before the bias pot was a 51k instead of the 15k... reverse numbers?? i don't know!!! Also, the amp was permanently set on the 4 ohms tap with a wire soldered from center tap to the 4 ohms tap into the amp but the cab was a 16 ohms... And the 16 and 8 ohms wire from the PT were reverse on the impedance selector and the old impedance button selector was missing... Also, 2 of the green 0.022 400V caps were a bit crumbled at one side, so i decide to replace them all for old mustards that i had.) So, i've replace all things correctly and puts some newer gold lions KT77 into it to try that kind of Power tubes. I've also put an old Westinghouse 12ax7 into V1 and a Mullard I61 on V2. With all this, i was desapointed of the sound results as the amp is very harsh in the high mids and see that the mids pots act like in the very high mids sweep and deliver more high than mids (like if the mids pot boost mids between 2k and 6k... Not between like 800hz and 3k... more in the upper high mids range... Not cool!) So, i want to change that part so here is my question: How can i modify and lower the frequency bandwidth of the mids pots? What parts into the circuit will i have to change and try for a better mids pot acting? Here are some pictures of actual PCB and the amp. Thanks and have a nice WE to you all! Dominic
