Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: slash1986 on July 29, 2018, 11:30:14 am

Title: Modification Of a Guitar Amplifier Circuit.
Post by: slash1986 on July 29, 2018, 11:30:14 am

Hello everyone, I'm here because I need your help.
I have this guitar amp: jetcity JCA20H.


This is the link to the machine diagram. (http://bee.mif.pg.gda.pl/ciasteczkowypotwor/SM_scena/Inne/jet-city_jca20h_sch.pdf)




I would like to modify the circuit a little, to get the sound and distortion typical of marshall amplifiers.
Do you have any advice?


Thanks so much.
Title: Re: Modification Of a Guitar Amplifier Circuit.
Post by: tubenit on July 29, 2018, 12:01:13 pm
Is this on a PCB board?   What speaker are you using?

Title: Re: Modification Of a Guitar Amplifier Circuit.
Post by: shooter on July 29, 2018, 12:08:24 pm
take the part of yours I highlighted and make it look more like the example

blending V1 make's it better than Marshall did  :icon_biggrin:

you already have a DCCCF driving the TS
the bigger ? what marshall type, can you buy a broke one and fix it instead of breaking a good amp you can't fix  :dontknow:
Title: Re: Modification Of a Guitar Amplifier Circuit.
Post by: slash1986 on July 29, 2018, 12:21:26 pm
Is this on a PCB board?   What speaker are you using?


Yes is on PCB. I use a Celestion Vintage 30. When i record the Amp i use a reactive load box with impulses.
Title: Re: Modification Of a Guitar Amplifier Circuit.
Post by: slash1986 on July 29, 2018, 12:30:48 pm
take the part of yours I highlighted and make it look more like the example

blending V1 make's it better than Marshall did  :icon_biggrin:

you already have a DCCCF driving the TS
the bigger ? what marshall type, can you buy a broke one and fix it instead of breaking a good amp you can't fix  :dontknow:


jcm800 style.


Yours is definitely good advice.  :w2:

Title: Re: Modification Of a Guitar Amplifier Circuit.
Post by: shooter on July 29, 2018, 06:28:45 pm
Quote
Yours is definitely good advice.

I wouldn't go that far  :icon_biggrin:
after 21 "builds" 5 of which are commercial-ish, doing the mixing with V1, driving, or recovering the TS with a DCC,CF has impressed the guys with guitars the most.

that said, basterdizing a pcb can and WILL cause you greif, but if you take your time and can solder well, maybe even use "add-on" pcb chips, it's very doable
Title: Re: Modification Of a Guitar Amplifier Circuit.
Post by: slash1986 on July 30, 2018, 02:48:13 am

What could happen if I did this:


could I use another valve a new input and bypass the first valve in the circuit?