Tweet
Hi,
first of all my compliments on this forum. As this is my first post a slight introduction might be in order. I have been playing guitar for many years and consequently owned almost every (tube) amp that is out there at some point in time. I started restoring/rebuilding (audio) tube amps about 2 years ago and in meantime I have succesfully brought back live into several oldies, such as the Phillips AG9015 & AG9016, Kontakt KT7, and some Bocama builds.
This time i am trying to build a JCM 800 like amp from an old TRIO pa amp and so far so good. I have fully stripped the amp and only new parts were used besides the power and output transformer.
The used schematic fot the pre-amp is a combination of the original JCM800 lay-out, some AX84 tweeks, and my own "inventions"....
As this is my first post I am not aloud to post links, so the schematics and jpegs of the pre-and power amp will have to follow.
Although I am very pleased with the results so far, there are still a few thinks that need to be de-bugged.
First of all, the power stage 2 x EL34 PP seems to be very loud, and I mean very loud in a unhealthy way... Turning the master up say 5 % already makes the attached 4 x 12 inch go very loud. I have checked the output level from the pre-amp, changed the R value of the feeback circuit, and today I tried several changes to the (fixed) Bias for the EL34's, but nothing really solved the problem, but perhaps somebody has an idea what might be wrong.
Furthermore it seems that somewhere in the circuit there is a signal leak. When I turn the master al the way down there is still a slight sound audible which normally wouldn't be such a hassle. However, as I have build in a switchable FX-loop based on a 12AU7 with adjustable send- and return controles, the "leaked" sound is of course then mixed with the signal from the return socket which makes the signal go out of phase and therefore the fx-loop more or less useless..
All things considered I am rather fund of this little amp. It does sounds a bit Marshall like but still has it's own character.
Once again I will post the links to the schematics and jpegs of the build.
All tips, suggestions and comments are more then welcome !!
Dutch66
first of all my compliments on this forum. As this is my first post a slight introduction might be in order. I have been playing guitar for many years and consequently owned almost every (tube) amp that is out there at some point in time. I started restoring/rebuilding (audio) tube amps about 2 years ago and in meantime I have succesfully brought back live into several oldies, such as the Phillips AG9015 & AG9016, Kontakt KT7, and some Bocama builds.
This time i am trying to build a JCM 800 like amp from an old TRIO pa amp and so far so good. I have fully stripped the amp and only new parts were used besides the power and output transformer.
The used schematic fot the pre-amp is a combination of the original JCM800 lay-out, some AX84 tweeks, and my own "inventions"....
As this is my first post I am not aloud to post links, so the schematics and jpegs of the pre-and power amp will have to follow.
Although I am very pleased with the results so far, there are still a few thinks that need to be de-bugged.
First of all, the power stage 2 x EL34 PP seems to be very loud, and I mean very loud in a unhealthy way... Turning the master up say 5 % already makes the attached 4 x 12 inch go very loud. I have checked the output level from the pre-amp, changed the R value of the feeback circuit, and today I tried several changes to the (fixed) Bias for the EL34's, but nothing really solved the problem, but perhaps somebody has an idea what might be wrong.
Furthermore it seems that somewhere in the circuit there is a signal leak. When I turn the master al the way down there is still a slight sound audible which normally wouldn't be such a hassle. However, as I have build in a switchable FX-loop based on a 12AU7 with adjustable send- and return controles, the "leaked" sound is of course then mixed with the signal from the return socket which makes the signal go out of phase and therefore the fx-loop more or less useless..
All things considered I am rather fund of this little amp. It does sounds a bit Marshall like but still has it's own character.
Once again I will post the links to the schematics and jpegs of the build.
All tips, suggestions and comments are more then welcome !!
Dutch66
Comment