The rack is Back?! Maybe not for everyone, but at least for me !

[fred.violleau]

Fellow ampgarage members,

I am thinking of putting together a class AB tube power amp (2 x 20 watts) in a rack and would probably then derive a 2x50 watts version.
My objective is to avoid building over and over the same power section for all the amps I have in mind, but also to allow swapping preamps and power amps.

I checked some Mesa Boogie schematics stereo tube power amps (2x20, 2x50, 2x90, 2x100) and besides the usual PI and power tubes, they all seem to have another gain stage in front. I suppose it's here to set the operation point at a 100k impedance so it works with valve preamp or SS preamps ?

I am planning to use these power amps with other tube preamps, and would like to keep the gain stages as close to what an amp offers : many preamp use 2 preamp tubes and then PI + Power tubes;
I want to build Dumble preamps with the output taken at the preamp out jack; That would be the level used to feed the power amp;
One of the potential drawback maybe the interactivity on the B+line between power and preamp.
What is your opinion and/or experience with these?
So far, in my little tube amp experience,I have not seen projects that allow to tap B+ current from a separate power amp to feed a preamp.
I know that commercially does not make any sense, but does it musically ?
Besides safety and security which are obvious issues, has it been done before ?

Thanks again for your valuable opinions!

Fred.

[bepone]

been there..add one small triode in front of PI, or small pentode triode connected.. you will miss some volume otherwise if run only from multi-effects board

[Reeltarded]

This ^^^


You are best of forgetting how pre works with power and using big headroom. Get everything out of the preamps.

This is another case of anything less than AC30 is a toy. 20w works but 50w works! There really has to be some way of making the things feel reactive like a normal amp.. that extra stage is the best you can do, probably. But it isn't bad. Honestly we are back to why complicate ot when you can use class D power..

Do not hate me.

[Reeltarded]

This ^^^


You are best of forgetting how pre works with power and using big headroom. Get everything out of the preamps.

This is another case of anything less than AC30 is a toy. 20w works but 50w works! There really has to be some way of making the things feel reactive like a normal amp.. that extra stage is the best you can do, probably. But it isn't bad. Honestly we are back to why complicate ot when you can use class D power..

Do not hate me.

I agree with Reeltarded. Ok, so the other thing is making a small power+/load that the preamps drive a small power section that is fully loaded and then to class D power.