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.

[fred.violleau]

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

Hey Bepone,

Thanks for the clarification. My plan is not to drive the amp with a multi effect, but rather to have a lot of flexibility between preamps and power amps coupling. I have a musicman PT and OT that I would like to couple them with any preamp to get the feel of those 700V without building 3-4 different amps (lots of tubes, and redondant parts, lots of wasted space as well).

I realized that Soldano SLO Power amp is the same as TR John Mayers and many others, so why should I bother build full amps, when I can have preamps on one side and different power amps on the other side that would allow flexibility on the output and configuration? I could have single 20 watts (6V6s, el84s etc..) and multiple rendition of 40-50 watters.

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 love 20 watt for the right room, and the right feel (amp slightly pushed) to get on the edge of breaking up the bigger bottles. Class D is probably the most efficient way to squeeze the juice out of the preamp, but that would only account for half of the part in a tube amp. I know some power amp designs try to keep the output stage clean (Two Rock John Mayer, Soldano, ODS and more), but I like the softness of the power tubes. Switching JJ 6L6s to TAD WGC STR 6L6 affects the sound in a big way. I don<t want to loose that extra mile.

I have stumbled upon Synergy amps, and they seem to do in an amp format what I am trying to achieve in a rack version :

SYN50-4.jpeg

This one is a 50 watts amp with the ability to drive two different preamps.
Has anyone been into one of these ? I like the concept, and would be curious to understand the biasing of the preamps;

Again, thanks for your opinions !

Fred.

[fred.violleau]

Found this gutshot that seems to show a tube on the left 12A_7 (PI? or preamp?)

SYN2-Midi-fix_start_sm.jpeg

And a thread that talks about the modules and found this schematic :

SYN module Structure.jpg

So they get 320V B+ DC from the power module (midi or amp I suppose). I like the old fashion eyelet board, not a fan of the PCB board yet, even though I know there are quality ones. What would you suggest as connector to get the B+ power from the power amp to the racked preamp?

Fred.