Drive vs Clean pre-amp stage

RobbieZ

I have a question for all you valve gurus out there. :bopping:

Is it viable, or even possible to do all the drive in the pre-amp and let the main amp section just amplify the signal it receives?

What I am aiming for is to have two separate pre-amp stages, one clean and one drive and amplify them both through a single amplification stage.

Robbie

ezietsman

RobbieZ wrote: I have a question for all you valve gurus out there. :bopping:

Is it viable, or even possible to do all the drive in the pre-amp and let the main amp section just amplify the signal it receives?

What I am aiming for is to have two separate pre-amp stages, one clean and one drive and amplify them both through a single amplification stage.

Robbie

Of course, this is how most modern amps work and this is how most people use their valve amps, pedal in front of clean amp.

AlanRatcliffe

Yup. That's how it's done these days. IINM, Mesa were the original culprits. ?

Of course, preamp and poweramp drive are different animals, but if you want drive at low volumes, you have to do it in the preamp.

ezietsman

Alan Ratcliffe wrote: ...but if you want drive at low volumes, you have to do it in the preamp.

There are at least two ways of avoiding that ?

singemonkey

Power amp drive is the sound of the electric guitar. Pre-amp drive is the sound of '80s Japanese tv show soundtracks. ?

Gearhead

singemonkey wrote: Power amp drive is the sound of the electric guitar. Pre-amp drive is the sound of '80s Japanese tv show soundtracks. ?

+1
But... A well balanced amp will allow both tonalities, just by adjusting amp master volume and guitar volume control. The difference is in just a few cheap components, so not to worry at design time.

What you could consider for channel switching is to make up the dirty channel by adding a gain stage to the clean channel instead of trying to make them separate. In other words, the clean channel just bypasses a cascade... Check out the Mesa Studio .22 schematic, iIrc it has this down to the T.
Your idea of having two separate preamps is only useful if you want to use separate tonestacks. Maybe Sean can show you the usefullness with your guitar plugged in, I believe his custom Craig amp has this. It is the more expensive option, though.

RobbieZ

Gearhead wrote: What you could consider for channel switching is to make up the dirty channel by adding a gain stage to the clean channel instead of trying to make them separate.

Thanks, I havent thought of that option.

RobbieZ

I was just thinking ☹, is a effects loop realy nessesary? Are there any effects that I cannot put in between my guitar and amp?

AlanRatcliffe

Depends on the effect and how you use the amp.

If the amp is clean and uncompressed, you can use anything in front of it. If it's distorted (especially preamp drive), it changes the dynamics, which doesn't suit some effects - a driven amp's distortion will mush reverbs and delays and the compression will make them louder.

petercornell

An FX loop could be a good place to add in a Boogie style extra gain stage if you want to keep your amp stock.

If you look at the Quad Preamp schematic, that is pretty much what they have done. The Lead Circuit is 2 stages of gain with its own level control.

So build a gain stage in an external box with its own footswitch and this might get you closer.

Peter