Making an amp with a tube pre-amp stage and a solid state power, how difficult?

[DougH]

Well, Iimagine it is diffucult to work out, but is it possible with little adjustment? The idea is to reduce cost by eliminating the output transformer and true cost obviously, but I think it would also tighten it up a bit...am I wrong?

 

Ok, Marchall Valvestate amps are Ok by me, not as cool as real tubes etc. but sound to cost ratio seems ok to me. I was wondering if a power amps these schematics could be adjusted to fit each other? The preamp stage of an ax84 project amp ->http://www.ax84.com/index.php?pg=legacyprojects&project=hioctane&file=/media/ax84_m89.pdf and the power output form this-->http://sound.westhost.com/project27.htm

 

The idea is to make a tight, higher gain amp channel with a clean solid state channel with more than enough watts so it has overhead. I have heard solid state is better at lower volumes, so is due to power amp problems?

 

The thing I notice is that the price of transformers cost a lot and three would be needed for this or two, one with taps for both power supplies? Do I need a buffer between the pre and power stages as they will be different , using a high volt pre?

 

So, I am tying to see if a High Octane Valvestate style amp is possible, but rectified high gain pre rather than a regular one tube faked sound...is this possible or do I have to put a low volt supply in it and change the circuit for a low volt tube, like the 1 tube pre amps and stick with one tube and use a Dr. boogey circuit ( http://www.beavisaudio.com/Projects/BATG/ ) or the double d circuit http://www.runoffgroove.com/doubled.html to drive it a bit?

 

There are quite a lot of examples in the Music Man amps, the schematics are in this list. http://www.schematicheaven.com/post70s.htm But I can't really see how it could be adapted as it has so many tubes and it is rectified.

 

Could I even just put the pre in a small pre amp form as a pedal to run an amp cab sim or a little combo amp?

 

It has a lot of tubes and is costly just for the pre really.

[el_tonto]

What's your output power target? Most tube preamps can drive solid-state power amps OK with only minor tweaking.

 

 

The idea is to make a tight, higher gain amp channel with a clean solid state channel

 

Do you mean you want a two-channel amp, or just a high-gain pre stage followed by a "clean" solid-state power stage? Do you want to drive the pre tubes into distortion?

 

 

I have heard solid state is better at lower volumes, so is due to power amp problems?

 

Better how? SS is probably lower noise, and is certainly is a lot more efficient because the idle current is a lot lower. But I wouldn't worry about efficiency.

 

 

but rectified high gain pre rather than a regular one tube faked sound...

 

What would be rectified? And you want to (maybe) use the Double-D circuit to drive the tubes? That looks like a very high-gain distortion circuit, so any subtle contribution by the tubes would be completely swamped by that distortion circuit. The mere presence of tubes in the audio path won't make it a tubey sound.

[DougH]

What's your output power target? Most tube preamps can drive solid-state power amps OK with only minor tweaking. Do you mean you want a two-channel amp, or just a high-gain pre stage followed by a "clean" solid-state power stage? Do you want to drive the pre tubes into distortion? Better how? SS is probably lower noise, and is certainly is a lot more efficient because the idle current is a lot lower. But I wouldn't worry about efficiency. What would be rectified? And you want to (maybe) use the Double-D circuit to drive the tubes? That looks like a very high-gain distortion circuit, so any subtle contribution by the tubes would be completely swamped by that distortion circuit. The mere presence of tubes in the audio path won't make it a tubey sound.

 

Well, the main thing would be the High Octane modded pre with a solid state power section. Since this sounds like it can be done not to difficultly I am thinking this is the way to go. The idea is 100 watts of solid state available, but run at 30-60 or so for less noise and more durability as I have heard solid state amps crap out sound wise when pushed.

 

The problem is I think most of the circuits for tube hybrids available is that they have some kind of lower power supplying the tube, so the harmonic structure is different as it reacts to higher gain. Another issue, as you mentioned, The Dr. Boogey would provide the to much level compressed distortion, so it wouldn't make a difference if it was driving the tube as it would already color the sound so much and stop the dynamics? SO basically I could build a FET pre and get the same or better results with using the Dr. Boogey or the double D? The double d actually has many gain stages and two switches to get hem all, a lot of sounds.

 

But from what I have read the single tube low power voltage approach leaves the tube less warm and harmonics are missing at lower volts and react differently. This is why many people think the tube in the Valvestate Marshall is useless, it is just a marketing ploy to many.

 

But, with a full voltage to the high octane pre will have lots of distortion within it's own tubes, so this is more likely to sound good?

 

Eliminating the output transformer and tubes there is over-all money saving? Not to sure right now and still thinking of the Mosfet power amps out there.

 

Maybe even just build the High Octane Pre into a rack, pedal or other box and play it thorough whatever the person chooses, whether Crate power block, Mosvalve or a Mesa or Carvin tube power amp. Maybe this is more practicical and even cheaper as used power amps well built can already be bought for about $100?

 

What I meant by solid state being better at low volumes was meaning it sounded better than itself (the same amp) at lower volumes, so the tube amp pre would be better if you where cranking 30 watts of the 100watts available in the linked guitar amp.

 

This is a long post! well, I am only getting started thinking about this and I will need help as I am not all that great with electronics. It is a vary vague and uneducated thought, so that is why I am asking.

[aortizjr]

What you are going for isn't that hard to build. Essentially you are building a tube preamp and a solid state power amp and basically connecting them together.

 

Essentially it is the same as having them in separate boxes.

 

A tube pre doesn't really require that much power. Higher volts yes, but not a lot of amps. Since you will have to use AC and rectify it up to the right voltage for the pre, you can tap off of the that for the power amp.

 

The poweramp won't really need a lot of voltage, but a lot of amps to output the wattage you are looking for. Essentially you will want that pre-amp to be clean clean, and get all your tone from the preamp. That is why Randall in their hybrids use like 300-400Watt poweramps.

 

So you will need to make sure those MOSFET's are heatsinked well and that the power supply has enough wattage to power it. Read the spec sheets on what you get.

 

Signal-wise I think would be pretty straight-forward. Getting the power right at the wattage you want will be the tricky part.

[DougH]

Cool, that is what I wanted to know. Thank you.

 

I will try to figure out how to do it and after I figure out about the impedence changes needed I will try to post back with two versions. One pedal, rack housed pre and a full amp to make using a common power supply to power the two sections and I am hoping for a effects loop and other goodies. But I suck at electronics and never quite learned anything other than what some of the parts do.

[El-Lardo]

If I was going to do this, I would go modular. Build them separately. Or just build the preamp and purchase the ss poweramp. There are tons of them out there.