tube solid state hybrid guitar amp, looking for schematic

[jmillerdoc]

Hello,
I have a LM3886x3 150w power amp module that I was thinking of using to build a head unit for a friends electric guitar. I was wondering if anybody knew of a guitar preamp schematic that I could graft onto this module. I would like to find something with the typical 2-3 12AX7 tubes that has the master, gain, treble, mid, bass, and presence features. If anybody knows of a schematic that has a tube front end connected to a LMxxxx chip amp for guitar use I would be greatly appreciative. I have heard of commercial amps that use a series of tubes for the preamp stage that use a chip amp for the power stage but I don't know any of the models. I am sure if I could learn of one of these commercial amps I could find the schematic and easily adapt my module to it.

Thanks,
Jeff

[kavermei]

I don't know of such a schematic offhand, but, as long as you don't overdrive the chip amp, I think it will work very well. The sound will almost certainly be very gross if you do overdrive the chip amp.

In practice you could just build any tube preamp you like, measure its maximum output voltage swing (with maximum drive or full clipping, preferably with a 'scope) then attenuate the output signal so it ends up just below the input sensitivity of the chip amp.

[Enzo]

I agree, instead of looking for a commercial amp that happens to be exactly what you want to build, just build your SS power amp, then build a preamp you like, and connect them together.

The tube section and the 3886 sections will need totally different power supplies.

How complex a preamp you want?
http://www.schematicheaven.com/newam...ter_preamp.pdf

[OneyedK]

I'd say, take the input stage and tone stack from a Fender bassman, an adjustable gainstage from an Orange tiny terror, an output stage from a Fender Champ, load that with a 4 Ohm dummy resistor and feed that signal into the power modules, with voltage adjustment in between offcourse.

[Ian444]

Ask your friend what types of amps he likes the sound of. If he likes overdriven Marshall, I built a Marshall pre using 2 tubes into a SS 100W kit project about 15 years ago, worked great. You won't get a "presence" control as that is usually in a seperate part of the amp schematic. You can use two small back to back mains transformers for heaters and B+. If he wants something "clean", try a Fender Twin Reverb schematic, uses only one valve. Most of the components are in the tone control section and you can hang them from the pots, very simple to build. Maybe these days there's much better stuff around like this this one, scroll down to the bottom.

[jmillerdoc]

Originally Posted by Ian444

....... I built a Marshall pre using 2 tubes into a SS 100W kit project about 15 years ago, worked great......

Can you tell me how you did it? The voltage swing into the chip or SS amp section, isn't it too wide? I thought most of these chip and SS amps only require about 2vrms to drive to full power. How do you step the voltage swing back down to the amount needed for the SS section? Or am I missing something or way off? I am only familiar with tube corcuits, have very little knowledge about SS circuits. I have built a couple of Gainclone kits before but anybody can do that. I had considered just taking, as has been said so far on the thread, the front end off of one of the Marshall or Fender circuits and mating it to the input of the chip amp module via a capacitor. Could a voltage divider be built to lower the voltage swing into the chip amp input? How did you account for this? Or did you even need to? Again, I am very naive when it comes to solid state circuitry and really need some hand holding with this.

Thanks,
Jeff

[jmillerdoc]

Ok, I found this and I like it: http://www.drtube.com/schematics/londoncity/dea70.gif
Can I just take everything in front of the phase splitter (right where the "treble" pot is) and couple this to my SS stage with a cap? Also, I can't tell from the schematic what the votage should be on top of the 12AX7's, any clue what voltage the preamp tubes should be run from?
Jeff

[OneyedK]

Originally Posted by jmillerdoc

Can I just take everything in front of the phase splitter (right where the "treble" pot is) and couple this to my SS stage with a cap?

Nope, you cannot do that, imput impedance of an LM3886 is far too low.
Also, you don 't want to couple a tube amp (high voltage) with an SS amp, doing that with a transformer instead of a capacitor will gain you a lot of reliability.

[jmillerdoc]

Originally Posted by OneyedK

Nope, you cannot do that, imput impedance of an LM3886 is far too low.
Also, you don 't want to couple a tube amp (high voltage) with an SS amp, doing that with a transformer instead of a capacitor will gain you a lot of reliability.

I am not sure that is so correct. If the LM3886 is connected as non-inverting the input impedance will be very high, megaohms and more.
If you use inverting mode the input impedance will equal the input resistor.

I think my main problem will be the voltage swing still.

Jeff

[HotKava]

Carvin used to build a hybrid guitar amp back in the 80's, so did Music Man.
They were short lived because while a solid state guitar amp looks great on
paper, it just doesn't cut it in the real world.