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Old 22nd August 2005, 08:30 PM   #1
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Default Tube differential input/buffer /w opamp output gainclone

I have a question for all you tube freaks out there. I would like to make a gainclone-esque amp for guitar purposes, and I am experimenting with hybrid topologies, but I wanted to bounce some schematics off you guys before I start blowing up components;-)
Much of the tone of a guitar tube amp comes from the interaction/clipping of the preamp stages and the schmitt long-tail phase inverter stage...which is just a simple differential stage. I want to preserve that, and run it into a tube buffer, and then a gainclone type output stage. My question would be how best to match the two up.
I understand that the inputs of lm3886/lm41xx chips are differential (like all opamps of that style) so should I run the outputs of my buffers (one positive phase and one negative phase) into the inverting and non inverting inputs of one chip, or into 2 chips (both set up the same in either inverting or non-inverting)? I assume I could do either, provided that adjust the values for the extra point-to-point ac wave to avoid clipping.
My OTHER question is if I use 2 opamps, how do I hook up the speaker connection? One to the positive and one to the negative terminal? OR Both to the positive and ground the negative? I usually work with tubes and an uotput transformer, so I am a little in the dark there.
I attatched 2 examples. Thanx for your help. The differential tube would be a 12ax7, and the buffer a 6922...I have been tinkering with those lately and am happy with the results...THANX!
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Old 22nd August 2005, 09:34 PM   #2
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Default Re: Tube differential input/buffer /w opamp output gainclone

You would probably get better advice in the tube forum, but so be it....

Quote:
Originally posted by aletheian
Much of the tone of a guitar tube amp comes from the interaction/clipping of the preamp stages and the schmitt long-tail phase inverter stage...which is just a simple differential stage. I want to preserve that, and run it into a tube buffer, and then a gainclone type output stage. My question would be how best to match the two up.
I sort of disagree with this. True that "much" is not an empirical quantity, but I would say that more of the tube amp sound is in the power stage clipping and the speaker tone. Before we get sidetracked into arguing this subjective issue with no black & white answer, let me say my point is that you should get more aggressive with your tube choices, say 2 stages of 12AX7 with high gain dialed in.

Quote:
Originally posted by aletheian
My OTHER question is if I use 2 opamps, how do I hook up the speaker connection? One to the positive and one to the negative terminal?
Yes.
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Old 23rd August 2005, 07:36 AM   #3
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Hey thanx for the reply man.
I meant for this to be strictly the power amp section (or post effects loop) with the input coming from an all tube preamp. I agree that the tube power amp is indespensable when it comes to nailing tube tone...I just want to see how far I can take a chip amp into tubeland.
I am curious to see how close the tone can come to a modern amp like a Mesa Dual Rectifier or a Peavey 5150. Both amps bias their output tubes sooooooo cold (like 12% idle) that not much is happening in there in terms of pentode tone goodness. The output sounds pretty "hi-fi" to me (as opposed to like a big fat fender bassman biased around 70%) hence the interest in running a chip amp output section, while preserving everything up to the power tubes.

Thanx again.

Alex
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