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I just came back from the Egnater amp building seminar. I learned a lot and honestly I doubt I will ever buy another amp again. I'm curious as to if you can match up pretty much any pre-amp with any power-amp design. Say I wanted a fender bassman style pre-amp with a vox style power section, could I literally just look at the schematics for both sections and run the wire from the master wiper in the preamp into the power section of any tube amp? Or do they have to be somehow matched...?
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That's pretty much the case - the section split is the preamp/phase inverter node. Expecting that combination to split the difference between Bassman and Vox is a mistake - at least not without a lot of fiddling and tuning.Originally posted by sburck View Post
You do need to mess with the power supply filter chain a bit to get the preamp the voltages it expects. Duncan's PSU Designer can help with that. His Tone Stack Calculator is fun, too. (both Windows-only)
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I just was at the Egnater amp seminar this weekend and was told to use the tone stack calculator, unfortunately they don't make it for mac's. Im not expecting two really have two amps in one, but I would like to use the mosfet switching assembly from mojo to create a duel channel preamp, one channel going through all gain stages and through the default tonestack which has marshall'ish values, and the second channel bypassing the first gain stage (just like the clean input jack on the amp does) and than set up a tonestack with more fender like values. Then for the power section I plan to keep it similar to a marshall 50 watt push pull circuit (which is basically what it is right now) but Id like to swap the transformer and tubes to have it run on kt88's hopefully for a cleaner power section with more headroom.Originally posted by Don Moose View PostComment
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Some advice:
First of all stick to the KISS principle ("Keep It Simple Stupid!"). Before you go ahead and build the amp of your dreams with a ton of features, build something really simple, like a Champ and then mod it to death. Make sure you get hands-on experience with what different cap values will do, lead dress and so on. Then go ahead and design the ultimate amp.
For your channel switching idea, I'd recommend building two separate channels and switch/mix them just before the PI. It will be a much more simple solution (less prone to noise, hum and other mischief), and it will be much easier to tweak and finetune each individual channel.
In many modern amps (e.g. Fender Blues Deluxe) you'll see how they make two channels out of the same set of preamp triodes by adding lots of relays and switching. This always leads to lots of compromises with tone, and the only reason they do it is to save the cost of an extra tube. This is relevant for mass-industry products, but for DIY, the cost of an extra 12AX7 is insignificant.Comment
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Originally posted by d95err View Post
PI = power section? Phase Inverter (is this the section right after the master volume where the phase is split)? is that the (what's the I stand for?) your basically saying just make two preamps to switch between, each pre-amp being completely independent of the other?Comment
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PI = Phase InverterOriginally posted by sburck View Post
Yes, make two completely independent channels. E.g. like on a Fender Deluxe Reverb.
http://www.schematicheaven.com/fende...b763_schem.pdf
(Automatic) switching between them will be easy to add. You can use relays, optocouplers, JFETs etc. You just mute the channel you're not using by switching the signal to ground just before the mixing resistors.
It will make the amp a lot simpler.Comment
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