Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: afinitemind on June 27, 2019, 03:03:28 pm
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Still obsessing over the B15 circuit, wanting a few different ways to get that sound loud enough for stage use. So I'm thinking about a dual preamp...combine the B15N's 6SL7 with a 12ax7-based F2B pre in a single chassis, then run that into my big SS power amp.
I understand that a lot of the B15 tone comes from the PI/Power amp/Speaker working together, so I'm not expecting an exact copy, just something musical and convenient for live shows.
I'm learning KiCad at the moment (first time doing any technical drawing like this), and this gives me a convenient project to cut my teeth on.
So...here's the first attempt at a schematic. Critique away!
I've read about the F2B's high output impedance...seems lots of people like a cathode follower at the end to drive longer cable runs. Would that be worth implementing for one or both preamp outputs?
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If your SS power amp has a high input impedance there's no need for a cathode follower.
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Cool, thanks! Thinking it'd be helpful to add a DI out as well - any suggestions on how to best implement that?
I've got just an F2B circuit built with a DI output tacked on, and it seems it has trouble driving the DI (10k:600 edcor transformer) at the same time as the power amp. Not sure why. Each output works fine by itself, just have lower level when they're both connected.
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The output impedance of your plan is over 100k.
Few modern power amps are this high.
If you add more frills, you will need some form of buffer.