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In Reply to: RE: Have you tried the AA-151 the SA2 predecessor? posted by DAK on April 22, 2016 at 11:55:30
Your mods to the AA-151 are absolutely required in order to turn it into a good amplifier. I've owned two, and both had a "squawkish" quality to the sound that drove me nuts. The majority of the problem was in the tone controls. I elected to sell them rather than tear them apart. Don't know if the SA-2 exhibits similar characteristics.
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Buy Chinese. Bury freedom.
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I don't like tone controls. Not on principle just in practice. They have too many things that can go wrong. And so many connections that "massages" the signal, to put it nicely. But a 6au6 in a tone control seems like a rather odd choice. I can imagine that it was a money saving decision. regards, Dak
Valid technical reasons are low Miller capacitance and high single stage gain.I too am not a fan of tone controls. However, if they are wanted/needed, do it "right". Max Robinson's "unity gain" take on Baxandall style is about as good as it gets. "Unity gain" makes for ease in totally defeating the circuitry, which rates to be the "normal" state of affairs. IMO, 2X 12AX7s/channel is OTT. However, it's easy enough to replace the cap. coupled cathode followers with DC coupled ZVN0545A source followers, which lowers the bottle count to 1/channel and reduces the number of caps. in the signal path too boot. Use the Sovtek 12AX7LPS, a genuine 7025 equivalent, if AC heating is to be employed.
Eli D.
Edits: 04/24/16
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