Re: Op-Amp RIAA Preamp with Tone Controls - Help!
The 1960's Quad 33 had 6 transistors per channel. Two in the RIAA, one emitter follower with taps on the emitter resistor to select output for tape recorder. That is followed by the volume control (50k), and then a bootstrapped input (so it doesn't load the volume control) emitter follower. The low impedance output from that feeds the Baxandall tone control wrapped around a bootstrapped transistor pair.
They packed a lot of subtlety into 6 transistors per channel.
But the use of an emitter follower feeding the volume control, and a high impedance bootstrapped emitter follower after it to feed the Baxandall circuit is exactly the right way to do it.
Just substitute unity gain op-amps before and after the volume control and that should sort the problems - at least in that area!
Craig
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