National LM 1972

[hifiZen]

I have to agree with your comments about opamps... when I first started getting serious about hifi, I was indeed skeptical of opamp sound, as I'd read all the bad press. But, the preamp I currently use is the best one I've built yet, and it's based on the OPA134 (with external output transistors inside the feedback loop).

...yes, I even think it's better than the SRPP tube buffer I experimented with, and definitely leaps and bounds ahead of the BUF-03FJ of Corey Greenberg's preamp, or any of the discrete MOSFET topologies I've tried. One thing I really like about solid-state: DC coupling - it can really make a big difference!

Back to volume controls though...

I think I'll just go ahead and order some CS3310's and try them out. In the meantime, I'm also considering a "digital" version of the log-approximation scheme used to turn a linear pot into an "audio taper" pot. Instead of using a pot though, I'm going to use a set of resistors connected in series, each one bypassed with a relay. Each DPDT relay shorts out one resistor on the top leg, while simultaneously un-shorting a like resistor in the bottom leg. This allows only 8 relays + 16 resistors to give 256 steps of linear attenuation (or 6 relays for 64 steps etc...). Add the resistor to ground, and you've got a log approximation attenuator, with good economy. We'll see if i actually build one of these attenuators, but I'll definitely report back on the CS3310s.

[fcel]

hifiZen,
I have read several post that mentioned that Corey Greenberg's pre-amp. I have seen that article in the Stereophile magazine but don't remember which issue? Do you?

[hifiZen]

let me see here...

ok, Nov 1991 and the follow-up article was Nov 1992. The power supply design is ok, but I'd have to recommend going with a different buffer. If you visit my homepage, you can see the circuit I'm using right now (KAP-4), directly in place of the BUF-03FJ. Only one problem... there's an error on the schematic: the opamp is shown upside down (+/- terminals reversed)! Unfortunately, nbci is being a bunch of $#!+heads and since May I have been unable to change or even delete my own website!! I'm very annoyed... Anyway, here's the appropriate URL: http://members.nbci.com/_XMCM/hifizen/preamps.html