Seventh Circle Audio

Hi all,

I came across the following suggestion from Jim Williams on proaudioweb:

'Get those knockoff kits from Seventh Circle and save $$$. Pop in some MAT-02 front end transistors in place of the LM394's and use some decent opamps, (not the dirty OPA604).
Try these: LME49710, LM6171, OPA134, OPA211, OPA827, LT1357, THS4051,THS4601, THS4631'

I am curious what people think of this suggestion.

cheers,
Roy

Before Jim makes suggestions perhaps he should give the C84 schematic another look - it needs a dual DIP op-amp. If you want something that will approach the OPA2604's combination of low distortion, low noise, low offset, fast slew rate, and high headroom, a good possibility is the new LME49860 from National, which isn't on that list. They're limited to +/-22V operation (as opposed to the +/-24V of the OPA2604), but they look promising.

As far as using a MAT-02, it ought to work but doesn't offer nearly the same degree of matching or noise performance as the LM394. The LM394 is unique AFAIK in that it's not just a pair of matched transistors on the same die, it's a whole array of transistors wired in parallel. This construction gives unrivaled matching between the two sides of the device.

thanks Tim.
Interesting to know.

I think it was the only less than 100% recommendation for SCA I've come across, and still a recommendation nonetheless.



Let me figure out this Paypal business and do some ordering...

Cheers,
Roy

It's clear from Jim Williams' posts that he puts a great deal of emphasis on high slew rate, but that's not the only (or even the most important) specification to consider when choosing an op-amp. For the C84, the OPA2604 is very hard to beat even though it's been around for a while. At 0.0003% THD, I'd hardly call it "dirty".