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What do you think of this preamp design?

I've been on the hunt for a preamp and came across the Audio-gd C3 final version:

http://www.audio-gd.com/Pro/pre/C3End/C3endEN.htm

It comes with schematic of the signal section. Does it seem to be well executed? Any obvious or subtle design flaws? It has had some positive reviews by owners on the web.
dracule1
dracule1 OP
1,085 posts
 
The Audio-gd C3 input impedance is 47 kOhms. I asked if it can be changed to 100 kOhms, and they said it was no problem. I wonder why they don't use higher input impedance.
kirkus
502 posts
 
It looks overly complex... A very competent solid state line stage could easily be built with about 1/3 the components. The op-amp in the feedback loop looks to me like an outright design problem...
The opamp is obviously an integrator (DC servo) used to set the quiescent conditions of the "BPM-7110" module, which appears to use current feedback, and a very high output impedance (current drive). The buffer stages are used to interface with non-CAST components. Really not so complicated.

Atmasphere, there's certainly not enough information here to trash this design so thoroughly, and English is obviously not his native tongue. While this is also not the way I go about designing a linestage, it's about as thoroughly "Power Paradigm" as it gets. To me, his stuff looks interesting, unconventional, and definitely reasonably priced compared to many.
atmasphere's avatar
atmasphere
12,116 posts
 
Kirkus, if that's a servo, as long as it is handled properly I would expect it to work fine. The schematic really did not offer timing data, and there should be some integration at the output of the opamp else the servo will not work correctly. We use servos in our preamps too as our outputs are direct-coupled. I agree his English could be better...

Dracule1, I was not proposing that the amp be modified by anyone in particular, and it is certainly work that the manufacturer could easily do. If you *did* decide that this is something you were interested, I would be happy to talk to whomever made your amp so they would know how to do the mod.
dracule1 OP
1,085 posts
 
Kirkus, I completely agree with you regarding the price of this unit. I'm not an electronics expert so I can't attest to the soundness of the design, but there is no US or EU based company (even if they manufacture in China) that can make a preamp or amp of this build quality for the price they're asking for. If this was a US based company, I wouldn't be surprised if the preamp was priced at $6000+.
dracule1 OP
1,085 posts
 
Ralph, I appreciate the offer. I may offend the designer of my single ended amp if I ask him to change his amp in any way (He is pretty legendary and has been building audio equipment since the early 70's). But I'll ask.
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