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CMoy based preamp for home stereo? - Page 2

post #16 of 21
Thread Starter 
Quote:
Originally Posted by sanderx View Post
Use separate op-amps instead of a dual. Pay attention to temperature coefficents when selecting components, esp from different manufacturers. Use bandwidth limiting caps in the feedback loop. Use good decoupling caps (more importantly, have them). If you haven't, consider the use of trimpots / caps to get the best possible tracking between the channels. Don't overdo the PSU.

There is a fair bit of difference between CMOY's, yours seems to be a fairly basic one.
My plan was to build kind of a "super cmoy", which in my head would be a dual mono construction, reasonable power supply (possibly dual mono), "better than normal" feedback loop and of course fine decoupling caps.

What do you mean with not overdoing the PSU? Don't complicate it, don't oversize it or both?
post #17 of 21
Hi Mannevond:

You might want to take a look at this article for the design of your Super CMoy feedback network:

ELECTRONIC DESIGN - December 14, 1998 - Walt's Tools and Tips - Op-Amp Audio

Cheers!
post #18 of 21
Thread Starter 
Thanks, that was quite a good read. I have bookmarked it
post #19 of 21
Quote:
Originally Posted by Mannevond View Post
My plan was to build kind of a "super cmoy", which in my head would be a dual mono construction, reasonable power supply (possibly dual mono), "better than normal" feedback loop and of course fine decoupling caps.

What do you mean with not overdoing the PSU? Don't complicate it, don't oversize it or both?
Both, cmoy is a fairly simle amp, don make it be all psu.

Oh, and keep us posted on what you did and where you got with this.
post #20 of 21
Thread Starter 
I haven't made much progress other than getting me an old CD player to put everything in. Contemplating reusing parts of it like the AC to DC part of the psu, but I have to measure it and see how much noise it puts out. I'll probably make the front plate from wood. Looks good and is by far the easiest material to work with.

For the portable amp, I made a small battery snap adapter so that I can connect 2 9V batteries in series and connect it to the 9V snap. Increasing the voltage made quite a big difference. It controls my DT 770s (32 Ohm) much better now. Noticeable change when I use it as a preamp in the living room too. I also changed the caps to 470 uF 25V in place of the 16V caps that were in it from before.

I have switched a lot between the AD823 and the AD8620 opamps. The 823 seems to sound better for preamp purposes, 8620 for cans. I guess I know what to put in the preamp.

I'll post updates and possibly a worklog when I start building the thing.
post #21 of 21
Quote:
Originally Posted by linuxworks View Post

you can switch at the spdif level before your dac (for the digital sources, at least)

Wondered if you could explain that further as I am doing a similar project involving Tripaths and Cmoy as a Pre-Amp would like to interface with a ESS dac board adding a Wolfson spdif module ??
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