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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Mon Apr 15, 2019 7:31 am
by mediatechnology
I meant to ask as I got in some 2068DD in readiness before you finally decided on the 5532. I assume the differences are small enough as to be not a worry in use?
I really don't know the answer to that but I suspect it may depend on the gain.
The compensation allows for either the NJM2068 or the 5532 and for the 5532 it can be relaxed a bit.
My recollection was that at maximum gain there wasn't any difference.

The NJM2068's niche is MM preamps and JRC's "secret sauce" seems to be having the right combination of noise voltage and current that gives it a slight edge, with my Stanton, over any other bipolar or FET op amp.
If the NJM2068 has an advantage in the MC preamp it will be at lower gains.

Now that I have a board I'd like to compare the OPA1612 (on an adapter) to the 5532 and 2068.
At low gains I bet the OPA1612 wins slightly over the 5532.
An NJM2114 is also worth looking at though they are EOL.

I'm shopping for a DL-103 right now.
I need to test it with a cart before I let this go out.

Also getting an extra ADC headshell.

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Mon Apr 15, 2019 10:17 pm
by KMN
Of course, my eyes are terrible but it is hard for me to see exactly how you dealt with the transistor thermal coupling problem. Are they face to face..bonded somehow? Do you have any close up shots of that?

I was thinking maybe if you planned to insert the TO92's 90 degree bent, the flat faces could all be thermally tied via board copper....maybe a mounting hole could be used to apply down force via flat washer or something along those lines.

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Tue Apr 16, 2019 3:52 am
by billshurv
That was mentioned as not fitted yet. Experiments to follow I believe.

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Tue Apr 16, 2019 5:00 am
by mediatechnology
They are back-to-back and will be epoxied together.

The small metal "hats" I made from 3AG fuse ends I found worked pretty good.
I like wearing tin foil hats myself and the transistors seem to like it too.