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21 Year Old NAD Monitor Series 1300 Preamp needs a rebuild

post #1 of 5
12/14/09 at 2:01am
Thread Starter 
I have this old NAD preamp that has a pretty decent MM/MC RIAA phono preamp in it that I want to put back into service for the casual listening/computer head fi setup but it's in need of a few updates (PSU rebuild and recap, some wiring/jack upgrades, resistors, diodes, IC OPA's).

The Preamp itself in stock trim is somewhat grainy and veiled in nature, certainly not what I would consider good enough for what it cost me back in '89 (900.00 CAD) but with a few parts upgrades in key spots it could shine once again. I have the matching 150W per channel amp that has been partially rebuilt and is currently being used for the den's 2 channel speaker/DVD HT system so that side of the equation is taken care of already.

The main problem I've run into with the Preamp thus far is finding a suitable modern and better performing IC OPA for the stock (and very poor performing ) JRC/NMJ 2043DD dual channel, bi-polar, DIP8 package opamps.

Does anyone know offhand what a good (or great) replacement for these would be ? The NAD Pre uses quite a few of these IC's throughout the circuit (9 of them) so changing these out to something better (if possible) is paramount to taking this project where it needs to go. I searched around for a suitable reference WRT compatible modern equivalents but came up empty in that search.

Any help with this would be greatly appreciated !!!

Thanks in advance for any suggestions, links etc...

Peete.
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post #2 of 5
12/14/09 at 8:10am
LME49720 (LM4562) is a safe bet. It's easy to find and cheap with regards to the performance. It sounds neutral with good details. There are better opamps like AD797 and maybe some from Linear. AD8599 vs LME49720 is a matter of taste. Some say that OPA2211/OPA1611 sounds better than LME49720, but I haven't heard it.

If there are electrolytic caps in the audio path you should try to change them to film caps.
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post #3 of 5
12/14/09 at 11:20am
Thread Starter 
Quote:
Originally Posted by diditmyself View Post
LME49720 (LM4562) is a safe bet. It's easy to find and cheap with regards to the performance. It sounds neutral with good details. There are better opamps like AD797 and maybe some from Linear. AD8599 vs LME49720 is a matter of taste. Some say that OPA2211/OPA1611 sounds better than LME49720, but I haven't heard it.

If there are electrolytic caps in the audio path you should try to change them to film caps.
Thanks DIM !

I'll have a look at the data sheets of those parts you suggest and make a choice. There looks to be some cheap caps in the signal pathways but I have to get a hold of the schematic to confirm the assumption. I agree with your suggestion and have a number of NOS PIO/PLIO/Teflon and poly film/metal film caps of various values and voltages to choose from for that particular job.

Peete.
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post #4 of 5
12/14/09 at 12:59pm
I just looked in the NJM2043 data sheet. It's specified to +/- 22 V so you might have to choose LME49860 instead of LME49720. It's really the same opamp under a different name, tested to withstand higher voltage. You have to look in the schematic or measure the rails.
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post #5 of 5
12/17/09 at 3:46am
Thread Starter 
Quote:
Originally Posted by diditmyself View Post
I just looked in the NJM2043 data sheet. It's specified to +/- 22 V so you might have to choose LME49860 instead of LME49720. It's really the same opamp under a different name, tested to withstand higher voltage. You have to look in the schematic or measure the rails.
Digikey has those OPA's (49860's) for a reasonable cost (4.00 ea). Thanks again for the help

Peete.
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