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johan.gorsjo 16th February 2003 05:58 PM

NAD512 CD player mod
I'm thinking about modding my old NAD 512 CD player by replacing the OP-amps (NE5532) with better ones (OPA2604).

Is this a worthwile tweak, or is there something else that will make a bigger difference sonically?

Best Regards

Chris 16th February 2003 06:27 PM

cdp tweak..
I just modified my marantz cd 63 mkII. I replaced the original opamps with opa2134 (burr brown), currently I use the opa2604 whitch I like better. If mount a opamp (dil8) socket in your cpd you can easly switch opamps untill you find one you like.
I also removed the muting transistors on the output plus some electrolytic caps in the signal path. I don`t know if this is possible in the nad 512. Maybe somebody else knows?
Is the tweak worthwile? For me it was. The sound didn`t change that much. It wasn`t a wooooooowh :bigeyes: change but it changed to the better, IMHO. The mod didn`t cost much and it didn`t take much time to do it either.


Marlowe 16th February 2003 06:36 PM

Perhaps you can improve the power supply for digital and analog circuts both.

johan.gorsjo 18th February 2003 12:45 PM

cd tweak
thanks for the replies.

There is a transistor close to the RCA out jacks which I presume is the mute. I don't have access to the service manual, does anyone know where I can get it?

"Improving the powersupply" - you mean having separate powersupplies for the analog and digital, right? What is usually done to improve audio quality and what is most important (transformer, regulators, caps etc)?

Best Regards

Hamish 18th February 2003 01:06 PM

try the opa2132 too. i got some 2134's for a preamp, but they sound too metallic. 2132's are nice and warm/neutral.

try NAD for a service manual. they are usually pretty good about that kind of stuff.

machinow 18th February 2003 05:49 PM

Output mute transistors
They are usually close to the RCA jack, bjt types /always/, emmiter connected to the signal path, collector- to the ground! Base voltage /with japaneese types one of the outermost/ drive should be around +0.7V when muted /CD off, or something.../ and under -5...-15V dc, when unmuted /CD playing/ ! My advise is to remove them!!! If you whant muting /without it there will be clicks and pops on power up/down/ better way is to use a relay!
Also check the total resistance between the last signal opamp and the RCA jacks - it shoud be lower than 200 ohms, it is the output impedance your interconnect sees. If it is high-prepare for sound-dependent-on-interconnects :) But do not make it under 100 ohms - the opamp may become unstable. Usually making the first-after-the-opamp-resistor about 100R, and all others - 0R /jumpers/ is quite successfull!!!
power supply -firs you can replace the filtering electrolytics with bigger ones - about 2-3 times the original value, especially on cheaper CD players. Watch out to have a docoupling cap of non-electrolytics type on every opamp/digital ICs. I don't mind to use a cheap ceramics here, nevertheless some audiphiles use only very-high-quality /and X-pensive/ Polypropylene caps. U decide!
Good luck!!!
U can also replace the DAC chips, but should be more experienced:rolleyes:

johan.gorsjo 19th February 2003 08:37 PM

Progress report
I desoldered the 5532's and replaced them with socketed OPA2604. After checking for any shorts or bad connections I put everything together and tested it. It sounds better, not a big change, but it feels more detailed. My wife claims that it sounds a lot better though :-)

This forum is really a very good place to learn - thank you very much!


machinow 20th February 2003 09:33 AM

opa2134 vs opa2132
the basic difference between the two is the input offset voltage! The other difference is the price, of course! So from now on I don't believe there is a SONIC difference between the two!!

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