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-   -   NAD512 CD player mod (http://www.diyaudio.com/forums/digital-source/11236-nad512-cd-player-mod.html)

johan.gorsjo 16th February 2003 05:58 PM

NAD512 CD player mod
 
Hi,
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
/Johan

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.

Chris

Marlowe 16th February 2003 06:36 PM

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

johan.gorsjo 18th February 2003 12:45 PM

cd tweak
 
Hi,
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?

Marlowe:
"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
/johan

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
 
Hi,
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!


cheers,
/johan

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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