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zebra100 30th May 2008 10:51 PM

NAD C520 Mod's
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I have recently carried out some minor modifications to my NAD C520 CD player and I would like to share my experience.

I was more than happy with the sound from the NAD, but I wanted to see if I could get more from it. I only spent just under 35, and it sounds awesome (IMO). I think it now compaires favourably with some >/=350 players.

Firstly I did the blutack mod to the clock (free). That tightened up the bass a little. Well worth it if combined with an isolation platform.

My next mod was the output caps in the analogue stage (x4). 22uF stock caps, rated at 25v. I replaced these with Black Gate standard caps 22uF at 16v. This proved quite revealing. It opened up the soundstage and seemed to make things more transparent (although a little harsh and bright until the caps had time to settle down). Once the caps had had about 60 hours of burn they had settled down nicely.

I then removed the muting transistors, which is also well worth doing (as it is free). This seems to improve the focus of the player (somthing to do with removing parasitic capacitance).

Power supply next.....

I changed the diodes in the power supply stage (both analogue and digital) for schotky diodes (11DQ10's), 9 in total. That dropped the noise floor like a stone. More transparency, and much cleaner sound.

The final mod was to replace the NE5532 op amps with LM4562 op amps (fitted in chip sockets). I wasn't convinced that they had made an improvement to the sound at first, but I gave them an extended listen. Still not convinced I decided to put the 5532's back in...... and that's when I noticed what a difference the 4562's made to the sound (IMO). Strange how the brain works.

Putting the old chips back in muddied the sound and took away the shine. With the 4562's back in the sockets there was bags more everything, but not just louder. The soundstage had more room to breathe. Bass that I did not know my speakers were capable of and the treble was sweeter and less tiering. The Phillips 5532's do have a sweetness with vocals, but I think that's because they are quite veiled in other areas and the vocals stand out more (IMO). Another worthwhile mod (10.00 for the pair)

Well worth the effort (about 4 hours work).

Mooly 31st May 2008 07:27 PM

Interesting to hear your findings. The 5532 in my opinion is not good from the "subjective" viewpoint. OPA2604's take some beating I find for this kind of application, and yes yes I know some folks must get fed up of me saying that, but it's true.
Incidently there's another thread in the "Chip amps forum" for some strange reason, on modding a NAD5240. You might be interested, the last posting was only yesterday 30/5/08.
Regards Karl

zebra100 1st June 2008 09:31 AM

You might be able to see in the picture that the original Op Amps were the Philips breed rather than the inferior (IMO) Fairchild or TI chips. The Philips NE5532 do seem to have a sweetness with vocals and are good generaly in the mid's and high's. The LM4562 is an all round improvement.

I did look at the data sheet for the Burr Brown variant of the OPA2604. I intended to try them, but found them difficult to source at the time, which is why I went for the LM4562's. I am more than happy with the outcome. As I installed chip sockets, I may have a play with other chips in the future.

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