NAD C521 Mods help

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paulomartires

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Joined 2006
Hi,

I'm a owner of a NAD C521BEE cd player and I want to make some mods to get the most of my player. I have already removed the mute transistors and lowered the output impedence. But I want more... so, if anyone has some sugestions I'll apreciate.

I'll upload the pcb layout and schematics.

Thanks for the help.

Paulo


Nad C521 Service Manual
http://rapidshare.com/files/46316614/NAD-C521.pdf.html
 
gmilitano

gmilitano

Member
Joined 2004
diyAudioProjects.com
I am not sure how the C521BEE compares to the C521, but I imagine it is similar. I have a NAD521i and I wanted to do some mods too. Here are the NAD C521 and NAD C521i Services Manuals.

Here is a good link to some mods for the NAD C521BEE which has some mechanical mods too:
http://www.head-fi.org/forums/showthread.php?t=210626&highlight=Modifying+NAD+C521BEE

I imagine upgrading the input and output caps could help a lot. If you go into a preamp or integrated amp with input caps, you could consider removing the output cap all together.
 
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zanash

Member
Joined 2005
A quick look at the schems shows me that the dc decoupling caps in the output C369 and C368 look prime targets ...swap these out and replace with either the very best electrolytics you can get hold of or fit 10uf 150v paper in oils [my personal fav]. I thing you will be as surprised as I always am at the emasculating effects of electrolytic caps in the signal path.

I'd also replace the opamps with good sockets and fit as an absolute minimum opa 2604 's...I like the opa2227 but that just my taste.

best bang for buck .....swap all the 1n4001's for 11dq10's or similar schottky diodes.

don't forget that a good power cable will have a large effect along with ic's
 
Sangram

Sangram

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Joined 2002
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Not that it's worth that much, but I removed the output caps totally (the 22uF bipolars as well as the bypass .47 uF film caps, plus the series resistors), as well as the muting transistors. I wanted to replace the output opamps, but I managed to find a buyer for the player before I got around to doing that or one of the many mechanical mods I had in mind (green LED, damping the case, changing the powercord) or the PS mods (replace the ceramic bypass PS caps, change the very hot 5 and 8 volt regulators to a discrete supply).
 
gmilitano

gmilitano

Member
Joined 2004
diyAudioProjects.com
paulomartires said:
Update: I've removed the output caps anda the sound got better, but I have some concerns about this. I didn't detect any DC at the outputs, but I'm affraid that it could damage something. Any coments on this?

BTW, any suggestions reggarding the power supply?

Thanks,

Paulo
Click to expand...


If your CD player goes into a commercial preamp or integrated amp, it most likely will have DC blocking on the input, so it should not be an issue.

You could have problems if you go into a amp without DC blocking.
 
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Baka

Member
Joined 2005
paulomartires said:
Update: I've removed the output caps anda the sound got better, but I have some concerns about this. I didn't detect any DC at the outputs, but I'm affraid that it could damage something. Any coments on this?
Click to expand...

As I understood from replies to my questions on DIYHiFi (http://www.diyhifi.org/forums/viewtopic.php?f=2&t=1170) DC at the output depends specifically on Input Bias Current (Ib) and difference between the resistances seen by the non-inverting and inverting inputs of opamp in that specific setup.

For NAD C542 and OPA2134 as default opamp there is no DC at the output hence no output coupling cap.

If you replace it with other opamp do measure DC though few mV are acceptable IMHO.

Baki
 
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