value of capacitors in signal path

[Oystein]

As I am preparing to upgrade my NAD C162 pre-amplifier with better capacitors in the signal path I have some questions about the used values in uF.

I see a total of two caps; 100 and 220 uF
Both parallel with small (> 1uF) caps.

What does the (total) values really depend on ? .. had it something to do with input/output impedance matching of the used circuits or would it help to change the values while I am in the process of making changes ?
What guidelines apply here ??

Thanks, Oystein

[AndrewT]

do you have a circuit diagram for the pre?

[Oystein]

Hi Andrew,

Yes, I ordered the servicemanual by our local distributor.
I could choose for a printed copy or PDF by email .... I choose PDF :-)
It is only a few pages but has the complete wiring diagram.

Oystein

[AndrewT]

Hi,
can you post the schematic here?

It will show what the input feeds through on it's way to the output.

We had a similar thread for a NAD power and it had all sorts of extra components in the route that could simply be removed.

[Oystein]

See enclosed 2 drawings:

The complete circuit diagram as received by NAD
An easier to "read" customised diagram of the amplifier section created by myself

[Oystein]

I noticed I made a mistake in the page orientation downsampling the amplifier.pdf because of too many kb in size.

See enclosed the correct version.

[Oystein]

I also included the internals of the line modules which show as a black box in the main diagrams

[Scott594]

The .1uf is to bypass the electrolytic's inherent inductance at high frequencies. Usually in high impedence circuits (which this should be, but I can't be sure unless I have spec sheets on the modules) the .1uf is all that is used to couple stages. For some reason NAD used the electrolytics as well. It seems that there must be a reason, but at 1st glance it looks to me like Andrew may be right. I'd try pulling the electro's and give a listen. If you lose low end response, then maybe take the .1uf to .47uf. If it sounds weak and thin or oscillates, then the electros are required. Seems a shame to put electros alongside good quality coupling caps though.

[Oystein]

The smaller caps are the common brown/caramel ceramics.
I would replace them anyway for MKP's.

I could try to remove the electroltic's and use the MKP only.
As I understand correct even the MKP's could benefit from using a bigger value ??

Besides this tweak ... if we go back to my original question:
What factor determines the value of the electrolytic capacitors ??

[Oystein]

Being in the mood already I will tell you another experience now the NAD is on discussion.

Looking at the amplifier diagram you can see that the LineOut module gets the signal from the volume/balance potentiometers.
At normal listening levels the volume knob is at 08:00 position and the LineOut module has to work with very low signals.
To increase s/n ratio and resolution I decided to experiment with the PreOut2 having the potentiometer RV5 set to minimum signal = -12 dB.
This way I can crank up the volume to the 11:00 position which will help the LineOut module dealing with a higher signal.
I do get more dynamics and resoltion and punch in the sound ...

The easiest tweak I ever did ...