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NAD 3020A - ceramic disc cap replacement in pre amp

Use the chart I provided. 752= 7.5nF= 7500pF, .027uF. Any time there's a "." it indicates microfarads.

This is a super nice 1% 7500pF polystyrene cap, and also the only film farnell has in this value. You'll have to heatsink each lead (gently attach to an alligator clip, locking pliers, needlenose, anything metal that can absorb heat, etc.) before soldering each leg, to absorb some of the soldering iron heat, or you'll ruin the capacitor. Once soldered in without damaging them, polystyrene are among the very best sounding capacitors you can hope for.

https://uk.farnell.com/lcr-components/fscex-7500pf-1-160v/cap-7500pf-160v-1-ps/dp/9520619

Nice 5% polypropylene .027uF cap- best of their selection for this value, in my opinion.

https://uk.farnell.com/panasonic/ecwfd2j273jb/cap-0-027uf-630v-film-radial/dp/3227736
 
Thank you, so speedy and really helpful.
I did look at the chart you sent but didn't feel entirely confident with my computation.
So, well worth swapping the old caps on this NAD for these replacements and likely that I'll hear a difference?
I have a feeling that you'll say yes, of course.
 
"50" = 50VDC. Anything over 50V will do (like my replacements). Well, I don't know if you'll notice a difference by replacing these exact pairings of mylars or why you chose them as opposed to replacing all the other mylars, but yes. If you were to replace all of them it will sound higher fidelity than it would otherwise.
 
Hifibythekg said:
Mylar capacitor replacement.
I want to replace two pairs of these green ones with polypropylene caps for the phono path but need to know what values to order. The marking on the sides are:
00752J 50VF
.027J 50VF
Does anyone know what values these are and what I should be specifying for the order, ideally from
https://uk.farnell.com/
Click to expand...
What are the board designations for these capacitors? Are they in the RIAA feedback loop?
 
Thanks guys.
They’re pair C413+C414, and C415+C416.
Leestereo, you recommended these locations as I’m trying to optimise the phono section.
 
Also, planning to just put the ceramics and films for the pre and phono section into only one channel in order to compare it to the original caps channel.
Good idea or any potential problem with doing this?
 
Hifibythekg said:
Thanks guys.
They’re pair C413+C414, and C415+C416.
Leestereo, you recommended these locations as I’m trying to optimise the phono section.
Click to expand...
What are the resistors in parallel with these capacitors? In the 3020B phono schematic, there are also C427/C428 in parallel with C413/414, is that the case with your 3020A?
 
Please post the parallel resistor values as well as those for resistors R411, R417 (connected to ground) and R431 (series R before RC pairs).
 
Hi Leestereo,

The 3020A and 3020B have different schematics and apparently there were a few revisions during production which aren’t referenced accurately in the schematics.

I should amend my previous reference on these caps, with more time I see that:

C415+C416 have R423 and R424 in parallel.
R423 and R424 are each 100ohms


C421 + C422 have R437 R438 R439 R440 in parallel.
R437 and R438 are each 22000 ohms
R439 and R440 are each 680 ohms


C417 and C418 have R431 and R432 in parallel.
R431 and R432 are each 180 ohms
 
The RIAA correction topology that NAD typically employs is a set of parallel RC pairs.
RIAA block diagram.jpg

Here is the 3020B version.
3020B phono RIAA.jpg

The resistor values you report would result in a very inaccurate RIAA equalization; e.g., R423/424 should be ~10kohm, not 100ohm.
 
If you can you post the values of the other resistors in the RIAA feedback loop in your 3020A, the accuracy of the equalization can be determined.
 
Thanks Leestereo, I’m not sure which are the resistors in the feedback loop, please could you state them?
In the meantime,
Quick question...
@leesonic mentions a Quencharc spark suppressor for the power switch ( I hear a little ’spark’ sound upon switching off) but on the Farnell UK website they’re listed at about $15 !

Is there any other brand or component that does the same job?
 
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