Nad 7225 - increase decoupling cap values in the amp section

[P. S.]

Hi,

I am about to recap the power amp section in nad 7225pe. The schematic calls for 2x 22uf/16v decoupling caps in some section of it. I only got 33uf/25v Nichicon caps on hand so I want to place them instead of 22uf caps. In reality the Nichicons test around ~30uf.

I am attaching the picture of the amp section where they would go. Can you advise what might be the sound effect of bumping up the cap values in this area of the power amp? Also - is it safe in terms of amplifier stability?

I tried to get some info about it and the only thing I found is that the bigger caps are in general better for sound quality at the expense of needing bigger current from the transformer. So - I think in the AMP section - I should expect clearer sound and a bit more power consumption? (given a very small 33uf capacitance - the current increase should not be the concern? .)

Thanks a lot!
Peter

 

[P. S.]

I will go ahead and put the bigger caps in. Before that - will do sound comparison. Will report the results ;-)

 

[teal'c]

Based on a post from dlucy some time ago, you may end up with too much bass.

 

[P. S.]

So I went on and increased the value from 22 to 33 and there was no noticeable difference in sound.

After that I went crazy and recapped the rest of the receiver - the phono stage and the preamp section with Elna Silmic II caps. On top of that I made a couple of my own "improvements" (or not - time will show):
- added a 0.68uf 100v film bypass cap for power supply filter electrolytics (6800uf/63v)
- in preamp section - replaced the 0.47uf/50v electrolytic polarized caps with WIMA film caps of the same value (C325, C326)
- in phono stage - replaced 4.7uf/50v capacitor pair with WIMA film 4.7/63v (C201, C202)

During the process I noticed that the schematic sometimes gives bad values compared to what is actually soldered in on the board. E.g. the C311, C312 coupling caps are 100uf10v on the schematic while 47uf is soldered in.

I've been breaking in this setup for the last few hours - here are my observation so far:
- the instruments are very well positioned
- there's a feeling of "vacuum" between different instrument (I imagine like each instrument can be heard separately on a black canvas layer)
- sound is more detailed (i can hear probably 30% more sound details than before preamp recap)

What I feel is lost (and hoping it will return as the caps break in):
- the trebles are super detailed and bit harsh - and my speakers are infinity Reference Studio Monitors with EMIT tweeters which usually don't overexaggerate the highs
- the bass is less present
- the receiver lost the feeling of "warmth" a bit (but not all) - sounding more detailed and neutral compared to when only power amp was recapped

Is that still the typicall NAD sound? Hard to tell - but I do believe in the capacitor break-in so time will tell.
If the tinny trebles persist after a few days of playing I think I will switch back C325 and C326 in preamp section from WIMA films to Elna Silmic II electrolytics.
So far I am mixed-happy with the result so I am keeping the original caps handy.

I also have a question about the film cap in the decoupling role. By design - film caps are not polarized - is this fine/safe to swap a polarized electrolytic cap with a non-polarized film in the decoupling role? (I know it's not recommended for power supply).

Thank you all for advice and have a great weekend!
-Peter

 

[50 Green]

Silmic II take a long time to break in and sound pretty bad until they do. Give it 100 + hours of break in time before contemplating any further changes.

 

[P. S.]

Yes that's what I read too about Elnas. I also observed similar process with the power amp break in (which has Nichicons). After 3 days the sound basically opened up and I found myself adjusting the crossover on my speakers.

I am more worried that I might have gone overboard with the 0.47uf film caps - that would be responsible for the shrill highs & super detailed highs. Whatever it is - I am giving it 5 days before switching back to 0.47 Elnas ;-)

 

[50 Green]

Yes that's what I read too about Elnas. I also observed similar process with the power amp break in (which has Nichicons). After 3 days the sound basically opened up and I found myself adjusting the crossover on my speakers.

I am more worried that I might have gone overboard with the 0.47uf film caps - that would be responsible for the shrill highs & super detailed highs. Whatever it is - I am giving it 5 days before switching back to 0.47 Elnas ;-)

If you're playing it 24 hours a day, that may be enough. I've found 3+ weeks of several hours a day to be needed to begin hearing a more pleasant sound.

 

[P. S.]

I reached the 100h burn-in mark yesterday.
From the time perspective - it all paid off. I kept Elna Silmic ii everywhere with 2 pairs of small Wima film caps in phono and preamp sections. Over time the sound smoothened out, the harsh and tinny trebles disappeared. I am super impressed with the accurate positioning of instruments and level of detail introduced by the film caps in the preamp section. I made an experiment 3 days ago and swapped them out with electrolytics (Elna). The resulting sound was "warmer" but way more distorted and less detailed and engaging. With film caps the sound is still smooth but there's lot more background detail in the music. Also instrument positioning and stereo panning is very accurate. I quickly went back to the film caps.

Overall - my recap result impressions went from mixed feelings right after to 99% full approval after 100h ;-) (still not sure if that's not my ears just accomodating ;-)

 

[gadget73]

for decoupling caps I'd probably go for a low ESR cap. You want a low impedance path to ground to get rid of any noise or signal from prior stages. If you're going to use caps sold as audio grade, I'd use them in signal coupling positions.

at least thats what I do, but all advice is worth what you paid for it