Need help choosing tone board film caps

[Willy Dio]

I recently recapped an MCS 3233 stereo from the late 70's (similar to say a 30-50 wpc Pioneer from the same time period sound-wise). I used Nichicon FG in power supply, and Elna Silmic II in the amp and tone board.

I noticed the amp board had a lonely set (1 per channel) of polyester film caps in the 47nf range, and decided to experiment and went with Vishay-Roderstein metalized polypropylene replacements not expecting anything going in, but again figured "why not" as I was already in there and thought it couldn't hurt going with something new and I was honestly curious if those little green film caps had any bearing on sound or not. I waited to do the Vishay's LAST and fired up the unit before installing them just to see what it sounded like with only the electrolytic replacement, and relied heavily on headphone comparisons to catch more detail. It sounded OK with just the recap. After installing the Vishay's, I was floored as they demonstrated a marked improvement I could clearly hear in the higher registers, along with an overall improvement from tighter low-end up to separated cymbal crashes vs. a more muddied together cymbal crash. I removed the Vishays twice and reinstalled the polyester caps and the sound improved/devolved with each swap, so it definitely wasn't my imagination. Was very pleased and surprised a $1.70 polypropylene cap had such a profound impact. I always wondered WHY a $300 film cap the size of a pop can went for so much money as thought there was NO way a cap in the nF range could have enough of an impact to warrant the cost and effort. Now I at least understand.

Anyways, the tone board still has 16 film caps in the .33uF/330nF, .22uF/220nF, .047uF/47nF .022uF/22nF, .015uF/15nF, .01uF/10nF, .0033uF/3.3nF, and finally .0022uF/2.2nF ranges.

My questions are, if I stuck with the Vishay's only, is it possible I could end up with too sterilized of a sound? The unit is punchy, has tons of low-end, has a mid pot that actually works, and a great overall sound with very dynamic range as-is. But I realize there is still room for improvement.

I understand 100% this is an entirely subjective question, all circuits are different, all stereos/amps are different, everyone's ears are different, etc. I'm looking for film cap advice in general and am hoping to get some detailed accounts from those of you that have swapped out your film caps in your gear, and what the brand you swapped to did for your circuit. Did the timbre change? Did clarity increase smoothly? Or did it get harsh? Was your amp "warm" sounding to begin with and stay warm?

Also, from the values listed above, any idea if they influence only certain ranges? Seems the 15nf are all grouped around the bass pot, 3.3.nF around mid pot, 2.2nF and 10nf around treble pot. 220nf seems volume and balance pot oriented.

Also, any point with replacing the ceramic caps on the tone board? Only 6 of them and all in pF range. Seem centered around volume and balance pot, which are far right of tone board whereas bass, mid, and treble are far left.

I'm just hoping to possibly balance everything out by keeping bass deep, tight, and clean. Mids sharp and clear. And highs ultra detailed. Thanks.

[stj]

Re: Need help choosing tone board film caps

see if a table exists showing the ESR curv at different frequency's

[budm]

Re: Need help choosing tone board film caps

Do you know if that 0.047uF is in the signal path or for power supply by pass cap?
A lot of audiophiles prefer polypropylene over polyester metal film cap.
Circuit diagram?

[montemcguire]

Re: Need help choosing tone board film caps

From your description, you seem to agree with my perception that polypropylene films sound better than mylar films. In my experience, polypropylene replacements will not lead to harshness, but to a generally more clear and detailed sound - they are much more accurate capacitors, and the only reason that I leave mylars in a circuit is because the 'fog' of a mylar is part of the desired tone of the circuit overall. (Example, I didn't replace the 1uF mylar coupling caps in a client's UREI 1176 that needed to sound 'stock' but restored.)

Most '70s stereo gear uses such simple circuits that if you want 'clean', then removing/improving components (like mylar caps) that can cause extra coloration is the way to go; you generally don't have to worry about removing one of a pair of complementary colorations and thus making things worse overall.

Aside from the Vishays, the WIMA FKP caps are very good, and the MKP are a very close second best if you can't fit an FKP due to its size, or if it is not available in a large enough capacitance.

It's not clear what to do with the ceramics without looking at the circuit, but in general, any ceramic can be replaced with a ceramic that uses an NP0/C0G dielectric, and this might result in less nonlinearity in the overall circuit. However, not all caps need to be extremely low loss, since their nonlinearities might not matter. And sometimes, ceramics with losses can make a circuit more stable, so replacing them with a 'more perfect' capacitor will make the circuit unstable and thus sound much worse.

If you have a schematic, it would be very helpful, but for now, I think it's safe to replace all of the mylars that you listed above with polypropylenes.