What do you seek to accomplish?
Im rethinking and reviewing my own habits from time to time. I also like to do this on the basis of a current hands-on project.
I thought it would be a good time to bring this up and see what other members think on the subject.
My own experiences are very mixed and inconsistent. The issue also touches the controversial topic of "capacitor sound" which is not only highly subjective but also difficult to measure.
I believe that the component (here capacitors) quality can play a role in terms of sound, but the circuit environment also plays an important role here.
I once compared numerous different capacitors of all qualities and prices with a dedicated apparatus and the results were disillusioning.
I wanted to believe in it, but the differences were negligible in a double-blind situation and, above all, not reproducible. In essence, it didn't matter whether it was an old used electrolytic capacitor from a cheap Italian organ or a super expensive "high end" MKP cap.
So it doesn't matter which capacitor you use?
Not quite. As I said, the whole thing must also be seen in context. In this case it was an coupling cap in a opamp headphone amplifier with a lot of negative feedback. However, as we know, there are also other circuit situations.
That's why I cited the example above. In very simple tube circuits without negative feedback, I could hear differences in the capacitors with the same technical data. It is still subtle but often audible.
I found the differences to be greatest in the cathode branch of tubes. Electrolytic capacitors are often used at this point, so it seems obvious to "pimp" them with a parallel film capacitor.
Here the situation was again inconsistent, sometimes I found it "better", sometimes not. I don't have the equipment (or the knowledge) to prove this metrologically, but apparently the issue is more complex than it appears at first glance.
The two capacitors seem to interact with each other, in my opinion there is no guarantee that the combination of electrolytic capacitor + film capacitor is necessarily better than a good electrolytic capacitor alone.
Again, this is quite subtle and also very subjective. At the moment, I'm just trying it out and letting my ears decide. When in doubt, I prefer to leave out the parallel film cap. I'll spare you my personal listening impressions and my pathetic attempts to describe them in a language that is still foreign to me.
Decoupling power supplies is a complex task and needs to take into account all the subtleties not only of the schematic but of the actual build (like trace inductance). It's easy to make things worse by creating resonance in the impedance response with a multicap system. There are good examples of measurements availible online.
Do you have a link? This is a similar situation and maybe these resonances are the interactions of the two caps I hear?
Use audio grade ones, like the Nichicon Muse series in the signal path, and you're good.
That's right, I also like to use Nichicons or other well-known brands. However, I often need axial caps and the available selection is now really limited. Nichicon has unfortunately also EOL´ed some axial types...
For C5 Neumann uses a really cheap "bad" electrolytic in the U87, nothing paralleled. In clones I've substituted it for a "good" film cap - and it sounded worse. I would leave Neumann designs alone, they know what they are doing.
The Neumann circuit is just an example but I agree.
I did some bench work investigating this concept back in the 70s (not on vacuum tube circuits). I was chasing down some unwanted phase shift at 20kHz caused by an electrolytic capacitor's ESL (internal inductance). In my testing I found that the parallel high quality capacitor needed to be 10% or more than the large capacitor's value to measure like a single larger high quality capacitor.
Interesting, I also follow the min. 10% rule of thumb. Phase shift is unknown territory for me in detail, but I think it can play a role here.
Caveat Lector, electrolytic capacitors have improved quite a bit since my bench work several decades ago. I would suggest defining exactly what you trying to improve and then make objective measurements.
Yes, electrolytic capacitors have become much better in recent decades. I don't think I have the equipment or the knowledge for reliable measurements ATM.
I'm going to try your 10% variant.
