I will post here what I recommended you in personal messages.
I thought to mention OS-CON, but they’re good only new-old-stock (NOS). Currently manufactured are not any close to the NOS ones sound wise.
I didn’t want to buy “NOS” from eBay because there is no guarantee that they were NOS. That’s why I didn’t mention these as an option.
It is good to use Bi-polar ELECTROLITIC capacitors as broadband as possible with low impedance at audio frequencies. But the leads could act as parasitic inductance. Also, they are sensitive to vibration, causing microphonic effect.
! ! IF ELECTROLYTIC CAPACITORS ARE USED FOR THIS MOD, THEY NEED TO BE SUPPORTED. BUT DON’T LAY THEM FLAT ON OTHER DEVICES ! !
Another ideal option wouldn’t be PPS film capacitors, but with their dimensions, it would be difficult to find the right size with the right nominal.
Therefore, good low-impedance electrolytic capacitors designed for audio are the best choices. The higher the quality, the better.
The AD8132s are very fast and operate up to 350 MHz. Accordingly, they can excite or amplify spurious interference over a very wide range. So, for these OpAmps, we need SMD ceramic type C0G/NP0, but I couldn’t find any value that could work in a small packaging. Thus, I chose from X7R, which is also very good for this application. And there are already two 1uF X7R already installed there from the factory. Won’t hurt to add more.
Tantalum caps will not fit here according to how they sound like. Tantalum is worse than aluminum oxide capacitors. And (maybe @tedsmith could comment on this?) TANTALUM capacitors have a very low impedance, and PSUs not designed for their use can start generating noise themselves. Most likely, Ted would have already said something if the stock power supply couldn’t work with tantalum capacitors on Vocm mode.
So I used a sandwich of ELECTROLYTIC CAP (+) SMD CERAMIC X7R (+) SMD film Polyphenylene Sulfide (PPS).
I have chosen:
- the best available polarized Kaisei 220uF 16V (bi-polar will do, too)
- SMD Panasonic PPS 0.1uF 16V
- SMD Murata ceramic X7R 1.5uF 100V
These electrolytic capacitors have low ESR, and these PPS and ceramic capacitors will suppress interference on HF. So, this sandwich provides noise suppression in a wide frequency range due to the use of three types of capacitors. It’s just that each type (by dielectric) of a capacitor works ideally only in a certain frequency range.