Polyproylene film capacitors--only legend?

It's an RIAA phono preamp,

Ok, you said photo preamp before and that would be another kind of animal. The main RIAA preamp requirement along with gain, is to linearize the signal's frequency response. The process of making a record requires that one amplify the frequencies below 1Khz and attenuate the frequencies of above 1Khz to a very specific response curve. This is call RIAA equalization ( RIAA equalization - Wikipedia ). The overall gain of your preamp circuit is probably less then 30db, not particularly high when spread over three opamps, however the more accurate the capacitor values are the better the equalization will be. So I don't think the type of dielectric used in the caps is as important as their accuracy. 1% caps would be nice, but may be hard to find. If one had a large quantity to choose from then of course by measurement one could hand select from the batch.

Lefty