Preamps w/ polypropylene caps in power supply?

There's a whole subculture around caps. Poly caps in the power supply are theoretically "faster" and definitely longer-lived than fluid-filled electrostatic caps. The biggest advantages of electrostats is that they are quite cheap and compact for the value of capacitance that they offer. To achieve the same capacitance in a poly cap requires physically large poly caps or a bunch of smaller poly caps wired in parallel. Practically, there's usually not enough room under the chassis to do this easily.

Many people believe that the advantages of poly caps in the power supply can be achieved by bypassing the electrostats with supplemental poly caps. John Curl has written some interesting papers on this practice.

I have no specific experience in replacing electrostats with polys, although I've routinely bypassed them in some applications. The biggest wins have been in other areas. I have had sonic successes with tube amps where I've replaced or supplemented power supply filter caps with oil-filled motor run capacitors.

Frankly, for me the biggest buzz and sonic payoffs are usually found for coupling capacitors rather than in the power supply. Modern electrostats have much lower ESR than was true a couple of decades ago, so the poly caps are not such a big improvement any more.

Just my $.02

I have used poly caps in all my components and replaced the electrolytic whenever possible(space limitation, values of cap, cost etc.) Not all poly caps are the same. Some may be good for bypass and not good for coupling. One has to try until having the desired sound.

I replaced with poly caps in my speakers' crossovers, the speakers are more quiet and clearer sound with deeper bass.

I replaced them in my cd player and the sound of the cd player become smoother. Some cases it changes the character of the sound for the better.

For the preamp, I actually replaced the electrolytic in power supply one by one and compare the difference each time. Each replacement made the music smoother and sweeter. Yes, in the power supply. I did that until no more electrolytic.

you can try that with inductors (for speakers) and resistors (for all).

Enjoy.

Those film caps can and do sound great compared to electros in many designs. But it depends on the power supply design, design goals, and type of amp. I have used computer grade, huge can electos to great effect. They do great things for a robust and kick butt power supply. Those film caps just don't offer large enough values for some designs.

Poly power supplies have many advantages with the biggest disadvantages being size and cost. However, when modifying a product's power supply over to all or even partial poly from lyrics is not as simple as replacing caps. Whenever you switch caps, you run the risk of altering the voltages due to difference in resistance. You always have to check voltages of the stock power supply before touching anything. You will likely have to modify dropping resistors to assure you end up with the same voltages as before you start. There are even times where you will not be able to obtain the proper voltage range. Sometimes you will end with voltages with the range accepted but this is rare depending on how extreme the modification is.
These different voltages are often the cause for the changes in sound.

We use polypropylene power supplies in all but the Econo versions of our Musica Bella products. Again, this is due to size and cost. This topic has been brought up several times and is becoming more popular. I have always finished with saying you have o pay attention to both the power supply and the circuit design. You can have the best circuit design in the world but it means nothing without a great power supply (poly or lytic) and visa versa. It the product as a whole that yields the best overall design. Unfortunately, most manufacturers usually concentrate more on the circuit design than the power supply but this seems to be changing more over the past couple years.

Dielectric Absorption.
Charge up an electrolytic capacitor and then time how long it takes for it to discharge to zero using a bleed resistor. Remove the resistor, wait a minute and read it again, there's more voltage left to come out. This is an example of dielectric absorption. It's like squeezing a sponge dry, and then some more seems to come out.

A polypropylene capacitor discharges faster and more completely than an electrolytic. In addition to electrolytic capacitors, some power supply designs use a big polypropylene cap (similar to start caps used on motors) to make reserve power more immediately available.