Capacitor Dielectric Question

[FourT6and2]

I know this can be a touchy subject for some. But this is maybe a slightly different take on it. Not talking about coupling or bypass caps, but the caps used for the "fizz cap," tone stack treble cap, bright caps on the gain pots, and the high-pass/treble peaker. This are all usually either silver mica or ceramic disk. Why? Can you use a polypropylene foil instead? What about polyester foil? Or metallized caps (MKP, MKT, etc.)? Why are mica or ceramic always the go-to for these positions?

For example, I know I CAN use something like this Philips foil polypropylene cap (KP Series / 460-464) as a fizz cap or bright cap or treble cap. But is there a reason NOT to? I ask because I have a bunch of 'em.

[JazzGuitarGimp]

All of the cap positions you speak of (fizz, bright, etc) require caps in the range of about 47pF to 500pF, but the cap you have pictured is 1.2nF. Just for reference, 1.2nF = 1,200pF. I am not sure you can find any film caps in values small enough to fill the positions you mentioned.

[Roe]

try and see if you like it

[FourT6and2]

All of the cap positions you speak of (fizz, bright, etc) require caps in the range of about 47pF to 500pF, but the cap you have pictured is 1.2nF. Just for reference, 1.2nF = 1,200pF. I am not sure you can find any film caps in values small enough to fill the positions you mentioned.

That's just a stock photo. I have those same caps in various values, including 47pF, 50pF, 100pF, 2700pF, 4700pF, etc.

[FourT6and2]

try and see if you like it

So there's no reason why those positions are always ceramic or mica? Other than maybe it's harder to find lower values in other types?

[JazzGuitarGimp]

try and see if you like it

So there's no reason why those positions are always ceramic or mica? Other than maybe it's harder to find lower values in other types?

Well, that's the (obviously incorrect) assumption I've been going on until you said this:

That's just a stock photo. I have those same caps in various values, including 47pF, 50pF, 100pF, 2700pF, 4700pF, etc.

It's nice to know there are other alternatives.

Ceramic discs are prone to microphonics as I understand it, and silvered micas seem to have become dodgy over the last 10 years. If I'm not mistaken, polystyrene used to be available in these lower values, but my last search on Mouser a year or so ago, returned dismal results, which leads me to believe they have fallen out of fashion. I agree with Roe, give'em a try and see how it goes.

[FourT6and2]

try and see if you like it

So there's no reason why those positions are always ceramic or mica? Other than maybe it's harder to find lower values in other types?

Well, that's the (obviously incorrect) assumption I've been going on until you said this:

That's just a stock photo. I have those same caps in various values, including 47pF, 50pF, 100pF, 2700pF, 4700pF, etc.

It's nice to know there are other alternatives.

Ceramic discs are prone to microphonics as I understand it, and silvered micas seem to have become dodgy over the last 10 years. If I'm not mistaken, polystyrene used to be available in these lower values, but my last search on Mouser a year or so ago, returned dismal results, which leads me to believe they have fallen out of fashion. I agree with Roe, give'em a try and see how it goes.

Yeah, I don't see anything majorly available as far as new products go. But there are NOS ones available at various places. Here's the data sheet for those Philips (also branded BC and Vishay): http://www.farnell.com/datasheets/28681.pdf

Here are some 470pF if anybody wants to try 'em out as well: https://www.tedss.com/2020007602

[Mr. dB]

Ceramic discs are prone to microphonics as I understand it, and silvered micas seem to have become dodgy over the last 10 years. If I'm not mistaken, polystyrene used to be available in these lower values, but my last search on Mouser a year or so ago, returned dismal results, which leads me to believe they have fallen out of fashion.

Not so much "out of fashion" as just out of production.

Although I guess that means they fell out of fashion with the industries that were using them in large quantities. Audio is like the red headed stepchild of the electronics industry.

Anyway, the old Roederstein Styroflex polystyrene caps were top quality stuff.

[chief mushroom cloud]

Ceramic discs are prone to microphonics as I understand it, and silvered micas seem to have become dodgy over the last 10 years. If I'm not mistaken, polystyrene used to be available in these lower values, but my last search on Mouser a year or so ago, returned dismal results, which leads me to believe they have fallen out of fashion. I agree with Roe, give'em a try and see how it goes.

encountering this a lot lately.....even nos film available are at reasonable prices if you go to ebay.de...for something that makes sooooo little difference tonally between cap types, just use the nos stuff or polystyrene from http://www.justradios.com...don't be a cheep bastard, pay up and like it

[FourT6and2]

Tried those Philips in my latest build and they seem to do the job. Tighter/punchier/more aggressive than micas and ceramics. They have the clarity of silver mica and add a bit of their own character like ceramic, but no graininess. I'll be using them from now on for sure.

[martin manning]

Did you use them for coupling or just the fizz and bright? I wouldn't think you'd see much difference for the fizz cap, but the bright cap yes, if the volume is turned down. Polypropelene is really one of the "best" dielectric materials due to its temperature stability and low dielectric absorption, but for coupling most people prefer the flavor of polyester.

[FourT6and2]

Did you use them for coupling or just the fizz and bright? I wouldn't think you'd see much difference for the fizz cap, but the bright cap yes, if the volume is turned down. Polypropelene is really one of the "best" dielectric materials due to its temperature stability and low dielectric absorption, but for coupling most people prefer the flavor of polyester.

I used them for the treble peaking circuit, the tone stack treble cap, and the PI fizz cap.

I'd like to try them for the bright caps in the switchable bright switches for each gain control (560pF/none/4700pF), but I'm not sure I have those in the right voltage. The 630v ones are maybe a little too large, physically. Right now the 560pF bright cap is mica and the 4700pF is a polyester Mallory 150.

For coupling caps, I used IC MPW (polypropylene). And they sound good to me. For bypass caps I used MKT1813 because the polypropylenes I had were physically too large to fit on the board.

[pdf64]

I suspect that when Marshall were first putting these together, ceramic or silver mica were what was available from Radiospares, hence the tradition was set.

[FourT6and2]

I suspect that when Marshall were first putting these together, ceramic or silver mica were what was available from Radiospares, hence the tradition was set.

Makes sense.

I recent years many people have reported silver micas leaking DC. So some suggest avoiding them. I personally prefer how micas sound compared to ceramic, which some say add a gritty texture to the sound. And ceramic disk caps have a tendency to—not be microphonic as some say—but to have piezoelectric properties. You can actually yell into a ceramic cap and hear it through your speaker lol.

So film/foil caps are a decent alternative it seems. So far, so good. I like these Philips KP caps. I think I've seen them used in a few other high-end amps, like in Larry Amps.

[martin manning]

I personally prefer how micas sound compared to ceramic, which some say add a gritty texture to the sound. And ceramic disk caps have a tendency to—not be microphonic as some say—but to have piezoelectric properties. You can actually yell into a ceramic cap and hear it through your speaker lol.

That's just another kind of microphonic.