Silver mica vs. Polystyrene

[dehughes]

Hello again,

I just swapped out some silver mica caps for some polystyrene caps in my AC30 build...just in the eq network (50pf) and the coupling cap off of the 1st gain stage (500pf). I noticed that with the polystyrenes some of the "quack" and top end has gone, but the amp seems to have a fairly more balanced feel in the preamp. I made the swap as I seem to recall that early AC30s had polystyrene caps in them....but I could be wrong about that...

Anyway, my question: What are the tonal differences between silver mica and polystyrene caps of the same values? Also, is there a break-in period required for polystyrenes, like there is on Sozo Mustard + caps, etc...or am I just hearing what I'm going to hear?

Thanks!

[Bob-I]

Interesting. I've never tried polystyrene in the pF range. Typically I compare ceramic to mica and prefer the ceramic.

[drz400]

Interesting. I've never tried polystyrene in the pF range. Typically I compare ceramic to mica and prefer the ceramic.

Polystyrene are smooth but very fragile, becoming hard to get
Silver mica are smooth as well to my ears a little closer to ceramics
I actually prefer the ceramics in most places, maybe a silver mica in the EQ section

[jelle]

My experience is that as a decoupling cap, mica caps sound very lineair and direct and the highs can be too much for guitar, ceramic caps sound sort of grainy without the piercing highs and this can be very cool, polystyrene caps sound smoother without being grainy. I like them too.
Depends on the sound I want to make.
Drz400 mentioned that they are fragile. Polystyrene caps do not like heat, so be careful when soldering them into position. IRRC, the ones with the black line across the cap are rated 1000v.

If anyone knows a source in europe, please let me know....

Jelle

[dehughes]

Interesting....thanks for the info. Any ideas as to their potential break-in period?

BTW, I used a heat-sink clip when I soldered them in, just in case.

[dehughes]

Well, I just finished play-testing the amp with the polystyrene caps in there. I must say that they DO sound noticeably smoother and easier on the ears at high-gain, low-master settings in comparision to the silver micas. However, at low gain, high master settings, (and, well, all other settings) I prefer the silver micas as they have more high end detail and articulation. This can be dialed back with the cut control or the treble knob, so that's not an issue, even though the silver micas are no where near as smooth when the preamp is driven hard. Being as the goal of this amp is killer clean/light OD tones, I'll probably stick with the silver micas, though I'll try a ceramic in the eq network just for kicks, as I have a new 47pf ceramic cap that I'm dying to try out...

So, in summary, the polystyrenes are more "closed" or "choked" sounding than the silver micas, but this works REALLY well for gainy tones...they smooth things right out. The silver micas are more articulate and airy at all other settings, albeit a bit harsh if the controls are set just right...

[dobbhill]

My term for mica caps is "peaky", like a cheap tweeter. I prefer the polystyrenes, especially for OD tones.
My 2 cents.
D

[dehughes]

My term for mica caps is "peaky", like a cheap tweeter. I prefer the polystyrenes, especially for OD tones.
My 2 cents.
D

Do you prefer them overall, or just for OD tones? What would you recommend I look to for nice AC30 vibe?

[dobbhill]

I like the 'syrene for both, but my understanding is that others like the ceramics better for the Dumble-style circuits. I play Telecasters. Humbucker guitars may require the more forward sound of ceramic/mica caps.
HTH, D

[dehughes]

I like the 'syrene for both, but my understanding is that others like the ceramics better for the Dumble-style circuits. I play Telecasters. Humbucker guitars may require the more forward sound of ceramic/mica caps.
HTH, D

That helps a lot, actually. Many thanks.

[David Root]

I used a NOS polystyrene 270 pF treble pot cap in my "mini-plexi", with SOZOs elsewhere, and that is a good combination, nice smooth OD, no icepicking. Tested with a Strat with Fralin Vintage+ pups.

I used a 250 pF NOS domino silver mica in the same position in a brown Fender tonestack, somewhat brighter, with PIO tonecaps elsewhere, that works well too, clean, and high volume, but heavy OD is rougher. Tested with a maple-clad SG special I built myself with 9K P-90s I also built myself. With the above Strat it's better behaved.

I guess it all comes down to trying different options and picking the one that goes "Yessss!!"

[dehughes]

...I guess it all comes down to trying different options and picking the one that goes "Yessss!!"

EXACTLY.


david

[JD0x0]

Old thread, but I recently swapped out a 180pF silver mica in the tone stack of a Hiwatt, back to a polystyrene of the same value and noticed a pretty apparent difference.
With the SM the 'treble' control seemed to have a much wider range, but from about 11:00 onward the tone got rather 'hard' and had a harsh metallic sort of sound to the high end, especially with OD. With the PS the tone is much smoother sounding, the control does seem to make a smaller difference through it's entire sweep, but much less harsh and tinny with the treble set higher. Not really sure which one I like better. The SM had an interesting articulation and openness to the tone, and sounded really nice with the treble set below 9:00. You could turn the treble to '0' and the tone would still have a really nice 'zing' to it, almost seems to increase mids, rather than reduce treble. The PS makes the treble control seem more usable, and has a nice smooth top end, but appears to have lost a bit of that articulation, nuance and touch sensitivity, but also less harsh.
Anyone ever try paralleling two different compositions?

[Structo]

Did you measure the capacitance of the two types of caps?

The change you heard could simply be a difference in value.

I remember reading an article a while back saying a lot of the new
production mica caps are terrible for tone and have wide tolerances.

I have changed some caps to polystyrene and thought it was a smoother tone.

In the Dumble I like using what Alexander used in his amps, if at all possible.