Calling All Cork Sniffers! (PF Content)

[Blackburn]

So I've noticed that many builders use certain kinds of caps for the pf values and I want to know what those here on TAG think of them tonally, assuming this hasn't already been beaten to death...

Most of the users here, including myself, use the standard, what I assume are Xicon SMs.

On the Komet and TW stuff, I see CDE SM caps. The yellow and brown ones.

And more rarely, the ceramic disk variety, like the Mark Kane amp just posted in the TW section used one for the treble cap. I rarely see these used across the plates of the inverter, but there's a Wreck that comes to mind.

Anyone have any word on the tonality these caps offer with regard to one another? Probably isn't a big deal, but I thought I'd see if I find any interesting opinions.

David

[Leo_Gnardo]

pF content, like picofarads? You could take a look at our friends @ Music Electronics Forum, they just spent a week kickin the heck out of capacitors, and in some cases, each other. Search 'Orange Drop Capacitors' on MEF, you'll have enough reading to put you to sleep.

Me, I generally use ordinary discs, whenever possible NPO rated which means no drift in value with temperature. 500V rated or more.

Sometimes a silver-mica, esp. in tonestack treble circuits. Some claim the silver-mica gives a 'clearer' tone compared to 'gritty' or 'sandy' with the standard disc. Cheap enough experiment, try some out. I've only once seen a silver mica fail.

On rare occasions a polystyrene but only if I'm sure not much voltage will develop across it as most are rated 50V. Sometimes on a "bright" switch. Again, clear tone as opposed to grit.

That cap you see in the inverter is probably to quench ultrasonic oscillations. I've had to do that in many Fender & other amps. Use as small a value as you can to knock down "parasitic" oscillations.

Old disc caps esp. as used in tone stacks or coupling stages, often are microphonic. Tap on these with your handy chopstick. Up to you whether you want that to stay in your amp. A couple little "microphones" passing a pok-pok sort of noise into the audio, especially in a combo amp - I'd change 'em out but some people may like that sort of thing.

[Reeltarded]

Same. I like the dirty disks enough to split values with silver micas. Little bit of both world's. Anywhere I ever needed 1000p and split it between the two was good.. so far.

[Gaz]

They all pretty much sound the same to me, but I like the blue ceramic Murata caps cause they're pretty, or NPO Xicon depending on what values they're available in. The shape of silver micas makes me feel weird.

[cbass]

I like disks in some amps Mica in others some both

[passfan]

I usually snatch up whatever's laying around on the bench. The majority of which is either 6ps , Philips made mustard , Russian pio or K73 Mylar , or CDE brown pulls. I use ceramic in dumble builds and silver mica in trainwrecks. I have used polystyrene in the Brite switch in a pinch before

[Blackburn]

Interesting answers, guys. I've been wanting to play around with different ones in all positions, but I feel like the most audible will be SM compared to ceramic disks. I guess I'm really curious (Splitting hairs, really) about how the CDE SMs compare to the cheaper Xicons. I'm thinking that, in a critical position, like the first coupling cap on the Rocket, there would be some sort of difference between two different makers of a SM cap. I'll be trying this out soon, and maybe can lend my own ear to this discussion.

[overtone]

For the Rocket first coupling cap I auditioned a few options and went with the old domino mica. The SM, both CDE and Xicon, had slightly more edge which I felt may have been useful in live situation, but I was looking for something less fatiguing in the long run.

Usually I use polystyrene as I have loads of old Siemens & Halske 500V pFs to use up and they were in the amps that I used back in the day.

[Blackburn]

Hey Overtone, you really felt there was less stridency with the domino? I have a few, Aerovox I think, and may be able to find a suitable value for that spot. Maybe even one for the 100pf on the volume pot, too. I wouldn't say this thing is as bad as other examples regarding brightness, but I always try to get the least high end as possible. I think I'll give that a shot.

[overtone]

I had about ten caps connected up to a rotary switch and there was an edginess to the SMs. That first cap is a good place to sniff.

The old domino, maybe it was Lemco or El Menco or something, was more of what I was aiming for. Like a big enveloping hug from grandma, rather than some girl tweaking your backside. Well that's how i felt about it.

Now, it has to be said that at that time I did not have an accurate capacitor meter, so there may have been some difference in the values.

Best, tony

[briane]

I tend to like the mica's - only cause they sound cleaner - less hiss to me versus the ceramic discs when I listen and try - especially when in signal path like a bright cap. I do sometimes use tantalum on the precense, and also tend to use ceramics for bleeders - I figure their going to ground so they dont introduce any hiss into the path. Xicons sound pretty clear, though a bit more sterile than the mica to me - and sometimes rolling a couple together also sounds best to get a little of both worlds....

answer: all of em in different places - just depends on what ya like where.

[gingertube]

I tend to NOT put ceramic caps in anything designed for audio.
They have bad dielectric absorbtion which tends to smear the sound. In HiFi Amps this stands out like the proverbial "canine testicles". If they are crap in HiFi Amps I assume they will be equally crap in Guitar Amps and avoid them.

With the abudance of good quality parts available I use ordinary garden variety brown 630V polyproylene caps nearly everywhere, occassional silver mica for low value (up to 500pF) and where voltage rating is not a concern I also like the newish dielectirc PolyphenyleneSulphide (PPS) caps (available only up to 400V rated) . Lower voltage rating PPS are available up to 4u7 and make a great alternative to electyrolytics for cathode bypass caps.
Cheers,
Ian

[Leo_Gnardo]

I thought this was about picofarad range - now that we're covering signal caps of all sorts let me expand a bit. I've been enjoying Mallory M150 mylars for the 0.001uF to 0.1uF range. Still keep in stock, and occasionally use Xicon MPP (Metallized polypro). For reasonable cost I find both deliver clear tone, no microphonics & I've never had one fail. I buy the 630V rated parts. Panasonic & a couple other manuf's make similar MPP caps. I'm sure any of them would work fine.

For use in presence I have a stash of 0.68 film caps I got from a surplus shop but when those run out I'll have to see what's around. Lately I had to put presence controls into a couple of stock 60-70's type Fenders. Smaller value pot & larger value cap are called for, compared to the classic tweed or Marshall parts. Used a 1K pot and 4.7uF film cap & customers were happy. CE/Antique has bargain priced MKP 400V film caps from 1 to 10uF. Kind of large but my ears are satisfied. I'd like to refine this presence with a reverse taper 1K pot. Any ideas on where I can find those?

[Blackburn]

It is about the pf range. We just got to talking about the first coupling cap on the Top Boost's brilliant channel. I want to get my hands on some CDE micas, the brown and yellow ones. I also need to measure my domino pulls to see if I have one that's usable and transplant it in there to see how I like. There's kind of a harshness in that amp. A kind of tone that's thin and papery that I feel may be due to the Xicons I have in there. Maybe I'm nuts? I've singled out almost everything, as I have NOS Mullards in every spot, an original Dynaco A-470, Sozo Mustards, etc. Good stuff, and like I said, the issue is with the treble frequency. All else is tops!

Three values. 500pf, 100pf and 50pf. If anyone has any CDEs or old micas, I'd by glad to buy if you're selling.

David

[David Root]

My default in the pF range is polystyrene, 500V or 630V. Smoooth.

Where ceramic disks are spec'd, as in Dumbles, I will use them, although in the later D's I am moving to polystyrenes, old ceramics have a lot of grit to them. Snubbers in D's can be anything so long as they're the right value. I have done a 102 ODS that needs to be smoothed out a bit in the OD, still working on that.

I just finished a 1st generation D and used ceramics where called for but I may well pull them and try something else, like maybe a domino mica or even a poly. I did use the correct old CDE mica (much bigger than the new ones) on the 500pF off V1A.

In my '57 Twin build I used a domino mica where it was originally used.

Xicons I only use in metal oxide PS dropping resistors, not their caps.