Mr. Marsh, you are right that it is the construction and mounting of most polystyrenes that give their microphonic behaviour.
But polystyrenes I've used in the past, even in packages that allow tight mounting to the PCB, show this.
The polystyrenes that the unwashed masses and Golden Pinnae brigade normally worship, are unfortunately prone to this fault.
From this, I gather that Rel Caps, if glued to your "hand carved from solid teflon by virgins" PCB, with Unobtainium epoxy (without nasty dielectric factors), will be as good as NPO/COG ceramics.
I'd still like to see some evidence that polystyrenes are better practical caps than NPO/COG ceramics.
We'll ignore trivial issues like soldering and reliability.
The Relcap 3 uf polystyrene with 0.01 Polystyrene caps that feed the R2 Raven Ribbons i use have noticably more refined detail and harmonic structure over the Film and foil Polypropelenes they replaced. The upgraded fully RelCap Film and foil crossovers i installed in the Martin Logan CLX'x all have 0.33/600v polystyrene bypasses were a big improvement over the stock metalized Solen polypropylenes. Try a nice Hi Def download or Hi res release of Stevie Ray Vaughn's Tin Pan Alley, Patron Anejo tequila, and a box of Qtips. ( one or more them will fix what ails you or your system)
I usually suffer from liquor absorption rather than dielectric absorption in my system
I usually suffer from liquor absorption rather than dielectric absorption in my system
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Well; ceramics are may be reliable, but when they die they go deadly short. Sometimes such a chance is unacceptable.
I can well imagine using microphonic capacitors in speaker crossovers may lead to "more refined detail and harmonic structure, huge soundstage bla bla."
But I have never tried Relcaps so it would be inappropriate for me to pontificate on their performance in speakers.
My love for NPO/COG ceramics is in very specific applications like capacitor mikes at the critical gate/grid. They are Unobtainium in the sizes required for speaker crossovers.
However, as a Blind Listening Test guru ala Lipshitz & Vanderkooy bla bla in my previous life, I seriously recommend you get your ears syringed out at outpatients rather than use a Qtip. Qtips are dangerous in inexperienced (or even experienced) ears and hands.
I actually have some reliable results on the effects of alcohol on Blind Listening Test performance but they belong to another thread.
Err..rh! Could you tell us how polystyrenes go when they die?
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John -- The dual ground plane I suggested to you all those many years ago, I still use. However, stray c is higher and important in specialized high Z circuits (like mic preamps). Never-the-less, I use it to great satisfaction when under distributed power traces to keep the Pwr Supply Z low and stable at high freqs. making the traces wide as possible and under the that trace put the pwr supply ground trace of same width. The signal ground plane should never cross the pwr ground planes. generally, if you make the pcb signal and power traces the same way you draw the schematic, all is well. I also put all signal traces on the TOP side of the pcb; Easier to repair, trouble-shoot and modify without tearing the thing apart. -RNM
Most caps used in speaker cross-overs are metalized film. They do not short when over-voltaged. They just burn-off met film area which over time reduces the c value. Not cool in cross-over filters. They are best used in low level signal apps.
The current capability of the ultra thin met cap is not the best for high current apps. You will get modulated esr due to temp rise. Often the C value is so large that only met caps are practical... unfortunately, the largest values are used where the current is highest -- low freq Xover- bass. I would rather parallel film and foils to get the total value required. The tweeter can usually be metalized (low current) without any side effects.
The film and foil is the more suitable choice for high current apps... like speakers and power supplies. but just be sure they are voltage rated far higher than any amp likely to be used on the speakers because they do short when over voltage causes film breakdown. But they will perform the best and stay like new sound forever in either PS or PP if made well... such as RELCAP. -Thx RNM
The current capability of the ultra thin met cap is not the best for high current apps. You will get modulated esr due to temp rise. Often the C value is so large that only met caps are practical... unfortunately, the largest values are used where the current is highest -- low freq Xover- bass. I would rather parallel film and foils to get the total value required. The tweeter can usually be metalized (low current) without any side effects.
The film and foil is the more suitable choice for high current apps... like speakers and power supplies. but just be sure they are voltage rated far higher than any amp likely to be used on the speakers because they do short when over voltage causes film breakdown. But they will perform the best and stay like new sound forever in either PS or PP if made well... such as RELCAP. -Thx RNM
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But polystyrenes I've used in the past, even in packages that allow tight mounting to the PCB, show this.
The polystyrenes that the unwashed masses and Golden Pinnae brigade normally worship, are unfortunately prone to this fault.
From this, I gather that Rel Caps, if glued to your "hand carved from solid teflon by virgins" PCB, with Unobtainium epoxy (without nasty dielectric factors), will be as good as NPO/COG ceramics.
I'd still like to see some evidence that polystyrenes are better practical caps than NPO/COG ceramics.
We'll ignore trivial issues like soldering and reliability.
RELCAP is a speciality cap mfr -- makes for military and communications industries, test equipment makers etal which have to have a long life in mission critical apps and will be in the field for dozens of years without failure.
The additional requirement of higher temp soldering practices make ps caps unsuitable for many uses today. But for High End audio, use them if you can find them. yes, not all caps are created equally... you get what you pay for in that component....except in most audiophile caps sold to the unknowing.
What does practical mean? Its different for different people... but here -about High-End- I dont care about practical... just informing. -Thx RNM
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I found the tin foil is best and second the aluminum foil. The tin has a slightly higher esr but that helps damp transient signals. In fact, if anyone cares to know -- optimum series R for critical damping occures with a .2-.3 Ohm series resistor (.22 or .27 works fine). This value is subtracted from any other series r -- pcb/wire trace, etc. [I had a patent on this added R internally but never used it]. I also like to keep the number of dissimilar metals in the cap's joint/junction to a minimum... thus tin solder to tin foil to tin/copper leads.
There are a lot of fine points in making a superiour cap for the Highest-End products. Thx - RNM
BASF (Germany) still makes "Styroflex".
Styroflex® Thermoplastic Elastomer - BASF Corporation Plastics Portal
(In Europe polystyrene capacitors are quite often called "Styroflex Capacitors".) And there are still other manufacturers of polystyrene caps, you even can get them at Mouser.
Are you sure. I know you are in the branch, but ....
Styroflex (SBC) - Products - Europe - Styrolution
http://www.styrolution.net/wa/steu~...ntent/products/styrenics/styroflex/properties
Styroflex (SBC) - Products - Europe - Styrolution
http://www.styrolution.net/wa/steu~...ntent/products/styrenics/styroflex/properties
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