ceramic capacitors ?

[pooge]

Whether or not Bateman's test setup is the best or not, all of the caps tested were tested on that common denominator, and valuable comparisons could be made.

The NP0/C0G caps looked really good in all aspects. They were at the top of the heap in just about everything. They practically appear to be the perfect cap.

However, he did not test microphonics. Whether or not this is a real issue, I have not been able to determine. Because Class 1 caps do not use barium titinate, a piezoelectric material, they are orders of magnitude better than Class 2 ceramics that do, which should not be used for such critical applications such as a feedback compensation cap. The best info I could find about microphonics wrt Class 1 caps is that microphonics are "low". However, while all caps have some degree of microphonics, determining the relative value of Class 1 ceramics vs. caps other than Class 2 ceramics has not been easy to find. If the microphonics of Class 1 is less than, say, silver mica, they could be a perfect low cost, easily available cap for those critical applications such as feedback compensation, etc.

[infinia]

Originally posted by pooge
Whether or not Bateman's test setup is the best or not, all of the caps tested were tested on that common denominator, and valuable comparisons could be made.

it's OK no biggie I just wanted a look see

The NP0/C0G caps looked really good in all aspects. They were at the top of the heap in just about everything. They practically appear to be the perfect cap.

I agree. Practical values (limit case size) are a little small for audio

However, he did not test microphonics. Whether or not this is a real issue, I have not been able to determine. Because Class 1 caps do not use barium titinate, a piezoelectric material, they are orders of magnitude better than Class 2 ceramics that do, which should not be used for such critical applications such as a feedback compensation cap. The best info I could find about microphonics wrt Class 1 caps is that microphonics are "low". However, while all caps have some degree of microphonics, determining the relative value of Class 1 ceramics vs. caps other than Class 2 ceramics has not been easy to find. If the microphonics of Class 1 is less than, say, silver mica, they could be a perfect low cost, easily available cap for those critical applications such as feedback compensation, etc.

Believe me microphonics are there and are very real. There are in direct proportion to the amounts of Barium T used in the caps. I was involved with a corp in developing a demodulation IC for TV settop boxes. And the analog tuner ahead of our chip was giving us high BitError rates in proto testing. Along story short the tuner's LO PLL had an X7R cap in feed back of loop filter integrator. You could tap with your finger on the bench and count the errors.
Had the tuner vendor change to film cap there you go all fixed.

My belief is harmonic distortion and microphonics are related to piezo mechanics of Barium T parts. Test crystal's with same set up.

[serengetiplains]

Infinia, send me a pm.

[jcx]

np0/c0g are very good but not quite perfect:

I have seen ~ -110 dB 2nd order difference in an amp with 2x series 100V np0 caps in a sallen-key 40 KHz low pass with 20 + 21 KHz 1:1 @ 8V pk sine drive

after replacing the np0 with polystyrene the 1 Khz diff dropped below my~ -160 dB measurement limt ( ~ -130 dB noise floor in a Lynx22 sound card + 30 dB gain @ 1 KHz)

[serengetiplains]

Hi jcx, Bateman's tests show that polyproplenes beat NP0s, and styrenes beat propylenes. Teflons are currently at the top of the heap for distortion, DA, etc.

Note that Bateman's test setup is not ideal for testing the better capacitors---though it does give some relative indication---as the measuring instrument he designed uses less than the best capacitors in all parts of the circuit.

[RetroAudio]

it's been shown before that all the dielectrics and the cap construction play a part in this performance,..and that they vary from cap to cap,..you just have to test them. some npo's can outperform other pp and ps caps,..just depends. not all pp caps are alike.

[forr]

Thanks for your help concerning FFT software.

JCX
---Cyril's circuitry isn't the best for the application - considerable simplification can be had with indirect nonlinearity measurements of IM differences---

Cyril is currently doing experiments with TDFD tests, a kind of IM measurements whose idea comes from Neville Thiele (1975) : almost unknown (at least to me till a few weeks ago), its sensitivity to non-lineraity can beat THD.

[pooge]

Originally posted by infinia


Believe me microphonics are there and are very real. There are in direct proportion to the amounts of Barium T used in the caps. I was involved with a corp in developing a demodulation IC for TV settop boxes. And the analog tuner ahead of our chip was giving us high BitError rates in proto testing. Along story short the tuner's LO PLL had an X7R cap in feed back of loop filter integrator. You could tap with your finger on the bench and count the errors.
Had the tuner vendor change to film cap there you go all fixed.

My belief is harmonic distortion and microphonics are related to piezo mechanics of Barium T parts. Test crystal's with same set up.

Class 1 ceramics (NP0/C0G) do not use barium T. X7R caps are class 2.

[serengetiplains]

Forr, any chance Cyril might update us on his project? I really appreciate what he's done in measuring capacitor distortions---one of the few guys with proper credentials and experience to pull something like that off.

[davidsrsb]

There seems to be some confusion between microphonics and piezo in this thread.
Even an ideal parallel plate capacitor with vacuum dielectric would be microphonic if the plate gap can be modulated. This only happens if there is a dc bias. Piezo voltage is generated by stress so it happens even with no dc bias or gap modulation.

Microphonics by gap modulation will depend on the capacitor construction, pcb thickness and pcb support