C0G ceramics vs humidity

I have an email out to TDK but no reply yet. I'll try others.

Bob

My goal is stability

On Thursday, April 9, 2015 at 11:40:27 PM UTC-7, Badbob wrote: [about] the affect of humidity on C0G capacitors?

My Boonton 75BDs have a 2-pF FS range. If you null the reading out, it'll just sit there reading 0.000 pF all afternoon. Wave a hand nearby and watch the reading go up by a few femtofarads, then back to zero. They're so cheap on eBay that I have to keep reminding myself that I already have four of them. (Well, two are analogue.)

Cheers

Phil Hobbs

Cheers

Phil Hobbs

I'm using a classic op-amp capacitive feedback topology. Simple and capable of high accuracy but needs stable caps for best results.

I'm aiming lower than that. Something that can select/match caps for precision filters, phono preamps, that kind of thing, in the audio range. I have a nice handheld but the accuracy barely 1%.

On a sunny day (Fri, 10 Apr 2015 10:07:20 -0500) it happened Badbob wrote in :

Ooops, audio.... Its past easter and rabbit ears.

Does it show dissipation factor or Q?

I like the 72B analog ones, and I have three. I had four until an idiot intern applied a couple of kilovolts to the bias input on one.

They are great. That 1 pF range is usable at the and of a few feet of coax between the meter and the DUT. And the AC excitation voltage is millivolts, so you can measure semiconductor junctions too.

Nope, just capacitance. Measuring the Q of a 2-pF capacitor would be a bit of a job, I expect.

Cheers

Phil Hobbs

Why do parts need to be accurate for audio? What would matter in a phono preamp?

Audio seldom makes sense.

Just a charging resistor and an ADC, or a couple of comparators, would work. But caps have dielectric absorption, so ramp-type c-meters are mediocre. If you want to assign a single accurate number to a capacitance, you really have to specify the frequency.

C'mon, John, anybody buying phono preamps today obviously has ears that can detect 0.001 dB departure from the holy RIAA equalization curve. ;)

But I can get behind anybody who's building his own test equipment. We need more folks like that.

Cheers

Phil Hobbs

There's the arm and needle and coils to consider. Not to mention that the recording studio probably used paper-and-foil capacitors in all its gear, and mixed and equalized it to hell until they liked the sound on whatever monitors they used. And it's going to be played back through speakers with paper cones, in a room with walls and chairs and stuff.

True.

No, don't see a way to do that with this kind of simplicity.