Relation between voltage and noise in capacitor

[luixssj3]

Hi guys!

I'm gettin'in Hi-Fi world so I'm building a simple phono preamp for my cheap turntables (MM cartridge).
I'm using the Thorsten schematic.

Since my cousin have an electronic repair shop I used hi voltage capacitor like ERO 1813 630V and wima FKP1 1000V, and a strange kind of capacitor in transparent plastic...

With a LCR meter I match them to the last digit! The same for resistor... opamp are OP275 since the original is difficult to find for me....

Now the question is: hi voltage capacitor is noisy than low voltage?

[Conrad Hoffman]

A pure reactance doesn't generate any thermal noise thus capacitors, inductors and transformers are inherently very quiet. Any internal loss that's represented as a resistor (the capacitors DF or the inductors Q) does, but it's usually negligible. Capacitors are also low impedance at higher frequencies, so HF noise will never be an issue. Noise pickup is another matter, and that's what you usually have to worry about. The capacitor voltage shouldn't matter, only the physical location and probably construction to some degree. Caps are also microphonic, some much more than others. IMO, you want polystyrene or polypropylene for RIAA equalization caps in a preamp for sonic reasons.

Conrad

[nigelwright7557]

You can get problems with higher value electrolytics capacitors at high frequencies.
Some people put a small capacitor across them to soak up high frequency noise.

[luixssj3]

Many thanks to all!

Yes the electrolitic is bypassed by 100nF wima mkt capacitor!

I never heard microfonic in capacitor! Is there any document? maybe with measure?

[Conrad Hoffman]

I've never seen much published on microphonics. Try a search. One could put an accelerometer on a cap and vibrate it, recording the output, but that's too much work! You can wire a cap to the input of a preamp and tap it with a pencil, listening for the output. Try it with a high dielectric constant ceramic cap and I think you'll be surprised at how much signal is generated. Cables have the same problem. Put a few feet of cable on a preamp input and tap that- it's a very common issue with microphone cables. There are special low noise cables with conductive layers that reduce the problem, but they're not common in audio; they're more common in low noise measuring equipment.

Conrad

[luixssj3]

OK Conrad! I'll try to search, and I'll try this interesting experiment :-)

For the cable I know they are microphonic, I build several guitar amp and fx and also experiment with cables!