Opinions on using NOS Ceramic Disc Caps

[multichamp12]

Hello everyone, I am building a NOS Acrosound S1001 preamp that I bought as a kit, and I am trying to decide if I should use the NOS disc capacitors that came with the kit (these are low value, from 20pf to 1800pf), or just put in new silver micas.

All the other capacitors are being replaced, as well as the resistors, but I do know that ceramic capacitors almost never need replacing. That being said, would it be a smart move just to use all new silver micas since I am building this from the ground up?

 

[s-petersen]

Ceramic disc capacitors are pretty poor audio wise, definitely go with silver mica, or some kind of poly film.

 

[multichamp12]

Thank you!

 

[Tom Bavis]

A 20 pF cap may be a stable, linear dielectric (potentially even better than mica) but the 1800 pF is likely a poor quality dielectric that's temperature sensitive, microphonic and non-linear. And likely used in a tone control where there is a large audio signal across it, so that non-linearity means significant distortion. Be sure to get at least 500V ratings - anything over 1000 pF may have to be film.

 

[EastPoint]

Disk caps age surprisingly poorly—I have seen them read up to 30-40% high or low, with done voltage leakage as well. Definitely put in silver micas.

 

[Pio1980]

Polystyrene or polypropylene caps are definitely preferable to ceramic in the audio path. Silver mica caps have a following as replacements.

 

[Bob]

C0Gs if you must have ceramics, or micas for low values, then polypropylenes (and derivatives)
for higher values.

 

[Retrovert]

BaTiO3 is piezoelectric, microphonic, pyroelectric (temperature changes result in a voltage potential across the electrodes), has non-linear capacitance reduction with applied DC voltage (voltage-dependent capacitor), time-dependent dielectric breakdown from applying a constant DC bias voltage, and is hygroscopic which causes property changes as the jacket ages and degrades.

That's off the top of my head. I'm sure I omitted another undesirable property.

Such capacitors were the only inexpensive option back in the day and confer no magickal properties. As above noted, PP or PS is a better choice. PP is inexpensive and small. The older silver mica capacitors have issues with silver migration so avoid NOS on those. The main advantage of SM is excellent temperature stability and low leakage, both crucial for RF circuits which must not drift over time as the unit heats. Most audio applications have no need of SM.

 

[gadget73]

have to agree, if you're going to the bother of building it, may as well use better parts now rather than change them later.

 

[Retrovert]

You may as well replace all of the carbon composite resistors, which were not good resistors when new and have likely significantly drifted since the original construction, with metal film.

Avoids a host of issues inherent in poor quality (compared to today's) components.

 

[multichamp12]

All resistors are being replaced by metal film, as well as all other components. I was just curious about the ceramic caps. Thank you all for your responses!

I will be posting a build thread soon.