low noise capacitors ?

[KLDVOX]

i guess its been asked and answerd many times but a cant find the correct post.

question is in audio aplications what type of capacitors give the least noise? i guess its polysomething.

any info apreciated

 

[JohnRoberts]

Capacitors do not exhibit self noise like resistors (Johnson or thermal noise).

Performance criteria for quality audio capacitors involve parameters like linearity, voltage coefficient, dissipation factor, dielectric absorption, etc..

JR

 

[KLDVOX]

thanks for that. crystal clear

 

[Khron]

Some formulations of ceramic capacitors can be microphonic, but that requires external mechanical stimuli, it's not noise resulting from electrical reasons as such.

 

[KLDVOX]

thanks mate, i was looking on the interwebnet thing and i saw a few adds for low noise caps. funnily they were all ceramics.

i can see how they could be microphonic, a bit like a piezo crystal i guess.

 

[Tubetec]

Electrolytics can makes odd noises sometimes ,
mainly something Ive seen on high voltage caps in tube psu's ,
It can take time for things to settle down from new , or if old and unused for a while rustling noises and mains hum breakthrough can occur , sometimes pops or squeaks too .

 

[ccaudle]

a bit like a piezo crystal

Exactly that. Some caps marketed as "low noise" mean physical noise, not electrical noise; in circuits with a fast rate of change of the voltage across the cap (like a switching power supply) some caps will buzz with a high frequency whine like a piezo buzzer. The low noise caps would usually be some combination of a material with lower expansion coefficient vs. voltage (i.e. less piezo effect) and a different physical connection method so they are no quite so rigid at the point where the ends of the capacitor plates attach to the PCB.

But those aren't really "audio applications" the way most people would use the term. The same principles that make a capacitor whine can also work the opposite direction, where vibration can be translated to electrical noise, but that would usually be a bigger problem in a high impedance circuit, and the places where you commonly have very high impedance are often pickups of some kind, like a microphone capsule or instrument pickup, which are orders of magnitude more sensitive to vibration than the capacitors.

 

[CJ]

physical shape

i had a problem with the big flat Wima caps in a Pultec EQ picking up more hum than a circular cap,

 

[Tubetec]

Where you connect the outermost foil can have an impact ,
A few interesting points here ,
https://www.tdk.com/en/tech-mag/electronics_primer/7its seems the oval caps might be non inductive , the tubular style is inductive ,
maybe there was some interaction with the original component that wasnt happening anymore with the oval cap that led to more hum .

 

[CJ]

i was thinking that the charge vectors might cancel in a circular cap,
kind of like the net charge inside a metal sphere will be the same everywhere,
easy to do an experiment, i will bring in some square Wimas and put them on the scope alongside a circular cap,

 

[CJ]

well now it looks like the Wima's are better for noise,

i hooked both a tubular and wima to input jack of amp and put hands on cap,

wima cap had much less induced hum than the tubeular,

i had trouble with Siemens square caps, not Wima, so i will bring in a few of those tomorrow to see if they are more noisy,

one experiment be worth more than a thousand theories,

 

[KLDVOX]

tested knowladge always beats received wisdom.

 

[Tubetec]

The non inductive construction alternates the termination and shorts the turns ,where the traditional radial wound has to have significant inductance .