Capacitor Tolerance and Capacitors in general

[RamonRivera]

I was wondering If the is a general guideline regarding Electrolytic capacitor tolerance, 20% seems to be the most common, also there's some brands that offer audio grade capacitors, what the deal with this type of capacitor? looking at the specs I can't seem to fid any apparent difference

Maybe somebody could school me on what's the deal regarding this while building pedals, thanks!

[rutabaga bob]

In building pedals, skip that 'audio grade' stuff.  Way too expensive!  Yes, most common electro caps have the +/- 20%. 

[bluebunny]

there's some brands that offer audio grade capacitors, what the deal with this type of capacitor? looking at the specs I can't seem to fid any apparent difference

Ah, yes - the difference isn't on the datasheet.  It's on the price tag.   

[EBK]

I believe "audio grade" for caps means they suck at high voltage and RF, aren't stable at high temperatures, and can't handle huge spikes, but they are good enough for non-demanding tasks like audio. 

[antonis]

Do I smell a rising argument about also gold-plated jacks and uni-directional wires..??

[Rob Strand]

uni-directional wires

The DIY version is to print a sticker with arrows using a label maker.
To me it makes all the difference but the AC signals are getting confused.
 

[RamonRivera]

So is buying better brands like Nichicon or Panasonic, etc. instead of Chang the ones I currently use going to make any difference?

I have the same question about resistors also cause I can only find carbon film 5% resistors here, and I read somewhere that this are noisier than than metal film

[Rob Strand]

So is buying better brands like Nichicon or Panasonic, etc. instead of Chang the ones I currently use going to make any difference?

Based on loose experience I'd say the better brands are likely to last longer.

I have the same question about resistors also cause I can only find carbon film 5% resistors here, and I read somewhere that this are noisier than than metal film

Technically that is true but more the issue is when it matters.  Only some resistors in a circuit contribute to noise.   Other parts like opamps are often the primary source of noise.   All resistors create noise the difference between carbon film and metal film is carbon film can add more noise and add it in when used under certain conditions.  (The extra noise is called excess noise.)

RG has made some comments on avoiding DC across large value resistors,

http://www.geofex.com/Article_Folders/modmuamp/modmuamp.htm

At the end of the day you can only use the parts available too you.   However you should have some confidence that all the noise you hear isn't just coming from those carbon film resistors.

I tend to use metal film for most things because the price difference isn't great.   The convenience of 1% tolerance and better thermal stability are important on non-audio stuff I do.

FWIW, you don't see people complaining about pots making noise, but they are often carbon composition, which have the highest excess noise.

[Slowpoke101]

FWIW, you don't see people complaining about pots making noise, but they are often carbon composition, which have the highest excess noise.

An excellent observation. I too have wondered why this is so rarely considered as a noise source. It can be quite bad as I found with some seismic sensing equipment.

[merlinb]

I have the same question about resistors also cause I can only find carbon film 5% resistors here, and I read somewhere that this are noisier than than metal film

There is almost no difference in noise between carbon film and metal film resistors. Carbon composition resistors can be noisy, but they are rare nowadays.
https://books.google.co.uk/books?id=VMjkDQAAQBAJ&lpg=PP1&dq=merlin%20blencowe&pg=PA66#v=onepage&q&f=false

[antonis]

BTW, plain, comprehensive & excellent book, Merlin.. 

[marcelomd]

I bought a few Nichicons last year to use on the power supply of my homemade tube amp. They were listed as 20% yet they were SPOT ON the value. Only one in 10 had like 1% difference from the value on the label.

Just a data point.

In my experience, the better brands last longer, and the sound difference is minimal (as in non existent). By "better brands" I mean consensus from industry, not from ultra niche markets.

[RamonRivera]

I have the same question about resistors also cause I can only find carbon film 5% resistors here, and I read somewhere that this are noisier than than metal film

There is almost no difference in noise between carbon film and metal film resistors. Carbon composition resistors can be noisy, but they are rare nowadays.
https://books.google.co.uk/books?id=VMjkDQAAQBAJ&lpg=PP1&dq=merlin%20blencowe&pg=PA66#v=onepage&q&f=false

This book looks great, thanks!

[Rob Strand]

I too have wondered why this is so rarely considered as a noise source. It can be quite bad as I found with some seismic sensing equipment.

I suspect it just falls between the cracks because it doesn't get directly associated with a resistor.

The seismic equipment is low frequency so it might suffer a bit more because of the 1/f shape of the noise.

I've had other problems with pots like mechanical noise and drift.   I had an RF oscillator with annoying frequency drift.  At first you suspect it's just drift of the L and C parts.  The drift  became a problem for me so I looked at the design.  As it turned out the drift was caused by supply voltage drift and that was caused by a carbon trim pot setting the supply voltage on an LM317.  I replaced the pot with fixed resistors and stability was improved enormously.

Back in the days of manually nulled distortion analysers I found the pots would wear around 1kHz and they were very hard to null.  You got noise but it was from bad contacts.  I discovered higher reliability polymer track pots.  They are usually single-ganged which made me look into single pot notch filters and oscillators.

There's something to be said about those old oscillators and filters that use the old variable caps.   The shielding is a pain but they don't wear out and the drift is pretty good.

Sadly I threw a lot of these away over the years.