Sound differences between cap brands? Test results?

[defaced]

Mark, the segments that I cut out weren't processed in any way. I made them with Sound Forge and I'm pretty sure this is bit-perfect from previous experience. Also, being WAV files they are uncompressed.

If they look different, it's probably because of how your audio software displays the waveform. When the display is zoomed out, it has to map several samples to one pixel and it won't necessarily always choose the same samples.

Since it is a two-terminal device, a capacitor can only distort the voltage that appears across it, not the voltage to ground. So coupling capacitors shouldn't generate distortion at high frequencies, where the signal voltage across them is negligible. Every graph I ever saw of capacitor distortion is worse at low frequencies, and falls off at least 6dB/octave. So, my suspects for capacitor distortion are undersized coupling caps, undersized cathode bypass caps, and the caps in the tone stack, particularly the treble one as it sees a lot of signal voltage in the midrange.

Dumb question (because I've never done a distortion test), what are the characteristics of the source material? Is it constant voltage variable frequency sweeps, or constant voltage and frequency steps, or ....? What does the waveform look like - I assume it's a sine wave. Even if there's a spec (that I can openly get) that would work.

[Steve Conner]

I use an old-fashioned analog distortion analyser. It consists of an oscillator section that gives a low-distortion sine wave at a frequency of your choice, and an analyser section that filters out the original sine wave with a self-tuning notch filter, leaving only the distortion products. A RMS meter detects the level of the distortion products and displays it as a percentage of the total signal.

A more modern analyser could automatically step through several frequencies to produce a graph of distortion vs. frequency. If I want to do that, I have to set the oscillator manually and type the results into a spreadsheet. I mostly use it for testing prototype solid-state amps, so I do most of my testing at a single frequency, 10kHz.

An alternative method is IMD testing, where you use two sine waves, and a spectrum analyser to detect the sum and difference frequencies. There are several different frequency combinations in use: I use 10 and 11kHz.

The biggest source of distortion I've found so far? Speaker relay contacts.

[guitician]

Steve, I had listened to Mojo's 5 clips that were all dimed and noticed subtle differences, the Pre-00 was obvious as the ending was clean. Your 5 clips all sound the same to me, nothing that I could pick out to differentiate between clips. There were just small sections of sounds sustaining with overtones that I could tell apart from clip to clip, just a second or less, and nothing to write home about.

Wouldn't high frequencies in caps have propagation delay effects? And amplified sounds will have those sum/difference frequencies out to above 20khz. I guess more when large voltages are being coupled.

[nickb]

I just find it odd nobody can figure out a way to measure the differences between capacitors in a circuit. Either changing capacitors changes the frequency response or adds distortion. Can't think of too many other effects.

It's been done. Google Cyril Bateman. He did a series of articles publishing his work in Electronics World.

[defaced]

Downloadable PDF link to the right:
Capacitor Sound
I'm just getting into it, but so far it definitely sounds like it's worth reading.

[guitician]

Hmmm... it seems there is a tone to be had from capacitors. C0G have the least "Tone", and thin ceramics have the most; with everything else falling somewhere in between. Whether or not you can hear it is a point best left to yourself.

[R.G.]

Down at the bottom of this is the human mind. The human mind has been shown to be willing to go as far as to let the body die in some extreme cases rather than recant some strongly held belief. The belief in issue may or may not be true, or testable; I suspect that the less testable the belief the easier it is go be extreme in the belief.

A person who believes in facts and measurements will change their mind when shown convincing enough facts and a logical, reproduceable testing method. A person who believes in beliefs can and sometimes does refuse to change their minds even in the face of any amount of evidence.

There is a wealth of testing and evidence on this nature of the human mind if you're into believing testing and facts.

[Jazz P Bass]

Which brings up the point of 'how' a capacitor functions.
There is not any physical transfer of electrons.
The different charges create an electric field 'across' the dielectric.
So it appears that it is somewhat like an fet & more like a transformer.
There are many different types of film caps used in coupling & tone circuits.
And they all have specific pro's & con's.
The fact that the type of capacitor under scrutiny is never named may have some bearing on the observed differences.

[Chuck H]

different charges create an electric field 'across' the dielectric.
So it appears that it is somewhat like an fet & more like a transformer.

Makes sense. I should think that film capacitors do have inductance and self resonance as properties that might change with construction. Just as the ideal transformer is only a model, an actual model requires all manor of peripheral components to simulate imperfections. Taken to it's extreme let's just say you have an average Mallory 150 @ .022uf in a circuit. Now replace it with a capacitor you made from a roll of cardboard and aluminum foil that end up the size of a football. Both are "film" capacitors of "similar" construction, right!?! Would they sound the same? Well, I still think it might be impossible to detect a single cap change. But what if you recapped a whole amp with these footballs? I know I haven't offered a concrete reason why they should sound different. But my gut tells me they would.

[Enzo]

I find the caps wound on the Cottonelle cardboard roll sound softer than those wound on the Scott Tissue rolls. Try as I might, though, I cannot find anything that sounds better than the Alcoa foil.

[Chuck H]

[Steve Conner]

I think a home-made capacitor the size of a football might well sound different. It would pick up a lot of hum while hanging out of the chassis.

I didn't want to be the first to admit it, but with the voiceover gone, I can't tell the difference between the 5 clips. They all sound the same. I thought I would be able to identify the NOS preamp tubes at least.

[Hellhammer]

I like guessing so here goes: #1. Mallory 150, #2 Sozo Vintage, #3 NOS tubes, #4 Sozo standard, #5 Mustards

[Enzo]

I probably have told this before, but...

Many years ago, more than 50 anyway, there was a project in Popular Electronics, build a Tesla Coil. it used carbon rods for a spark gap and needed a high voltage cap. I mean a seriously high voltage cap. They made the cap by gluing aluminum foil onto either side of a pane of window glass. Multi-kilovolt rating but maybe only 500pf.

[Steve Conner]

Best score so far is 1 out of 5...