Paper in oil lie

[Nando Vallart]

Hello!
I remember reading a post of one of our forumates telling pio capacitors as ütter lies and EXPLAINING TECHNICALLY why a capacitor won't change the tone of the guitar.
Damn is, I can't find this post and it was like 5 or 10 years ago...

I watched a video comparison on the same guitar of ceramic and pio, by Wez Venables, who installed a switch to change between then and the result was just like the guy said: no difference at all...

Does anybody here can explain why capacitor doesn't change the tone?
Cheers

 

[Rick]

Why it doesn't?  I thought it did!  I know someone here knows the answer.  The question I have is how does it (not) change the tone.  I'm sure it's doing something, though it might have something to do with how tone interacts with volume?

 

[JohnnyHardtail]

When it comes to capacitors, the electrons aren't affected by the dielectric material used.    The electrons do not actually flow through the dielectric, they are only gathering on the metal plates because the dielectric material is an insulator.    So no matter whether it is ceramic, plastic film, or paper, these types of dielectric material can perform the same role.  If capacitors are analyzed with sensitive lab equipment there can be small amounts of non-linearity distortion, but it would be less than parts per million.  If you record with 24bit digital capture, the ADC process is likely to have worse performance than the capacitor.  Of course the ADC will also have a lot of capacitors inside of unknown origin.  Once you have a magnetic pickup, tube amplifier, coupling transformer, speaker, dynamic microphone, then every single part of the signal chain would totally swamp the distortion caused by a single capacitor.

 

[mayfly]

I was working on a huge answer to this question, but I got side-tracked with something else.

In a nutshell, there are many different types of capacitors out there, each is for a specific requirement.  For example, high DC voltage, low inductance, low distortion, constant exposure to heat, flameproof casing, constant exposure to high AC voltage (type-X and type-Y), High vibration, small package, etc etc.  These extreme conditions often require a very good capacitor, otherwise it won't behave much like a capacitor.  It might even break on you - sometimes in a spectacular manner! (tip - don't wire a tantalum capacitor backwards.  They tend to turn into little rockets.)

BUT!

A guitar tone circuit is not an extreme operating environment.  Because of that, almost any capacitor (of the right capacitance, and not polarized) will do.  Some folks will say they can hear a difference, but not in any double-blind tests AFAIK.

I typically use a film cap in the tone circuit, pulled right out of the parts drawer without looking at it too much.  And not an expensive polystyrene or polypropylene film cap either - good old polyester!! Just like a cheap suit - works just fine.

BTW, I'm currently deep into the specs for MLCC caps for SMD boards.  You really have to watch those caps.  Some dielectrics are great (NPO, COG), but some are really really crappy (X7R).  X7Rs are probably the worst caps out there period - but they typically are not used in guitar tone circuits. 

 

[Sadie-f]

I have to defer to @mayfly as he sure seems to be an electrical engineer, I'm a mech e and materials eng who dabbles in signals etc.

My understanding for the purposes of the  simple low pass filter used in a tone circuit, or treble bleed circuit, the type of cap is close to immaterial.

The difference between different capacitor families, is that no design is an ideal element. If they were, then capacitors would exhibit no inductance, and inductors would have no capacitance. If they were, then one could design an rc, rl, or lc filter circuit, and it would behave exactly as the formulas say.

So where it matters, is for instance in the DC rails that supply power to an amplifier or pedal, a low pass filter that in theory works extremely well at filtering out everything above say 40 Hz, might actually ring substantially at a high frequency in your switching supply or environment (my house has a *lot* of noise at about 9.5 kHz).

So for the best 2 element filter, one might choose a film capacitor, and to get better, one might build a multi stage filter, using different capacitor types.

Probably Mayfly will know how I'm wrong or over complicating / simplifying

 

[mayfly]

Ya Sadie is right:  different types of capacitors behave differently under different conditions.  Unless you know different

As she states, it's not uncommon to see a large electrolytic in parallel with a much smaller film capacitor especially in power supply circuits.  The electrolytic works great as a large reservoir at lower frequencies, but it's crap at higher frequencies where the film cap excels.  The film cap can be much smaller than the electrolytic because the energy at those higher frequencies is much less.  you can make film caps at the same values of electrolytic caps, but they end up being much larger.  Insanely large actually.  And insanely expensive.  So designers learn the strengths and weakness of all their tools and apply them appropriately to accomplish their goals, including using multiple types in the same circuit.

 

[stratamania]

Perhaps it was this thread you were looking for...

Caps

 

[Rick]

Now I get it!

 

[DuckBaloo]

To start ...

• The cap just selects the cutoff frequency, above which the signal passed through to Ground. All caps with the same capacitance (to exact measurement) create the same cutoff frequency
• All the signal that passes through a cap goes to ground, what you hear in the amp is the signal that does NOT pass through the cap
• The placebo effect can never be underestimated, all hearing by all people is perception based, our minds process the sensory data in shorthand and with prejudice

That said, not all caps behave the same ...

• The big difference in cap composition is in the "knee" of the cutoff, the shape of the frequency change at the point of cutoff, on some are rounded and less exact, others are immediate and more exact. This can be confirmed on an oscilloscope. It can also make one cap seem warmer or not.
• Most caps have relative wide tolerances that mean the caps vary from their marked capacitance. For instance old PIO have a massive +/-20% tolerance, some ceramics have a +80%/-20%, most modern poly caps are +/- 5% etc., that's manes one .05 mfd can could be anywhere from .03 mfd to .07 mfd or even .09 mfd, that's a wide range
  

Since we aren't mass producing by the thousands and buying in scale, buy whatever cap you prefer, one $20 cap from time to time isn't a risky outlay.

 

[mayfly]

To start ...

• The big difference in cap composition is in the "knee" of the cutoff, the shape of the frequency change at the point of cutoff, on some are rounded and less exact, others are immediate and more exact. This can be confirmed on an oscilloscope. It can also make one cap seem warmer or not.
  

er, no.  That's not at all true.  A capacitor cannot affect the Q of a circuit (the shape of the cutoff knee and filter slope after cutoff).  Only the circuit topology, that is the number of poles designed in the circuit, affects that.  Oh - and you can't see a frequency domain plot on an oscilloscope

 

[JohnnyHardtail]

There is really nothing special about tone control application.    It is not high frequency, and it is not dealing with high currents or voltages.  Also the capacitance values of 0.05uF at most needed aren't very large.    A variety of capacitors are perfectly suited to this task.  You are simply not going to find differences between each type, unless the idea was previously seeded in your head.  Polyester film capacitor is the most sensible choice IMO, and they should be dirt cheap.

Normally I say that tolerance variations can affect the sound, but you would be unlikely to notice a 10% difference in the value of a tone cap.  I have swapped the 0.022uF for 0.033uF, which IMO is a very subtle difference.  If you change the value of a volume pot by 10%, they it will be different, but changing the "corner frequency" of the tone control is a lot less noticeable to me.

 

[amigarobbo]

Well, according to the math the manufacture type of cap shouldn't make any difference, so I'd be more surprised if there was a difference in 'tone' when using the, errr tone control, and the difference would be similar magnitude to setting it to 5.6 rather than 5.5.

I was watching some videos by Shango066* where he repairs old TV and radios, and he was saying every single vintage Black Beauty cap he sees is faulty and he just replaces them on spec. and he's really not one of those Re-cap everything types.

* https://www.youtube.com/user/shango066 Warning may contain politics as well as All American Five radio repair.

 

[mayfly]

yea those old Mallory black beauty caps fail short circuit.  Not great. 

But then again, the failure of those black beauties lead to the development of several self-healing film types including the Mallory 150 (my current favourite for high voltage tube applications).