Increasing the filter cap - does it have any impact on the sound?

[yeeshkul]

Many circuits have a filter cap between voltage and ground, it usually varies between 2u2 and 470u. What impact on the sound it can have if i increase such a cap?
For example in TB this cap is 47u and i use something like 220u, MFZ-1 has 2u2 and i used 470u .... Is it gonna have any influence on the tone?

[humptydumpty]

http://www.generalguitargadgets.com/richardo/distortion/index.html

that page has a section on filters, if it helps you any

[yeeshkul]

Thanks but I am not making a filter, i just want to know if there is any change in the sound to be expected in case i increase that one cap. That cap i often increased when you need some better filtering of your wall-wart or so.

[humptydumpty]

okay, maybe im tired and am just missing what youre saying, could you post a schematic of what exactly youre talking about?

[.Mike]

I think you're talking about the electrolytic capacitor placed directly across the power supply.

If I understand correctly, it is a decoupling/bypass capacitor, and it serves two purposes.

The first is to shunt noise to ground. It is a low-pass filter. The resistance of the wire leading to the capacitor combined with the capacitor to ground sets the corner frequency. Often you will see a small resistor, like 100-ohms, connected in series with the power supply, before the capacitor. This lowers the corner frequency, and allows more noise to be sent to ground.

The second function is to store power and reduce ripple. If there is a sudden current draw-- lighting an LED when the effect engages, for example-- the capacitor helps to temporarily source the extra current needed to prevent the power supply voltage from sagging.

So the long and short of it is that if you increase the capacitor, you lower the cutoff point for the low pass filter, and shunt more power supply noise to ground. If you lower the capacitor, you raise the cutoff point of the low pass filter, and potentially allow more power supply noise into the circuit.

If I'm wrong or left anything out, I'm sure someone will come in to correct me.

Mike

[yeeshkul]

It is not a decoupling cap. It is a filter cap. Decoupling caps are between the stages not across the voltage (they decouple the stages so the DC bias can be set independently), filter caps mainly filter the power ripples, but also and that is what i am not sure about - may influence the high end of the signal.

Yes i mean that one cap across the voltage. One leg straight on the voltage, the other leg on the ground. As simple as that.
You have this one in Tonebender, Rangemaster, TS808 and plenty of other pedals.

And the question is: does the value of this cap/the cap itself influence the sound (signal)?

edit: i may add a schema but i don't think it is really necessary.

[R.G.]

It is not a decoupling cap. It is a filter cap. Decoupling caps are between the stages not across the voltage (they decouple the stages so the DC bias can be set independently), filter caps mainly filter the power ripples, but also and that is what i am not sure about - may influence the high end of the signal.

Yes i mean that one cap across the voltage. One leg straight on the voltage, the other leg on the ground. As simple as that.
You have this one in Tonebender, Rangemaster, TS808 and plenty of other pedals.

And the question is: does the value of this cap/the cap itself influence the sound (signal)?

Yes, the value of this cap does influence the sound - but the answer is more complicated than you'd like it to be. You want it to be something like this:
- The bigger the capacitor value, the more [highs, or lows, or mids, or distortion, or cleanness, or something].

But it's not that simple. This is a special case of the question I answered first thing today for a self-professed newbie. The answer is "It depends." Here's that earlier quote.

Quote from: Blatant on Today at 01:26:27 AM
what do the parts in a pedal do to sound individually?
IE: a capacitor, resistor, diode, transistor does what to sound?
I know how they effect current, etc but how does that alter what we hear?
That question can't be answered directly in that form. At least not like I think you want to hear.

You can't, for instance, say that bigger resistors add/subtract anything from sound (aside from thermal noise, hiss; and even that's dependent on the rest of the circuit). Using a bipolar transistor instead of a JFET, or a germanium instead of a silicon, or a bigger or smaller capacitor cannot be said to affect sound in one specific way.

It's the interconnection of parts that affects sound. For instance, the simplest filter is a single resistor and a single cap. Whether this combination is a high pass filter or a high *cut* filter depends on how they are connected. Getting a sound you want is not as simple as getting the "right" capacitor, resistor, transistor, and so on. It's how you connect them. It's very much like having a winning football team isn't as simple as getting the biggest, strongest lineman, the fastest receivers and the most-accurate quarterback. It's both *how* they play together and *how well* they play together, which are two different things.

And I can hear you thinking it: "But that's not what I asked. I want to know how a change in the power filtering changes the already existing circuit sound."  Yep. There are two answers to that version of the question. One is what I told Blatant. The other is "It's at least slightly different in each circuit, so here's the 112,834 answers."

Let's slice the question up and work on pieces.

Many circuits have a filter cap between voltage and ground, it usually varies between 2u2 and 470u. What impact on the sound it can have if i increase such a cap?

It can have any effect from nothing at all (in simple, non-tricky circuits powered from fresh batteries) to being the only thing that lets you get any sound at all (in complicated, ready-to-oscillate circuits). It also depends on something you can't control much - the quality and "perfectness" of the capacitor you use. Capacitors being imperfect, as they are, have extraneous parasitic effects. For instance, every capacitor has an impedance that decreases linearly with frequency - until at some point, it stops decreasing, acts like a resistor for a moment, then starts INcreasing like an inductor (which is what it is for all higher frequencies). The capacitor's physical construction and material composition determine what that turnround frequency is.

It is not a decoupling cap. It is a filter cap. Decoupling caps are between the stages not across the voltage (they decouple the stages so the DC bias can be set independently), filter caps mainly filter the power ripples, but also and that is what i am not sure about - may influence the high end of the signal.

It is indeed a filter cap. But it's also a decoupling cap. "Decoupling" is not just DC blocking, although it can mean that. In fact, DC blocking caps are most often described as "coupling capacitors", because they couple the signal through. It is just as valid to call it a decoupling cap for decoupling the biases as you've used it. But it's also correct to call a cap from voltage to ground a "decoupling cap", and that is in fact what most people mean by the term. A capacitor hooked up like this does decouple stages from one another by in effect shorting out any portion of the signal currents that are fed through the power supply which would otherwise get coupled into another stage. Filter? Decoupling cap? Both.

And the question is: does the value of this cap/the cap itself influence the sound (signal)?

Yes. But in the sense of "bad things happen if you don't have enough and the right kind." If you have too small a cap, or the wrong kind (meaning, too much parasitic stuff in the one you used), then the stages interact and/or have other unforseen and usually undesirable effects. You have to have enough of the right kind of capacitor.

[.Mike]

Huzzah! At least I was right on some of what I posted.

[yeeshkul]

R.G. hat off! Thank you very much for your time, the explanation is just excellent. Thumb up.