Definitive value for volume pedal pot?

[ashcat_lt]

why wire the guitar that way? or maybe i should ask, why play a guitar wired that way? just curious, not criticizing!

Mostly because I never use the V pot on the guitar at any setting other that 0 or 10, and if I want to do swells while playing, it's a lot easier to do by foot.  I gave up on the volume pedal years ago, and have found that I don't hate the unloaded sound anyway.

[antonis]

Mostly because I never use the V pot on the guitar at any setting other that 0 or 10, and if I want to do swells while playing, it's a lot easier to do by foot.  I gave up on the volume pedal years ago, and have found that I don't hate the unloaded sound anyway.

It's definately a matter of taste, but a single pot is always more "robust" and long healthy living than a pinion/rack/pot/e.t.c. combination...

[pinkjimiphoton]

> It is known that this kind of system dont fully rotate the potentiometer, so i either you end up with not fully closed or not fully open, but if the pot is high enough in value, the diference is not noticeable

I do not understand this.

The pot dont rotate its full 270º.

I am aware of the pedagogical risk of explaning one fact with many examples, but ill take my chances:
If the pot dont fully rotates its 270º you can set it up in a way that when the pedal fully backward, the pot is fully shorted to ground,letting no signal pass thru, but on the other (heel?) position, the pot is not fully open, ther is some resistances between the in and the out, plus a resistance to ground makin it a voltage divider.
The other case is the oposite, having no resistance between in and out on the (heell?) position, but when it is backwards, the signal is not fully shorted to ground, letting some audio pass thru.

I know a schematic would be useful, but its just a voltage divider.

How does any of that change with a high value pot?

the higher value pot will shunt less signal to ground, so you may be able to get closer to the desired sweep than with a smaller one... you generally lose less treble and bass in a passive device that way. but it's imperfect still. a lot of times it may be easier to set it for max volume on a sweep, and add a smaller secondary pot to control the minimum level, as in an ev5 or whatever.

depending on what the use is will change it. as an expression pedal, 10k is VERY common these days. this works well with most keyboards and effects. but for a passive volume control. 500k is a good medium point IF it's the first thing after the guitar. if it's in between a mess of pedals, i'd go between 10k and 100k. too high a pot too early in the chain can make you pick up a lot more noise and interference.

like everything, it's a compromise. you need to figure out where in your chain you want the volume pedal to work, and adjust value accordingly. there is no "definitive" "best" value... it depends on the player and the application.

jmo's based on dicking around with this crap for decades. YMMV

[ashcat_lt]

It's definately a matter of taste, but a single pot is always more "robust" and long healthy living than a pinion/rack/pot/e.t.c. combination...

Like I said, I'd only use it for swells anyway, and that really doesn't come up as often as you'd think.  I gave up on the pedal mostly because I couldn't find a good solution to the issues raised in this thread.  Also because the "variable impedance" buffer that I put in with it had a nasty noise problem that I couldn't sort out.  And I had put it in a Crybaby shell and used the power hole for the Z switch, and didn't want to try to drill another through the thick sides so the power had to go through the bottom but even with right angle plugs there wasn't enough clearance under the pedal so it had to be jacked up ...

Then I inherited a couple of EB volume pedals which just work.

I generally replace all of the pots in my guitars with rotary switches to give me more different coil combinations, which gives me way more control over volume and tone than I really need.  Honestly, when I'm playing live I just set it to something that works and go, in the studio I have plenty of tools to get subtler shades.  And like I said, I've come to dig the little extra zing I get without the extra load.

[EricCook]

Hello,

I hope this message finds you well, healthy, and most importantly ... Happy!

I read this entire thread, and I'm not quite sure you ever really got your answer, so I'll give it a go ...

Passive pickup's (no batteries) as far as I understand, have higher resistance in the 250k - 500k Ohm range and active pickups, like those in some bass guitars that require a separate power source (aka batteries) for the pickup(s) or keyboards have lower resistance in the 50k ohm range, although the Ohm ratings on potentiometers, as I understand them, are for "RANGE", so those measurements of resistance shouldn't really matter in the design of your machine.

The real thing to consider for a pot in this application, at least in my humble opinion, would be voltage and current (or amps) that the potentiometer can safely handle. I'd say that is the starting point to answer your question as to the "definitive" values for your potentiometers. In your case, you'd just need to assure the mechanism controlling the value of the potentiometer, whether it be a Linear Pot or Rotary Pot, allows for that full range of motion you spoke of, possibly by adding some small gearing to your design if the current one is not cutting the mustard as is.

The older I get, the more I'm NOT 100% positive about ANYTHING really, but I believe pots are more ratio based, i.e. a 10k pot has 1/10 the "ADJUSTABILITY" that a 100k pot has in the same amount of physical distance (volume 0 through 10, volume 0 through 100 respectively, with same amount of distance traveled when turning or sliding the pot)

For a typical electric guitar (passive w/higher resistance) OR keyboard (active/powered w/lower resistance) volume pedal I'd imagine a 10k pot wouldn't give you enough "adjustability" and a 250k pot would be too much "adjustability", so for this case I'd think a 100k or maybe even 50k pot would be the best as long as it is rated for the amounts of voltage and amperage coming from the source (i.e. guitar, keyboard, etc.)

All that said, I am NOT a guitarist by any stretch of the imagination, or a pianist for that matter, although I can make a fool of myself equally efficiently on both, so this could all be a bunch of HOOEY as I've never built this myself!!! However, if this were my project, I'd pull the volume pot for the instrument you're making the volume pedal for, considering it is analog of course. None of this will work if the instrument your trying to use the pedal to control volume for has a digital volume controller. I'd look up the specs or data sheet for that specific model of volume pot in the instrument your making the volume control pedal for, then get a SLIDER pot with identical specs to the rotary pot that is most likely in your instrument. I think the slider pot will make the problems you mentioned easier to deal with in design. Then you only need 2 - 1/4" female jacks for I/O, and 3 pieces of wire for the entire circuit - no resistors, capacitors, etc. should be needed as far as I can see in this application.

Then some sort of belt, wire, or string to hook to the slider pot or to two points on the rotary pot and either end of the pedal ensuring it was it absolute zero at the near end of the pedal when depressed and moved to 100% at the far end of the pedal being depressed ... if any of that makes any sense at all.

Of course, obviously, you'd have to build the pedal part as well, or maybe use an old busted one and take the guts out or something to that extent, and maybe even experiment with different pots to see the differences in sounds you can create.

Hopefully after all the time that has passed since this was posted, maybe this will still help answer your questions a bit better ... or help someone else in the future "¯\_(ツ)_/¯" Those were my intentions anyway. If this works for anyone, or you have any questions, lemme know. I'd be happy to help if I can and if needed.

Much love!!! ✌
       .ƹ.

[R.G.]

Passive pickup's (no batteries) as far as I understand, have higher resistance in the 250k - 500k Ohm range

Typical single coil pickups are 4000 - 6000 ohms resistance and 1-2H of inductance. Humbuckers can be up to 18K of resistance and 4H or more inductance. The inductance is what kills you on these. The impedance rises with frequency. A 2H inductor has an impedance at 5kHz of Zh = 2*pi* 5000Hz * 2H = 62000 ohms inductive plus the resistance. This is worse with humbuckers, of course, which is why they often have a reputation for being "darker". To avoid selective treble loss, the impedance the pickup drives has to be much greater (generally defined as "more than ten times") than the pickup impedance. For the concocted-but-realistic 62k ohm example, you'd really like the thing it drives to be 620k ohms or more.

the Ohm ratings on potentiometers, as I understand them, are for "RANGE", so those measurements of resistance shouldn't really matter in the design of your machine.

The ohm rating on pots is just the resistance from the two ends. I don't understand equating this to range.

The real thing to consider for a pot in this application, at least in my humble opinion, would be voltage and current (or amps) that the potentiometer can safely handle. I'd say that is the starting point to answer your question as to the "definitive" values for your potentiometers.

A guitar pickup can put out on the order of 100mV to 1V of signal, peak. I don't know of any pots that can't handle much more than 1V. As to current, passive pickups have that resistance/inductance thing internal to them. At low frequencies where the inductance doesn't matter, a 1V signal would have to go through that 4K or more internal resistance, so the maximum current for a 1V signal into a dead short would be 1V/4000 ohms, or 250uA. I don't know of any pot that can't handle 250uA of current. I think this means that all pots can handle guitar pickups just fine, so it's not a good starting point for picking one.

The older I get, the more I'm NOT 100% positive about ANYTHING really,

Me too!

but I believe pots are more ratio based, i.e. a 10k pot has 1/10 the "ADJUSTABILITY" that a 100k pot has in the same amount of physical distance (volume 0 through 10, volume 0 through 100 respectively, with same amount of distance traveled when turning or sliding the pot)

I think it's more about signal loading for guitars. If you hook up  a pot as a variable resistor using only two of the terminals, then yes, a 10K pot can vary only 1/10 of the amount of a 100K pot. But for volume controls, it's nearly universal to hook them up as three-terminal devices. This means the signal drives one end of the pot, the other end is grounded, and the wiper touches the resistance somewhere along the way. This provides a voltage at the wiper that is proportional to the amount of distance (around the pot for rotary, along the pot for linear) from one end to the other. In the three terminal use, you get 0% to 100% for any value of pot. 10K has the same 0-100% as a 100K. Of course, that's 0 to 100% of whatever voltage the signal source can drive across the pot. Using a 10K pot across typical passive pickups loads down the signal a great deal, so the signal is much lower, and it loads down the high frequency signal much more because of the internal inductance of the pickup itself.

As I understand them, all pots have adjustment ranges of 0 to 100%, but may load down the signal source.
This is an oversimplification, but it's a very appropriate and useful one.

I did the circuit design for a commercial volume pedal some years ago. We went through testing with all of the common pot values from100K to 1M, and settled on 250K as the best compromise. The compromises were to steer the best course between loading down the signal (and hence excess treble loss) and causing too high an impedance out of the pot and into the amp (and hence extra hiss and hum pickup). It was a compromise. As a final step, I put in a switch that switched in or out a dual buffering system. The switch could insert an input buffer to avoid nearly all input treble loss, and an output buffer to drive the cable to the amp with lowest hiss and hum pickup. The difference was small, but audible.

Ask questions where I've just made things muddier by explaining.