What Does This Pot Do?

Tom Bradshaw · Post by **Tom Bradshaw** » 28 Apr 2009 2:37 pm

I obtained a rather old Ernie Ball volume pedal. It has a potentiometer on the right side front of the base section of the pedal. It is hooked up to the true volume potentiometer by several wires and can be controlled by a knob located on the outside of the pedal. Wires are hooked up to it from the main volume pot. From the pot, there are wires leading to each of the pin lugs on the output jack and the input jack. Between these two lugs is also a small capacitor (no value shown on it).

Can anyone tell me what this potentiometer is supposed to do? At the moment it seems to have no impact on the volume control, regardless of whether it is turned on or off. I am thinking it is supposed to be a taper control, but I'm not sure since it doesn't seem to do anything. Perhaps it is designed to be a tone control, but it doesn't seem to alter the output tone of an instrument in any manner. The pot doesn't seem to be damaged and an ohm meter reveals that it is working by moving the needle in the ohm meter to full off to full on.

Does anyone have a clue? ...Tom Bradshaw

John Bechtel · Post by **John Bechtel** » 28 Apr 2009 2:54 pm

I only recall that at one time Goodrich made such a Volume~Pedal with a rather large Knob on the side, near the Output~Jack and it was called a Tone~Wheel. I think it was endorsed by Chaulker! That's all I remember and I might be dreaming!

Gary Jones · Post by **Gary Jones** » 28 Apr 2009 3:38 pm

Tom
Having worked for the EB company making volume pedals, I can answer this question.
The small pot is a taper control, changing the taper of the main pot.
With the taper pot in full deflection the main pot is more sensitive in the last half of travel. With the taper pot in no deflection the main pot is more sensitive in the first half of travel.
Most people did not like or use this feature, and at some point EB removed it altogether.
The small pot is not in the active tone path, and only acts as a variable resistance to ground for the main pot.
I hope this helps. Just trying to describe it made my brain hurt.

Gary Jones
Yes, I'm still alive, it just hurts when I laugh

Jon Light · Post by **Jon Light** » 28 Apr 2009 3:45 pm

My old '80s BMI pedal has this pot too. It's sort of subtle and I agree with EB's decision to ditch it---it's one more thing to mess with and I spent more time trying to decide how I wanted to set it, or to decide if it mattered....in my opinion, now, it didn't, it doesn't.

Donny Hinson · Post by **Donny Hinson** » 28 Apr 2009 4:11 pm

As Gary said, the additional pot is a taper control, changing the "feel" of the volume change as the pedal is advanced. The small cap is a high-frequency tone enhancer (bypass, actually). It's primary purpose is to allow a little more highs through at lower volume settings, countering the complaint of some players that the pedal loses highs as it's backed off.

Tom Bradshaw · Post by **Tom Bradshaw** » 28 Apr 2009 4:31 pm

OK, it looks like the extra pot on my EB pedal is a taper control. Does anyone know if a schematic exists for a really good taper control to work in conjunction with a regular volume control; one that would lead to getting what you want in a taper control? I ask this since I sell a lot of pots to players with volume pedals. I've discovered that some players like their volume to come on fast, others want it to come on slowly, then have a huge volume surge at the bottom end of the pedal's excursion, and still others simply want the volume to come on in a gradual "full off to full on" over the full travel of the pedal's treadle. I was thinking that if the circuitry for a taper control pot could be supplied that would lead to accommodating everyone, I'd become immortal

. ...Tom

John Bechtel · Post by **John Bechtel** » 28 Apr 2009 5:12 pm

Back when Taper~Pots first became popular with Sho-Bud Players & Pedals, even though 500K A~B Audio Pots were generally used and quite obtainable, I was told that any pot could be used as a Taper~Control and I have. There were no capacitors or resistors involved. They were just wired between the two (+) terminals of the volume-pot with 2-wires from the taper-pot. (Either Terminals #1 & #3 or #2 & #3.) >It's been a long time and I forget which.<

Brint Hannay · Post by **Brint Hannay** » 28 Apr 2009 7:29 pm

IMO that cap between the jacks is the best feature of the old EB volume pedals (I have two). I've only used an EB pedal for guitar, never for steel, though, because there's more resistance/friction in the pedal action than I like--it doesn't "float" freely enough for a delicate touch. Again, IMO.

Richard Sinkler · Post by **Richard Sinkler** » 28 Apr 2009 10:36 pm

I have one of the old Goodrich Chalker pedals. The difference was that it had a built-in matchbox type of circuit (needed a 9v battery) and a big wheel on the side that just changed the tone similar to the pot on the matchbox. Seeing as how I already had a matchbox that clipped to the leg and using the knob with the foot was awkward, I removed the electronics from the pedal and made it a straight volume pedal. I had to buy the pedal because the pot in the pedal I had crapped out real bad one night at a gig and the only store here in the Bay Area at the time that had steel guitar stuff, didn't have just a pot. THe next day I had to buy a whole new pedal and that was all he had. I needed it for a gig that night.

Ron McLaren · Post by **Ron McLaren** » 29 Apr 2009 1:29 am

Tom Bradshaw,
going by your standards of help and service, you'll be immortal anyway.

Best Regards Ron Mc

Frank Bradley · Post by **Frank Bradley** » 29 Apr 2009 5:42 am

In case anyone is wondering what the VP John and Richard are referring to, here is my(near)30 yr old Goodrich pedal of the same type. This uses a 9v battery. Replaced the pot with one from Tom. Works great again... thanks Tom.

Brad Sarno · Post by **Brad Sarno** » 29 Apr 2009 6:16 am

Here's a link that discussed this topic:

http://sound.westhost.com/pots.htm

The problem with tweaking the taper of a pot with added resistance is that the pot is no longer a fixed value thru its travel. This means that the loading on the pickup will change as the pot sweeps. This can have a tonal effect that may not be desired.

As I understand it, they just don't seem to make tapers as smooth as they used to. It's actually a lot more work to have a truly smooth log taper. Most pot makers today will basically emulate a log taper instead of manufacture a true log curve. They do this with a series of 2, 3, or 4 linear segments of resistance in the track hoping that the kink at each transition is gradual enough so you don't notice it, but we do. The effect overall is something resembling a rounded log curve, but really it does have these kinks in it. Some do it smoother than others these days. It's still hard to beat the good old stock military spec pots with that taper that was much more truly logarithmic.

I do think that the best tweak that we can do with pots is to really dial in the start and stop point to our liking. Since most string/pulley pot pedals don't utilize the full 300 degrees of travel, you can decide if you want the pot to turn all the way off or you can make it turn all the way on. Personally, I like to set it so it never completely turns off, but just right at the edge of being muted. That seems to give a smooth onset and place the taper appropriately in the travel. I've had good luck with the Dunlop pots that Tom sells. The taper isn't as round and smooth as a vintage AB or Clarostat, but so far it's my favorite new pot. I've also had a good number of the PEC's go scratchy in a short period of time. While I like the PEC's feel, they for some reason aren't holding up all that well to the rigors of steel guitar use.

Brad

Lee Jeffriess · Post by **Lee Jeffriess** » 29 Apr 2009 8:42 pm

I agree, the Dunlop is the best thing out there, but I wish it had that old AB swell.
Lee
BTW, Tom did the parallel caps work??

Colin Mclean · Post by **Colin Mclean** » 30 Apr 2009 10:56 am

I agree it is probably a treble bleed cap adjust, maybe a taper adjust too...I must have missed this thread when I started my own about installing one of these on my Sho Bud pedal!

Try adjusting the pot when the pedal is adjusted for a lower volume, you should hear a difference in treble response there. It should not make any difference in tone with the pedal at full volume. If not, maybe it's for volume pot taper but if there's a small cap in there I'll put my money on just a treble bleed adjust.

Frank Bradley · Post by **Frank Bradley** » 1 May 2009 6:10 am

Need some suggestions regarding my VP (the pix I submitted on the thread). Any suggestions on a good setting for the tone knob? I've played around with it and would rather turn the knob totally open or closed and adjust the tone with my amp. Everytime I have to move the pedal the knob gets bumped and the setting changes. I like a nice mellow sound with some "bite". I just recently acquired my BMI D/10 and it is a great sounding old steel and I'd like to get the most out of it's vintage sound. Also... the VP's model number has worn off and I was told it was a 6122... anyone know for sure from the pix? I bought it sometime back in 1977-79.
One final question... the serial # on my BMI is 229. Anyone have any idea when it might have been built? I've tried contacting BMI and have gotten no response. Thanks.