Volume pedal help (again)

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

I coundn't get the reply part to work so I'm posting a reply with a new post.

After looking at this photo for a bit, I agree this is a version of the "Myrick" mod.

But, there is a problem with the method used by the builder of this pedal !!

1) He is using two (2) discrete pots.
2) They do NOT rotate together as a singular unit.
3) This setup as pictured, is useless as to what is intended with the "Myrick Mod". Unless both pots turn together as singular unit, the 2nd pot may cause more problems than it fixes. I can see where this setup (as pictured) would cause several problems with tone, and volumne levels.

The object of the "Mod" is to keep the pick-up coil as hot as possible in relationship to the Pre-amp, thus as the volumne is reduced, the coil is also moved (electronically) closer toward the pre-amp. in order to prevent loss of hight freq sounds. (read this as keeping the impedience of the coil at a constant relationship to the pre-amp at all times.) now if the 2nd pot stays at a given point, and the "volumne pot" is rotated a bit, the results will not be as one would have it be.

The 2 pots MUST have a singular shaft that controls both wiper arms together as a single unit in order to achieve the constant impedience of the coil as seen by the pre-amp.

This is how the circuit should look electronicly.

[This message was edited by Bill Crook on 13 September 2000 at 06:47 AM.]

C Dixon · From: Duluth, GA USA

What you are saying is basically correct, but since many (if not most) steel players use a Peavey Nashville 400, why not simply use a "3 cable" hook-up and not have to be concerned with the volume pedal's resistance regardless of where it is set?

With a 3 wire cable the PU coil is connected directly to the amp. The volume pedal is not even in the circuit at that critical stage. It is only put in the circuit at a later stage and totally isolated from the PU.

So if a player has a Nashville 400, AND he hears a tone shift at different positions of the volume control, a 3 cable hook-up will solve this malady instantly.

Incidently, I have always been very dubious about any discernable hi frequency loss using the standard guitar-pedal-amp set-up. But if someone does hear it, the 3 cable hook-up is the answer IMHO.

God bless all,

carl

Jon Light · From: Saugerties, NY

Thanks for this explanation, Bill. The pedal above is simply the pedal that Zane Beck was selling at the time (early 80s). I always assumed that this was indeed the mod everone talked about. I see now that it is something else.
As I said before, the good news is that it is another knob to tweak your tone.
The bad news is that it is another knob to tweak your tone.

But it is specifically a manual adjustment, not pedal activated.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Good diagrams Bill. Interesting arrangement.
I'd like to experiment with this arrangement using inductors arrangements added to it. Also capacitors to see what would happen.

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Jack Stoner · From: Kansas City, MO

The Myrick mod did not use two pots in tandem. The standard volume pedal pot and a separate pot for the "color" or "tone". The pots do not turn both at the same time.

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

The "Myrick" mod was not intended to be another type of "Tone Control"

It's function is to keep the tone (not volumne)from changing as the volumne level is lowered. (as the p/u coil is moved away from the pre-amp by changeing the resistance of the pot,this also changes the di-nymic(sp?) range of freq responce,in other words,the lower the volumne, the more muddled the high freq becomes resulting in a more bassy sound.) Unless the pots work in tandem, we may as well have a modified "tone control", which isn't what we are trying to achieve here. We wish not to loose the highs as we decrease the volumne level. As C.Dixon stated,

Jack Stoner · From: Kansas City, MO

In 1971/72 when I worked for Little Roy Wiggins at his lower Broadway music store I did a lot of "Myrick" mods to pedals including Hank Corwin's and Terry Bethel's and many more including my own Emmons pedal. Hank brought me the original mod information, that he got from Weldon. It did not entail a "ganged" second pot. The second pot was separate and had separate adjustment for Tone.

If you have a different ganged pot modification it is not the original Myrick mod, that was popular in the early 70's.

Jack Stoner · From: Kansas City, MO

I don't have the schematic of the Myrick mod reloaded on my PC yet. I'll post the schematic after I get it restored (I had to reload my PC). However, the picture at the top and the schematic shown are not the Myrick mod. The Myrick mod used one additional 500K pot that was mounted on the right side of the pedal. It was across the input and out of the pedal but like I say I have to reload the schematic so I can give you the correct info. We've talked about this several times and the schematic has been on the forum several times, I don't know if a search would turn it up or not.

Jack Stoner · From: Kansas City, MO

Here's the schematic that I have for the "Myrick Mod" to a volume pedal. I redrew it from a handwritten sheet I have.
The pots are separate, not ganged together.

[This message was edited by Jack Stoner on 16 September 2000 at 07:06 AM.]

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Great diagrams Bill and Jack. Jack, I think Bill's diagram is the same as your's, if there were two pots, instead of the dual pot on one shaft. These are interesting ways to wire pots. I can't really see where the tone change is coming from. It may be in the capacitance of the two pots used in tandom. This may keep the impedance more consistant as the pedal moves. I suppose this is the whole idea behind the arrangment. I'd love to try your circuit Jack. I would want to try it with a pre-amp in front of the pedal. Interesting.

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Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

Keith....

There are two ways to look at this mod.

1) Jack's diagraphm of the schematic is electronicly the same as the one I posted.

Beings that he did work for "Shot Jackson" in that time-frame, I would not even begin to question his expertise in how the mod was originally designed.

BTY jack, I do remenber talking to you a few times when the shop was in the "ally" behind the Ryman Adutoriumn. At that time my intrest was on the "SHOBUD" christmas tree amp. Of course this was many years ago when I was only beginning in the field and was hunting for any and all that might teach me in the amp field.

2) jack's theme using two descrete pots does indeed create a tone control. I see this as only moveing the tone pot from the axe down to the pedal, Now givin' the quality of the amps durin' that time frame, I can see why onw would wish to have a bit of extra tone control then.

The gained pot method is primarly intended to prevent changes in the tone,

Got to go, The wife is gettin' upset at me for not being ready for church. Will finish when I get back...

Jack Stoner · From: Kansas City, MO

Bill, thanks for the complements but I worked for Little Roy Wiggins at his "Music City" store across the street from Sho-Bud.

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