passive mid "boost"

[gmoon]

Ever check out Craig Anderton's "Passive Tone Control"? It's a very similar passive LCR filter.

http://i86.photobucket.com/albums/k99/jprak1/Passivetone.jpg

Beats me if you can still get the RS 273-1378 inductor / transformer, but it's spec'ed at 88-100 uH.

The original schematic (from the Ele. Proj. for Musicians book) doesn't have the POT... And some of the caps are different values.

[PRR]

"On full" it is really just a cap. The pot is there to get "less". The fixed resistors don't seem to do a whole lot; they may be for mechanical support (some cap leads won't reach?).

[El Heisenberg]

It does not sound like just a cap...i swear to god, try it.

[El Heisenberg]

This is alot like the varitone control. I put that in my guitar last year. It doesn't have the 50k depth pot, nor the switch to change the inductor lead. It doesn't have the 47k resistor either. Cap values mightbe different but they look the same.

[El Heisenberg]

I have craig andertons "electronic projects for guitar" book and I never saw that in there.

[Shepherd]

Beats me if you can still get the RS 273-1378 inductor / transformer, but it's spec'ed at 88-100 uH.

http://www.mouser.com/ProductDetail/Xicon/42TM019-RC/?qs=LQJGOuQCHKQk%2faBX9yNCGw%3d%3d

[El Heisenberg]

This is my vari-tone control. It's in my rickenbacker 330 COPY. It's got humbuckers. The first setting doesn't do much anything. Cuts out some treble buzz maybe. I should change it. Also, my inductor is different.




craig andertons:





What does the 47k resistor do? I'd try this in my guitar but it's already equiped with 4 push/pull pots and the rotary.

[gmoon]

I never tried that circuit, but the Anderton book had one of those "flex" demo records and I recall being impressed with the sound--for a passive filter (OK, I bought my copy 30+ yrs ago...) That version is simpler, but I found this: http://mia-amps.com/images/varitone.png , which is apparently from the same book, but must be a later printing. Somewhat different cap values, but otherwise the same as that other schematic...

Re: the 47K R -- isn't that combination of RLC a pretty standard band-stop filter?

While rare, there must have been several guitars that had some resonant filters standard. In fact, this morning I just recalled that my oddball Norma "Barney Kessel" has an onboard inductor.


The guitar uses a LMH (Low, Medium, High) rotary switch. Never "reverse engineered" it, though. There may be some active resonance in "High"; in the other settings, it's more like a low-pass filter.

[Paul Marossy]

I never tried that circuit, but the Anderton book had one of those "flex" demo records and I recall being impressed with the sound--for a passive filter (OK, I bought my copy 30+ yrs ago...) That version is simpler, but I found this: http://mia-amps.com/images/varitone.png , which is apparently from the same book, but must be a later printing. Somewhat different cap values, but otherwise the same as that other schematic...

I ought to try something like that ciruit you linked just for kicks.

While rare, there must have been several guitars that had some resonant filters standard. In fact, this morning I just recalled that my oddball Norma "Barney Kessel" has an onboard inductor.

I seem to remember that a specific Gibson electric had one in it. The Blueshawk, IIRC. I wonder why it never caught on in a wider scale? I'm guessing that people didn't like it that much and/or they didn't want to spend $20 more on the manufacturing costs per guitar.

[El Heisenberg]

I think the varitone is a popular circuit for hollow body guitars. BB king has em. He's always messing with it. So I put it in my rickenbacker 330 copy I had. It's such a weird guitar. A really thin and narrow neck with a zero fret. And it's hollow instead of semi-hollow. With DiMarzio humbucker pick-ups. It was made by these guys that made Gibson copys mostly.

The vari-tone works great. But I'm gunna switch up the cap values. I started this thread for work on a new guitar and now I'm messing with a different guitar.

Isn't this the same as the varitone posted earlier? I don't see a difference?



Same cap values

[gmoon]

@El Heisenberg
Sorry--I'm just trying to identify if that last schematic is actually from C. Anderton, rather than discuss the merits of each. None of these match the Anderton circuit in my book (close, but not exact to say they are Craig's for certain.)

Re: the 47K resistor--it does reverse the operation of the filter, from mid boost to a notch (also attenuates the signal somewhat overall, 9 or 10dB.) So it's definitely different. The resister value also has an effect on the Q--the smaller the value, the narrower the notch.

Here's some Gibson Varitone schematics, which are somewhat different from all the others...
http://www.flatearthguitars.com/files/Gibson_Varitones.jpg

Paul, I'd like to try it on something with humbuckers...

[Paul Marossy]

Paul, I'd like to try it on something with humbuckers...

Yeah, same here.

[El Heisenberg]

Yeah, I was calling it varitone, but it's not.

Maybe i'll record clips or something. But I want to get another inductor and try it with a 50k push/pull pot, exactly like this one. I'd have to get rid of something else on this guitar tho.

You say the schem of the circuit I'm using, and the one with the 47k resistor will sound really different???

[gmoon]

You say the schem of the circuit I'm using, and the one with the 47k resistor will sound really different???

Hmmm. Playing with LTSpice, I thought so. Until I set the series resistance of the AC signal source to a non-zero value (something like 5K, to match a pickup.) Then they both behave as notch filters. Anderton's book certain describes it as a notch filter.

The 47K broadens the notch, so it resonates over a wider freq. range.

But if you're getting a midboost rather than a cut, maybe one or more parameters of the sim inductor (or signal) are "ideal," and the sim is not behaving in a real-world way...

Edit:
Testing your original varitone, adding a coupling cap after the signal source yields a similar sim graph as CynicalMan's notch, followed by boost (the blue "pen"... If the series resistance is "default") YMMV for sims; the cap is probably not necessary...

[El Heisenberg]

Oh, gmoon, the mid "boost" we were talking about is a differetnt circuit. I don't remember somehow we started talking about rotary controlled tone switches.

[El Heisenberg]

Hey, what does switching to the middle lead of the inductor sound like?

[PRR]

> set the series resistance of the AC signal source to a non-zero value (something like 5K

No, a pickup has a strong inductive component.

5K resistance plus 5H inductance will show the general effect of external loads.

Stuff that throws a capacitance directly on the pickup, that inductance really matters. What "should" be a low-pass becomes a ringy lo-pass with a substantial boost before the droop.

And dropping-in that 47K between the pickup and the cap spoils the ringiness, simpler low-pass with little or no bump.

[gmoon]

@El Heisenberg
Yeah, just try to help answer the "what does the 47K R do?" question... I probably sent this OT. Still, they are all simple LCR filters...

> set the series resistance of the AC signal source to a non-zero value (something like 5K

No, a pickup has a strong inductive component.

5K resistance plus 5H inductance will show the general effect of external loads.

Stuff that throws a capacitance directly on the pickup, that inductance really matters. What "should" be a low-pass becomes a ringy lo-pass with a substantial boost before the droop.

And dropping-in that 47K between the pickup and the cap spoils the ringiness, simpler low-pass with little or no bump.

Right, I realize that a simple AC source in SPICE does a lousy job simulating a pickup.

Would an inductor (with a set DC resistance) in series with the AC source be a better sim? Or an inductor with a series resistor, perhaps?

[CynicalMan]

Right, I realize that a simple AC source in SPICE does a lousy job simulating a pickup.

Would an inductor (with a set DC resistance) in series with the AC source be a better sim? Or an inductor with a series resistor, perhaps?

sites.google.com/site/distorque/home/articles/spice-humbucker-model

I use a inductor, a series resistor, a cable capacitance in parallel, and volume and tone controls in parallel.

[gmoon]

sites.google.com/site/distorque/home/articles/spice-humbucker-model

I use a inductor, a series resistor, a cable capacitance in parallel, and volume and tone controls in parallel.

Good stuff, thanks.