What about a scoop-shift control?

[Mark Hammer]

The standard midscoop filter consists of a pair of series resistors, with a cap to ground from their junction, and a bypass cap straddling the whole thing.  The bypass cap allows treble to pass, and the pair of resistors and cap to ground provide a lowpass rolloff and level balancing that results in a broad midscoop when everything is put together.  This same general structure is used in a bunch of Shin-Ei derived products like the Superfuzz and its variants, as well as the FY-2 Companion fuzz, and the Fender Blender.

Normally, there is either the scoop filter, or a switch to select between a midscoop and a no-scoop setting that has approximately the same volume.  To my pleasure, I realized some time ago that the depth of the scoop could be altered by simply inserting a small variable resistance between the cap to ground, and ground.  The larger that resistance, the less treble rolloff, and the shallower the scoop.  Note that it has no impact on the content of the bypass cap that lets the treble through; only on the treble content of what passes through the dual series resistors to be combined with the bypass cap content.

It occurred to me that, since the amount of resistance needed is modest (usually less than 10k in most instances, and often less than 5k), it might be feasible to have a scoop-shift control that might adjust where the scoop is focussed and how deep it is.

Imagine that, instead of one cap to ground (on a Superfuzz, this would be the 0.1uf cap, situated between the 10k and 22k resistors), you had two of different values (e.g., 0.1uf and .033uf) in parallel.  Each of those caps goes to ground through a pot (let's say 10k linear).  The caps each go to one of the outside lugs, and the wiper goes to ground.  Rotate the pot fully in one direction, and you have whatever scoop is set by that cap.  Rotate it fully in the other direction, and you have whatever scoop is set by the other one.  Positions in between would yield everything from slightly lesser amounts of each scoop to no scoop whatsoever.

Strikes me as providing an interesting, but simple and low cost, means for producing new flavours from some classic circuits.

Make sense?

[StephenGiles]

Mark, all this talk of scoops together with the canned Italian operatic voices here in the hotel which at a particular point in the CD or whatever bursts into O Sole Mio (is it?) or as I remember from the TV ad - Just one Cornetto.....give it to me, all set in gondelas in Venice, makes me crave for an ice cream!

I like your idea by the way, do they know what they are talking about on the tap tempo thread I wonder???

[slacker]

Nice idea Mark, I'll give it a try.
In a similar vein have you ever looked at the contour control in the Marshall Shred Master? That's a similar thing except the second cap is before the scoop circuit and it forms a lowpass. So at one end of the Contour/Scoop pot you get a mid scoop and as you rotate it the other way you get a treble cut. It smooths out the tone and I think it's supposed to sound like a mid boost.

[RDV]

The standard midscoop filter consists of a pair of series resistors, with a cap to ground from their junction, and a bypass cap straddling the whole thing.  The bypass cap allows treble to pass, and the pair of resistors and cap to ground provide a lowpass rolloff and level balancing that results in a broad midscoop when everything is put together.  This same general structure is used in a bunch of Shin-Ei derived products like the Superfuzz and its variants, as well as the FY-2 Companion fuzz, and the Fender Blender.

Normally, there is either the scoop filter, or a switch to select between a midscoop and a no-scoop setting that has approximately the same volume.  To my pleasure, I realized some time ago that the depth of the scoop could be altered by simply inserting a small variable resistance between the cap to ground, and ground.  The larger that resistance, the less treble rolloff, and the shallower the scoop.  Note that it has no impact on the content of the bypass cap that lets the treble through; only on the treble content of what passes through the dual series resistors to be combined with the bypass cap content.

It occurred to me that, since the amount of resistance needed is modest (usually less than 10k in most instances, and often less than 5k), it might be feasible to have a scoop-shift control that might adjust where the scoop is focussed and how deep it is.

Imagine that, instead of one cap to ground (on a Superfuzz, this would be the 0.1uf cap, situated between the 10k and 22k resistors), you had two of different values (e.g., 0.1uf and .033uf) in parallel.  Each of those caps goes to ground through a pot (let's say 10k linear).  The caps each go to one of the outside lugs, and the wiper goes to ground.  Rotate the pot fully in one direction, and you have whatever scoop is set by that cap.  Rotate it fully in the other direction, and you have whatever scoop is set by the other one.  Positions in between would yield everything from slightly lesser amounts of each scoop to no scoop whatsoever.

Strikes me as providing an interesting, but simple and low cost, means for producing new flavours from some classic circuits.

Make sense?

I remember mentioning something like a variance control for the mid-scoop on the Superfuzz circuit to you back when I was building my SF. You didn't seem too excited about it then. Perhaps it was the way I was trying to implement it. My DIY Superfuzz is still one of my fave fuzzers.

[RDV]

Here's the thread I mentioned.

RDV

[Mark Hammer]

The Shredmaster is a very good example of a single control that does a few things at once, and is the sort of thing more people should be inserting into their designs.  By applying a treble cut at the same time as the scoop is made shallower, you get something much more immediately useful than a simple mid-lift; essentially, one has two different "personalities" obtainable via the same control.  I figured that "personality" can be made to sound different by relocating where the scoop is.  Of course, since the suggested control has no impact on the highpass portion, but only the lowpass portion, it not only adjusts how much scoop, and where the scoop is centred, but also how broad the scoop is.

Naturally, it is the sort of thing yu'll want a healthy amount of signal amplitude to apply to, since it is a passive control with the expected passive loss.  Still, for those fuzzes where people would like to keep an intense top and big bottom, yet change the character a bit, this seems useful.

Stephen, Stephen, Stephen.  As my former Milanese office-mate taught me to say years ago (with arm extended, palm upward, and thumbtip pressed against middle finger):  AY!  Che cazzo FAH-te?!   It is obvious that it is well past your bedtime.  Anne needs to tuck you in for the night.  Obviously too much Chianti circulating in that cerebrum.

Ricky,
Nice to see you here.  Hope all is well health-wise.  I looked through the linked thread.  If I got you correctly, what you were suggesting was a pan control that ranged between the attenuated unfiltered signal, and the scooped signal, without altering any of the filter properties per se.  What I'm proposing here (and it is not better than the Shredmaster control, just something different) is someting that only dickers with the filter properties, in ways which can result in more or lesser amounts of output in the process.

[Ben N]

Hey, Ricky, good to "see" you! I hope things are well with you.

Mark, that sounds like a really interesting idea, especially useful at the higher gain end of the spectrum.

[transat]

Hi. I've built a GGG Shin-Ei Companion Fuzz as my first project and would like to add Mark hammer's suggested 10k linear pot for scoop control. But i'd like to use a cheap Washburn Lyon Wah to comtrol the scoop. My understanding is that i could use its 100k audio pot. Could someone please explain to me how to do this? Do i need to add a resistor to turn the 100k wah pot into a 10k pot? If so, does it really matter that i might end up with a 10k audio pot rather than a 10k linear pot?

regards,

clém

[John Lyons]

If you solder a resistor across the outer lugs of the wah pot you can change the resistance.
I'd temporarily solder in a 100K pot across the existing pots outer lugs.
(use the wiper and one side of the temp pot)
The twiddle the pot till you get the right resistance for the effect you want.
The once you get a good resistoance just carefully desoder the temp pot and measure the
resistance and put in a fixed resistor of that value. ta da!

The taper of the pot will be changed with the added resistor to more of a linear
taper anyway...no big deal.

john

[earthtonesaudio]

The Shredmaster's "Contour" control reminds me of the "Contour" here:
http://www.indyguitarist.com/schematics/boss/bossxt2.jpg

[transat]

Thanks John. I'll give it a go.

[Paul Marossy]

Interesting idea. I'd like to hear that in action.

[earthtonesaudio]

I just converted the tone control in my Boss XT-2 to a "Scoop-Shift" control.  All I did was move the top of C16 from one side of R26 to the other (schematic link above).  It's much more versatile now, and offers some useful new sounds.