Mid Scoop on a toggle switch?

[audioguy]

I want to add a mid scoop on a toggle switch to my tone-stack-less Dr. Boogey... but I'm having a hard time finding a circuit snipit that shows a scoop. People point out full EQ circuits and the like, but I think that might be more than I need.
Isnt there a simple way to scoop the mids with just a couple of components?

Thanks!

[slacker]

Here's a simple scoop circuit.



It's basically the notch filter off a Univox Superfuzz. Close the switch for a scooped sound and open it for normal. Or replace the switch with a 5-10k pot for a variable depth scoop.

[audioguy]

Thats perfect. Is there much of a volume drop? It doesnt look like there would be.

Thanks!

[Mark Hammer]

Isn't there a simple way to scoop the mids with just a couple of components?
Thanks!

There sure is!  Here's our reference diagram: http://geocities.com/electrictabs/dr.boogey.png
Here's our other reference diagram: http://filters.muziq.be/files/schematics/univox_superfuzz.pdf

The Superfuzz includes a 2-position switch that is labelled "Notch/Normal" here.  The notch is created by 4 components: .001uf and .1uf caps, 10k and 22k resistors.  The 47k/10k pair simply provide an unscooped sound that is at roughly the same volume as the scooped sound.  Note that a midscoop filter WILL eat up signal through passive loss.  Of course your tone stack will too,so we're not inheritting any problems here.

The 10k resistor and .1uf cap in the notch filter act like a lowpass filter.  A second parallel path is provided by the .001uf cap,which permits the highs to bypass the lowpass filter.  When you combine the highpass and lowpass together, you end up with a tone lacking mids - a scoop.  The location and breadth of the scoop can be tweaked by varying component values.  If the .001uf cap is raised in value, more upper mids and lower treble gets through to the output.  If the .1uf cap is lowered in value, more upper bass gets through unimpeded.  With the values shown the resulting tone is big bottom and sizzling top.

The Superfuzz is not the only distortion to use such a scoop.  It's actually pretty common.  I've even seen them on some SS Fender amps.  Here's a case where I made the scoop variable: http://hammer.ampage.org/files/modded_fy-2.gif  Since the .1uf cap bleeds mids and highs to ground in order to achieve its lowpass function, I stuck a pot between that cap and ground to create a variable resistance.  As resistance goes up, the scoop goes away.  Turns out that in this instance, the resistance doesn't need to get much above 15k or so for the scoop to virtually disappear, so a 25k pot, and maybe even a 10k, is sufficient.  As you increase the resistance, not only does the scoop disappear, but the volume increases as well.

The Dr. Boogey has a 100k "presence" control which is really a treble cut.  It would not be unreasonable at all to have a single pot do variable scoop and treble cut duty simultaneously.  Take a 100k pot, as shown, and connect the wiper to ground.  Now connect one of the outside lugs to the .1uf cap on the scoop filter, and the other outside lug to the 3n cap shown (I gather this is actually 3300pf).  Since both controls work by varying bleed to ground, our single pot has a complementary action in one direction, the ground path for the .1uf cap goes low (more scoop) and the treble-bleed path to ground goes high (keep more sizzle).  In the other direction, our .1uf ground path goes high (no scoop) and our treble-bleed path goes low (lose sizzle).  This single pot should be able to nail you tones from death metal to rounded warmer blues tones.  You may need to adjust the cap values to get it to nail all the tones you want, but it should work.

I think he took it down, but Jack Orman had a nice little article at AMZ on notch filters and creating scoops.  One of the things you might consider doing here is inserting a pot to vary to width/location of the scoop.  You will note that there is a 10k and 22k resistor in series, that provides a second path in parallel with the .001uf cap.  The .1uf cap just "taps" a point along that path.  Consider the following.  Run a 10k resistor to the outside lug of a 10k linear pot, and tie a 12k resistor to the other outside lug of the pot.  This path now replaces your 1k+22k with an equivalent series resistance.  Instead of connecting it to the 10k/22k junction, connect your .1uf cap to the wiper of that pot.  Now you have a .1uf cap to ground which can "tap" a point along that path anywhere from 10k to 20k (10k+pot).  This will move the scoop around and add some more variation.  As the resistance gets bigger, the treble rolloff at the low end of the scoop (which you'll hear as a bass boost) will move downward.  If you wanted to arrange for even more variability, use a 25k pot instead, and stick a 3.6k resistor on one side and a 3.3k on the other (instead of 10 and 12k).  Some of those sounds may be wild and some may be unusable, but I'll let you be the judge.

So, what do you remove from the Boogey?  Everything from the junction of the last FET and thetone stack, right out to the presence control (keep the 22k/3n/100k).  Since there is no way for stray DC to make it out to the volume pot on the stock Dr. Boogey, you probably want to stick a cap between the presence control and the input to the volume pot.  Something between 1-10uf ought to do the trick.

EDIT: Slacker was quicker on the draw, in both senses of the word!

[slacker]

EDIT: Slacker was quicker on the draw, in both senses of the word!

Hee hee, that's because I'm not as good as explaining things as you Mark, I already had the schematic so I figured it would be quicker just to post it.
I should of mentioned that the pot idea was yours, it's a great mod, sounds really good on my Superfuzz.

[John Lyons]

Here is a way you can see what each value change does:

T-notch filter:
Go to Duncan's amp page and download the "tone stack calculator"
Click on big muff tone stack and plug in these values
Make the resistor to ground at the top 20M or so to take it out of the circuit effectively.
Make the bridging resistors 330K or so. One will be the pot, slide that all the way to the right.
Make the bridging cap 1nf and then the cap to ground 10nf
Just tweak from there until you get something that looks good.

John

[audioguy]

Wow... thanks for the great info guys!
Heres what I've done- I built the Dr. B. without the tone stack. It sounded really cool, but I wanted to try a single knob tone control... I used the Moonlight circuit from Adams Amps and it kinda lost my high end- like a blanket had been put over the amp. So now I want to try to rip that out and just replace it with a removable mid scoop.
With luck I'll find some time to tweak it tonight.

EDIT- In order to make it 'stackless' I ripped everything out after Q5. I believe that was at the suggestion of Basicaudio

[Mark Hammer]

EDIT- In order to make it 'stackless' I ripped everything out after Q5. I believe that was at the suggestion of Basicaudio

More or less.  I think you will probably want to retain some capacity to tame the high end, if only for hiss management rather than tonal shaping.  That doesn't HAVE to be a control.  It could simply be one cap to ground ahead of the volume pot.

[stm]

Here is the step-by-step design procedure for Bridged-Tee notch/scoop design:

http://www.diystompboxes.com/smfforum/index.php?topic=50531.msg378167#msg378167

Cheers.

[audioguy]

More or less.  I think you will probably want to retain some capacity to tame the high end, if only for hiss management rather than tonal shaping.  That doesn't HAVE to be a control.  It could simply be one cap to ground ahead of the volume pot.

Thats odd because it actually had crappy high end... Probably just the tonestack I added.

Here is the step-by-step design procedure for Bridged-Tee notch/scoop design:

http://www.diystompboxes.com/smfforum/index.php?topic=50531.msg378167#msg378167

Cheers.

Wow, thats cool... thanks STM!

[Mark Hammer]

More or less.  I think you will probably want to retain some capacity to tame the high end, if only for hiss management rather than tonal shaping.  That doesn't HAVE to be a control.  It could simply be one cap to ground ahead of the volume pot.

Thats odd because it actually had crappy high end... Probably just the tonestack I added.

I've actually never listened to one, and I don't know what your definition of poor high end is, but I know this:

• unless one lives in a eutopia, high gain = hiss accumulation
• midscoops can often appear to exaggerate high end, maybe moreso than a tonestack does

There may be no real requirement for a treble cut for you to get the tone you want out of this, however there MAY be a requirement for a treble-cut to get back to the tone you want. from bypass mode, if and when you find you need to goose the treble on the amp for clean sounds.  Some folks need that flexibility, some don't.  Certainly don't do it because I said to do it.  Do it because you need to.

[audioguy]

My trouble, which is leading me to experiment with the mid scoop is that when I added the tone stack I mentioned earlier to the Dr. B. it sounded like I put a blanket over my amp- muddy and no real clarity to the highs. Prior to that, as I recall, it sounded full with plenty of highs.

[Mark Hammer]

Sounds like maybe you had some kind of glitch in your tonestack.  A conventional tonestack is capable of creating notches/scoops.  Doesn't mean that it would be more to your liking than a midscoop as discussed in earlier posts (or vice versa), just that maybe you haven't had a valid opportunity to hear the tonestack performing properly yet.

[John Lyons]

The Mid and High end it the thing I mostly fiddle with on the DB.
I would either settle on a toggle for the mid notch, maybe three  position, flat, small notch and then big notch.
Then add basic tone control kbnob. I recommned Marks "Stupidly Wonderful Tone Control" which will shape the high end nicely.
Either that or dig up a dual concentric pot with stacked knobs fo mid notch depth and high end control with the SWTC.

John

[WGTP]

Here is what I have been using.  http://aronnelson.com/gallery/WGTP/BassBoostNotch?full=1   

[audioguy]

OK after all of the valuable tips here I went ahead and added a mid scoop switch to my Blackfire... exactly as detailed above and the volume cut is so extreme that even with the volume maxed you can hardly hear it... but it IS scooped!
Can someone suggest a nice gain recovery stage?

Thanks!

[amonte]

Does anyone have a graph that shows what frequencies these filters cut?  Something like what Duncans Tone Stack calculator.

Speaking of which, would it be a bad idea to use the BMP's tone stack and adjust the values to make it a mid cut?

[Mark Hammer]

OK after all of the valuable tips here I went ahead and added a mid scoop switch to my Blackfire... exactly as detailed above and the volume cut is so extreme that even with the volume maxed you can hardly hear it... but it IS scooped!

That shouldn't be.  There IS signal loss, but with a circuit having that much gain, there should be something left over.

[audioguy]

There was something, but not much at all. Not even a usable amount at full volume.

[R O Tiree]

The BMP tone stack is a mid-scoop, with the added bonus of being able to boost the lows/cut the highs or vice versa. By playing with the component values, you will be able to induce more or less of a mid-scoop.

If you have not already downloaded the tone stack calculator from Duncan amps, do so now. It's a truly brilliant resource.

Got it? Right, see R2 (22k)? You can get that down to about 2k or so before really seriously weird things start to happen. So, wire a 2k resistor in series with a 25k pot and you can control the amount of mid-scoop to insane levels (-13 to -32 dB), as well as get about +/- 15dB change in bass and treble with the "normal" pot when you have max amount of scoop and +/-7 dB (bass) and +7/-25 dB @ 10 kHz (treble) with min scoop.

What you'll find is, the more mid-scoop you select, the more the bass and treble control you have. You probably don't need to go as low as -32dB of mid scoop, perhaps...

This is such a neat idea... I might just implement it in something I'm building. If you don't mind, of course.