Tilt + Mid Cut/boost tone control

[iainpunk]

Crude drawing:



The values A,B,C,D, are up to taste, however, i recommend the big muff values.

This is a crude amplitude response a teacher of mine drew:



If you are owkay with cutting notches around the 500 and the 1300, this is good-ish. The 1000 hz is not affected. The notches exist because of the phase difference between the 'inverted' and the normal bmp filter.

[ElectricDruid]

@ Tom: Thanks heaps! Some very good information, indeed. In the meantime, I found the 1980 National Semiconductor Audio Handbook which has some information on Baxandall type mid controls. This might also be interesting for you or others, if you don't have it already. They use a wider Q with the capacitor on the wiper being larger than the bridging capacitor.
I'm wondering if the ratio of 15 isn't a bit too much.

The Handbook can be downloaded here: https://ia800604.us.archive.org/9/items/bitsavers_nationaldaAudioRadioHandbook_17034677/1980_National_Audio_Radio_Handbook.pdf

That National book is very helpful, thanks. Finally a proper reference, instead of just the usual circuits regurgitated.

A lot of experimenting to do 

Yes indeed! You might very well be right that the ratio of 15 is too much. I suspect that beyond ten it doesn't actually make much odds, but we'll see. I've run up a PCB to test out this idea, and I'm going to experiment with the values a bit once I get the board.

@iainpunk: That's a pretty interesting little circuit, and a quirky response. Would give something a character of it's own, for sure. Bookmarked for future reference!

[iefes]

... I've run up a PCB to test out this idea, and I'm going to experiment with the values a bit once I get the board.

Definitely looking forward to the results. I'll as well try to play around with the values a little bit on the breadboard.

[iainpunk]

Got something:



It has 3 parts:

A)
Standard big muff tone stack
B)
A rather wide notch filter in the feedback loop of an opamp, making it a booster. The bandwidth is from 400 to 1500 and the boost is 20db. This counter acts the intrinsic mid cut from the bmp tone control and even boosts the mids with 6db
C)
Buffer and mixer for amount of mids boosted.

Hope you like it. Im gonna test it tomorrow around this time. Ill keep you updated

[iainpunk]

Hope you like it. Im gonna test it tomorrow around this time. Ill keep you updated

Yeah, 'tomorrow' became the day after tomorrow, which is today. It does work, i haven't checked simulations, but it works irl. It does a good mid boost, the mid scoop leaves something to be desired, maybe change up some capacitor values there, but over all, it works quite well.

I tested it after a simple fuzz pedal that i build a few years ago and a jfet distortion, it works best on the distortion, but the fuzz really benefits from a mid and trebble boost.

[marcelomd]

Just found this in the wild. It is the tonestack for Wampler sovereign. Its response is not necessarily like the first post, but is a simple way of getting a tilt + mid control.

[ElectricDruid]

Here's what I've got so far - a fairly basic high gain distortion with these tone controls:

https://electricdruid.net/wp-content/uploads/2018/09/HardBargainSchematicPg1.jpg


https://electricdruid.net/wp-content/uploads/2018/09/HardBargainSchematicPg2.jpg


This is test platform as much as anything. I expect to tweak the values (particularly the cross-over point of 800Hz for the Tilt and Mid controls). You'll also see I've left the option of asymmetric/symmetric clipping open, and not decided how much volume and top-cut to apply. With tone controls set flat, I don't think you want all the high-end fizz, so some roll-off is probably required, but I don't know how much yet. There's some in the drive stage already, so apply to taste.

The variable part of the gain goes from x2 to x102, but given that there's a x4.3 gain on the way in, that's really x8.6 to x438! That's pretty serious gain. In fact it might even be too much, we'll see. The main point is that the parts are in the right places and the values can be tweaked once I've got a board to play with. It also breaks an unwritten rule of mine and uses an odd number of op-amps. If you're going to use three 8-pin chips, you might as well use six op-amps as five. But I can't see much benefit in adding a sixth, so I've left it as-is. Suggestions welcomed if you think it would benefit from one more.

Thanks,
Tom

[Scruffie]

Buffered V.Ref could be helpful for the layout with that much gain or a buffered volume pot never goes amiss, neither adds any parts and well, why not.

[diffeq]

The variable part of the gain goes from x2 to x102, but given that there's a x4.3 gain on the way in, that's really x8.6 to x438! That's pretty serious gain. In fact it might even be too much, we'll see. The main point is that the parts are in the right places and the values can be tweaked once I've got a board to play with. It also breaks an unwritten rule of mine and uses an odd number of op-amps. If you're going to use three 8-pin chips, you might as well use six op-amps as five. But I can't see much benefit in adding a sixth, so I've left it as-is. Suggestions welcomed if you think it would benefit from one more.

Thanks,
Tom

Hi, Tom. Is the input buffer really necessary? Maybe it could be skipped, with appropriate changes made to a drive stage gain. For example, VR1 can be 500k, R9 can be 6.8k, making the gain from 7.8x to 501x. Without a buffer, there are only two TL072 to be laid out.

Watching this thread with interest, this tone control looks promising. Can't wait to hear the demos.

[ElectricDruid]

Buffered V.Ref could be helpful for the layout with that much gain or a buffered volume pot never goes amiss, neither adds any parts and well, why not.

Thanks Scruffie

I did wonder about buffering after the volume pot for the reasons you give, but buffered Vref hadn't occurred to me. Do you think it might help keep noise down?

[Scruffie]

Probably only so that Dougal would notice But it's nice to over design sometimes.

[iainpunk]

I do recommend a buffered vref. or as some manufacturers call a buffered vref., "Phantom Ground". But i usually use a type of opamp with a Phantom Ground output pin already embedded in the ic: the TS925.



I would almost suggest a single wave folder stage, it really gives a distortion pedal a 'grindcore' tone and feel, if you are in to that kind of stuff.



Putting a switch parralel to the diode pair negates the wave folding effect. I recommend a gain of 5 to 10 before the folder for the best effect.

Im sorry if my post is kinda/partially off topic, but this thread really ties in with my preamp project.

God speed,
Iain

[ElectricDruid]

I do recommend a buffered vref. or as some manufacturers call a buffered vref., "Phantom Ground". But i usually use a type of opamp with a Phantom Ground output pin already embedded in the ic: the TS925.

In thirty years, I've never come across one of those! Just goes to show that there's always stuff to learn!

I would almost suggest a single wave folder stage, it really gives a distortion pedal a 'grindcore' tone and feel, if you are in to that kind of stuff.



Putting a switch parralel to the diode pair negates the wave folding effect. I recommend a gain of 5 to 10 before the folder for the best effect.

That's an interesting little snippet too. Compare and contrast with the typical allpass filter stage from your favourite phaser.

Thanks Iain.

[Scruffie]

Putting a switch parralel to the diode pair negates the wave folding effect.

Wouldn't that also invert the phase? Not always a problem of course but worth mentioning.

That Op Amp type is a new one on me too, rail-to-rail to boot but digikey at least is listing all versions as obsolete, that was a fun new part for 30 seconds.

[iainpunk]

Wave folding always does stuff with the phase, and even the frequency. It blurs the line between in phase and put of phase since it is amplitude depending where the peak of the wave lies.

Ow, i only know of the parts existance because i discovered 2 of them in a pile of electronic components i inherited from my grandpa. They work good, but im not basing any designs on that opamp because its obsolescence. I'll try to find a suitable replacement one day, but ill keep using this one on my breadboard for convenience. Most of my prototype pedals never make it off of the breadboard anyway. (Although i regularly use my prototypes at gigs or jam sessions)

But let's not go to far off topic.
I made a mistake in this comment:

Hope you like it. Im gonna test it tomorrow around this time. Ill keep you updated

Yeah, 'tomorrow' became the day after tomorrow, which is today. It does work, i haven't checked simulations, but it works irl. It does a good mid boost, the mid scoop leaves something to be desired, maybe change up some capacitor values there, but over all, it works quite well.

I tested it after a simple fuzz pedal that i build a few years ago and a jfet distortion, it works best on the distortion, but the fuzz really benefits from a mid and trebble boost.

It should say "it does a good mid scoop, but the mid boost leaves something to be desired" in stead of the other way around

[PRR]

> I've never come across one of those!

Because generally, a 14-DIP plus two resistors beats a 16-DIP pack.

Although the TS925 does not seen to come in any sort of DIP.

NO stock at Mouser. DigiKey has some in-stock, but Two Bucks each, yowsa! All listed as "obsolete".

I can buy TL072 for 19 cents (SMD; DIP has risen to a buck at DigiKey). Two '072cp and two 2-cent resistors *may* come to the same price as a TS925, but better layout flexibility.

The TS925 does add a Vref buffer and high output current. Interesting part. But I've obsoleted several chips already. ATM a '07x seems like a better long-term bet than something ST introduced 6 years ago and is already rare.

[Scruffie]

I tried yours out Tom, the interaction was good in that it offered several different tones but wasn't so interactive as to be a pain to set but I would say it's better for shaping a sound than tailoring it, the best analogy I could give would be good for a muff, bad for a screamer, uninspired for cleans.

It might be preferable as a more universal tone control using a Klon style shelving filter.

[ElectricDruid]

Ok, that doesn't sound entirely negative! That's a good start!

What do you mean about the "interaction"? In theory, these controls shouldn't interact much, but in practice it will feel like that because the mid control boosts or cuts the centre region that the tilt control also affects. Is that how it comes across? Anything else you can tell me before I get a chance to play with it? Did it make you feel that the mid peak/scoop should be lower/higher? Is the boost/cut range reasonable? Or totally way over the top?

I guess the question is: "Could you do better with only two knobs if they were somehow otherwise arranged?" You could have simple Bass and Treble knobs and leave a gap in the middle for an apparent mid-boost or mid-cut, for example. Would that be an improvement? To me, I doubt it, but I haven't played with it much yet. Or you could have a simple parametric EQ, with a frequency control and a boost/cut control, and leave it at that. That offers some different possibilities, but in some ways isn't so versatile. It's a difficult question, with no right answers I suspect.

I had an email today that the boards for this have shipped, so I might have something to report shortly...ish. Usually it takes them weeks to get through customs, but that's normal, if tiresome.

[Scruffie]

I only had 15-30 minutes to try it so I can't offer a huge amount of insight yet, they were just the first feelings I got running it through an low gain overdrive design I had.

That is precisely how it comes across in terms of interaction, actual placing of the scoop etc, well it depends what you're going for, from what I remember I wouldn't say the mids were placed well if you wanted a scooped mids boosted bass metal sound and the Q could have been a bit wider at the peak for a more screamerish response but they weren't out of place. The cut and boost was very pleasing actually, from playing with these before they can be a bit OTT but the range was where I'd want it.

Two knobs is always difficult as there's always going to be that little something missing. I do think it would be more practical with the Klon style where you've got a fixed response up to 700hZ and can then cut or boost the treble just because it's rare you want to remove all the bass or all the treble and as long as the circuit has ample of both already you're in to tailoring territory which I would say with the restricted control is probably the best use of this sort of set up.

Certainly not a write-off though, it just depends what it's stuck with and what you're hoping to achieve in the individual circuit, which is true of any design.

[ElectricDruid]

I've got a "background project" in mind for this too, which is a multi-voice drive pedal. The idea is; take the input, split it three ways, add a variable drive to each channel, then run it through one of these tone stages, followed by a short (chorus-ish) delay.
I was hoping that the tone controls would be enough to give two or three significantly different drive responses, such that if they were mixed together with slightly different delays they would give the effect of multiple guitarists playing *very* tightly! So one more bass, one mid-scooped, one more peaky, perhaps. Dunno which of those should be un-delayed, and which should be later. Haven't tried that yet, either. But I reckon there's room for a really FAT drive sound with multiple separately tuned drives all working together. I may yet be proved completely wrong about this, we'll see. It's happened before...