Tilt + Mid Cut/boost tone control

[iefes]

Hi all! Any new insights gained from breadboarding/prototyping?

I got the idea to implement the two tone-controls just using one opamp (+ input buffer), similar to the baxandall style circuitry. Spice says it should work, but is there any disadvantage to do it like this?

The frequency response seems to act a bit strange close to maximum settings. E.g. with the tilt control rolled fully back and the mid-boost cranked, there's no pronounced mid-hump observable. But the extreme settings are probably not being used anyway. Or maybe with some fine-tuning we could work out good values.

What do you think of this? I'll try to put it on the breadboard this weekend.

Btw: I breadboarded the mid-control and found that using 15n for the wiper-cap and 4n7 for the bridge cap yielded more like a volume-control because the band was to wide. I've now values of bridge: 10n, wiper: 4n7
I've read that the cap on the wiper should be bigger than the bridged cap and that's how it's done commonly in baxandall style controls, but in my case I couldn't really get a nice mid-range control out of it.

[ElectricDruid]

I got the idea to implement the two tone-controls just using one opamp (+ input buffer), similar to the baxandall style circuitry. Spice says it should work, but is there any disadvantage to do it like this?

No, I don't think so. The magic of op-amps is such that it should be equivalent to doing it with two. And who doesn't like to save an op-amp?!

The frequency response seems to act a bit strange close to maximum settings. E.g. with the tilt control rolled fully back and the mid-boost cranked, there's no pronounced mid-hump observable. But the extreme settings are probably not being used anyway. Or maybe with some fine-tuning we could work out good values.

With the tilt control all the way to one side or the other, the mid peak just brings the level of the centre up to the boosted level of the tilt, so you don't see a hump although it's still there. What you do get is a choice about whether the centre is boosted or not, effectively changing the centre point for the tilt.

Btw: I breadboarded the mid-control and found that using 15n for the wiper-cap and 4n7 for the bridge cap yielded more like a volume-control because the band was to wide. I've now values of bridge: 10n, wiper: 4n7
I've read that the cap on the wiper should be bigger than the bridged cap and that's how it's done commonly in baxandall style controls, but in my case I couldn't really get a nice mid-range control out of it.

Keep experimenting, I guess. The values I used gave me +/-14dB for the mid boost/cut.

Look into ".step" for stepping through parameters if you don't use it already. Being able to see a range of responses on one graph is invaluable for things like this. There's examples of using this to "fake a pot" on my LTspice screenshot from 17th sept.

[iefes]

Thanks for your thoughts! I've used the .param command before but not in a more complex way like you did for the potentiometer simulation. Thanks for the tip. Attached is an updated version of the circuit together with the frequency response. This gives me roughly +/- 6dB of tilt control and +/-8 dB of mid control. I think this should be enough range for my purpose. I loved the tilt-control in my Diamond Compressor and the +/- 6dB it provided were plenty.
The center frequency of the mid-control seems to shift a bit depending on the position of the tilt-control so this will need some tweaking on the breadboard.

[ElectricDruid]

Looks good!

T.

[rankot]

Lots of interesting ideas here! Thanks to everyone!

[iefes]

I need to add, that the response with both circuits sharing one opamp does not give the same response like with two individual opamps. I suspect the parallel resistances of both parts influence each other. Have a look at the attached screenshots. One with the mid-control parallel to the tilt-circuit and one with the mid-control disabled.

Any ideas how to achieve the same response with this setup?

Without mid control:


With mid control:

[ElectricDruid]

Sorry, but I'm not yet convinced that what you're seeing is down to interaction between the two parts of the circuit.

I notice you've got "50k * (1+Rm*mp)" and "50k * (1+Rm*(1-mp))" for the values of the two halves of the Mid pot. The "50k" isn't necessary, since that's the value of Rm (Rm for "resistance of mid", mp for "mid position"). Whether that causes any problems, I don't know.

I guess I should try sticking the two pieces together in my own LTSpice sim and see what happens...

[iefes]

Yea, the "50k *" is used to fix those resistor values for the moment. The "*" just disables the equation. I did it like this to see just the tilt-equalizer working and leaving the mid-control centered.

However, let us know what you find :-)

[ElectricDruid]

Ok, I get it, thanks.

But in that case, you've got 50K for the value of the pot in the first case, and 50+50K =100K in the second case.
Again, dunno if that makes any difference.

[ElectricDruid]

Ok, I tried it.

Looking at the mid control on its own, the combined version loses some resonance (the mid isn't so peaky, and the response shifts higher as you turn it away from centre. And the maximum boost/cut drops from about +/-14dB to +/-4dB.

Looking at the Tilt control on its own, it's not as badly affected, but the control loses symmetry between low and high (less highs) until you turn it up to maximum.

So I agree that the tilt network interferes with the baxandall mid control. The two networks seem to step on each others toes.

[iefes]

Thanks for confirming! Have you tried it on the breadboard or "only" simulated it?

However, in the meantime I tried out the mid control together with a low-gain OD I have on the breadboard at the moment and I really liked it. I used 4k3 resistors on pins 1 and 3 of the mid pot (50kB). 15n for the bridge cap and 3n3 on the pot wiper. Like this the center frequency is somewhere around 800 Hz. I tried it through my highly modified Mesa Subway Blues, which is now more of an EL84 AB763 with Master-Volume (GREAT tone!). With the mids boosted slightly I could definitely get some marshally tones out of the otherwise pretty transparent overdrive. On boost-settings above 3 o'clock the OP275 started to distort (any advice on that? I already ran it on 18V). The scooped settings are nice as well, but the overall volume seems to be lower with scooped mids. This could be improved with a narrower bandwidth. However, it is probably just "normal" that it appears more quiet to a human ear with less mids involved.

I have the tilt-control hooked up as well now, but didn't get around trying it out. My 1-year old daughter is keeping me busy

Attached is the schematic of the mid-control how I used it. Any tips on how to reduce distortion at higher boost settings?

 

[ElectricDruid]

Thanks for confirming! Have you tried it on the breadboard or "only" simulated it?

Only simulation. But in my experience, if it doesn't even work in the sim, there's no way it works in reality. Sometimes you can get stuff that works in the sim but won't work in reality (the models not being perfect) but it rarely if ever seems to go the other way, at least for me. I realise that isn't that logical, but that's just how it goes!

However, in the meantime I tried out the mid control together with a low-gain OD I have on the breadboard at the moment and I really liked it. I used 4k3 resistors on pins 1 and 3 of the mid pot (50kB). 15n for the bridge cap and 3n3 on the pot wiper. Like this the center frequency is somewhere around 800 Hz. I tried it through my highly modified Mesa Subway Blues, which is now more of an EL84 AB763 with Master-Volume (GREAT tone!). With the mids boosted slightly I could definitely get some marshally tones out of the otherwise pretty transparent overdrive. On boost-settings above 3 o'clock the OP275 started to distort (any advice on that? I already ran it on 18V). The scooped settings are nice as well, but the overall volume seems to be lower with scooped mids. This could be improved with a narrower bandwidth. However, it is probably just "normal" that it appears more quiet to a human ear with less mids involved.

Yes, I'd guess so. The human ear is most sensitive to that frequency range, so we'll notice the lack of it disproportionally.

I have the tilt-control hooked up as well now, but didn't get around trying it out. My 1-year old daughter is keeping me busy

Attached is the schematic of the mid-control how I used it. Any tips on how to reduce distortion at higher boost settings?

You say you're running the op-amp on 18V, but you don't say what the signal level is. There's a decent amount of gain in that stage for some frequencies, so you need to keep the signal level sensible. +14dB is x5 gain, so with 18V, you might get 15V max output before clipping, and that implies a 3V max input before clipping. If you're feeding in significantly less than that, something else is going on.

[iefes]

Thanks for that info. I think I'll have time to test the whole of the circuit tonight.

Attached is the current schematic of the overdrive I'm working on. It's a MOSFET boost running into a JFET stage, so there is probably a quite large voltage entering the tone-section. What voltage swing should I expect on the output of Q2 if I'm running it on 9 or 18V?

First tests show that the circuit seems to work nicely except the clipping op-amps with high boost-settings. I'm still not sure if there are some parts that I don't need (e.g. R9?). So if you see anything which is not necessary or otherwise if I missed something important let me know please.

[ElectricDruid]

Ok, I've made some progress with this. I finally got my boards back:



And I build one up and tested it. Apart from a few very minor stupidities on the PCB, it all works fine. And I'm pretty happy with the tone controls.



I'd hoped to be able to go from a heavy mid-scooped sound to something very forward and in-your-face. And the Mid control does pretty much do that. At maximum cut, it gives a heavy scooped sound, and you can darken it or lighten it a bit with the Tilt control. I found a little bit of treble tilt helped sharpen it up.
With the Mid right up, you get a very clear sound that I associate with the sixties. That bright crunchy very forward sound, almost a cocked wah sound. Like that, I found I was happy leaving the Tilt neutral, but you've got more bass or more treble if you need it. You can also back the gain off smoothly to give a much softer overdrive sound.
Ignoring the Mid control for a minute, you've got the basic Big Muff range of tones on the Tilt control, but without the slight mid-scoop, unless you put it back with the Mid control. So...it's not half bad, and probably more interesting than "Bass" and "Treble" controls, which is the other obvious two tone control combo.

By now, you probably want to hear what it sounds like.

Here's some funky chops with lots of mid and plenty of gain:

https://electricdruid.net/sounds/hardbargain/HardBargain1.mp3

Now a really dirty fuzz sound with a sixties edge to it:

https://electricdruid.net/sounds/hardbargain/HardBargain2.mp3

Something heavier and more doom-laden. This sounds a bit rubbish on laptop speakers but kicks a$$ in reality:

https://electricdruid.net/sounds/hardbargain/HardBargain3.mp3

The "Sunshine" riff with a softer, more overdrivey sound:

https://electricdruid.net/sounds/hardbargain/HardBargain4.mp3

Enjoy!

[antonis]

Tom, you rock, man.. !! :beer: :beer: :beer:


<Apart from a few very minor stupidities on the PCB>
Could you plz elaborate..?? 

[ElectricDruid]

<Apart from a few very minor stupidities on the PCB>
Could you plz elaborate..?? 

I generally use a 0.3" footprint for caps, as you can see on the silkscreen/PCB. This lets me add an extra pad in the gap in-between and then I can fit either 0.2"/5mm or 0.3"/7.5mm spaced caps, depending on what I've got handy. Makes the board more versatile.
On this one, I added all the extra pads, but there are four of them I forgot to connect up to the 0.3" cap footprint. I had to bend the cap legs over on the solderside to make a connection to the 0.3" spaced pad. A nuisance, but not serious.
I noticed this on one cap before I started building, and then buzzed them all through and discovered I'd forgotten several.
Apart from that it fired up first time perfectly, so that's a success.

[iefes]

Great stuff Tom. My Overdrive is still on the breadboard but I'm also quite happy with the tone-controls on it. What are the center frequencies you settled with? And how much boost/cut do you have available for each the mid and tilt-control?

[ElectricDruid]

Great stuff Tom. My Overdrive is still on the breadboard but I'm also quite happy with the tone-controls on it. What are the center frequencies you settled with? And how much boost/cut do you have available for each the mid and tilt-control?

It's centred at 800Hz, and it has 14dB cut/boost on the Tilt control and a bit less on the Mid (maybe +/-10dB)



It's basically the circuit from the simulation I posted back in September, now actually built in reality. I posted the schematic too:

https://electricdruid.net/wp-content/uploads/2018/09/HardBargainSchematicPg1.jpg
https://electricdruid.net/wp-content/uploads/2018/09/HardBargainSchematicPg2.jpg

I built the first one as per the schematic. I used 47K/470pF for R12/C8, which gives a 6dB roll-off above 7.2KHz after the clipping. That prevents things getting fizzy. I left out R13 (so no volume reduction after clipping) and I included the one-diode-vs-two-diodes asymmetrical clipping for a little bit of harmonic interest. It'd be easy to add a SPST toggle around one of those diodes to give a Symmetrical/Asymmetrical Clipping switch, and I might add pads for that on the final PCB, but I'll tack a couple of wires on mine to see if it adds anything first.
I haven't messed with the centre frequency yet (it needs a bit more working out, since you have to re-jig both stages) but I'd like to try one with a lower centre. Maybe that 640Hz geometric centre that Rod Elliott talks about. I'll probably build another board up with different values and see which I like best.
I'm also going to add a buffer after the volume control as per Scruffie's suggestion because needing two types of parts bugs me, and it'd be a neater design with three dual op-amps rather than two duals and a single.

[pruttelherrie]

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.

What do you mean with 'a grindcore tone and feel' ? Middle-of-the-road Napalm Death, wall-of-mush Insect Warfare or tight-and-precise Obligatorisk Tortyr? Or more towards a mid-heavy-hm2-grind? Or maybe all-of-the-above?

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

Please elaborate on your preamp project, I'm interested
Separate topic, if necessary.

[tubegeek]

Catching up to this topic - has anyone else tried the "Bone Ray" tone stack a la Merlin B? Seems like it goes in this direction. It's not totally flat in the neutral setting though.

https://books.google.com/books?id=9kMDBAAAQBAJ&pg=PA206&lpg=PA206&dq=%22bone+ray%22+tone&source=bl&ots=Oz5oUrvdgC&sig=ACfU3U1fwRtWWjE7xveWgxEKetiIeCdbqQ&hl=en&sa=X&ved=2ahUKEwi2-pvJ_ermAhUST98KHVXrCOMQ6AEwBHoECAoQAQ#v=onepage&q=%22bone%20ray%22%20tone&f=false