This is odd. I would like to have a swtc(2) turn into a mid boost with the flick of a DPDT switch. I've been messing around with stuff on the breadboard but nothing seems to be doing what I want.

These are the values I choose for the actual swtc circuit. I replaced the volume pot with a 15k resistor to ground. The output impedance of the stage driving the tone circuit is around 15k. The only part I've really figured out in order to make this work is a switch I have that puts a 22nf cap in parallel with the 2.2nf. I can't figure out where or how I put a lowpass filter in where the response  is still flat on the lowest pot setting.

What makes you think this topology would yield a bandpass?

Quote from: FiveseveN on March 21, 2025, 01:48:10 AMWhat makes you think this topology would yield a bandpass?

Absolutely nothing. I'm sorry. I think to get something similar to what I want I'll use this topology

And have the switch remove the lowpass section. The only problem with this is that it'll be flat around 0db and go down in volume while the knob is turned up and I would prefer something that is flat at around -18db where either the treble or mids are just added back in. That way I can just add a booster to the end to make it a crude frequency boost. That's why I was hoping the swtc(2) had a chance to do what I want through something I wasn't seeing.

You could use just the Mid control of a Baxandall circuit, like this:


(From https://sound-au.com/articles/eq.htm#s4)

If you notice, you'll see that the Mid control is identical to the Treble control, except with an extra cap across the pot. If you had that cap switchable in and out, you might be able to get a treble boost / mid boost switch. You'd probably have to play with the values a bit though. And if you only want boost, replace the 10K pot with a 5K pot with a 4K7 resistor below it. Oh, and this is a low input impedance ciruit too, so it'll need to fed from some sort of buffer stage in front.

HTH

Quote from: ElectricDruid on March 21, 2025, 08:56:04 AMYou could use just the Mid control of a Baxandall circuit, like this:


(From https://sound-au.com/articles/eq.htm#s4)

If you notice, you'll see that the Mid control is identical to the Treble control, except with an extra cap across the pot. If you had that cap switchable in and out, you might be able to get a treble boost / mid boost switch. You'd probably have to play with the values a bit though. And if you only want boost, replace the 10K pot with a 5K pot with a 4K7 resistor below it. Oh, and this is a low input impedance ciruit too, so it'll need to fed from some sort of buffer stage in front.

HTH

Hey I might do that. I can eliminate the transistor output boost stage on my circuit if I implement that and I'll really only be adding like 2 or 3(?) parts to my BOM. I just have to make sure I like how it sounds   

Hey this may sound stupid but is there a reason that I only get good sound for 2 seconds out of that tone control and then starts to sound misbiased and stop altogether only to come back 3 seconds after I stop playing? I have a normal vref with 2 10k's and a 22uf smoothing cap and stuff. The buffer is fine. This hasn't happened to me before

Could you plz post a schematic of your particular build..?>?

Certainly

Quote from: Transistor-Transistor on March 21, 2025, 02:56:09 PMget good sound for 2 seconds out of that tone control and then starts to sound misbiased and stop altogether only to come back 3 seconds after I stop playing?

What is the DC voltage at "?", the "-" input of U?B?

Related question: voltage at U?B p7 Out?

In ideal theory, both are undefined. In practice it depends on unspecified leakage in '4558 inputs, plus any signal effects.

Now I don't want to disappoint anyone but I kinda decided a tone control wasn't necessary for the rest of my circuit and I already took this off my board...
Sorry if I wasted some of your time but thank you for the help anyway

The OP's request is puzzling.  What is the objective?  Is it to have some sort of mid-bump added to an otherwise "flat" low end and high end?  Is it to have a sweepable bandpass with attenuated content above and below the passband?

Is a fixed midbump acceptable, or does it have to be continuously variable?

Many BBD-based circuits will use a pre-emphasis/de-emphasis strategy for optimizing S/N.  For instance, here in the Boss CE-2, R4 and C3/R5 provide tweo parallel paths to the input of IC1 on pin 6.  Because R5 is a lower resistance than R4, it results in more gain.  But because C3 is there, that additional gain is limited to content above roughly 2.3khz, with symmetrical attenuation provided at the output stage by C15/R23.

A person could easily provide a fixed mid-boost by providing two similar parallel paths to the inverting pin of an op-amp, along with a selected feedback cap in parallel with the feedback resistor.  The parallel input pat provides the treble emphasis, and the feedback cap provides a selected high-end rolloff, with the two yielding a midbump.  A DPDT toggle can engage/disengage the parallel input path and feedback cap at the same time.

Quote from: Mark Hammer on March 21, 2025, 09:06:07 PMThe OP's request is puzzling.  What is the objective?  Is it to have some sort of mid-bump added to an otherwise "flat" low end and high end?  Is it to have a sweepable bandpass with attenuated content above and below the passband?

Is a fixed midbump acceptable, or does it have to be continuously variable?

Oh well what I wanted was a tone control that could be flat with the knob all the way down and either mid boosted or treble boosted when the knob is turned up y'know

Sorry, it was me who sent them off on the baxandall. I should have maybe remembered that the mids doesn't work on its own. You have to put something else in to replace the bass control that would ordinarily provide the DC conditions. Like this (ignore the tilt control on the left):



Still, if Transistor has given up on the idea, it's only relevant in case someone comes along and finds this thread in the future...

Quote from: ElectricDruid on March 21, 2025, 09:57:21 PMStill, if Transistor has given up on the idea, it's only relevant in case someone comes along and finds this thread in the future...

Yeah and I know that this kind of tone control would be pretty helpful in other designs

Quote from: Transistor-Transistor on March 21, 2025, 09:55:25 PM

Quote from: Mark Hammer on March 21, 2025, 09:06:07 PMThe OP's request is puzzling.  What is the objective?  Is it to have some sort of mid-bump added to an otherwise "flat" low end and high end?  Is it to have a sweepable bandpass with attenuated content above and below the passband?

Is a fixed midbump acceptable, or does it have to be continuously variable?

Oh well what I wanted was a tone control that could be flat with the knob all the way down and either mid boosted or treble boosted when the knob is turned up y'know

The hypothetical circuit I suggest could do that as well.  You'd just need a 3-position on-off-on DPDT.  Middle switch position is flat.  One side position connects the parallel treble-boost input pair and the feedback cap for mid-bump.  The other side position also connects the treble-boost input pair, but a different feedback cap to permit more treble (but keep any hiss manageable).