Noob question - Bass, mid, treble control for overdrive/distortion

[ElectricDruid]

Vb must have a cap to GND.. 
(both for voltage stability & AC grounding..)

Just exchange places between 47μF & 100μF..

P.S.
It should be advisable to lower enough voltage divider resistors values (down to 10k say..) and place a series resistor of 470k - 1M between them & Vb point..
(noise issues prevention..)

+1 what Antonis said. Make the two Vb resistors 10K and use the 47uF cap for the dotted cap. The 100uF will do a good job in the position of the 47uF.

Aside from that, there's only the reversed "+" and "-" symbols on that first op-amp, but as Lime said, the pin numbers are all correct.

[Fancy Lime]

Vb must have a cap to GND.. 
(both for voltage stability & AC grounding..)

Just exchange places between 47μF & 100μF..

P.S.
It should be advisable to lower enough voltage divider resistors values (down to 10k say..) and place a series resistor of 470k - 1M between them & Vb point..
(noise issues prevention..)

+1 what Antonis said. Make the two Vb resistors 10K and use the 47uF cap for the dotted cap. The 100uF will do a good job in the position of the 47uF.

Aside from that, there's only the reversed "+" and "-" symbols on that first op-amp, but as Lime said, the pin numbers are all correct.

-1 what Antonis said 
The non-inverting inputs of the opamps should go straight to the intersection of the two resistors and the cap, without an additional 470k-1M resistor. That would only apply if you were using the opamp in non-inverting configuration. That technique is known as noiseless biasing but it does not apply here. The non-inverting input of an opamp used as an inverting amplifier (which is what both of your stages are) needs to be nailed to Vb with no extra resistance if you want it to behave linearly, which you do. Also: If (and only if) you will be using only the two halves of a single TL072, 100k bias resistors are fine in my oppinion, because the TL07x series has absolutely tiny input bias currents (as all JFET opamps do). if you were using, say an NE5532, RC4558, or even NJM4556, somethink like 10k or 22k would certainly be advisable. if I were you and I were set on the TL072, I'd go with the 100k-100k-1u combination. But going 10k-10k-10u (or 47u) would give you mere flexibility for swapping opamps. It will suck more juice from the power supply though, which would be an issue only if you plan on using it with a battery.

Cheers and don't let us confuse you,
Andy

[iainpunk]

i just noticed that the led is always on when the pedal is powered, it that what you want or is the switching jut not drawn?

on the same topic, this might be interesting to read

[jfrabat]

i just noticed that the led is always on when the pedal is powered, it that what you want or is the switching jut not drawn?

on the same topic, this might be interesting to read

Ah, I had not noticed I did that!  So it would be technically a pad for soldering the LED lead, and the negative would go to the stompswitch.

Here is the latest draw:



Any other issues you see?  Do I move to breadboarding?

[ElectricDruid]

-1 what Antonis said 
The non-inverting inputs of the opamps should go straight to the intersection of the two resistors and the cap, without an additional 470k-1M resistor. That would only apply if you were using the opamp in non-inverting configuration. That technique is known as noiseless biasing but it does not apply here. The non-inverting input of an opamp used as an inverting amplifier (which is what both of your stages are) needs to be nailed to Vb with no extra resistance if you want it to behave linearly, which you do. Also: If (and only if) you will be using only the two halves of a single TL072, 100k bias resistors are fine in my oppinion, because the TL07x series has absolutely tiny input bias currents (as all JFET opamps do). if you were using, say an NE5532, RC4558, or even NJM4556, somethink like 10k or 22k would certainly be advisable. if I were you and I were set on the TL072, I'd go with the 100k-100k-1u combination. But going 10k-10k-10u (or 47u) would give you mere flexibility for swapping opamps. It will suck more juice from the power supply though, which would be an issue only if you plan on using it with a battery.

Cheers and don't let us confuse you,
Andy

Thanks for spotting the bit I'd missed about the resistor to Vb - totally right, they're not required. (Isn't it the case that you can use them in an inverting configuration too, to try and help balance offset voltages at the two inputs and therefore the output? - for audio this mostly doesn't matter, since we don't care and AC-couple the output anyway).

I think you worry too much about the 10-10K-1u versus 100K-100K-47u. 20K across a 9V supply is 0.45mA - not a huge amount. I admit 200K across a 9V supply is significantly less! And back when we used to use batteries by default, I *did* use to worry about stuff like this (and use TL062 and LF444s for jobs where they're weren't the best, but they didn't drain my PP3).
Either way will be fine...

[jfrabat]

Noticed a couple of mistakes when I went to redraw it in Eagle.  Here is the latest schematic:



IMPORTANT NOTES:

• OpAmp will be a TL072; I just did not have it in my eagle library, but the OP249 has the same pinout and footprint, so I used that one for the schematic
• Although I intend to use BAT41s, again, my Eagle library only had BAT42s.  Diodes may change completely once I breadboard, though.
• I know I am mixing and matching European and US capacitor symbols; I did not have the patience to make them all the same.

So, can you guys spot any other thing that needs fixing?  Or something I may have missed when drawing it up on Eagle?  If not, it is off to the breadboard... and if that works, getting some boards done!

[ElectricDruid]

Those op-amp inputs on the first op-amp (IC1A) have got flipped around again...

[Elijah-Baley]

1. The Active Baxandall layout and the Tone TwEQ has the 1M from input to ground (pulldown resistor). In the schematic drawn above that resistor has been omitted. Is it necessary or I can we omit it without any problem?

If you wire your 3PDT switch with Input grounded when effect by-passed, you shouldn't have any problem by omiting pulldown resistor...

2. I'm using large 10uF input and output caps. Is the cap in front the TL072 be necessary non-polarized? I would like use a 10uF polarized there even there.

Use of non-polarized cap isn't necessary..
It mainly depends on HPF cut-off frequency (here set at 13Hz with 220nF & 56k) hence cap's capacity value..
(10μF cap there should be useless in the mean of low frequencies filtering..)

Thank you, Antonis!
But what I meant was the 1M input pulldown resistor in the Baxandall and in the TwEQ, but I have to put in front of one of the EQs an non-inverting opamp booster. So the will be not in the input, aymore. I don't know if I have to includede it or not. I can't notice changeing in the sound.
Actually, that pulldown resistor is missing in the schematics drawn here, distortion + eq (between the two sections). So, I assumed it's not necessary, but what happens if I include it?

About frequencies, I got these emulations:
(The three caps are input, output and the coupling cap in the middle of the Tone TwEQ. Just that circuit).



With the stock caps I got a line not very flat, but just with a slightly lack of mid/low end.

Nice topic, and sorry my interference.

[antonis]

Can't catch your diagram but pulldown resistors are only needed before IN and after OUT caps..
(the second only in case of Volume/Level pot absence..)

If you use Baxandall or Tone TwEQ as a separate, independendly chain activated effect, you might need them..

[antonis]

+1 what Antonis said.

-1 what Antonis said. 

Zero total shouldn't be considered as profit motive, should it..?? 

@Andy: Could we shake hands on keeping 10k/10k resistors and omit 407k - 1M bias resistor..?? 

[Fancy Lime]

+1 what Antonis said.

-1 what Antonis said. 

Zero total shouldn't be considered as profit motive, should it..?? 

@Andy: Could we shake hands on keeping 10k/10k resistors and omit 407k - 1M bias resistor..?? 

Sure! Like I said: -1. Not -2  10k/10k is fine, or 22k/22k, or 47k/47k. As long as we are not trying to squeeze out the last minute of service from a zinc-carbon battery, it really doesn't make a difference. I normally use the 10k/10k combination as well because I have lots of 10k resistors and never use batteries.

Cheers,
Andy

[Elijah-Baley]

Ok. I get that 1M resistor to the ground between my preamp and the Baxandall (or Tone TwEQ) is not necessary. But now I have it on the board.
I hope that the 1M resistor is just useless. Or is it better take it out?

I find the 10k/10k thing very interesting!
I'm using my preamp + eq on board, with the battery. I'm using a TL061 on the preamp and a TL062 on the EQ. Is in this case is advisable to use 200k/200k for the VB to reduce the battery consuption?

Thanks!

[jfrabat]

Those op-amp inputs on the first op-amp (IC1A) have got flipped around again...

Crap!  You are right!  I will fix it tonight.  I will also start breadboarding.

[jfrabat]

Those op-amp inputs on the first op-amp (IC1A) have got flipped around again...

Crap!  You are right!  I will fix it tonight.  I will also start breadboarding.

Fixed!  Dont have the pic, though.

Quick question; can I substitute the 56nF cap in the power part of the schematic with 68nF?  I do not have 56nF in stock...  I got 47nF too, if that is better, but I think 68nF is OK, right?

[Fancy Lime]

Those op-amp inputs on the first op-amp (IC1A) have got flipped around again...

Crap!  You are right!  I will fix it tonight.  I will also start breadboarding.

Fixed!  Dont have the pic, though.

Quick question; can I substitute the 56nF cap in the power part of the schematic with 68nF?  I do not have 56nF in stock...  I got 47nF too, if that is better, but I think 68nF is OK, right?

47n or 68n are both ok in this position. In fact, any cap larger than 10n, which isn't an electrolytic is going to be ok. The purpose of the cap in this position is only to filter out high frequencies that the big 100u electrolytic cap can not catch because nothing is ideal and electrolytics have an increasing impedance at high frequencies. Film or ceramic caps do not have this particular problem, so together the two caps make up one "almost ideal" cap.

Andy

[ElectricDruid]

+1 what Lime said. I often use a 100nF ceramic in this position (they're cheap, I have lots around from logic decoupling duties). It acts in association with the electrolytic cap to make (as Lime neatly put it) an "almost ideal cap". Exactly. The 100nF deals with the stuff that the 100uF can't cope with, and vice versa. Together, they've pretty much got it covered.

[jfrabat]

IT'S ALIVE!

OK, this is where we are at as of right now:

Schematic corrected with:

• OpAmp corrected
• Some pots turned around (in my breadboard, the EQ and Gain are backwards)
• Changed 56nF cap to 68nF for the power module, and added a 47nF and a 10nF for the highs (as I said, I dont have 56mF, so if I print it, might as well print for what I have, right?)

Here is the breadboard:



Notice the transistor is in a reachable position so I can switch it to 2N222 or 2N5089 or something along those lines.  Also notice the diodes on the bottom; by only reconnecting one wire I can switch between 4 types (may play with it even more later on)

And the sound test (WARNING, English is not my first language!):

Overall, it is working as expected, but I do have a couple of small issues:

• Mid frequency control not really having much of an effect
• When high is full high, there is a bit of clipping (goes away with the slightest turn of the pot)
• There is a bit of noise from the pedal (not worried about that, since it is still in breadboard form!)

[Elijah-Baley]

Maybe the high control boosts too much signal. I got something like that with the Active Baxandall. It's the same thing of the Tone TwEQ, but with differents value and without mid control. In my case I don't get any distortion, but I heard a lot of highs. In front I have a clean opamp preamp/booster.

About the mid control. Are you sure you connected it fine? I'm trying to find some circuit like this with a mid control. I tried to connect an external board of the mid control on my Baxandall, but I failed twice. I thought it was my fault.
I'm building it in these days, I was trusting in the Tone TwEQ, it should work, it must work! Someone built it with success. I guess.

[antonis]

About the mid control. Are you sure you connected it fine?

Can't see any discrepancy between Felipe's & Tone TwEQ Mid control other than x10 underscaled pot wiper to virtual ground cap (C10)..

[Elijah-Baley]

Indeed, C10 shoul be 33nF not 3.3nF. If on th breadboard there's the wrong cap jfrabat should get almost half cut/boost and higher frequencies of the mid.

It could be useful: https://guitarpcb.com/wp-content/uploads/2018/07/BD_Tone-TwEQ.pdf