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

[287m]

that drawing need voltage divider/bias for pin 3 and 5

[Ben N]

... and Vcc to pin 8.

[pinkjimiphoton]

Thats how its setup in the schematic above.  I am still new at this, so I took out what I think was the filter from from the Tone TwEQ diagram (the overdrive alreaady has one, right?) but I need someone with more knowledge than me to check it.

By the way, the cap after the in (shown as 100uF) and before the out (shown as 220uF) will both be 68uF.

Anyway, let me know if this will work...  I intend tonstart breadboarding once I get back home Thursday!

Felipe

hey felipe, nice work, man.  68uF is really big to use for input and output caps. gonna let a lot of subharmonics thru that likely will just make it unstable, muddy, and prone to motorboating.

i think you mean 68nF, not uF. 68n/.068uF <same thing for our uses> is plenty for guitar. since you're gonna breadboard the circuit thursday, i'd suggest just trying different value caps til you like it.

generally anything from about 10n/.01uf to 4.7uF should be fine for the input filter of the fuzz part. you are right, since you already have an output cap on the fuzz, you can skip the input cap of the eq part of the circuit.

tonally, 4.7n input cap to the fuzz will make it a treble booster, as you climb the scale, it will get more and more dirty the bigger the cap is... more bass gets thru, more bass = more fuzz.  you can also limit the bass at the end of the circuit, too if needed.

i generally like about 47n-100n for input caps usually on most of the stuff i cobble together. or, google up faking a variable cap... in that case,  use a pot of 100k-250k or so and a small and a large cap... then you can vary the input capacitance and control the overdrive tone of the fuzz somewhat, and make it versatile enough to sound good from a rickenbacker to a les paul... just turn the knob to the sweet spot.

love to see peeps learning to roll their own like this. awesome job, brother.

[jfrabat]

that drawing need voltage divider/bias for pin 3 and 5

... and Vcc to pin 8.

How do I do this?  Any advice?

i think you mean 68nF, not uF. 68n/.068uF <same thing for our uses> is plenty for guitar. since you're gonna breadboard the circuit thursday, i'd suggest just trying different value caps til you like it.

generally anything from about 10n/.01uf to 4.7uF should be fine for the input filter of the fuzz part. you are right, since you already have an output cap on the fuzz, you can skip the input cap of the eq part of the circuit.

I did mean 68nF...  Sorry!

Love to see peeps learning to roll their own like this. awesome job, brother.

Thanks!  It is a lot easier to try and do stuff when help is just a post away, so thanks to all of you!

[Ben N]

that drawing need voltage divider/bias for pin 3 and 5

... and Vcc to pin 8.

How do I do this?  Any advice?

Look at the power supply part of the Tone TwEQ schematic--the part that is connected to +9v. There is some filtering and a polarity protection diode hanging off the 9v line, and then a pair of 10k resistors to ground, with a tap off the junction of the two 10ks going to "Vb". That is your bias voltage, which is half of the main supply voltage, and it goes to the non-inverting inputs of the two opamps, pins 3 & 5 - just like it shows on the schematic.

You need a bias voltage because the opamp is designed for a bipolar supply, in which a positive voltage is connected to Pin 8, a corresponding negative voltage is connected to Pin 4, and the whole thing is referenced to ground through the non-inverting inputs 3 & 5 (in an inverting configuration). But we only have +9v, so we "fool" the opamp by treating the midway point between 0v and 9v as the reference (i.e., "ground"), and 0v as the "negative supply"--creating, in effect, a +/-4.5 volt bipolar supply around the artificial "ground" at +4.5 volts--the bias voltage. I hope this makes sense.

Pin 8 is the main supply (+9v) to the opamps, which is also shown on the schematic but a little less clearly. Between D1 and R11 in the bias supply (i.e. post filtering and polarity protection) there is a line down--that is the connection to Pin 8, and you will notice, there is also a connection from Pin 4 to ground. Pin 4 is the connection for the negative power supply, which, in our case, is 0 volts==true ground, as explained above.

You could just connect the power supply for the eq as drawn to the raw 9v power source, although you might be able to save some caps by combining the two power supplies for the drive and the eq.

[iainpunk]

there were some wonky biasing mistakes in the drawink, i fixed it.
also, dont forget to hook up the power and ground for the opamps


EDIT: I MADE A MISTAKE AND OVERLOOKED THE FACT THAT THE SECOND OPAMP IS INVERTING, ONLY ADD THE CAPACITOR IN THE BOTTOM CIRCLE, NOT THE BIAS IN THE TOP CIRCUIT

[jfrabat]

OK, I will redraw the circuit with the proposed changes so that we can review it.  But question; if I fix the voltage dividing / bias from the original Tone TwEQ, do I still add the bias corrections iainpunk is suggesting?

[PRR]

> So something like this should work, right?

Where did you get those cap values? They all look 10X-100X too big.

Almost like you confused "n" for "u".

http://www.zen22142.zen.co.uk/Circuits/Audio/3bandton.gif

[jfrabat]

Almost like you confused "n" for "u".

I did; I mentioned that above...

[jfrabat]

OK, so if I understood everyone right, this is what I need to breadboard:



Is this right?

[ElectricDruid]

Is this right?

Nearly. You've lost the 100uF cap that you had on the Vb supply. That's important. It should go between Vb and ground.

Also Iainpunk corrected their original post - you *don't* need that 100K to Vb on the tone control circuit. Like he said, it's an inverting op-amp arrangement.

The cap values all look much better!

[Fancy Lime]

Also: your second opamp half has two non-inverting inputs. That's not a thing. You want the upper inputs in your schematic to be the inverting (-) and the lower ones to be the non-inverting (+) inputs. For both opamp halves.

Andy

[antonis]

A rough (by heart) calculation says that 68nF Input cap sets HPF cut-off frequency at about 230Hz..
(with a, rough again, estimation of total input impedance of about 10k..)

If you want all guitar frequencies unaffected, raise about 10 times input cap value..

[Elijah-Baley]

I have some questions becuase I want to use a Baxandall or a Tone TwEQ after a preamp.

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?
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.

[antonis]

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..)

[jfrabat]

You've lost the 100uF cap that you had on the Vb supply. That's important. It should go between Vb and ground.

OK, now I am confused; I changed the voltage protection I had for the power module of theTone TwEQ.  In theory, that one should be complete (it does have a 47uF electrolitic to ground; not sure if that is the one you mean?).  Or should I ad a 100uF directly to Vb (after the 10K resistor)?

Also Iainpunk corrected their original post - you *don't* need that 100K to Vb on the tone control circuit. Like he said, it's an inverting op-amp arrangement.

Got it. I will only keep the 220nF cap

Also: your second opamp half has two non-inverting inputs. That's not a thing. You want the upper inputs in your schematic to be the inverting (-) and the lower ones to be the non-inverting (+) inputs. For both opamp halves.

Thanks, Andy.  If I understand you correctly, you are talking about the 2 + signs, right?  If so, the top one was a drawing error (you can see in the pic that I tried scribbling the - in).

A rough (by heart) calculation says that 68nF Input cap sets HPF cut-off frequency at about 230Hz..
(with a, rough again, estimation of total input impedance of about 10k..)

If you want all guitar frequencies unaffected, raise about 10 times input cap value..

Maybe I will increase to 100nF, but I want to limit that somewhat.  The Tone TwEQ uses 220 and that includes usage for bass...  I can always play with it once on the breadboard.

[jfrabat]

How about now?  And do I need to include the 100uF cap that is dotted?

[Fancy Lime]

Better but no cigar yet. The second Opamp half (the one in the EQ section) is correct now but the first one before the EQ is still not. Flip the + and - and that is fixed. The numbers are correct, by the way. But port 2 is the minus (which should be on top as the 2 is in your schematic) and port 3 is plus (again, the 3 is in the right position but it should have a + beside it).

The dotted cap is not necessary, strictly speaking, but it will greatly improve stability and therefore reduce unwanted additional distortion from the EQ section. So definitely put that in there. Make it large enough so that the two resistors, which it is connected to, which should be 100k each, in parallel form a RC low pass with the cap with a corner frequency below the audio band. Terrible sentence. Make the resistors 100k each and the cap 1u or larger, is what I'm saying. 100u is definitely unnecessarily large. Just takes up more space than necessary for no added benefit.

Andy

[antonis]

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..)

[antonis]

Terrible sentence.

Indeed...!!!