Mid-Fi Demo Tape Fuzz

[Domin321]

Hi, any ideas how to change that tonecontrol to something like BMP tone control? I want to make 3 knob version of this. Or is better idea to put gain on max and use only volume knob and have both bass and treble pots? Thanks for ideas and advices

[Domin321]

I made this schematic, its not same, second stage is just for signal loss of a BMP tone control...What is your opinion?

[iainpunk]

welcome to the forum,

ever heard of a ''inverted Big Muff Tonestack''
check the latter half of this thread:
https://www.diystompboxes.com/smfforum/index.php?topic=126259.msg1207110#msg1207110
the schematic posted there is basically a big muff tone stack flipped on its head, it either boost bass mids or trebble. the values on the schematic itself is more wah-like, but replacing them with normal BMP tonestack values gives a more usefull tone control.

cheers, Iain

[anotherjim]

You've got rid of the Vref circuit, so the 2nd amp has to get bias from the 1st amp, which means you have no DC blocking cap going in between, BUT you have a DC path to ground via R9 which will upset the bias. You can fix that by returning R9 to ground via a cap (1uF?).
Are you sure the tone pot is only 1k and not 100k?

The Muff control has a mid-scoop, if your idea of Tascam 424 sound has the bass & treble boosted, that will be ok. OTOH, if you wanted it to have a flat response in the middle, you can juggle the values to reduce the scoop.
Here's a calculator...
https://www.guitarscience.net/tsc/bigmuff.htm
Your RIN will be 0 since you have an op-amp driving it. Your RL will be huge since its only the op-amp input, but you can leave it set at default 1M.
Or, you can just grab the values in here...
https://www.coda-effects.com/p/big-muff-tonestack-dealing-with-mids.html

[iainpunk]

sorry initially didn't notice this post due to images not loading on my PC sometimes...

I made this schematic, its not same, second stage is just for signal loss of a BMP tone control...What is your opinion?

R3 has to go to 9v, not 4.5, or you have to remove R2 alltogether.

R9, that currently goes to ground, should have a 10uF cap in series to decouple the DC path, that would solve DC problems.

cheers, Iain

[antonis]

I want to make 3 knob version of this.

There are plenty of 3 knob versions for a Baxandall EQ.. 

[Domin321]

Ok, so how to bias second Opamp from first? 
Yes, I looked at original schematic, it chould be connected to 9V instead of 4,5V...
About tonestack pot, yes it's not 1K, I just forgot to change it to 100K and adding that cap to ground should be betweet R9 and ground or parallel with R9?

[iainpunk]

Ok, so how to bias second Opamp from first? 
Yes, I looked at original schematic, it chould be connected to 9V instead of 4,5V...
About tonestack pot, yes it's not 1K, I just forgot to change it to 100K and adding that cap to ground should be betweet R9 and ground or parallel with R9?

in series, so DC doesn't flow there, just AC.
this also fixes the bias problem

cheers, Iain

[Domin321]

So after putting that cap I dont need to bias second opamp?
Thanks Iain

[antonis]

P.S.
10μF cap serves as "crackle-free" Tone pot accessory..

[Domin321]

Thanks a lot! But it will be hell to make layout I hate dual Opamps and with 2 single opamps it will be too big, but I'll see...

[iainpunk]

P.S.
10μF cap serves as "crackle-free" Tone pot accessory..

the tone pot wil still crackle, there is a DC path from the 4.5V to ground, through the 22k and the 100k pot.
the solution is putting the 10uF cap in series with R9. you can then also leave out the 1M to 4.5v and the 10uF cap inbetween the first opamp and the tone stack.

cheers

[antonis]

Yeapppp..
(omited another cap between pot wiper & bias resistor..)

@Iain: In case of using bipolar op-amps (like 4558), non-inverting input bias current is sufficient to cause pot crackling due to direct DC coupling..
(IC1 out -> 39k -> pot lug3 -> pot wiper -> IC2 non-inverting input..)

[anotherjim]

Can I just point out that you're going away from an important point of emulating the Tascam pre-amp. 50k input impedance!

[Domin321]

Somehow I got lost, sorry So if I put 10uf cap between 22K and GND I dont need to connect + input on 2nd opamp to 4,5V?

[iainpunk]

Somehow I got lost, sorry So if I put 10uf cap between 22K and GND I dont need to connect + input on 2nd opamp to 4,5V?

it depends on the opamp, if its Jfet input (like these, but not limited to : TL072 TL062 TL082), you won't need any caps in the path between the first and 2nd opamp, as long as there is no DC path to ground.

cheers, Iain

[Domin321]

Now I understand it little bit better...and biasing?

[antonis]

50k input impedance!

Pas mal du tout.. 

Any self-respecting wannabe fuzzy design ought to severely load its source..

[antonis]

Now I understand it little bit better...and biasing?

Directly from IC1 output..
(DC gain is rolled-off to unity due to C3..)