Tried to design a distortion based on a TL084 but I get no sound at all

[antonis]

Calculate C3 based on input impedance of Tone controls at 800 ohms to 26 K Ohms depending upon frequency and amount of Bass boost. Maybe 5uF ?

Maybe into an electronics museum..?? 

[11-90-an]

That would give me a volume boost won't it?

Yes. After the tone stack, you might need a little boost. this one will give around 51k / 10k = 5.1 gain

[Vivek]

It is normal for a designer of this kind of circuit to try and have different diode options and to switch between them.

Maybe you want to consider that as an option and keep place on your PCB for different clipping diode combinations, in case you feel like doing that in the future.



I particularly like a different system where we have two sets of diodes, one set clips at a low v1 and other at a higher V2, and a compliance pot in there that lets you continuously adjust all kinds of clipping in between V1 and V2. More flexible

[Vivek]

That would give me a volume boost won't it?

Yes. After the tone stack, you might need a little boost. this one will give around 51k / 10k = 5.1 gain

Gain of 5 in last stage will make the last stage clip based on settings of the tone controls.

Maybe some people will find that as "good"

[antonis]

I particularly like a different system where we have two sets of diodes, one set clips at a low v1 and other at a higher V2, and a compliance pot in there that lets you continuously adjust all kinds of clipping in between V1 and V2. More flexible

Is it possible to post a draft schematic, if you plz..??

[11-90-an]

Somewhat like this, I assume? Of course, there is no need of specific diodes, but Ge < Si diode's forward voltage seems to be something most of us understand...

[Ams76]

It is normal for a designer of this kind of circuit to try and have different diode options and to switch between them.

Maybe you want to consider that as an option and keep place on your PCB for different clipping diode combinations, in case you feel like doing that in the future.



I particularly like a different system where we have two sets of diodes, one set clips at a low v1 and other at a higher V2, and a compliance pot in there that lets you continuously adjust all kinds of clipping in between V1 and V2. More flexible

Yes. I've actually drawn it with these diodes, but when I'm going to build it I'll keep my options open and maybe even add that pot maybe some LED's for softer clipping. I'll breadboard it and see what sounds good

[Vivek]

Last stage

0.1uf and 10K = 160 Hz

Maybe you should change that to 40 Hz, especially if you push Bass through this pedal

[11-90-an]

also, if you ever will use this pedal on bass, consider changing all decoupling caps to 2.2 uF...

[Vivek]

Somewhat like this, I assume? Of course, there is no need of specific diodes, but Ge < Si diode's forward voltage seems to be something most of us understand...

VFE uses this topology

The problem is that 50K is too huge and then the Pot really does its stuff at the ends of the travel

Maybe 5K is more appropriate here

I also made a separate post.

[ElectricDruid]

That would give me a volume boost won't it?

Yes. After the tone stack, you might need a little boost. this one will give around 51k / 10k = 5.1 gain

Disagree. This isn't a typical amp "tone stack", which is passive. It's an active circuit, so it doesn't lose any volume, unless you count turning both the bass and the treble down.
Adding gain after it just risks the output stage clipping.


I'm surprised no-one else apart from me has made a fuss about the 100K input impedance of the input buffer. I thought everyone liked 500K-1M these days. 100K is *so* 70's...

[antonis]

Somewhat like this, I assume? Of course, there is no need of specific diodes, but Ge < Si diode's forward voltage seems to be something most of us understand...

Can't figure out the reason for higher forward voltage drop diode pair existence..
A series pot (wired as variabale resistor) with Ge diodes should result into same effect..

[Vivek]

Check out the shunt clipping diodes and pot

I think the pot is too large. I feel 2k to 10k is better. Maybe 2K is the best. The calculation for best compliance resistor actually depends upon the Vpeak that is fed to that stage and the difference in the Vf of the 2 sets of diodes.

[Vivek]

I'm surprised no-one else apart from me has made a fuss about the 100K input impedance of the input buffer. I thought everyone liked 500K-1M these days. 100K is *so* 70's...

I'm with you, Tom

Input impedance is 100k

Which is low and will load the pickups

Better to have impedance at least 500k if not 1Meg

[Vivek]

Why cannot gain stages 1 and 2 be combined into one Op amp with input impedance over 500K, output impedance below 500 ohms and max gain over 200 ?


What is the reason to have 2 IC to accomplish that job from guitar input jack till input of tone control stage ?

[Vivek]

See one input stage with high impedance, high gain, low output impedance


Brother AMS76, please see the Fat control. I recommend this !!!!

[antonis]

Input impedance is 100k
Which is low and will load the pickups

That might be an issue for a clean preamp..
(for a distortion pedal it might be a will..)

P.S.
OP initial design input impedance was 10k..
By raising it up to 100k it's a acceptable compromise between input inverting buffer and impedance..

[Vivek]

Coring diode noise reduction gate which is suitable for high gain, high distortion circuits with high signal levels.

[Vivek]

Input impedance is 100k
Which is low and will load the pickups

That might be an issue for a clean preamp..
(for a distortion pedal it might be a will..)

P.S.
OP initial design input impedance was 10k..
By raising it up to 100k it's a acceptable compromise between input inverting buffer and impedance..

After choosing an inverting buffer, an input impedance of 100K seems to be the best possible outcome. But maybe still not good enough outcome.

But why choose an inverting buffer ? What advantages does it bring ?

[antonis]

But why choose an inverting buffer ? What advantages does it bring ?

Academic interest queries should confuse more OP, shouldn't they..?? 
(after all, it's his own design choise..)

P.S.
IMHO, a - more or less - simple distortion effect implementing various "smart" tricks & building blocks will result into a sterile impersonal character..