Mistakes on my striplayout ? (tube screamer)

[fuzzo]

the sound is odd comparated to an original tube screamer. If i don't activate the two diodes with the second AOP, I've less gain than the tube screamer pedal, . Tommorow I'll try with my peavy Vk112.

[frank_p]

I found what did not work in my circuit so now I have an output.  However if I probe with the oscilloscope in the gain stage (1st part of the opamp) there is no clipping that is going on there.  So the sound is pretty clean...

Well much too clean. 

[frank_p]

In fact I have to put a four volt p-p signal at the input so it start to clip. What kind of diodes did you put in yours ?

P.S.: I've tryed to put the R C line to ground on the other side of the negative feedback loop (IN - instead of OUTPUT of OPA1) it is making all the difference, the signal is getting distorted but not clipped at a OK voltage supply.

À plus tard.

[fuzzo]

I used the "classic diodes": 1n4148 for each AOP.!

So the sound is pretty clean...

Well much too clean. 

I've the same problem in mine with the first stage. with the second the sound is better, a real overdrive.

The pot gain didn"t work well, I put it before the circuit to create another gain pot and I put a 1M resistor between "e-" and output. With the secound stage the sound is better, a real overdrive

[frank_p]

Yes, as I said the diodes are useless in the first stage unless you change the lowpass filter (to ground) on the INPUT_NEG leg of the first opamp.  Otherwise these are components that are there for about nothing. 

And also, yes, the fist pot. do not make big changes (if at all).

[fuzzo]

yeah, it works more like a big booster with the first stage. and I don't know what  ? I've did a tubescreamer circuit

I've put a 33nf in the place of 47nf in the low pass filter, I haven't 47nf in my stock anymore.

[frank_p]

I don't remember the amplitude change but perhaps that there is too much signal going to ground before hitting the diodes "funnel".
This is a guess...   It would be nice that someone give an hand at explaining what is going on the way yours was designed.

What I don't understand is how the impedance equation changes when using the two methods.

[fuzzo]

Yes, if somone can explain why We've this problem

[frank_p]

Commin back later, gonna try a bit of reading and thingking on this.

À +.

[fuzzo]

I played with this pedal while 2 hours today, and the sound is cool, I used the mode 2 (overdrive with the two gain stage).
What I can put like tonestack ? (I've two empty holes in the boxes, so I think a banxendal (bass and treble) can be fun or a tone control and a mid control.

What do you think about those ideas ?

Maybe a big muff's tonestack with a "body control" to add mids (like  in this document from AMZ muzique)

http://www.muzique.com/misc/presence.pdf (page3 : the version 2 of amz control)

[frank_p]

You would put the tone control at the end ?  I don't know if you would need an output buffer.

Did you change the place where the RC to ground is connected ?  I tell ya it makes a big difference.

[fuzzo]

a buffer ? why ?

tomorrow i'll make a millenium bypass and maybe i'll change the 33nf (in the first Low pass filter) cap to a 100nf or 470nf, maybe l'll change the role of the switch for those caps and keep the sound with the 2 AOP together)

[frank_p]

The output buffer is for having a low impedance at the output so you can be able to plug in a low impedance input (the one after your effect)  without having problems.   It will also "isolate" your tone stack from what it will be plugged in so making it more "independent" by hitting the high impedance on the input of your output buffer.  Well I think this is the explication...

Jack is better than me:
http://www.muzique.com/lab/buffers.htm
http://www.muzique.com/lab/superbuff.htm

[fuzzo]

It's done I finsished.

I changed the 33nf in the first RC to a 100nf.

I put a tonestack (with the components I've) like described in the AMZ document I posted. It works well but not the best tonestack for this circuit. When the mids control is at min, there's a big hollow in the mids (it's odd for a tube screamer)  Maybe I'll try a baxendall when I'll buy components for that.

this pedal has a big volume and the volume pot don't work so well, Just 5% or 10% is usefull, after that, I kill my ears and my neighbors. (maybe i'll put a trimer to control the volume, but not today, I spend so many time in working on it )

[fuzzo]

the pics!



Vol/drive/tone/mids and bypass tone (switch)

[frank_p]

Nice !

[fuzzo]

thanks !

And the sound is good !!