Can someone check my vero board layout for my tube screamer / Voodoo Lab OD

[cdwillis]

I'm mashing up the Son of Screamer with the second half of the Voodoo Lab OD with a low pass filter from a Rat in between the clipping and recovery/boost stage. I was wondering if someone could compare my schematic with my vero board layout and see it if looks ok or if I mixed anything up. 








My idea was to increase the low end in the clipping section.  I changed the resistors so that the lowest point in the gain pot would be cleaner, but still have a decent amount of gain. I modified the values in the VLOD's recovery stage from 150k/47k to 470k/47k for more gain, so in theory I can push the front end of the amp a little more with the gain pot down for a clean boost.

[PRR]

What does R5 C8 do? In fact R8 and C5 look useless also. Maybe things got turned around?

Why no noise bypass on R12?

[cdwillis]

I didn't think I'd need a capacitor for noise after r12 since I had the 100uf and 100nf capacitors filtering power before the voltage divider. Should I move the 100nf to after the voltage divider?

I don't understand what you mean about the second half of the Op Amp? It's pretty much the same as the voodoo lab overdrive but I changed R8 from 150k resistor to 470k in an attempt to increase gain. Can I simply put the resistor and capacitor in the feedback loop to increase gain without running that part of the loop to ground? Sorry if this is basic stuff, I'm learning a lot still.

[antonis]

I presume Paul talks about HPF (R5/C8) and LPF (R8/C5) cut-off frequencies..
(which are 3.4Hz & 1.5kHz respectively..)

Lower R8 & R5 values by a factor of 10 and lower C8 value by a factor of 5 to 10 (depending of HPF corner frequency of your taste)..

Check here: https://www.diystompboxes.com/smfforum/index.php?topic=118497.0 for mods..

[EBK]

I believe Paul was suggesting that R5 and C8 should go on the other side of the feedback loop (connected to op amp pin 6 instead of pin 7) in the schematic. I would agree, as that matches the verbal description (i.e., same as Voodoo Labs OD).

[antonis]

I believe Paul was suggesting that R5 and C8 should go on the other side of the feedback loop (connected to op amp pin 6 instead of pin 7) in the schematic.

Aoutchhhh...!!! 
(nice Erik..)

[duck_arse]

https://www.diystompboxes.com/smfforum/index.php?topic=118497.msg1103381#msg1103381

hhuuuuggggggeeeee circuit shown in that thread at post 1, and also has bypass cap on bias divider.

[cdwillis]

Thanks for the help everyone.

I got the voltage divider turned around and put on pin 7 when I was trying to copy that part from gaussmarkov's schematic where the pin 5 and 6 are flipped.

I was trying to keep low end in the circuit (it's the thing I don't like about tube screamers really). Maybe 3.4Hz is too flubby. If I change the 1uf there to a .01uf the knee is 338.8Hz which would still have some meat to it. I haven't breadboarded this yet, but the 470k/220pf/1.5khz knee seemed like it would work fine there.

This is where I'm at now:




Am I correct in thinking that at minimum/maximum gain theres a 723798.5Hz/1444.7Hz knee in the clipping section?

[antonis]

Am I correct in thinking that at minimum/maximum gain theres a 723798.5Hz/1444.7Hz knee in the clipping section?

Yeappp..
(but that only stands for up to 0.6V/1.2V pin 1 signals - outputs of higher amplitude are bypassed from LPF..)

P.S.
IMHO, C11 should be of much higher value..
(as it is, it forms a LPF with R12 of 159Hz corner frequency - higher than rectified mains supply..)

[cdwillis]

I barely understand how an RC filter changes the frequency response of an amplified signal, so the capacitor's power filtering is even more unknown to me right now. I changed out the .1uf there for a 100uf.

[cdwillis]

I built it on a vero board and tested it with a breadboard before putting it in an enclosure. Overall I like the sound, reminds me of a beefier SD-1, which isn't surprising. I used a linear pot for gain, I think I need to swap it for a logarithmic pot because the gain jumps up at like 5% of the pot being turned then doesn't increase like you'd expect. I used a 1k resistor instead of 1.5k with the 100k tone pot as in the schematic because that's what I had on hand (either that or a 2k resistor). There's quite a sweep, but the darkest 3/4 of the sweep isn't that usable. I think I could swap a 50k pot in and get a better sweep. I've got a spreadsheet where I'm crunching some numbers on the min/max range I can get with different filter combos. The volume is pretty much exactly what I was looking for as far as output.

[cdwillis]

After reading around some more, I've realized I basically built a Run Off Groove Tube Reamer with an adjustable low pass filter between the stages instead of the fixed LPF. Of course someone else had thought of this before. 

I'll post the schematic in case anybody comes across this thread