Help me improve my overdrive design

[Freppo]

Hi there!

I've been trying to design my own circuit. After spending hours and hours of testing out some ideas on the breadboard, and finally getting a very decent sound, this is the design i've come up with.

EDIT. removed the old schematic :)

It's basically a couple of transistor gain-stages with asymmetric soft clipping diodes at the second gainstage, followed by a tone control into a final makeup gainstage. I've borrowed ideas from all over, so I can't say any specific circuit that it mostly resembles, it's all very basic stuff. All the values are tweaked by ear.

I would like to improve upon this circuit as I can hear great potential. It sounds great at low gain but gets a bit mushy and too distorted and noisy at the top of the gain range. I've tried to lower the gain, but I loose to much overall volume.

Can anyone have a look, maybe give me some direction where I should start tweaking or generall ideas on how I can improve it? :)

Cheers / Fredrik

[Dave]

Cool, are you making these to sell or just for your own use?
Have you thought of adding a charge pump or something? Supposedly it may give you more headroom, keep it from being mushy.....
Thanks
Dave

[Freppo]

Thanks for the suggestion Dave!
It's just for my own use (for now anyway).

I made a complete overhaul of the circuit today and solved many of the issues I had.
I'm very happy how it sounds now!
It has very little noise. Goes from pretty clean to a medium overdrive / distortion.

This is the final schematic (for now anyway):


I'm working on a very layout for it.
Now I just need to figure out a cool name for it... any suggestions?

/ Fredrik

[Vince]

''Don't tread on me''

But that kinda defeats the object.... actually I might use that.... *rushes to the copyright people....

(joke, obviously)

[Freppo]

Vince wrote

''Don't tread on me''

But that kinda defeats the object.... actually I might use that.... *rushes to the copyright people....

(joke, obviously)

Lol! That's great

EDIT. I renamed it the Stepping Stone overdrive.

I made a vero layout for it that should be ok. Gonna build it tomorrow to verify and make some sound samples if anyone is interested.

Here is the layout


cheers
/ Fredrik

[Vince]

lol... That's a great name. anything with the word 'fuck' in it can't fail.

I'll be interested to hear it when you're done

[Dave]

Cool, I look forward to demos too!
Thanks
Dave

[Geezer]

Very cool.....I'm for anything "anti-opamp" :-)

The pot values don't match from the schematic to the vero.....can you verify what is correct?

Thx, J

[Freppo]

I built it today, works like a charm.
I renamed it the Stepping Stone overdrive.

If someone wants to build it the correct pot values should be
Gain: 100k log
Tone: 100K log
Volume: 50K lin

I updated the schematic and the layout to match, i've also made a few minor changes.
Changed the last transistor (Q3) to a BC109B. I noticed that only a few of my 2n2222 few gave a loud enough output. The BC109B made it consistantly LOUD (but still very low noise). :)

EDIT
I will make a new video soon with the updated layout which is a bit louder and bassier

[Freppo]

I made a short soundclip as promised. Please have a listen :)
soundcloud

I don't feel like the soundclip does it much justice though.. Sound so much better in the room. And my playing could be alot better... :P

I played on a Gibson SG though a small cheap vox modelling amp, because all my good amps are in the studio. Tone control was set center (neutral). Distortion on max all the time. I played alittle with the dynamics, it cleans up very well with light playing or backing off the volume on the guitar.

I will do a better soundclip later when I get to the studio.

I would be very honored if someone would build it and maybe write a review. :)

[Silver Blues]

Well if the clip doesn't do it justice then that thing must sound damn good because the clip sounded nice. It has a kind of undertone that makes me think it might make a good bass drive.

Hmm...

[Freppo]

I built it today and boxed it. Tweaked in alittle more,
now the pot values are perfect... Sounds great.

However...

When I plugged in a boost pedal in front of my overdrive (a zvex sho), it killed my pedal  (or at least the j201)... It started to sound very misbiased and sputtery and faded out and died. I changed the J201 and it was fine again.. until I tried it again with the SHO (duh... i'm stupid) and the same thing happened.

How can this happen and how can I solve it? I've been looking a a few schematics with J201's, but I can't figure it out.

I need som help! Mark, Miro, anyone?

[mirosol]

I've ran into the same issue with one of my designs. :)

All JFETs need to have a shunt resistor from gate to ground. Place a 1M resistor there ans your problem should be gone.

As the gate gets saturated with signal, it needs a path to "cool down" so to speak. If you check out any other design with any JFET, there's always a resistor between JFET gate and ground.

Let us know if that fixed it.
+m

[Freppo]

YES! That solved it!

Weird, I tried that yesterday but it didn't work. Tried it again today and voila!
I did use a larger value resistor this time (2.2m insted of 1m), maybe why?

Anyway, thanks Mirosol!
Updated the shematic and layout.

Cheers
/ Fredrik

[mirosol]

Good to hear!

Weird that the 1M didn't work though...
+m

[john]

Sounds Awesome Freppo, really good work. I hope that my creation I've been working on comes out as well as yours when I'm done. BTW, I don't any of the changes on the layout, unless I'm missing it.

[Freppo]

Thanks for the kind words John. I really appreciate it.
I'm very happy how it turned out. :)

Oh, interesting. Please do share when you have it done!

The layout is updated with the new changes (see R11).
I built the new layout yesterday and it's working fine. :)
Sounds great as a bass distortion as well.
When I have time I'll make a video and add some build-pics.

Cheers
/ Fredrik