Auto wah

[deadastronaut]

^ cool, do you have the schematic that includes the decay mod. ? as i prefer pcb.

[induction]

I used the schematic from the other forum (the thread is long, so it's easier to find it at Revolution Deux). There's a pcb layout as well.

But I didn't mod the decay section, it works great as is - nice range of decay speeds. The only mod I did was to replace the 20k resistor in front of the sensitivity pot (R18 on the schematic) with a 47k to give a better range of sensitivity. There are other mods on the other forum on page 14 of the thread. I tried them on the breadboard but didn't include them in my build.

[Kipper4]

cool i might have to socket the R18 and try it when i build mine.
This is going to be my most exciting build to date. I cant wait.

[Pojo]

Or taking a leak during a solo. That sets them wild!

[jvanginkel]

i just built a couple of the Snow White Auto Wahs on veroboard from the sabrotone website. I'm so happy with them. I did the revolution deaux mod on one and not the other. I did the decay pot resistor change on them both. I'm very happy with how they turned out. Here's a video of both of them if you're interested.

Joel

[disabled_shredder]

Man those sound nice! The first licks were reminiscent of a gig I played in Germany for the us army command Christmas party. Very smooth.

[jvanginkel]

What an opportunity! I get to play one of those pedals tomorrow night, but its not quite the same as playing for the military commanders. I get to play at a Christmas carnival for my oldest son's elementary school (I also get to play at church every weekend, which I love). Thanks for the kind words.

[Mark Hammer]

The stock Snow White appears to be wired as a lowpass filter.  Don't quote me, but I think - using the schematic shown here http://revolutiondeux.blogspot.ca/2012/07/mad-professor-snow-white-auto-wah.html - that if C9 on the output path is lifted from where it currently is and is connected to the output of the first stage (i.e., the junction of R14 and R8) it will be a bandpass filter, instead of lowpass.  Lowpass is better for bass, but bandpass has its delights too.

here's the schem for the DOD FX25, which configured as a bandpass.  See the similarities?:

[tranceracer]

Very nice job, sound great and lots of control over the tone!  Thanks for the video, VERY helpful.  

My Boss T-Wah (which I loved) died and I'm looking to build one of these too.  Noticed a little distortion when the Resonance was cranked and at 2:39.  Was that from the amp, camera, or the pedal itself.  Not a deal breaker for me because I use the auto wah very subtle to get that Schenker open wah tone.

Btw, liked your "phunky" riffs!   ((:

[disabled_shredder]

Mark could you link to the fx25 schem I cannot see the photo on my phone. Thanks.

[Kipper4]

Yes please Mark that would be really helpful
Let me also see if i can find it.

here we go

http://topopiccione.atspace.com/pjimages/DODfx25.sch.gif


from this thread


http://www.diystompboxes.com/smfforum/index.php?topic=66837.0;prev_next=next

[Mark Hammer]

Mark could you link to the fx25 schem I cannot see the photo on my phone. Thanks.

I thought I pasted the link properly.  I think I fixed that now.  See earlier post.  It<s the one at the topopiccione site.

[jvanginkel]

Very nice job, sound great and lots of control over the tone!  Thanks for the video, VERY helpful.  

My Boss T-Wah (which I loved) died and I'm looking to build one of these too.  Noticed a little distortion when the Resonance was cranked and at 2:39.  Was that from the amp, camera, or the pedal itself.  Not a deal breaker for me because I use the auto wah very subtle to get that Schenker open wah tone.

Btw, liked your "phunky" riffs!   ((:

Thanks for the reply. I'm glad the video was helpful. At the 2:39 mark of the video I have the sensitivity cranked all the way back so that the bias is working like a sweep filter. It is just woolly sounding because the envelope won't open, it doesn't sound distorted in real life. I can hear how it would sound distorted on the video. That being said, with the resonance cranked, it is much sharper and quackier. It has a better chance to distort in that setting. I like making the pedal more sensitive, rolling the resonance back and bringing the bias to about 9'oclock. Then the effect is more subtle and less dominant. It is so smooth and it reacts a lot to your pick attack, volume pot, and pickup selector, although I did not adjust those at all in the video. If you do want to build this effect, I found BC550c transistors at mouser, and I also bought some from a guy in Romania! There is no audible difference between the two.

[jvanginkel]

I wanted to tune one of these for use with bass guitar. Does anyone know how to mod this circuit to fit better on bass? It's not great as is.

[Mark Hammer]

You can change the overall range of the filter by varying the values of the two .022uf caps to ground in the filter portion.  Make them higher (e.g., .033uf) and the corner frequency range is bumped lower.  Make them a smaller value, like .015, and the range is bumped upwards.  The general rule of thumb in such matters is that doubling the value shifts things down an octave, and halving them shift it up an octave.  Since there are no .044uf caps out there, you may find that 47nf (.047uf) may work better for bass.  If it's too dark, move to .039uf.

[jvanginkel]

Thank you so much. I could just add another .022uf  in parallel. Maybe I'll start there. Thanks for the quick response. I need to donate to this forum.

[Mark Hammer]

My pleasure.  Remember, BOTH of those caps need to be increased in value, not just one.  You probably knew that.  I just didn't want anyone else reading this to misunderstand what you wrote and end up doing the wrong thing.

[jvanginkel]

I see how what I wrote could be misleading to someone. Is there also a resistor in this circuit that could speed up the decay pot overall? I've seen another autowah discussion about that.

[Mark Hammer]

The decay time can actually be made pretty fast already, though if a person wanted it to just come and go pretty quick, replace the 2u2 cap to ground i parallel with the decay pot with a smaller value, like 1uf.

[jvanginkel]

Thanks for the decay info. As for the filter caps,  I put the .047uf caps going to ground in place of the .022, and it made a huge difference. I only have my telecaster and a fender champion 600 to test it at the moment, so all I know is that its much deeper. Looking forward to plugging in a bass and not relying on a 6" speaker to determine what I'd prefer.