Special Sauce mk. II [Chorus, Doubler, Slap Back, Vibrato]

[Aleph Null]

While I was very happy with the circuit, I was never happy with the finish on my original vero build. Having decided to learn to design PCBs, this circuit seemed like a good candidate. The thread on the original goes into details about the circuit, but basically it's a short delay with envelop control pitch bending. This makes for unique chorus, doubling, slap back, and vibrato effects.



The enclosure is a Love My Switches limited run. The face plate is a one-sided aluminum PCB from JLCPCB.



The face plate made finishing a breeze and makes it easier to hide mis-drilled holes!



I've been experimenting with ribbon cable and am liking the results. I'm considering making daughter boards for bypass and inputs for future projects to streamline things further.



The circuit is unchanged except for the boost section. The boost has been revoiced to cut frequencies below 140Hz or so. At the lowest setting, there is no frequency cut. The boost gets "brighter" as the gain is increased. This keeps things tight when boosting into an overdrive or dirty amp.

Here's the original demo.

I have extra PCBs and face plates. If anyone is interested in building this, please DM me.

[BricksnBeatles]

Super interesting build! I love 2399 based modulation. Sounds nice

[jessenator]

very nice indeed

intrigued by the envelope modulation; sounds great

[gordo]

Very cool to see something different.  The pedal itself is cool enough but also a great demo and very creative presentation.  I'm very intrigued with the envelope control.

[sethwitz]

Hey there! I made your original version using the stripboard layout you provided. The circuit sounds really great! Not sure if you're looking for any feedback or not. Let me know and I'd be happy to share some additional thoughts.

[Aleph Null]

Hey there! I made your original version using the stripboard layout you provided. The circuit sounds really great! Not sure if you're looking for any feedback or not. Let me know and I'd be happy to share some additional thoughts.

I'm glad you like it! I'm definitely open to feedback.

[sethwitz]

Hey there! I made your original version using the stripboard layout you provided. The circuit sounds really great! Not sure if you're looking for any feedback or not. Let me know and I'd be happy to share some additional thoughts.

I'm glad you like it! I'm definitely open to feedback.

Before I make any remarks, I'll note that I had to make two substitutions in my build based on what I have on hand:

• I had to use a 33pf in place of the 20pf
• And I had to use an A20K pot for the Mix control

I'm not knowledgeable enough to know how significant of an impact such changes would make, so my apologies if the feedback below would be addressed if those substitutions hadn't been made.

First of all, I love the sound of the circuit when the Boost is full CW. It reminds me a lot of the flavor you get when adding either tape or tube saturation to the signal (e.g. what you'd get from either an EP-3 boost or an Electra-style circuit). If possible, I think it would be really cool if this circuit made it possible to crank the Boost and get that same chewy overdrive/fuzz sound without adding more decibel output (kind of like a Speaker Cranker). I'm not sure how complex that kind of tweak would be, but it would be really sweet. Could also be cool to have a toggle switch to engage or disengage a decibel boost when the Boost knob is cranked. More parts/complexity though, of course.

For the 100% wet setting, I wasn't getting much modulation when Lag was set all the way CCW. I wasn't sure if this was because of the substitutions I made or if it has to do with the PT2399 chip I used. I've heard those can be somewhat different from chip to chip. Having made other PT2399 delay/chorus/vibrato pedals (e.g. the Deluxe Pitch Pirate), I'm familiar with the fact that there's only so much modulation you can crank out when the delay time is set to its shortest setting. Nonetheless, the modulation on this sounds exceptional when additional delay time is introduced. The vibrato is definitely chewy and the chorus very lush. If there's any way to bump the modulation at that shortest Lag time, that would be sick.

Overall, this is a really, really great circuit and I'm definitely going to box it up. I think I can fit it into a 1590B with top-mounted jacks. It really succeeds at each of the functions you've listed: chorus, doubler, slapback, and vibrato. Thanks for making this available!

PS: On your vero layout, I think you might have a minor typo. There's an electrolytic capacitor labeled as "100nf" and I think it's supposed to be "100uf."

Cheers!

[Aleph Null]

Thanks for the feedback. It's wonderful to know that other people are making music with something I made!

To make things easier to track, and since the vero and PCB version are basically the same, I'll use part designatioins from the schematic posted here to refer to parts.
 
The Substitutions
The substitutions you made shouldn't change much and definitely won't impact the vibrato. The 20pF capacitor, C6, forms a low-pass filter with R6. This starts rolling off frequencies above 8kHz or so. The 33pF cap will start rolling off at 5kHz or so. This is a gentle filter and is just there to minimize any artifacts in the delayed signal. Depending on your amp and cab, you might not be able to hear the difference in these two values anyway.

The Mix control value isn't super critical either. If the value is too low, you won't be able to get full dry or wet signal at the extremes. If the value is too high, all the action is in the middle of the sweep and you get dead spot at the extremes. 20k should work just as well as 25k.

The Boost
The boost section is somewhere between a ZVEX Super Hard On and an Orman Mosfet Boost. It can get gritty like the ZVEX, but turning the knob doesn't cause the circuit to crackle. You could add a volume control to the end of the circuit by omitting R11 and putting an A100k pot in it's place: connect the original output to lug three, lug one to ground, and lug two becomes the new output.

The other option would be to slap some diodes front to back at the end of the circuit (like a Speaker Cranker). You could omit R11 in this instance too.

The Vibrato
This design is different from others in that the modulation is actually strongest at lower "Lag" settings. Every guitar and guitarist has a slightly different envelope, so the envelope response will be a slightly different. I used a guitar equipped with PAF-style humbuckers for the demo. Lower-output pickups, like most single coils, won't pitch bend as much, for example. 

That said, there are a few parts you can tweak to get more out of it. VR1 (the "Detune" control) and Q2 (the 2N5089) have the biggest effect on how much pitch bend you can get. The gain of the transistor effects how much pitch bend it can produce in the circuit, so a transistor with a higher hfe rating will produce a stronger effect. Sommething like a 2N3904 will work, but will be mild compared to a 2N5089. You might audition different transistors to see if you can find one you like best.

The "Detune" control, VR1, moderates the effect Q2. Larger values will give you more vibrato. I found 5k to get pretty seasick. 10k was capable of full octave drops in some settings. You might find that one of these values is just right for you.

The Enclosure
It'll probably fit into a 1590B, but I haven't measured.

The Typo
Yep—that's a typo; it should be 100uF, not 100nF.

[sethwitz]

Thank you for providing such a detailed response—this was very helpful! I'm relieved to hear that the 33pf and B20k substitutions were alright to do.

I followed your suggestions and wound up swapping in a B5k pot for Detune and adding 3 1N60P diodes at the end of the circuit. The Detune effect is much more pronounced now when Lag is set to a minimum. And good call regarding the impact of the output of the guitar pickups by the way! I play a Tele with lower output single coils, so using a B5k made a very nice difference. I'm really pleased with the effect. I might even try seeing what kind of chaos comes out with a B10K in there.

As far as the Boost section is concerned, there's still a decent increase in volume when Boost is all the way CW, but certainly less so that with the stock set-up. I goofed and didn't realize that the 1N60P diodes I have are *not* the same thing as the germanium 1N60s that were used in the Speaker Cranker, so that probably explains the issue. I might play around with some other diode options to see if I can limit the volume boost a bit more, but I'm more inclined to simply add a master volume pot.

All in all, great circuit here. I'm really looking forward to boxing this one up and putting it on a pedalboard!

[Aleph Null]

I'm glad I could help you get it dialed in! Are you going to to a build report once it's boxed?

P.S. If you want real chaos, disconnect the Detune control entirely and play hard choppy chords—you'll get wet robot farts!

[sethwitz]

I certainly can! I'm unfortunately not yet good at designing artwork for enclosures, so it'll likely be a plain spray-painted sort of affair. I'll try to get a build report and demo up this coming week.