SWAH v5 Build Notes & Mods

[Cybercow]

Just got in a couple of GuitarPCB ‘SWAH’ boards and built one of them out with some sockets in special locations for conducting some listening audits to check how to get the best SWAH-ish-ness (“quack”) from this circuit.

I was able to futz around with one of the SWAH (v5) builds today. I socketed D3, D1 & D2, and R17 to test various things.

I went with the BOM initially – except R17 – in which I socketed a 47K resistor and proceeded to do some listening/plectrum tests. D3 was a socketed 1N34A @ 0.33v Fvd. D1 & D2 were socketed 1N914/1N4148s @ ~0.78v Fvd.

That formula works well and I was able to easily find the sensitivity adjustments within a somewhat wider range than when I swapped out the 47K at R17 for the 22K (BOM suggested) resistor. I went back and forth a couple times with the 22K and 47K at R17 and with both my single-coil and humbucker settings, the best pedal circuit performance found with the 47K at R17. R17 really needs to be 47K – not 22K as suggested in the BOM. (And yes, I saw the mod notes in the build document on this element and agree – 47K is better than 22K at R17.)

On to the next tests with regard to D3 . . . .

I found the Vfd of a true germanium 1N34A (and other low Fvd valued Ge diodes) to work best here. Using some of my high Fvd valued germaniums (~0.75v to 0.88v Fvd) provided the same poorer performance response as 1N914/1N4148 diodes. Again, I went back and forth between hi and lo Fvd values and the lower the Fvd, the better the SWAH-iness – or “quack”. So I get the idea that the lower the Fvd of D3 the greater the emphasis on the effect. Higher Fvd values there tend to diminish the overall effect – as in “less wah-ish-ness”. (IMO)

Now regarding D1 & D2 . . . . .    I know you didn’t ask anything about those two diodes, but I thought: “What the hell. Let’s futz with shit!” After the above mentioned tests, I left R17 socketed with a 47K resistor and D3 socketed with a 1N34A @ 0.33v Fvd and proceeded with the following changes to D1 & D2 . . . .

The BOM calls for 1N914/1N4148 silicon (@ ~0.7v Fvd) at D1 & D2 and changed them first to 1N34As and the overall effect went to hell. It seemed to result in an extremely minimalist auto-wah effect and the ‘quack’ was definitely less defined. So I went in the other direction with regard to the Fvd of D1 & D2 and socketed a pair of red LEDs @ 1.88v Fvd (matched). I’m convinced that using LEDs for D1 & D2 is a superior choice as they seem to open up amount the ‘quack’. Thinking I was fooling myself, I swapped back & forth a few times between the 1N914/1N4148s and the red LEDs at D1 & D2 to be sure. I definitely like the red LEDs in D1 & D2 better than 1N914/1N4148s. The difference is subtle – but noticeable.

So, bottom line on a primary concern about D3: Yes! I find the lower Fvd of a 1N34A or other low Fvd valued germanium does a very good job of clarifying the ‘quack’ and makes for a better overall “SWAH-ness”.

I also tried the new SWAH with low voltage 9v (about 7.5v) battery. The SWAH still worked, but with a bit less ‘quack’ and requires a softer touch on the plectrum. So a 9v wall-wart or DC brick is recommended.

I’ve yet to complete the enclosure, but wanted to share these build notes/findings for the new SWAH v5 circuit.

 

 

This last photo is the second PCB without sockets for D1, D3 & D3. R17 is currently socketed, but I will remove the sockets and insert the 47K resistor there directly.

[Barry]

The SWAH Build Document has been updated to have a 47k at R17. No Mods.

Thank you for taking the time to do some testing for me. That is an excellent report on your findings.

[Anonymous]

Can I ask where the PCB for that test rig came from? That is cool.

[Barry]

[Anonymous]

Yeah, I have a couple test rigs setups but none that fancy.  Aside from having an audio probe option, the one PCB rig I have doesn’t do much else aside from keeping everything organized and compact…which can be solved by building it into an enclosure without the PCB.  The only other thing I have added to one of mine is a voltage sag pot.  But the one in the picture…tone generator, charge pump, audio probe…my eyesight is not good enough to tell what the sockets and jumpers are for.  Pretty cool, indeed.

Also…great information on the SWAH circuit…thanks!

[Cybercow]

Barry – thanks! And you’re welcome!

For those asking about the test rig . . . . .

Please remember that this forum is primarily about GuitarPCB build support and camaraderie. With that in mind, I’ll tell you.

There are no jumpers really. Just some unused direct access points for sockets. The existing sockets are redundant connection points for ‘In’, ‘Out’, ‘V’ and ‘Gnd’.

About 3½ years ago, I was going to conjure my own testing board/jig and was looking for bits and pieces of schematics from which to compile a comprehensive test rig. But then I bumped into Fuzz Dog who had already done the very thing I had in mind. Before covid hit, getting things from the the UK and elsewhere in the EU was easy. Now it’s stoopid expensive to get things from across the pond. I paid $15 for just the PCB (including shipping back then) and built it out myself. Now the shipping alone is over 25 bux. Hopefully, Barry will eventually acquiesce to designing such a test rig of his own to add to his delightful selection of pedal project boards. You know, for his state-side clientele. 😉

But more importantly, I find it more excitement getting to work with Barry on some of his projects and be (one of) his “Guinea pig” builder(s)/tester(s). I’ve always loved experimenting with circuit bending or just futzing around to find what works best. And Wilkie is always around for questions, answers & ideas also working closely with Barry. I’m sure there are others in the fold, but I’ve yet to identify or meet them.

Oh, and here’s the final photo of the build without any socketed components. I settled on a 1N34A for D3, a 47K for R17 and a pair of matched red LEDs (@ 1.88v Fvd) for D1 & D2. I’m not using R31 or D6 as I will be using one of Barry’s “Variable-Brite” 3PDT Wiring boards for the stomp & bypass LED.

[Steve]

I built this minimalist ‘breakout box’ several months ago but would gladly pay for a PCB like that one if/when Barry deemed it a good investment to add to his repertoire of most excellent PCB’s! 

[Anonymous]

I would be in on a test rig PCB also…if nothing more than to continue down the one (or more) of everything path.  Add a silent relay footswitch board to that wish list too…

[Anonymous]

Hi, This is Martin sending greetings from Bavaria.

I have a question to the SWAH Forum.

I just finalized the SWAH and it works great with a guitar – I am a Bassist though.
Can anybody help me figuring which components to alter to make it properly working in the frequency range of a bass?

Thanks, Martin

[Barry]

Martin the SWAH should work fine with a standard Bass. However that is not always the case anymore. You could change C1 to 68n so this will match the coupling capacitor at C7 and will allow more instrument frequencies through. Furthermore you could build the pedal using our Buff N Blend circuit and Blend in as much full signal as you need. This can also be done with any guitar pedal circuits using our ParaMix.

[Anonymous]

Hi Barry, that was exactly the hint I needed. Moving C1 to 68n “opens up” the Bass’ G-String. I did 100n and then 220n which “opens” also the A-String. I will keep testing and move also C7 to higher values accordingly.

[Gavin]

So I just finished this build, and socketed D1/D2 and tried with leds. I like both. If I wanted to hook up a switch here to give me both options, how would I do that?

Thank you

[Author]

Posts