Park Auto-Wah circuit modifications

[sharaynishi]

Hello, I have recently made one of these from : https://1.bp.blogspot.com/-GUWyUx9T064/YD6NrmVpTZI/AAAAAAAAEO8/inksXLNZmKEOvvwBKEexVw0ul5DyDpqAwCLcBGAsYHQ/s1062/Park%2BAuto%2BWah.png

It's an alright circuit, however the slowest speed of the lfo is too quick for me and I'd like to tame it down even more. Do any of you have an idea which components should I alter to achieve that effect?


Looking forward to hearing from You.

[induction]

Try increasing the value of the speed pot to 100k. That should increase the speed range to include slower speeds at the bottom of the pot range, but will retain the faster speeds at the top of the pot range.

If you want only the slower speeds, keep the 47k pot and add a fixed resistor in series with the pot. You can experiment with values to get the range you like.

[sharaynishi]

Hey, thanks for your quick response, however, I already added a 100k pot in hopes that it will help, but if I'm not mistaken it's the same, except the speeds just get faster.

[induction]

1. Is the speed pot connected on lugs 2 and 3 only?
2. Does the speed increase or decrease as you turn up the pot?

If the speed increases when you go up to 100k, you probably have an error in your build. If you post photos, maybe we can help.

[sharaynishi]

yes legs 2 and 3 are connected and speed increases when i turn it up. the build works fine, i need to change something else probably :)

edit: messing around with 22k resistor connected with Q4 Base + Pot 3. It changes the speed when i put a higher value resistor than the stock 22k one

[induction]

If the lfo gets faster with a bigger pot, then the build is not working correctly. But if you're happy with it, that's what matters.

You can certainly increase the 22k resistors connected to Q3 and Q4 bases. I would keep them equal to each other so the lfo doesn't get washed out. By the way, this is electronically exactly identical to increasing the speed pot. Just saying.

You can also reduce the speed by increasing with the 4k7s and/or the 2u2s in the bottom right corner of the layout. Again, I would keep them equal to each other for best results, but you can obviously do it however you like.

Here's the schematic in case you haven't seen it.


The LFO is the subcircuit on the bottom-left. Note the symmetry in R12/R13, R14/R15, C9/C10. Note also that R12, R13, R14, and R15 are in series with the speed pot. They serve the same function. The circuit can't really tell the difference between changing those resistors and changing the speed pot.

[sharaynishi]

Damn. Thank You for the technical explanation on how it works.
Uum I have socketed that resistor and attached a switch with two different resistor values and did get a "slow reggae"  setting and a fairly quick/standart ones, but I have noticed that the circuit has behaved differently and the lfo indeed became as You've stated - washed out.

So these "mods" were more like weird downgrades lol.

So what You're saying is I should probably stick to the stock 22k which makes sense as it's identical to the ones working along with the other transistors, right? that will at least make the most usable lfo range.

As for the 100k pot I think it did make a difference from the first one i tried which was 50k, but it was still too fast or barely different to 50k for whatever reason.

[induction]

Glad to help.

It's hard to say for sure without a demo, but if you think the LFO is not slow enough at 100k, there might be an issue with the build. If any of the components I mentioned in my last post have bad solder joints, the LFO speed could be affected. Here's a demo video you can use to compare the speeds that should be available with a 50k pot:

You can try a 500k speed pot too. It should slow things down noticeably at the low end of the pot range. You might not want to keep it, but it's worth a try just to make sure the build is behaving as expected. You could just as easily sub a fixed 470k resistor for the pot as a quick test.

If you'd like to mess around with the fixed resistors or caps in the LFO, it's totally fine. Those values are just chosen to get the speed range you want. It shouldn't hurt the operation of the circuit to modify them, as long as you keep the symmetry. That's what happens when you change the setting on the speed pot anyway. I just recommended changing the pot value because it's quick and easy.

[sharaynishi]

Yep, it sounds very similarly to what it sounds like in the video, I just don't find even the slowest setting usable all of the time, so I wanted something slower, for more variety.

So if it all seems to be working as expected I should just try using a bigger value pot (250k+) and that should be good enough.

[sharaynishi]

Hello. Just tried a 250k pot and the circuit seems to be working fine + I get slower speeds + it doesn't make the lfo sound like shit.

So I basically caused this mess of a thread by being a dumbass.

Thanks for helping out, I'll also try slightly higher values for the remaining 2 pots.

[induction]

Good work. I'm glad you got it how you want it, and I was happy to help.

Don't be hard on yourself. This kind of exploration is how you figure this stuff out. Plus now other folks can read it and benefit from your exploration. The system is working as intended.