Repeat Percussion troubleshooting

[induction]

I did steps 3-5 slightly differently:

3. kept 33R in place
4. 1K changed to 2K
5 3K9 from B2 to B1

I guess it amounts to roughly the same thing. I'd trust R.G. over me, but this worked very well.

I ended up using the MU4892 for no reason other than pure mojo.

[nocentelli]

Many thanks, Gentlemen. My usual cheap UK supplier sells 2N6027s at 25p each, so I'll definitely give this a try.

[R.G.]

I did steps 3-5 slightly differently:
3. kept 33R in place
4. 1K changed to 2K
5 3K9 from B2 to B1
I guess it amounts to roughly the same thing. I'd trust R.G. over me, but this worked very well.

There are generally many solutions to a design problem that will work fine. The resistors you used for the gate divider are less than a 4% difference from the 2.7K and 4.7K I used, smaller than the typically 5% tolerance of the resistors. What matters in this case is the voltage on the divider, and that's almost identical. It works with the 33R in place, but I liked the timing better without it. My solution's no better than yours.

[induction]

That's good to know, thanks.

I don't want to take credit for the solution, though. I got those values from Moosapotamus. I should have mentioned that before.

[Gavanti]

So I took out R5 and ran this through a couple of pots set up as trimmers and then pulled those off and threw various resistors on the lead wires to see if that would work. Nothing doing. The fault seems to be either something I haven't found in the build yet or faulty UJTs. I'll order a few more (and some PUTs to boot) and go ahead and rebuild the circuit. One way or another, I'll get this working. You've all been super generous with your comments. Thanks.

[kaycee]

On thing if you do get it going is be prepared for it to tick, I spent weeks trying to stop my builds from ticking but nothing would shut it up completely.

It is *possible* to do a non-ticking version. The secret is to realize that all wires are resistors, and that current through a resistor makes a voltage.

The tick comes from the sudden discharge of the timing cap through the 33 ohm b1 resistor. If any part of the analog circuit, including the modulator transistor, shares any part of the copper trace between the capacitor negative and the 33 ohm resistor, it will tick, and nothing can be done about it. The fix is to make that current path have one and only one wire back to the power supply negative.  If the tick changes the + power, that will tick as well, but there is already good decoupling on that.

So, I've been thinking about this for a couple of days trying to get my head around it. The capacitor negative goes to ground, so does the the 33 ohm resistor, so how can I keep them apart?? Grounds all connect don't they?

My build of this is haunted  I've tried multiple ways of multiple layouts and not got rid of the ticking, I've had a pot go bad, and most recently the footswitch crapped out.....still, the box looks nice

[nocentelli]

On thing if you do get it going is be prepared for it to tick, I spent weeks trying to stop my builds from ticking but nothing would shut it up completely.

The tick comes from the sudden discharge of the timing cap through the 33 ohm b1 resistor. If any part of the analog circuit, including the modulator transistor, shares any part of the copper trace between the capacitor negative and the 33 ohm resistor , it will tick, and nothing can be done about it. The fix is to make that current path have one and only one wire back to the power supply negative.  If the tick changes the + power, that will tick as well, but there is already good decoupling on that.

OK, I understood this to mean that the smaller electrolytic (the one connected to the emitter [for UJT] or anode [for PUT]) and the 33 ohm need to share a copper trace, BUT nothing else should share this trace, and that this trace should be connected directly to the power negative, and all other grounds use a different wire to connect to power negative. This seems to be borne out by my limited breadboard tinkering so far.

[R.G.]

So, I've been thinking about this for a couple of days trying to get my head around it. The capacitor negative goes to ground, so does the the 33 ohm resistor, so how can I keep them apart?? Grounds all connect don't they?

It is hard to get clear in one's head. There is one huge thing you need to get clear first before thinking about grounding issues. That is:

==> ALL WIRES ARE REALLY RESISTORS. <==

They're low-value resistors, but resistors none the less. They will always generate a voltage of V = I * R when a current flows through them.

If you have sudden spiky currents of any size at all, you generate sudden, spiky voltages. That's your tick. If your amplifier circuits are on the side of the ground-resistors that have this spike, you get a tick.

The way to separate them is to move the capacitor negative as close to the ground-side of the 330 ohm resistor as you can. When the UJT fires, current flows in a loop from capacitor + through the UJT, through the 33 ohm resistor, through any "ground-resistor" and back to the capacitor negative terminal.

You want them connected tightly together, with one and only one wire from there to the signal circuits, for a zero-voltage reference only.

[nocentelli]

Built this veroboard version of Moosapotamus' modifed VRP ("Skippy"), hopefully correctly utilising RG's anti-tick advice. There is a very small amount of ticking audible when not playing with the depth up high, but on par with my smallstone in terms of tolerable background noise. There is virtually no plosive tick when actually playing, which is what i was really after. I grounded all points (e.g. volume pot, depth pot, power negative and "DIRECT ground" (LFO) together on the input ground.

[Gavanti]

Just resurrecting this one to say thanks. I got the RP working (picked up some pre-tested UJTs from a guy in Vienna and rebuilt the circuit). The thing beats like a drum, and it's now housed in the pedal at the link, which has been super fun to play. Someday, I'll learn to wire cleanly. Until then, no internal pics. At some point, I'll have to work through the original circuit again to see if I can sort out the problem. In the meantime, I owe y'all for the education.

https://www.dropbox.com/s/v6amzx0t17865g9/photo%20%288%29.JPG

[Luke51411]

I'm thinking about building the vero layout that nocentelli posted as I have just built the tagboard effects layout and I'm not happy with the amount of audible ticking. I've modded the tagboard layout some to remove some of the ticking but there is still entirely too much. On my build, the depth pot doesn't have much control and lowering it makes the ticking louder. The lower half of the pot travel does nothing as the depth has bottomed out. Is that normal with this circuit? I'm also curious as to how much tick this layout eliminates. On my build the ticking isn't bad at slower settings but is audible throughout.