I've narrowed this down to a combination of power noise and current draw from the TAPLFO chip.
I was building another Tap Tempo Cardinal today and I ended up with the dreaded ticking in square wave. Hadn't experienced this with the first build, so this was a good time to look for a solution.
The first thing I did was start poking around with a cap. I strapped a 100uF across the +5 to ground and that killed some of the noise.
The Tap Tempo Cardinal has a 47R as a filter resistor. I jumpered this and it killed most of the noise on its own even without the cap. I've updated the build doc for that.
I suspect that jumpering R15 in the twin peaks might help as well. Someone else who has one built might want to experiment.
A better solution is to keep the 47R (or whatever value) resistor, but tap off before this to feed the voltage regulator - you get better filtering of the analogue circuit. Something like the power section of this:
https://dl.dropboxusercontent.com/u/11996927/ACE_Tremolo_2_Schem.jpg
I have also found that if you round the corners of the square wave just a little bit, then it can make a big difference too, without sounding any different. This is done in software, but if you flash you own chips, this is a relatively easy 'fix'.
Hi Jon,
This sounds interesting. I can't check the Cardinal schematics at the moment as google docs are blocked here at work.
The resistor you are jumpering is in the power supply filtering, right ?
The R15 resistor in the TP you mention seems to refer to an older version of the schematic.
I presume it's the one listed as R12 in this build doc?
http://www.davidrolo.com/wp-content/uploads/2014/11/Twin-Peaks-Tremolo-2.1-build-doc.pdf
I am a bit puzzled about what jumpering that resistor does, as I thought it would help decouple the power from the audio path's power?
In any case, well worth trying out, especially the bigger cap on the regulator's output.
Thanks for sharing
Looking forward to reading this thread. My Twin Peaks 'thumps' hard in square wave. I was able to fix it by changing the offset, but that drastically changed the bias (it wasn't even close to 50/50).
Dave: Yes, R12 in that schematic most likely. You could say that the resistor provides some isolation for the power supply, but there's resistance across the 5V regulator, too, and your filtering is after the regulator (as it should be). The 33R is adding a voltage drop to a part of the circuit that draws FAR more current than anything else in the circuit.
Again, I'm just speculating for your design. In the Cardinal, the LEDs are connected to the +9V supply, whereas you have three different power rails in yours.
Samhay: Unfortunately it's not an option for me on the existing PCB. Given the current requirements of the Cardinal's dry path, though, the 47R isn't trivial there, so in my case it actually improved the whole thing to just leave it off.
The fact that not everyone encounters the problem makes it a bit more of a mystery.
Fair enough, and something to try for version 3.
I wonder if the degree of ticking might depend on the LED(s) used. Some have much higher capacitance than others, which will help to smooth out the spikes in current draw.
Quote from: midwayfair on April 18, 2016, 09:33:04 PM
The fact that not everyone encounters the problem makes it a bit more of a mystery.
Yes, weird indeed. In any case this is well worth trying next time I hear someone complaining about it. Thanks for sharing!
Thanks Jon, I am going to pop my Twin Peaks back open this weekend and give this a go. As of right now, I still have a little bit of ticking in the Black Face mode.
Cody
Quote from: selfdestroyer on April 19, 2016, 03:52:11 PM
Thanks Jon, I am going to pop my Twin Peaks back open this weekend and give this a go. As of right now, I still have a little bit of ticking in the Black Face mode.
Cody
Oh! I should note: The only ticking in my original (and in the one I just built now) is when I'm actually playing. I do hear a little click on the attack of the waveform if there's any signal running through.
Quote from: midwayfair on April 19, 2016, 04:47:09 PM
Quote from: selfdestroyer on April 19, 2016, 03:52:11 PM
Thanks Jon, I am going to pop my Twin Peaks back open this weekend and give this a go. As of right now, I still have a little bit of ticking in the Black Face mode.
Cody
Oh! I should note: The only ticking in my original (and in the one I just built now) is when I'm actually playing. I do hear a little click on the attack of the waveform if there's any signal running through.
Noted. Mine is the same if I remember right... I have been having so much fun with the Bass & Treble modes that I almost forgot about the BlackFace mode ticking.
Cody