MusicPCB Echobase build: No sound

[naught101]

Fair enough. The guitar I was testing with has humbuckers, but mine doesn't, so I'll probably just leave it for now. Good to know it's working as intended

Cheers!

[Granny Gremlin]

*sigh*... U3 pin 4 had a cold solder joint, which was even visually obvious after I noticed it via testing. Sorry for the run around, and thanks for all the help, I think I learned a few things about debugging.

Then this is a net positive.  I had the  (same thing on one of mine, which is why I suspected as much.

I can easily get 20 clean repeats. After about 2 O'clock on the feedback knob, I start getting self oscillation, and some crazy cool noises as a result.

Look up the feedback mod (change the 20k resistor below the feedback pot to 100k).  If you do that you'll get more fine control of the repeats and oscillation won't start until about 3-4 o'clock on the dial.  Loves that oscillation. 

[slacker]

Glad to hear you got it working, I was seriously running out of ideas as to what the problem could be.

[naught101]

This thing is awesome. Thanks heaps for the design and PCB slacker and Taylor, and to everyone else for helping out (including Felix at the local makerspace).

Here's a demo:

Sorry about the poor quality - just a phone video.

I'm not sure, but I think at least part of the background noise is from the pedal - the PA's a lot cleaner with just the guitar. It's better if I turn the guitar volume and level up, and the PA down, but then the PT2399 distorts more.

I'm mostly interested in this for making crazy noises that I can record and sample in a DAW. It's gonna be fun. It'd be nice to reduce the noise, but it's totally usable as is.

I'm not really planning on on using it in a live environment much at the moment, but it would be really cool later to have an foot pedal control on the delay time. I guess I could just do that by breaking out a stereo jack that switches off the time pot ground when it's plugged in, and uses a standard expression pedal, is that right?

[Taylor]

Cool! The Time pot is used as a variable resistor in this circuit (2 terminals), and isn't connected directly to ground. To have an expression pedal jack for it, yes, you could use a stereo switching jack and just have the expression pot take the time pot's place in the circuit when plugged in. So your time pot would connect to the tip and ring switch terminals on the jack, and the regular tip and ring connections on the jack would connect to the outer pads for the time pot on the PCB.

In this configuration, the pot value in the expression pedal would determine the max delay time. For it to be the same as the time pot, it would need to be 50k, which I think the Moog expression pedals are. A larger value would mean longer delay times (with lower audio fidelity) were possible at maximum.

You could make it voltage-controllable instead by using the switching jack to switch between the LFO and your CV going into the Mod Depth pot. Could probably get some weird noises by patching a control voltage from the Microbrute there (key tracking of delay time or send a VCO there for audio rate modulation...)

[naught101]

That sounds awesome. I think I will eventually do that, but I've got a PhD to work on, so I might get as much use out of it unmodified as I can first

I was wondering about the modulation. It basically just sends a (triangle?) wave to the time pot, which is roughly equivalent to wiggling the time knob back and forth, right? What's the range that it sweeps? Maybe 10-15 degrees (=±50% delay time?), on maximum Mod Depth? And that range could be increased by lowering the value of the Mod Depth pot, right? 

Yeah, I was wondering about CV input. I was thinking of having it modulate the time directly though, not modulate the modulation. Especially since the Microbrute also has LFO and ENV out (both 5V). So the possible values at the VCO pin are ~0-5V? And is that roughly the range/amplitude of the mod wave, too? or is that 9V? If it's 9V, then CV is only going to have half the range of the modulation, isn't it? So it might need a transistor+resistor to boost it up a bit?

[Taylor]

That sounds awesome. I think I will eventually do that, but I've got a PhD to work on, so I might get as much use out of it unmodified as I can first

I was wondering about the modulation. It basically just sends a (triangle?) wave to the time pot, which is roughly equivalent to wiggling the time knob back and forth, right? What's the range that it sweeps? Maybe 10-15 degrees (=±50% delay time?), on maximum Mod Depth? And that range could be increased by lowering the value of the Mod Depth pot, right? 

The modulation goes to a transistor, the emitter and collector of which are in series with the time pot. I'm not sure what the maximum modulation amount is, perhaps slacker could answer that. I think a better way to increase the mod range would be to decrease the value of the 240k resistor that feeds the mod depth pot.

Yeah, I was wondering about CV input. I was thinking of having it modulate the time directly though, not modulate the modulation. Especially since the Microbrute also has LFO and ENV out (both 5V). So the possible values at the VCO pin are ~0-5V? And is that roughly the range/amplitude of the mod wave, too? or is that 9V? If it's 9V, then CV is only going to have half the range of the modulation, isn't it? So it might need a transistor+resistor to boost it up a bit?

I think you misunderstood me - I didn't describe that in such good detail. What I meant was that your CV would replace the signal coming from the LFO when a plug is in your CV/expression jack. So the CV would control the delay time. That's the simplest way to do it because otherwise you'd need to add an active mixer stage to mix the CV with the LFO to have them both simultaneously. I recall that it's technically possible to just stick CV right into the time pin on the 2399 (as in the Modulus Magnus IIRC) but this is more experimental territory.

The LFO is not quite in a normalized range like 5v or 9v. It's probably closer to 2 or 3 volts peak to peak, again slacker probably has a better idea than I do here. So feeding your 0v-5v signal in will probably clip the waveform so you'd want to attenuate it, but if you use the scheme I described, the mod depth pot would work as a CV attenuator.

[slacker]

Great demo that Microbrute looks like an interesting bit of kit

The way the modulation works is the PNP transistor acts like a voltage controlled resistor, as the voltage into the base increases the resistance increases. This only works over a certain range, once the voltage at the base goes above a certain level the transistor is completely off and its resistance doesn't get any larger. There's two ways to increase the amount of modulation you can decrease the value of the 240k resistor like Taylor suggested, if you make this too small you'll run into the issue mentioned above, this will be pretty obvious the modulation will sound lumpy as you're basically chopping the top off the triangle. The other way is to increase the value of the 39k resistor in parallel with the PNP transistor, this sets the maximum resistance the transistor will sweep to, I'd start there.
A 5 volt CV works fine, a few diy synth guys built CV controllable versions, basically disconnect the clockwise lug of the modulation depth pot and feed your CV into that lug through a resistor. Start with say 10k and adjust it until with the modulation pot on full you get the maximum range you want.

[naught101]

Awesome. I may be back in a few months with more questions