tonepad rebote 3 modulation section

peterg · January 27, 2015, 09:59:23 PM

I built the tonepad rebote a while ago, set it aside and tried it out again.

http://www.tonepad.com/getFile.asp?id=156

The modulation section, which contains IC1, the rate control and depth control, doesn't do much iif anything. I'd like to figure out what its suppose to do by bread boarding it. What should I be looking for? How do I test it?

bluebunny · January 28, 2015, 02:50:34 AM

I'd check that IC1 (pin 1) is actually wobbling. With the rate set to "slow", you'd probably be able to spot this with a DMM - otherwise use a scope. I've seen suggestions elsewhere that some op amps don't play well in LFOs. But this is a verified design, so I'd expect it to work...

And yes, you could breadboard the LFO part to be confident that it would wobble as designed.

peterg · January 28, 2015, 08:40:45 AM

Thanks Marc. I'm still a noob on the technical stuff. Is the wobble a DC or audio measurement?

bluebunny · January 28, 2015, 09:47:15 AM

By "wobble" I mean that you'll see the voltage at this point rising and falling - if the LFO rate is low enough. If the rate is too high, the DMM won't keep up and you won't be able to see anything. Unless the LFO rate can go high enough (above 20Hz), it won't count as audio.

peterg · January 28, 2015, 11:39:10 AM

Thanks Marc

peterg · January 28, 2015, 08:05:35 PM

Ok I have wooble but its very subtle. Are there any mods I can do to make it more pronounced?

bluebunny · January 29, 2015, 03:34:04 AM

It kinda depends on what "subtle" is, and how "unsubtle" it needs to be. Any further speculation on my part would be stepping beyond my pay-grade (hell, putting on my own shoes and socks is beyond my pay-grade). So did you probe the wobble at pin 1? Have you checked all your parts in the LFO? And are you using Tonepad's board, or did you do your own?

peterg · January 29, 2015, 09:12:38 AM

There is wobble at pin 1. I used Tonepad's layout as a starting point and modified it slightly to accommodate the components I had on hand. If i set the delay, level and repeats pots to 2 or 3 I can make out the wobble in the audio. Adjusting the rate and depth knobs has some effect but overall the LFO section doesn't contribute much to the overall sound. I guess I'm hoping for a simple fix but swapping out one or two components.

Morocotopo · January 29, 2015, 09:23:25 AM

You could try making R27 smaller, up to 1K even, to get more "wobble". That is, if the thing works correctly in the first place, and the amount of wobble is subtle by design.

peterg · January 29, 2015, 01:12:09 PM

Thanks Ariel. I'll give it a try.

peterg · January 29, 2015, 06:56:46 PM

I notice that the Delay control for similar PT2399 LFO sections is arranged differently that the Rebote 3. The pot (labeled TR1 and Time on the linked examples) is used as a variable resistor and connected to the transistor collector while the Rebote 3 pot is used as a voltage divider (I think) and connected to the transistor base.

http://blog-imgs-24-origin.fc2.com/d/r/u/drugscore/LFOs.gif
http://static1.squarespace.com/static/54696a3ee4b05a85cbfe56e5/t/5469759be4b05145d3fd695e/1416197531945/Echo-Base-build-PDF-updated-051810.pdf

How does this different arrangement affect the circuit?

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tonepad rebote 3 modulation section