LFO-1A:

Tri / Sqr LFO - scratch built - design by EFM

LFO-1A was my first LFO. It's one of Tom Gamble's earlier designs (He called it the Maxx Dual LFO-1A). Each half of the module has a rate control, a TRI/SQR switch and an output jack with a pot for output level. It uses one LM324 and about a dozen other passive components.

I need to revisit this module at some point. I'd like to remove the output level pot, since I now prefer to have a level control on all inputs (not outputs) for more flexibility. I'd also rather have TRI and SQR outputs on seperate jacks, rather than a switch and one output. Lastly, I'll probably install a high/low range switch and tweak the value of the timing cap a little.

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LFO-2A:

555-based LFO - scratch built - design by Moo Synth

This module has been retired. It was from the now long-departed "Moo Synth" website, and it was the second LFO that I built. It was a simple 555-based oscillator taken almost directly from the 555 application notes. It had the usual SQR output, but it also had a buffer hooked to the 555's timing capacitor. The wave form on the timimg cap was a weird malformed triangle wave. It had the typical log curves of charging and discharging a cap.

Anyone who's attempted using 555 timers probably knows about the "crowbar" effect it has on the V+ supply. The 555 will tend to drag down the supply voltage at every cycle, causing oscillators to detune and other nasty effects. I tried various things to get this timer to behave (large bypass caps, a small series resistor at the power input, etc) but I could still see the power fluctuate slightly in the rest of the modular (and my VCOs would detune a few cents). I decided that I would give up on the 555 and retired the module. It is possible to use the 7555 timer in place of the 555... but at that point I would probably clone the Paia Fatman VCOs and add exponential control and a larger timing cap and turn it to a voltage controlled LFO.

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LFO-5A:

Multiple waveform LFO with Noise, S/H and staircase generator - Design by EFM

Tom's LFO-5A is based on the same triangle core found in LFO-1A. A CA3080 is added to give it voltage controlled rate, and an additional wave shaper was added to provide saw output. The LFO-5A schematics are available here.

In addition to the LFO core above, there is also a white noise generator, a S/H and a staircase generator. I have each of these normalled together (SQR out to S/H clock and staircase clock; white noise to S/H input) but I used swithching jacks for the ability to use them independently. There was a problem with the S/H drooping with the .01uF cap Tom specified - increasing the value to 680nF seems to solve the problem.

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