Magic Smoke Electronics |
I was able to evaluate the new Magic Smoke Electronics prototype of the Thomas Henry An Analog Synthesizer for the 21st Century LFO module as discussed on the Electro-Music forum.. There are a few modifications required for the Rev1 PCB and I came up with a few enhancements of my own.
Calibration
The first adjustment is the symmetry and offset using a 10 Hz triangle wave.
The second adjustment is the sine distortion for best symmetry and offset.
The third adjustment is the ramp connect for a nice smooth waveform.
The last adjustment is the volts/octave trim and the LFO temperature must be stable. I used my keyboard as the voltage reference and disconnected the coarse and fine controls so 0 volts input would have 0 volts on the trimmer so it would have no affect on the frequency. That way I could measure the base frequency at 0 volts and adjust the trimmer for 2X the frequency with 1 volt input. Then I checked and adjusted the trimmer for 4X the frequency with 2 volts input and 8X the frequency with 3 volts input. This adjustment is more difficult with the controls in the circuit as the trimmer then adjusts both the upper and lower frequencies
Gate and Delay Trigger
It took me a bit to understand the delay trigger functionality. A delay trigger forces the gate low and attenuates the output until the delay is complete when a new output cycle begins with a new trigger and gate output.
The lag control attenuates the amplitude of the LFO output at the beginning of a new cycle. This image shows a short delay with a short lag.
This shows the delay control set to minimum and the lag control set to maximum. The maximum delay is just over 5 seconds and the maximum lag is about 2.5 seconds.
Waveforms and Modulation
The polarity switch changes the ramp waveform from positive to negative, or as I call them, from a ramp to a saw.
The LFO sine output hard sync's to the square wave on the sync input. You need fast edges on the sync input and a triangle wave will work if the frequency is high enough.
This shows the LFO output modulated by a low frequency triangle wave on the FM input.
My prototype had a 2 µF timing capacitor for the 8038 which produced a frequency range of 0.5 Hz to 160 Hz. The sine wave holds it's shape to 0.5 Hz although the amplitude drops off below 1 Hz. The triangle and ramp hold a reasonable shape to about 1 Hz and then deteriorate and the amplitude decreases below 1 Hz. Here is a 0.5 Hz sine wave with amplitude about +/- 3 volts.
Front Panel
A designed a 2U MOTM-style panel. I reversed the delay and foot positions on the selector switch to correspond with the orientation of the gate in, trig in, and foot sw jacks
An Analog Synth for the 21st Century LFO FrontPanelExpress design file