Published on Sep 8, 2015 noystoise
Some pics and initial details via noystoise. Be sure to click through for more.
"The synth is based off of a Yamaha HS200 that the musician had owned since he was a kid. the keyboard is a regular piece of his performance rig, so the finished product needed to stay compact. i had never had the chance to play an HS200 before it was shipped to me. the keyboard is actually pretty powerful for its size. it has 5 timbres, 4-note polyphony, and sustain. the keyboard had some issues, as most toys of this age usually do, but after a good tare-down and cleaning, the keyboard had a lot of potential. one interesting thing about this keyboard was the auto-power-off function. it was actually a separate dedicated IC made by Yamaha. never seen that before. needless to say, i took it out of the circuit..."
"The HS200 itself has a pitch control circuit that can be modulated manually, by the LFO, by the EG, or by the CV input jack. the range is pretty limited but enough to get some great warping sounds. the keyboard also has a 5-position switch to select the timbre, as well as a single on/off switch that engages the sustain mode...The LFO is pretty cool. it is the same dual op-amp triangle wave VCO i use a lot, however, this time i added a triangle-to-sine wave-shaper after. the wave-shaper can actually be swept from triangle, to sine, to square-wave gradually. this is a great circuit to have in the toolbox. more fun to play with than a three position switch. might have been cool to add a CV input to control the wave-shape. maybe next time. the frequncy of the LFO can be controlled manually, by the EG, or by the external CV input to the LFO. the LFO has a depth control knob that controls the level to the internal parameter it is set to. the LFO has a CV output, but like the EG CV output, the signal is output at full, and can not be controlled with the depth knob. the LFO has a 5-position slide switch that can be set to modulate either the HS200 pitch, 12db filter cutoff, echo rate, echo HP filter, or echo LP filter..."
This thing looks killer. A surprising amount of features for what it is. Definitely the sort of thing a lot of us dream about finding in a junk shop. Very cool.
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