Analog Rotor "RotoMatic"

[Neutron]

I am building up a modular synthesizer with various DIY modules from oakley sound etc.
One thing i really like on scope is the "rotor" so just for a laugh i tried to make one in an electronic simulation program (Texas instruments Tina Ti) anyways it appeared to work, so i have built it up on a protoboard.
I am still waiting for the VCA chips, but the controller section is working perfectly and almost exactly like the simulation (i had to change some minor things for stability)

This is just 2 out of 4 of the controller cells, because my oscilloscope only has 2 channels and the protoboard is too small
all using common and cheap quad TL084 opamps and a few common jfets. (VCA chips are slightly harder to find but still made THAT2180.) and 90% the resistors are 10k

rotomatic prototype.jpg (733.88 KiB) Viewed 946 times

rotomatic scope.jpg (510.3 KiB) Viewed 946 times

Nobody else has a circuit like this for analog modular, so if it works out well, I will do a small run of boards and panels, and see how they sell on muffwiggler (yes thats the name of a major modular synth forum!)



an analog circuit has been made to emulate something on DSP

diagram1 copy.jpg (329.4 KiB) Viewed 946 times

Differences between this and the scope version of "scope dsp module rotor"
Scope version has a built in oscillator, while this uses an external control voltage or oscillator.
Scope version only works in one direction, this can be 1 in to 4 out, 4 in to one out, or 4 in to 4 out
This version has adjustable "width" of the on time as well as adjustable slope. the on times can overlap or be separated by silence.

What can a rotor do?
Waveshaping
Wavesequencing
Key zones
Velocity mix
Send to different effects depending on velocity, key zone etc.
Envelope or LFO controlled mixing
surround panning
lots of cool things i haven't thought of yet

[dante]

Control voltages for the 4 inputs of a musicolor unit ?

[Neutron]

one of these? http://www.deltacreative.com/Products/Musicolor.asp
anyone circuit bent one yet?

[dante]

No, the original MusiColor was a Dick Smith product - a 'kit' from the 80's, also reffered to as a 'Color Organ / Light Chaser'. I still have one.

Pump music into a stereo input, it divides the signal over 4 fixed frequency ranges then activates 4 different color lights according to the amplitued of each.

I used to preface the input with a graphic EQ because of course because depending on the track 2 out of 4 of the lights would flash while the other 2 hardly activated at all. But then I'd have to change the EQ depending on the track....

I suppose what it really needed would be a more intellegent input that could somehow sample the bandrange of incoming material and divide that into 4 equal spectrums....rather than having the bandrange of each 4 predetermined... dunno how easy that would be. Fast Fourier on the fly ?

Maybe the idea is a curcuit that measures the average output of the 4 bands over the last 5 seconds and any that are too low, automatically widen the frequency range until they were all roughly even ( within some predetermined limits ) in terms of % contribution to full band output ( you wouldn't want all 4 lights to come on when music stopped ).

[Neutron]

My friend built something in England called a "chromachase" or something like that, It was mostly for sequencing lights though i think it had a color organ setting as well. that was in the late 70s or early 80s and i do not remember what magazine the project was from, maybe it was a similar thing? i remember it had a lot of TTL ICs in it as well as the usual op amps and SCR drivers.

I am building a much more cheapo thing which is basically a 7 band spectrum analyzer chip (used in car radios and things) with the bands controlling a great big RGB VU meter, which will have the 7 bands superimposed with different colors. using arduino of course because its easy and i am lazy

I think you could use that chip as well you just input audio and it outputs control voltage for each band.

http://www.bliptronics.com/manuals/MSGEQ7.pdf

bliptronics only sells the SMD version but i got some DIP ones from china.

you could put an AGC after it, I think you just need a capacitor on the outputs connected to a poor mans VCA (very easy and quite nice VCA made from 2 jfets and 2 op amps.)

[dante]

I spose I could build something in Modular with crossovers to divide frequency ranges into 4 then a compressor to maximize each output. Then output the 4 channels to 4 ADAT outs and then turn down the 4 sensitivty knobs on the musicolor...

A few vodka and orange at night to listen to mixdowns in disco'fied studio ain't bad. Beats looking at a specral analyser for kicks....

BTW ok by you if I run a feature on that Paradox ?

[Neutron]

Yeah the modular idea is the easiest thing to do if its just for chilling out, you could come up with lots of fun stuff with that,

By all means write something about paradox, no need to ask!

[dante]

Well we'll know I've done a good job on the Paradox article if Wolf reads it and you get yer dough back LOL!!!! LOL!!!!!

Woops I forgot its free....

[Neutron]

Actually i bought the spEQtrum, so it wasnt free

[dante]

I know - I meant the Paradox was free..... I read the stuff bout SDK users etc.