Finished: vco vc-waveshaper arraived at the front! Schematic

[Uncle Krunkus]

Sorry Zip,
you lost me about six posts ago! Good luck though.

[zipzap]

I´m sorry i lost you! What happened? You always bring up great idas.
I´m thinking of somehow modding this schematic for my needs.
It´s supposed to run on 15v, i use 12, and it´s said to limit everything from 1,8v on.
I guess since i´m dealing with a symetric wave i don´t need that fancy recitifer, just 2 buffers a diode, cab and resistor. I´ll see if it works.

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[zipzap]

I did it! Will write schematic later, i can tell you now that is has to do with vactrols and needs a lot of trimming.
I was happy when i finaly saw a triangle morpfing into a almost square with the amplitude staying at 5vpp!
Here are two examples of how it sounds. Not very musically ones but you´ll get the point. The VCO is recorded directly through a VCA. The first example starts with a sequence beeing modded by an lfo from tri to square. later the second sequencer row is faded in making some of the notes more sawish.
The second short one uses more saw and sounds silly.
I added some virtual cathedral to make it nicer to listen to.
If you listen to these please tell me that all of this was worth the efford

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[Scott Stites]

[Mikmo]

Cool.

How does it sound if you sweep fast (or very fast) between the two waveforms ?

[zipzap]

I´ll add a sample soon. Not as good as slow modulation. The tri-square sounds best slowly fading, going sawish is best with a sequencer or envelope.

[zipzap]

Ok People: Here it is.
3 little circuits have to be build for the mod. The Saw offset circuit with (rough) amplitude compensation, the distortion vca for tri to square and the output limiter to keep the the output at one level.
2 Words first. It needs a lot of trimming, but not as much that it can´t be handled one by one.
Some of the values depend on the vactrols being used and the psu. I use lc-leds because 3* 20ma is 60ma and 3*2ma is 6ma for three bright leds.
Lets start with the first circuit. I post it again here to keep things together.

It´s basically opamp cv summing for the saw offset done by ic3-d on the august2003 vco. I added some limiting for the summed cv because if the manual pot and external cv add up too low or high the tri will turn into a wrong direction ramp or the saw will be squashed.
The first (inverting!) summing amp acts like a ideal diode, so cv can not go above 0.
Connect no cv and set the pot to ground. Now trim the pot at the right hand inverting summing amp till you see a perfect triangle. Use good trimmers!
Now turn the manual shape pot all the way to the right. The wave becomes a saw. If it is squashed use trimpot by the manual control pot till it just gives u a nice saw.
Now the middle trimmer with the diode can be set so that it just keeps a saw. Going too far will move things back to tri again. Now if the summed cv gets too high the part being too much will leave over the diode rather than squashing the saw. This is working more or less i must admit.
With the leddriver ldr thing on the output the amplitude can be compensated. It is too replace R25. At tri it should be double of R28 on the vco schem, at saw it has to be the same. This can be achieved by maybe changing R28 a bit and using a series resistor. In my case i trimmed the led so that the vactrol was between 80 and 175k so i just added another 25k in series. Done,

Next thing is to replace R15 going to the sineshaper with this vactrol vca. Leddriver is the same as above without the 100k trimmer going to +12v.
just adjust the gain trimmer till it can be swept from very silent triangle up to bright square.

The Limiter is a common design. I used a fullwave recitifier because changing to saw will add some offset and that can´t be handled by a simple diode. Actually now i think that a cab would do the trick, so a simple diode would work as well. Maybe better, saves some parts. I adjusted the gain trimpot after the rectifier and the led resistor till the light was always a bit bright and following well.
Now the first trimmer can be adjusted. It´s basically setting the threshold of the limiter until everything keeps the same level.
Have fun!



EDIT: The limiter can be made simpler. The last opamp isn´t needet. Just put the vactrol directly to the cab without the buffer. So now there is a free opamp for the wave output. Set it to give you the desired out-level. The whole mod then needs 8 opamps instead of 9, so basically the whole thing is 2 TL084, 3 vactrols, 4 transistors and a cab.

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[zipzap]

Just rememberd: The PWM of the original vco will not work anymore like this because it´s using the tri-wave. Has to be hooked to the sawcore instead.

[bigtex]

It sure sounds cool. It's always nice to hear a more animated waveform, something dynamic that isn't just the exact same harmonic structure all the time. Keep the sound samples coming!

I'm afraid I've had a little trouble following the descriptions of all of your modifications and experimentation. Perhaps a single unified schematic, once you are done, would help illustrate what you have done a little better.

[zipzap]

[bigtex]

I think I got one of Ray's last PCBs from the previous version, unfortunately. I haven't built it yet, but I'm definitely going to use your mods. Maybe I'll buy one of the current ones to do your mods and come up with some of my own for the older version I have. I guess I should compare the board I have to the current version...

Anyway, thanks for posting this. I really like how the VCO sounds with your mods. That last sample sounds like the VCO is sick and dying.