Electronotes 129 Thru Zero VCO MOD

[Sebo]

Hi:
I recently finished building the Electronotes 129 TZ VCO based on the PCB posted at this thread:
http://electro-music.com/forum/viewtopic.php?highlight=electronotes+129+tzvco&t=40616
Thank you Forbin for the PCB layout!!!
Reading the original article by Bernie Hutchins (thanks to him for the design):
http://electronotes.netfirms.com/EN129.pdf
I realized that if I want to modify the Thru Zero depth (using the initial linear knob) It also modifies the frequency of the VCO, as Mr. Hutchins explains at the end of the article. He also proposes a complicated way to avoid that (using a second exponential converter).
After thinking about it I came with a simple solution: to substract the voltage at the Initial Linear pot to the voltage that sets the VCO's reference current).
The MOD worked perfectly at first time.
The only trimming needed is to adjust the 20K trimm to null any pitch variation when moving the Initial Linear pot.
Also I'm posting a picture of the module (there are some errors in the labeling, as I did the panel before building the circuit).
I will try to post a video demostrating the MOD soon.

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Electronotes TZ VCO - Back.jpg
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Electronotes TZ VCO - Front.jpg
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Electronotes TZ VCO MOD.jpg
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[Luka]

Nice work sebo

[forbin]

Hey that's very cool! It also really nice to see the board made up. I have had a few PM's from people that have made the board successfully. I must drag mine out again as I had some tweaks that did a sort of sync thing as per what Ian Fritz was talking about... have been so busy over the last year or so Synth stuff has taken a bit of a back seat to life etc. Hopefully when we move into our new house in a month or so I will be able to get it all setup again...

[Sebo]

Hi Forbin, thanks again for the layout
The VCO works great, I'm just starting to explore it, but is great!!!

[Sebo]

Here is a video exploring a bit the sound palette:

http://youtu.be/XHX8rdDEKOE

[ryktnk]

Hello

I hope somebody can help.

I get some weiredness wiht this VCO when I
use a Linear FM freq obout 1khz and above.
When the VCO freq is lower.

Seems to get really unstable and produces some
unpleasant and unpredictable sound.

With FM freq below 1khz it is great.

Anybody else had this experience ?

Cheers
-ryk

[Sebo]

Hi, in the video the frequency of the VCO is always 2, 3 or 4 octaves above the modulator frequency. I use it that way because when they are at the same frequency the timbres I get are less interesting, and when the frecuency of the VCO is lower than the frequency of the modulator I get the modulator wave at the output.
But I didn't experiment any unstability at any frequency combination.

[CJ Miller]

Nice work! I was just thinking about this VCO today, might need to try etching a few.

[ryktnk]