Buchla 258 adaptation functional was: triangle VCO help please

[mark verbos]

I have completed a working version of the oscillator we have been discussing.
I took the Buchla 258 and changed the descrete OTA, that used a rare matched
pair, to a 3080. the fet source follower and transistor inverter to an opamp
buffer. Of course I had to use the PNP exponential converter because of the
3080. I used only 3904 and 3906 transistors and 3819 FETS. 4148 diodes.
SO..... no hard to find parts.

There were some problems with my board layout so i will edit that today and
make it available to anyone who wants to build it.

NOTE: the saw wave is not really very nice looking but the sine is real clean.
from voltage you can sweep from sine to "saw" or you can configure it with a
few resistor changes to sweep from sine to square. This sweep is kinda like a
lowpass filter sweep but unlike any filter I have heard. This will be a single
space FracRack panel with board mounted pots.

thanks for the help, even though the problem was the scope. ;)

mark




Martin Czech wrote:

> Q7-Q9 is the Schmitt trigger.
> R37-39 determine the positive feedback (hysteresis),
> thus amplitude. You have to determine the levels at
> base of Q8.
>
> I think there are much better options today (offset?):
> 3080 with constant bias can also work as comparator.
> Pretty fast, see Harris 3080 app note.
>
> And dedicated comparators like 311 are also nice,
> if they are used in the right way.
>
> m.c.
>
> :::Date: Sun, 26 Nov 2000 01:52:09 +0100
> :::From: mark verbos <a0284520 at addcom.de>
> :::To: synth-diy at node12b53.a2000.nl
> :::Subject: triangle VCO help please
> :::Content-Transfer-Encoding: 7bit
> :::
> :::Hello,
> :::
> :::I have built a triangle VCO based on the Buchla 258 and the Electronotes
> :::
> :::Option 2 Triangle VCO. I have a small problem.
> :::http://www.simple-answer.com/258mod.jpg
> :::
> :::The waveforms looks  right at all the locations in the circuit (as the
> :::buchla design) however insted of being +/- 2 volts at the point
> :::indicated, mine is just under +/- 200 mVolts.
> :::
> :::Where in a triangle oscillator does that gain come from? Is that because
> :::
> :::of the 3080? The Electronotes one used a 3080 and the Triangle output is
> :::
> :::right off of it so I know that one has a bigger voltage. I have been
> :::trying all kinds of things with no luck.
> :::
> :::can anyone help me? All the waveshaping after that point depends on this
> :::
> :::level being higher.
> :::
> :::
> :::--
> :::mark verbos
> :::
> :::"if you want something done right, build it yourself."
> :::
> :::verbos at simple-answer.com
> :::www.simple-answer.com
> :::
> :::watch out for...
> :::on my new label SIMPLE ANSWER "only a danger to myself"  and "Culture
> :::Shock" out now.
> :::also...
> :::coming soon "World of Illusion" Simple Answer 003 now distributed by
> :::Integrale, UK
> :::I have moved to Berlin!
> :::
> :::
> :::

--
mark verbos

"if you want something done right, build it yourself."

verbos at simple-answer.com
www.simple-answer.com

watch out for...
on my new label SIMPLE ANSWER "only a danger to myself"  and "Culture Shock"
out now.
also...
coming soon "World of Illusion" Simple Answer 003 now distributed by
Integrale, UK
I have moved to Berlin!