Cgs synth

I am about to start building my first CGS-48 VCO (Rev 0.4 board) and I
just want to make sure that I understand the correction instructions
correctly. Specifically the instructions to "Cut the track between Pin
5 of the TL072 in the bottom right corner and the 47uF capacitor."
and "Jumper pin 5 to the Saw AC output terminal via a 100k."

It doesn't look as if this modification is reflected in the schematic
and assuming that it isn't, is this modification the same as connecting
the TL072-pin 5 to the negative side of the 47uF cap with a 100K
resistor instead of just a plain old trace?

Thanks in advance,

James

>It doesn't look as if this modification is reflected in the schematic
>and assuming that it isn't, is this modification the same as connecting
>the TL072-pin 5 to the negative side of the 47uF cap with a 100K
>resistor instead of just a plain old trace?

The trace goes to the wrong spot on the Rev0.4 board which is why it needs
to be cut. The resistor is just a "safety measure". The schematic is Rev0.2,
though apart from this additional resistor, should be correct.
_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>

I had the day off due to winter storm and so I took the spare time to work on my modular... finally got around to calibrating several modules that I had built, but never tweaked.

I am currently working on my Bi N Tic.

Frequency Panel control has too much slop. I have tried adjust the zero point, but it seems that there is no happy medium. The most response I can get from this control is about 50% of rotation.

On my scope I can see that after a certain point it stops getting any lower in frequency and when turned up to a certain point I lose pulses at the input of the 4040. The pulses die at around 3.9khz

The oscillator seems to be working good. It will oscillate from just under 1hz all the way up to 116khz. The first 20% rotation of the panel control does not increase the frequency at all, but from there on out, it behaves nicely.


I used a BC550 instead of the BC547, but those are pretty similar transistors.

Any tips, or tricks to calibrating this circuit? Is this just typical behavoir?



Tony

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>The oscillator seems to be working good. It will oscillate from just under

1hz all the way up to 116khz. The first 20% rotation of the panel control
does not increase the frequency at all, but from there on out, it behaves
nicely.

Put a trimmer in series with the lower leg of the pot, and trim out the
"bad" area.

Ken

_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>

I assume you mean 4024, not 4040.

It depends on how old your PCB is. I believe there was an issue with
layout that had to do with the clock for this circuit. I think the
diode might have been in the wrong place. Search the messages. I
think Richard Brewster wrote about it.

I had the same problem with non-clocking, but at very low
frequencies. Basically the 100N capacitor forms a high pass filter
and stops clocking the 4024. I suppose the transistor change, wrong
parts values, or even the PCB error could all be contributing to this.

I changed mine to a level shifter and eliminated the transistor. I
don't know if you problems are similar but the details are at:
http://modularsynthesis.com/cgs/bi-n-tic/bi-n-tic.htm

Dave


--- In cgs_synth@yahoogroups.com, Anthony Rolando <goldenechos@...>
wrote:

Sorry, I can't help, but I'd like to know
wich FET are you usig on your VCO? (2N4856 on the diagram)
and wich value for the integrator capacitor? (2n2 on the diagram)

Thank you,

Fernando