WG: New version and (Re: Haible_Juergen'

Haible_Juergen#Tel2743 HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Tue Jun 13 00:27:00 CEST 1995



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Von: Haible_Juergen#Tel2743
An: Rick Jansen
Betreff: AW: New version and (Re: Haible_Juergen's comments on VCO)
Datum: Montag, 12. Juni 1995 15:20

> I thought so, but the data sheet is a bit confusing. The HC(T)4066
> can switch voltages up to 12V, but it may be that this means voltages
> between -6V and +6V. In the latest version the cap voltage is
> less than 5 V, with control signals of 5V.
>
> There is also a 4316 quad switch, which contains a level translator
> so you can switch analog voltages outside the range of the digital
> control signals. But I have no data on Ron for this ic, so I stick
> to the HC4066.

I have to admit, I don't know much about the HC version of the 4066.

> > (3) Personally, I would avoid coupling capacitors where ever
> > possible. You have so many components already, why not
> > adding a little level-shifting instead of just AC-coupling?
> > Every VCO can be a very useful LFO ...
>
> I've thought about this too. Using a capacitor seemed so easy.
> I could of course shift the sawtooth down. Is this what is done
> usually?  The new circuit uses level-shifting.

You have precision voltage regulation on board, now. If You
use 1% resistors and derive the level shifting currents from the
precision voltage, You don't even need trimpots anymore.


>
> > (5) You could implement linear FM by simply adding one
> > resistor ... but You surely know that!
> Uh, not really in this schematic? You'd have to introduce control
> after the exp generator, where would you do that?

Just connect a 1Meg Resistor to the collector of Q1. (It's a
virtual gnd point, after all!). The other side of the resistor
goes to an input jack, et voila: lin FM. Add a poti if You like.


>
> > (4) I would replace the current source by a simple resistor.
> > I'd invest in a good on-board voltage regulator instead.
>
> I now use an LM329 (6.9V) reference and fix all voltages
> with it, i.e. the reference current, and both comparator levels.
> (I'll go for the two-comparator solution, one comparator detecting
> the upper, tho other the lower level.)
>
> A bit controversial may be that the power supply for the digital
> (sorry!) chips is derived with an opamp from the reference voltage.

Now, going two-comparator-design, You won't need any +10V point
for the capacitor anymore. Neither do You need all the digital stuff
and electronic switches. While the corners are set by two comparator
points, You can brute-force-discharge the capacitor with a transistor
now. I'm adding a design *idea* for that.
I know that it works with the discharge darlington and a CD4011 flipflop
(with 15V supply!!), but I think that the flipflop even can be built
discrete with only two(!) additional transistors, using the open collector
stages of the comparators as well ...
I'll send You the picture, and I'll send a copy to the list without the 
picture,
to spare bandwidth.
Any comments / further ideas etc. welcome!


> > The triangle converter looks interesting. Where do You have the circuit
> > from?
> > How does it work, exactly? (must be a resistor to gnd at the input, btw)
>
> It's a circuit that is in both S. Franco's Design with Opamps and
> W.G. Jung's IC-Opamp Cookbook. It's a circuit evolved from others,
> I added a short explanation at the bottom of the wave shape converter.
> This is a unity-gain saw-to-triangle circuit.

The bulk resistor compensation circuit is new to me, too. Good idea!

JH.




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