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Question about the 3340 VCO datasheet
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Question about the 3340 VCO datasheet
acidblue
Looking at the as3340 datasheet circuit is simple enough.
But i have a question shouldn't the frequency pots be wired one side to +15 and the other to -15 or should it be +15 and ground?

Datasheet:
https://cabintechglobal.com/pdf/ALFA_RPAR_AS3340.pdf
devinw1
acidblue wrote:
Looking at the as3340 datasheet circuit is simple enough.
But i have a question shouldn't the frequency pots be wired one side to +15 and the other to -15 or should it be +15 and ground?

Datasheet:
https://cabintechglobal.com/pdf/ALFA_RPAR_AS3340.pdf


Which pot are you talking about? The trimmer pots for scale and high frequency?
acidblue
Sorry I should have been more clear.
I meant the CV inputs on pin 15, one or two for Coarse and Fine control
will be pots, should those pots for frequency control be wired +15, -15
or +15, GND, for the opposite ends of the pot?

like this:
groove
+V and ground, afaict. Just be careful going to far below ground - I think you shouldn't exceed -6v or you're going past the negative rail inside the chip. That seems risky. Not sure what the actual usable range is though.
DozenCrows
I'd wire the coarse between 0V and 15V, and the fine with resistors between -15V and 15V to limit the range. Then you can set a base frequency with coarse, and adjust it up/down with fine.
BugBrand
I would begin with a stable +10V reference source (eg LM4040).
Coarse Tune would be a pot between +10V and 0V summing through a 100k resistor (as shown on the datasheet) - this would give a 10 octave range.
Fine Tune would be a similar pot but summed through a 1M resistor (giving 1Oct range).
CLee
This I agree!
acidblue
BugBrand wrote:
I would begin with a stable +10V reference source (eg LM4040).
Coarse Tune would be a pot between +10V and 0V summing through a 100k resistor (as shown on the datasheet) - this would give a 10 octave range.
Fine Tune would be a similar pot but summed through a 1M resistor (giving 1Oct range).


MMM I'll have to try that.
I got the circuit on bread board, dont have a LM4040 or any reference voltage chip for that matter, so I guess I'll use a volt divider and pass that thru a buffer on spare op amp for now.
Thanks for info guys.
Let you know how that works out.
CLee
Using a voltage divider and buffer would be fine for testing, but the advantage to what BugBrand is suggesting is that your pitch control won’t be dependent on the stability of your power rails. The reference will stay stable even if your power supply voltage sags, so your pitch won’t drift.
acidblue
Yeah that works great.
I get a nice full sweep of ranges.
Before when I had the freq pot wired 15 and -15 it wouldn't kick in till about 10 o'clock on the pot and it seemed not to be a smooth sweep.
I got better results when I had wired between +15 and Gnd, but not great.

the 10v reference is the way to go, I think the Roland MKS 80 did this way.
Thanks BugBrand applause
BugBrand
Good!
I would also wonder whether the +10V ref should be used on the Freq Cntrl Inputs Offset resistor (currently 360k in the datasheet) and the one on the Linear FM (1M5).
I've still not played with the 3340, but would try 1M on the Linear (2/3 of 1M5) and perhaps implement a trim for the Freq base offset. (maybe 200k fixed resistor with 100k trimmer -- purely guesstimating that though!).
Tweak that to get a good base frequency with the Coarse & Fine controls set to minimum (eg. 10-20Hz).
Silesius
Hi, I have couple of questions regarding this matter. I’m building a triple 3340 Vco that I intend to use inside a stand-alone monosynth. It will have keyboard, arpegiator, quantisers, so I’m thinking about ways of making them rock solid in terms of pitch stability. I’m so worried about this that none of them will have PW control or PWM (because of the reported problems about pitch instability when using PWM).
So I would like to use some voltage reference, but I’m not sure about how to do it. For instance, a tl431 is used in the vco maximus build, but it’s not used for the pots: it’s used to power the chip. This makes me wonder a couple of things:

-Can the same tl431 be used to give a stable reference for the pots as well? Or should I use a dedicated reference for the pots? I have tl431’s and ref01 here, so maybe I can use the latter for the pots. But would that be redundant?

-If I use -12 for the pots, do I need a reference for this as well? That would seem logical...

-And finally, since the three Vco’s will be on the same board, can the same voltage reference be used in all of them? (maybe one tl431 to power the three chips and one ref01 for all frequency pots).

If someone has any ideas about this it would be great smile
DozenCrows
I used two LM4040 10V references to provide +10V and -10V references for control signals and the connection on pin 13. I also used a 79L05 for regulated -5V on pin 3 and a TL750L10 for regulated +10V power on pin 16.

I picked the TL750 as it has pretty low drop out, and would regulate 10V fine even after my +12V rail went through a protection diode.

These would probably work across multiple 3340s, but you'd need ensure your current draw is within limits, and to set up the associated supporting components so regulation/reference accuracy is maintained across the larger load. E.g. LM4040 external resistors are calculate based on load, as given in the datasheet.
djerickson
I'm building a '3340 based polysynth so lots of 3340s. One trick I like is to provide a -5V supply instead of the dropping resistor to -12V. The chip will burn less power since V- is 5V instead of 6.8V, and also because the internal shunt regulator has no current. A nice side effect is that at lower power the chip is cooler and frequency drift due to temperature rise should be less too.

Cheers,
Dave Erickson
groove
Silesius wrote:
Hi, I have couple of questions regarding this matter. I’m building a triple 3340 Vco that I intend to use inside a stand-alone monosynth. It will have keyboard, arpegiator, quantisers, so I’m thinking about ways of making them rock solid in terms of pitch stability. I’m so worried about this that none of them will have PW control or PWM (because of the reported problems about pitch instability when using PWM).
So I would like to use some voltage reference, but I’m not sure about how to do it.


As food for thought, the Alfa AS3340 claims to have better stability and may allow you to include PWM back into your circuitry.
acidblue
After playing around with the tri and saw outputs i decided to hook up the pulse out.
But Im not getting any output, I have it hooked up according to the datasheet with 51k to GND on pin 4 and the out put just before that into opamp buffer.
Checked with volt meter and its 0.00054v which is pretty much ground.
I dont have the PWM control hooked up I left that part blank.
Any ideas?
infinitemachinery
acidblue wrote:
After playing around with the tri and saw outputs i decided to hook up the pulse out.
But Im not getting any output, I have it hooked up according to the datasheet with 51k to GND on pin 4 and the out put just before that into opamp buffer.
Checked with volt meter and its 0.00054v which is pretty much ground.
I dont have the PWM control hooked up I left that part blank.
Any ideas?



Look at the datasheet Typical Electrical Characteristic/PWM. From my understanding, you need to supply some voltage in order to get > 0% pulse width.
acidblue
AHA! I knew it.
That works, using trimmer with 10V as ref, but Ill have to get that down as 5.6V is max.
acidblue
What kind of buffers should I put on the outputs?
Right now I have Unity gain buffer on the outputs except the tri out, I put a gain of 2 since the output is low compared to the others.

That's OK and works fine on bread board, but If I want to design a PCB, should I change them or leave them as unity gain buffers?
Silesius
acidblue wrote:
What kind of buffers should I put on the outputs?
Right now I have Unity gain buffer on the outputs except the tri out, I put a gain of 2 since the output is low compared to the others.


If you are building for Eurorack, normal practice would be raise the level of the outputs to the +5/-5v standard. I'm not an engineer, so what I do in these cases is to look at some proven designs, like the Vco Maximus from Thomas Henry... There are several 3340 designs around. Just follow the wave outputs and look at how the buffers are implemented. One opamp per buffer should be enough.
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