Need help with 4046 VCO

[acidblue]

Using a Philips HEF4046BP chip
and a TI LM324 all running from the same supply @ 9V
I believe this is a schematic PHobO"S uses.
Cant for the life of me get this to work.

Only changes I made are I left out the glide pot on pin 9 and
I left out the High/low switch on pin 6 and using a single 470nF
across pins 6 and 7 plus using a single 100nF to ground on pin 9 and no short/long switch.

Have nothing going into the CV in, though I have tried using a AR gen
with no results.
I believe the offset pot can be used as a frequency pot when there
isn't a CV input.
Getting no sound form any of the waveform outs.


Voltages from 4046:
1; 0
2: 9
3: 9
4: 9
5: 0, grounded
6: 0
7: 0
8: 0, ground
9: 0
10: 0
11: 0
12: 7.3 v
13: 0
14: .5 V
15: 0
16: 9

Schem:

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[PHOBoS]

Yeah that circuit should work, I did make a small change later to have a better level control but it should work fine without it.
Could you measure the voltage you are getting out of the second opamp (pin 7 of U1B in the schematic) with the level pot at min.
setting and offset at max. It should be around half the supply voltage. You can also twist the pots to see if the voltage varies.

[acidblue]

I'm getting 0V and the voltage does not vary when I adjust the pots.

EDIT:
After using a different LM324 on a different breadboard with same power supply, I get a constant .04V from pin 7, no variation when I adjust the pots,
pin 7 stays at .04V

The voltage does vary at the respected pots wipers.
Voltage at the 47k's divider into pin 9 is 3.79V.
Voltage coming out the 100k R into pin 8 is .08V.

More EDIT:
If I take the out put form the junction of the 2 47K resistors before pin 9
on the LM324 It seems to work, even the CV in works, sort of.
The problem seems to be the circuit for the LM324.
How to fix it is beyond me, any help would be appreciated.

[PHOBoS]

what are you getting on pins 1, 7, 8 of the LM324 ?

[acidblue]

With level set to min and offset to max I get the following:

1: .04v
7: .04v
8: .08v

BTW I have gone over the schem several times and made sure my bread boarding is correct.

[PHOBoS]

oops, that should have been pins 1, 5, 10, but it doesn't really matter since they are all connected, so knowing the
voltage on pin 1 is enough. This should be at half the supply voltage which is the same voltage as on pin 3.

[acidblue]

Ok I think I got it working now.
Although the saw output is kinda wonky, using the buffer in the schem
doesn't work very well, going straight to out put works better, but not by much, level is low, may be instead of a buffer maybe a little gain would be better, i'll have to experiment.

Also I'm getting no output form pin 1, pulse out: 0v
One of my bread board pins was broken, no + going to pins 1 and 3.(LM324)
Just for fucks sake I double/triple/quadruple checked my power connections
that's when I discovered the broken pin.

Any suggestions on the pulse and saw outs??
Haven't tried the xor or mod in yet, not sure what to do with them or how
they work??

[PHOBoS]

[PHOBoS]

btw to get a better level control, that is: a level control that doesn't affect the pitch when nothing is connected, you only need to make one
simple change. Connect the side of the level pot that is now connected to - to pin 1 of opamp U1a.

[acidblue]

Thanks Phobos, I'm gonna play around with this VCO.
But first I need some food and maybe some sleep .

[acidblue]

Should pins 12 and 15 be tied to GND/VCC or is it ok to leave them floating??

[PHOBoS]

no you should leave those floating. With pin 12 you can set an offset to the frequency range and I think pin 15 is an
output that can be used as a reference voltage. Hmm I actually never did any tests with that pin.

[acidblue]

Having a little fun with this VCO.
But I got a couple of questions.
Shouldn't the VCO go quite when I have a signal going into the CV In?
Example: when i have a AR/LFO gen gong into the CV the VCO still
oscillates in between the beats of the LFO.
Like this beat-oscillate-beat-oscillate.
Shouldn't it be: beat-beat-beat??

Tried adjusting the offset and level, but it still oscillates in between the beats.

Also Putting the pin to the OP amp 1 pin instead of ( - ) like you suggested doesn't really help that much, it tracks slightly better , but then adjusting the offset pot doesn't adjust the frequency that well.

Is this the nature of the beast as it being CMOS?

I rather have a dedicated frequency pot than an offset for the CV, bet hey
you cant have every thing right?

Still got this on bread board and would like to put it on a proto board PCB,
but I like to work out the kinks first.

[Steveg]

Hi acidblue,

The 4046 never stops oscillating. If there is no CV in then the 4046 will be oscillating at the frequency defined by the capacitor and the resistor at R1.
When you apply a CV the pitch will rise to whatever freq that voltage produces.
At no time will the 4046 ever be quiet.

Cheers.

[PHOBoS]

As Steveg already mentioned a VCO generally never stops oscillating although there are some exceptions.
One of those is the 4046 VCO I designed for the Moon Base Xplorer.



For that one I used a transistor to disable the VCO when the CV drops below a certain level. It is a rather crude method and at the treshold level
it might behave a bit weird but it works. So since you have it on breadboard you might like to give that a try. The CV section is probably also a bit
of an improvement so you could copy that and leave CV2 + U3d out to use that for the saw just like the other version does.

As for a dedicated frequency control instead of the offset control it is actually the same. VCO's (and other voltage controlled devices) often have
a mixer on the input, sometimes it is made with just a transistor in this case I used an opamp. Usually one of the CV inputs is connected to a variable
DC voltage and used as the main frequency control, but it will also function as an offset for any other CV inputs. If you would have 2 CV inputs and
you use 1 for pitch and one to add some modulation (like a vibrato effect) then the modulation just adds a varying offset voltage to the pitch CV.

And to get back to why the change to the level pot connection: this has to do with it being a single supply circuit. The level pot is just an attenuator
and with a dual supply it would be connected to GND since that is the reference voltage used for control voltages. So a higher voltage will increase
the pitch while a lower voltage will decrease the pitch. By connecting it to GND it can attenuate both positive and negative voltages and when set
to 0V/GND it will not have any effect. However on a single supply you can not use a negative CV so to still make it possible to go both up and down
in pitch the reference level is at a different voltage which is half of the CV range. If you would connect it to GND as it is in the original circuit it will
also add a DC voltage and as a result it will affect the pich when no CV is connected. I think the CV section used for the Moon Base Xplorer probably
has a better control and might be more to your liking. Depending on the CV range you are using you could make some change to it.

[acidblue]

Thanks guys.
Back to the lab for more experimenting.