a n00bish question

[JAMESveeder]

Okay, so I have put together a vco using a LM741 using this schematic:



Rf = 100k
R = 18k
C = 10nf

it's suppose to create a sine wave... but somehow i ended up with a squarewave, although the diodes i'm using are not the zener diodes, they are 1N914s. I may post my breadboard up and have you guys take a look if you don't mind, a sine wave would be nice.

Anyways, I would like to create a gate/AR envelope for use with this VCO, so I've been trying to think of how I would trigger the AR... I guess I don't quite understand how I would use the trigger/gate and would love if someone could explain this to me in detail.

I'm creating a very simple AR envelope, here's the schematic I'll be using.

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[andrewF]

Hi
to e-m

its a good idea to start building with simple circuits, so you are certainly on the right track. The 1st circuit you posted would be hard to control with a voltage source (like the AR EG).
The AR EG needs a gate signal to work, which is a (say) 5V voltage that stays at 5V for as long as you need it to, then it returns to 0V.
The simplest way to achieve this is with a momentary switch wired to +V on one side and to the gate input on the other (via a resistor, say 10k, would be nice)

May I suggest you have a look at the circuits designed by Nicolas on this forum. Especially his super-simple VCOs.
They are only slightly more complex than what you are attempting but are quite elegant and work very well. Build a few of them and you have the makings of a very good inexpensive synth.

Have fun

[JAMESveeder]

Hey, andrewf, thanks for the quick reply! Okay, so the AR EG would be the VC source? I think I may be a little confused.

So would the envelope come "before" the oscillator, controlling the voltage (output level i'm assuming?) with timing via the momentary switch?

I dunno, I feel like I have a good understanding of how a synthesizer works considering my experience with VSTs and VSTi programming, but now that I've moved over into the hardware realm it seems to be much different.

Also I did check out those schematics, looks like there's some great stuff there. Can't wait to get into more complicated, fun builds, as I've created many 555 circuits, but now I'm looking for something more.

[andrewF]

Usually controlling a VCO with a voltage (such as the output from an EG) means you control the frequency of the VCO (the pitch).

To control the output level (the volume) you need a VCA

So, yes you can use an EG to control a VCO's frequency, the EG can also be used to control the volume when it is routed to a VCA.

To be honest, the momentary switch was only suggested as the most simple means of getting a gate signal, it is useful but its more fun to have simple sequencer or LFO to do the work for you.

you should be familiar with most synth words from VSTs but this glossary might help for any new ones:
http://electro-music.com/forum/topic-18425.html
Also for more simple circuits, check out the Lunetta forum
http://electro-music.com/forum/forum-160.html

[JAMESveeder]

Ah of course, I figured I was missing something, so voltage to the VCA would control the output, and of course voltage to the VCO would control the frequency.

So it would go VCO->VCA->Envelope

I did start the baby10 sequencer, started soldering it to a PCB, but I messed up and I've got to get out of my lazy phase and fix it.

But until then I'll probably just use a momentary switch for experimentation.

[JovianPyx]

I think this is what you are trying to do...

Hope it helps.

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[JAMESveeder]

Thanks for the block diagram!

So if I were to have a momentary switch would it look something like this?

i feel like this is wrong, so feedback would be nice

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[JovianPyx]

I can't see the image.

[JAMESveeder]

reattached

[JovianPyx]

Well, I'd bet it won't do what you want it to do ... However, build it and see, perhaps I'm wrong.

What I see happening is this - when the switch is closed, the EG is started and the VCO pitch is set to whatever V+ means to it. while the switch remains closed, the EG goes through it's cycle. Once the switch is opened, the VCO pitch will do ??? because with the switch open it really has no input, so the pitch could be anything.

[JAMESveeder]

Okay, well this is what my understanding of the circuit is...

The voltage in sets the pitch of the oscillator
I also need voltage fed to the gate in to trigger the envelope which is sent to the VCA controlling the output level.

and just for simple learning purposes i want to use a momentary switch to do this

wouldn't the switch need to be able to send voltage to the oscillator (pretend there is a resistor controlling the voltage to the oscillator after the momentary switch?) and gate in in order to trigger both blocks?

[JovianPyx]

What would be more interesting is to vary the pitch independantly from the gate signal. Even something like a pot delivering a voltage to the pitch CV input of the VCO.

[JAMESveeder]

Ah, I see, so I would have constant voltage to the VCO, and use the momentary switch for ONLY the gate, am I right?

[JovianPyx]

Yes, but the VCO pitch CV doesn't have to remain constant. If you supply that voltage using a pot, if you change the pot while GATE is on, then the pitch will change.

[JAMESveeder]

So if I had the gate in, what would be sending it voltage? (E.G. the positive terminal for a 9v?)

So far I have something looking like this:

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[JovianPyx]

The GATE is a voltage, but sort of special. It's either on or off. It is considered more of a logic signal than anything else and often it's input range is confined. Many systems use 5 volt gate, others use 10 or even 15 volts. However, as I stated, it is an "on or off" signal, meaning that the voltage is either "high" or it should be zero. "high" being what the circuit expects for gate - if it expects 5 volts, then use no more than 5.

For this example, let's assume the GATE needs to be 5 volts for "on" and zero volts for "off".

The diagram below is an example of how this is achieved with a switch. When the switch is OPEN, GATE is _ON_. When the switch is CLOSED, GATE is _OFF_

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[JAMESveeder]

Okay, that's really simple!
Well I think I'm ready to start this build... time to start buying some parts.

Thanks a LOT for your help, I appreciate it.


I'll finish soldering my baby10 for this one.