basic volt per octave keyboard schematics

[Cfish]

Can point at a Chinese 3080 that I know is good at about a dollar each American. I actually suspect that the problem is in the schematic. The EFM VCO I showed required greater cap values to get it in to usable audio range. I'm not sure EFM was truly known for testing everything they put out. Think they sold kits then disappeared.

[alanwilder81]

hey Chris,
i'd like to ask you another question regarding the third op amp used in the VCO schematic,that i circled in red. It's not quite clear to me how its connected.
Seems it has both inverting and non inverting input shorted and tied to ground
it's confusing me a bit

---

ph.png
Description:
Filesize:	245.12 KB
Viewed:	665 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

[alanwilder81]

it's a good news to hear about a cheap source for our OTAs. Have they proved reliable then? i'd be interested also in other components !

[Cfish]

To alanwilder81 I feel like something is missing. Are you sure it's all there?

[PHOBoS]

[Cfish]

Thanks PhoBos

That's what I thought. Was.nice they threw in a diod or 2 to make it look useful. Ugh.

I know EFM sold this as a kit. If you figure out that OTA I would love to know

Have heard some EFM kits had problems.

[alanwilder81]

hello chaps,here the second half of the VCO schematic!
sorry but i cant seem to screenshot and paste more than one picture at a time !

so,it's a way to terminate an uncommitted op amp? good to learn! i would never have thought !

thanks Phobos, thats priceless

---

VCO.png
Description:
Filesize:	143.94 KB
Viewed:	649 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

[alanwilder81]

anyway,
it's late night here in italy, and really time to go to bed.

A big thanks to both Cfish and Phobos for the prompt support.
we'll talk tomorrow

[Cfish]

My personal respons would be, that is a lot of parts for a VCO that isnt temperature compensated and is no more than it is. Almost as many parts as a Thomas HenreynVCO1 without the bang for your buck.

[alanwilder81]

yes cfish,

it's very high parts count,almost ridicolous compared to other VCOs that are more minimal yet offer some means of temperature compensation.
But i want to get this together just to do a quick and dirty test of the Yves Usson keyboard circuit.
That aside, as soon as i make sure the keyboard is working right,i can disassemble the VCO. It's not meant to be definitve nor to go on my synth whatsoever !!

[alanwilder81]

hello chaps,
update !
The above VCO works correctly,it outputs a wide triangle and square waves signals over a resonable frequency range. sounds ok.
i employed TL082 in place of the LM358 specified.
The schematics suggests to power the circuit with +- 5 V dual supply,but i wonder if i can power it with the regular +- 12 V i use for all my modules !
it'd save me the bother to hook up another extra supply just for this testing VCO

Cheers !

[PHOBoS]

I was going to say it should work fine on -/+ 12V since it doesn't have any reference to the supply (except for that fake GND) but if you use
a dual supply GND becomes V- and it does have the transistor and R10 attached to it. So allthough it will probably work you might have to
adjust some values. There is a way to find out of course

[alanwilder81]

thanks Phobos

great news is that today i was able to test the Yusynth keyboard circuit with the VCO we discussed earlier. Designed to cover 3 octaves, it did an ok job from what i see.I cant wait for others to get the same circuit done and compare the results

As for that simple VCO, another noob question, so please bear with me

i am already driving the VCO with a dual +-5 V supply,so i dont get the point where you state ""but if you use a dual supply GND becomes V- ""
i wonder why the original design specifies only that low voltage when all synth modules get at least 12 v or more

[PHOBoS]

The only place I see a negative voltage is on P3 which I assume is a connector. I don't see it used anywhere in the circuit itself.
So if you would power it with a dual supply you connect V- to what is GND now, and you connect GND to what is Vref now (you can leave
out those resistors). As for the low voltage, I don't know. Maybe a second set of regulators is used to create a more stable isolated supply
just for the VCO.

btw, I am probably more of a noob than you when it comes to VCO's

[alanwilder81]

Phobos thanks for all those ideas !i must admit need to get a better understanding of virtual ground, voltage reference and similar concepts that i am still trying to get a grasp with !
i will look further into some theory,as i really, really need it !

[alanwilder81]

hello chaps,

been playing around with the keyboard circuit.it's doing well
Now, another one of ""those questions"" of mine.

I needed -10 V in the trimmer circled in red.
Not having a negative voltage regulator handy , i grabbed a single power supply and plugged its +10 volt cable to GND rail, and its ground cable to the trimmer.
Not at all sure whether or not it's proper,but ,the trimmer circled in red, has now a -10 V voltage about GND



any suggestions? cheers !

---

gnd.png
Description:
Filesize:	50.57 KB
Viewed:	439 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

[alanwilder81]

to Phobos

right now i came across your wonderful ""PHOBoS DIY Synth schematics"", and as i read along, i found the woodworking part of your project.
In there, you mention lacquering and the bother of waiting for every coat to dry.
Well,immodestly i thought I might come in handy with some advices, as i do wood restoration and painting jobs both as a hobby and a for a living.
Water based finishes are the answer, because they are not toxic , dry quickly and generally have little or no residual odor after less than a couple of hours.

I am planning on building my little modular with pine wood painted with those water based varnishes.

Definitely off topic, but hey, might be beneficial to many

[PHOBoS]

You are absolutely correct about waterbased finishes. The main reason for using the paint I used was because it is what I have.
I originally bought it for another purpose but that never happened and I still have a couple of cans. So to keep it cheap I use that.
For smaller projects I usually use acrylic spraypaint which does dry very fast and it usually makes it possible to finish painting
something in a single day (unless I use multiple colors than I let it harden a bit longer).

and to go more off-topic. For a short while I worked at a place that fixed (wooden) furniture or gave it a new purpuse. But they
also made new furniture for daycare centers and schools that were usually painted in bright colors and for that waterbased paint
was used. So I am familair with the advantage of it, but thanks for mentioning it.

[alanwilder81]

hello Phobos

it's not off topic.It's never off topic when it come to talking woodworks I dont know whether or not we should open a new thread for cabinets making,lacquering,gluing and stuff, but for the moment i'd be very happy to share with you and other chaps our experiences in this field.

I find myself doing carpentry more as a hobby nowadays,as the crisis in italy has nearly sunk my little business. i too worked in a nice antique furniture restoration shop, when i lived in London. Amazing times then.
I learnt the shit out of those experienced craftsmen who put so much effort and love in restoring furnitures, doors and alikes.

Also, i truly believe that woodworking is an essential skill to develop within synthesizers DIY producing.
I happen to love the wood warmth together with the analog sound warmth itself.The result is bigger than the sum of the single parts!
So soothing to make detuned PWM lines out of a synth with a walnut cabinet !

so, i am totally open to any new ideas,projects, design you might come up with to realize and discusse !
back to electronics, i think my above question regarding the -10 V thing went unnoticed watcha think?

cheers !!

[PHOBoS]

[alanwilder81]

thanks Phobos,

no, i dont have that component right now. I plugged that external 10 V supply just for a quick and dirty test, well aware it's rough and far from ideal.

Now,looking for a definitive solution.I only have LM 317,(positive regulator), but not the LM 337 which will do the job from what i've heard.

I have also a bunch of zener diodes of many values.Which do i pick and how do i connect it?
Fixing this little thing is proving to be more difficult than the actual building of the whole circuit !

thanks !

[Grumble]

[alanwilder81]

grumble,
believe it or not,i haven't got a negative voltage regulator to do the job

[alanwilder81]

moreover,it seems that there are different methods of achieving that, all quite obscure to a total green horn like me.
its gonna be a tradeoff. Best efficient solution with the components i have available

[wackelpeter]