The VCO-555

[Cfish]

Hi Alanwilder81 sounds like you have a poor ground connection somewhere.

If you are still on breadboard. I would add a couple of extra grounds from your power supply to different ground points on the breadboard.

Had a breadboard loose contact to a section of ground strip right in the center once.

Could try ohm testing your ground points back to the power supply ground, to see if you have totally lost a section of ground strip.

[alanwilder81]

thanks Cfish,
yes i am still on breadboard !

so you are suggesting that i add extra ground wires from my power supply to different ground points on the breadboard ? If so,i can easily try to cure the problem ,assuming it's a poor grounding issue.
Fingers crossed i want this puppie to work soon !

[alanwilder81]

to Cfish,
by the way,did your VCO work straight away?
And, as for the PWM affecting the pitch? it drift about a semitone

[Cfish]

Yes mine worked good.

PWM is a comparator with its reference voltage being adjusted. There almost has to be a mistake on your board.

I have actually used that exact PWM circuit in many things, including a guitar synth.

If you imagine a triangle or sign wave being passed in to a comparator to turn it in to a puls wave ( the comparator opamp is just a switch turning off and on at a certain voltage) then you adjust the voltage the comparator turns off and on at.

The on and off point of the comparator are moving up and down the triangle or sign wave changing the puls width.

Only thing I can think of other than a mistake on the breadboard is a seriously undersized power supply. Then it could cause a volt drop to the oscillator as the comparator stays on longer.

[Cfish]

that is if you are sure you don't have a loose or floating ground problem.

[Cfish]

All PWM is happening in the green circle

That section should only receive signal from the triangle output.

Should not affect any pitch

---

IMG_0682.JPG
Description:
Filesize:	1.18 MB
Viewed:	454 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

[alanwilder81]

thanks Cfish for the consistent feedback !

sure PWM should't at all affect the pitch. I checked the board three times,it might boil down to PSU poor specs once again.
But at the end of the day, i only have the 555 VCO plugged in for testing,so i wonder how a 250 mA PSU,as modest as is can be, could be so heavily affected by a single module

[Cfish]

I still suspect it's in the ground circuit somewhere.

I would sit down with the ohm meter and test every ground point back to the power supply. Should be close to 0 ohm everywhere.

[alanwilder81]

excuse the dumb question, but what do you mean by each single ground point ? for instance,every grounded component leg ?
So,i should connect one DMM probe to each of those legs, with the other DMM probe connected to the PSU ground ?

[Cfish]

Yes alanwilder81

That is what I would do next.

[alanwilder81]

thanks Chris,

i'll let you know what i come up with. What about your works ? how are you doing ?

[Cfish]

Doing good. My modular is becoming a monster.

I have several posts up of my progress. Check it out, if you get time.

[alanwilder81]

yes, i've seen somewhere your posted material.Cool pics and threads.
I'll take a look at that very soon

[alanwilder81]

to Chris,

just out of curiosity, do you do also woodworks ? i seem to notice tools and stuff in some of your pictures.
i am a hobbyist joiner and i love making cabinets for music instruments,i've occasionally built some for my friends. Great and soothing pastime

[Cfish]

I use to be a building contractor. Specialized in fire restoration, and high end trim work.

I built all my own cabinets. Though they still need a lot of finish work.

[alanwilder81]

by the way i left a comment on your project thread.Awesome stuff there !
once i get the electronics part right, i plan on putting together a pine wood cabinet coated with water based varnish

[fonik]

so here you go. a GND issue. make sure it is properly connected to your PSUs COM/0V.

[alanwilder81]

yes, i am going to make it sure

[alanwilder81]

hey Cfish,
you were absolutely right about the PWM affecting the VCO pitch issue.
it cleared up today when i got a meaty PSU suited for electronic labs. and guess what?

it outputs 1A current and the PWM works like charm. No more VCO pitch fluctuation. You suspected it was caused by the comparator during the ON phase. Can't answer that, but now, with a higher amperage the VCO behaviour is more consistent.

thanks for the tip. More considerations to come

[Cfish]

Glad to hear you got it.

I would have thought 250ma would have been ok. However if it's not smoothe, all sorts of strange things can happen.

[gdavis]

[elmegil]

One suspects that all his modules together are drawing more than the old supply

[Cfish]

🐟

[alanwilder81]

hey folks! thanks for the feedback!

And no, it's the PSU capable of outputting 1 A, it's not the VCO consumption.

Well, i also thought 250 mA would be alright at least for testing single modules or a couple of them.
Yet, it wasnt. As i said on another thread of mine, that smaller PSU crapped out even with a tiny LFO and a VCO connected to it.
Guess what, the VCO pitch started fluctuating even when the LFO was not plugged in.
I've come to believe that it was due the undersized PSU.

Now i've got an ok one, and more modules can be fed with it

[alanwilder81]

by the way I like this Thomas Henry VCO a lot. Are there PCB pdf files for that ? i'd rather not build this on perfboard, it's a bit too complex for me