The VCO-555

fonik · Posted: Sun Oct 28, 2012 6:22 am Post subject:

my observations so far (no conclusions):
it is true, while all other outputs are 10Vpp, the sine is way weaker on my build - just 6.4Vpp when trimmed round nicely!
when i built the VCO i had no TL074 on hand, so i used TL084 instead. nevertheless, in regards to output voltage swing these parts are speced to be the same!?
today i replaced both TL084 with LM324, and now i get a nice 10Vpp sine.
i wished i could try a TL074, alas, i have only tons of TL072 in my drawer...

diablojoy · Posted: Sun Oct 28, 2012 2:09 pm Post subject:

Interesting result matthias.
thanks

AlasdairMoons · Joined: Dec 03, 2011 Posts: 105 Location: East-Belgium

fonik · Posted: Sun Oct 28, 2012 2:55 pm Post subject:

thank you for your kind offer! great comradeship here!
but no need to rush. will order a batch this week along with other stuff.

Thomas_Henry · Posted: Sun Oct 28, 2012 3:22 pm Post subject:

Hello Fonik,

Just a quick comment: the sine is buffered by one of the Darlington pairs in the LM13700. Thus, if the triangle wave is a legit 10Vpp, then changing op-amps elsewhere shouldn't influence the sine. A more likely place to look is at the resistors surrounding the OTA.

By the way, changing the sine trimmers will change the output amplitude. Remember, the "best looking" sine is not necessarily the "best-sounding" (i.e., lowest distortion) and may lower the amplitude due to too much curve-bending. Use your ears only if you haven't already done so, and only afterwards look at the scope.

Scott and I spent a lot of time going back and forth on setting the resistor values to give 10Vpp with lowest distortion. But I suppose LM13700 variation could change this. I don't have the circuit on my breadboard anymore, but maybe Scott does for confirmation.

And, hey, how about that sync!

Thomas Henry

fonik · Posted: Sun Oct 28, 2012 4:05 pm Post subject:

diablojoy · Posted: Sun Oct 28, 2012 4:33 pm Post subject:

sonic · Joined: Dec 02, 2010 Posts: 106 Location: Victoria BC

Only just discovered this, and oh lordy! This sounds GREAT! I have all the parts already. Count me in for 2 PCBs, though I'm so excited I want to say more!

elmegil · Posted: Sun Oct 28, 2012 6:06 pm Post subject:

AlasdairMoons · Joined: Dec 03, 2011 Posts: 105 Location: East-Belgium

fonik · Posted: Mon Oct 29, 2012 2:56 pm Post subject:

in this special case i
1st: feed the 1V/oct input of the 555-VCO with a cv sequence. then
2nd: i apply a square wave from another VCO (fixed freq and PW) to the sync input (gives this robotic synced sound). then
3rd: i apply a small amount of a triangle from a LFO to the exponential FM input (gives you these phasing overtones).

Silesius · Joined: Feb 12, 2010 Posts: 65 Location: Berlin

Hi, I'm thinking on building a couple of this vco's. I've been waiting for the pcb's, but I'm not sure if this is going to happen, so I think I'm going to try a stripboard version. The circuit is simple enough, and I think I am able to do it, if I am careful.
But I've never tried to match transistors, and I think it's a little too much for me. It would be nice to just buy some matched pairs. I've been looking a little on ebay and some online shops, but I can't find matched 2n3906's. So my question is: is there any easy substitution for that? Would any general purpose matched pnp's work here (let's say a bc557)? Or something like the ssm2220?
Any suggestions would be very appreciated. Thanks!

fonik · Posted: Mon Nov 19, 2012 10:38 am Post subject:

it will happen, the new prototype PCBs are ordered allready and should arrive early in december.

re transistors. i did not match mine, i just used two from the same batch. as you can hear in the demo vid this is sufficient, i don't can show you any measuremtns, though.

Silesius · Joined: Feb 12, 2010 Posts: 65 Location: Berlin

Thanks, fonik. I think I'll wait for the pcb's in that case. You can count me in for two of them. By the way, is there any chance to get the TH controller LFO pcb's as well? Maybe at the same time? That would be great.

sonic · Joined: Dec 02, 2010 Posts: 106 Location: Victoria BC

AlasdairMoons · Joined: Dec 03, 2011 Posts: 105 Location: East-Belgium

JingleJoe · Posted: Fri Nov 30, 2012 3:33 am Post subject:

oculus · Joined: Oct 30, 2011 Posts: 35 Location: Iceland, Reykjavik

fonik · Posted: Sun Dec 09, 2012 12:19 pm Post subject:

you can run it on 12V without any changes.

oculus · Joined: Oct 30, 2011 Posts: 35 Location: Iceland, Reykjavik

fonik · Posted: Sat Jan 05, 2013 2:45 pm Post subject:

re sine output.

powering the module from +/-12V, i had to lower R27 to 33k in order to get the 10vpp amplitude on the sine wave.

my recommendation for any build, even 15V systems:
lower R27 to 33k, raise R24 trimmer from 25k to 50k (or even 100k multiturn). then you should be fine.

stubbyfex · Joined: Sep 08, 2009 Posts: 8 Location: Denver, Colorado

Hello!
I'd like to order one of the 555 VCO PCB.
I'm using Thomas Henry's VCO-1 currently, with good results.
My synth is a homemade 5MU style.
Thanks very much.

elmegil · Posted: Sun Mar 03, 2013 8:09 pm Post subject: AAArrg

This is what it looks like if you short all your inputs and outputs together because you wired all the two pin connectors backwards

I'm going to take the lazy man's out and turn the pin connectors around instead of wasting all these (press in type, so they aren't easily reversed) sockets. And I don't think I want to switch so all my green wires go to the tips, cos that will confuse the hell out of me at some point in the future too.

For the record, I am no longer ordering the press in type of sockets, I just ran out of the crimp pin sockets and had these available....

Edit: yellow is pin 3 of the 555, blue is what all the outputs looked like.

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MrZ · Joined: Jan 14, 2013 Posts: 11 Location: Finland

Hi,
This vco sounds great but I get bleeding to other modules thru the power rails.
Any idea for a solution ?

fonik · Posted: Tue Mar 19, 2013 1:08 am Post subject:

bleeding is an issue that comes up in the forums from time to time for all kind of VCOs.

1st check your PSU. do you see a voltage drop? in other words, can it deliver enough current?