1145 VC LFO Module

Chats about this beast right here!

I’ve been playing around with an Android app that emulates an analogue synth, and using a LFO to drive a VCO is one of the first things I tried. That’s a lot of fun!

As a person who was a teenager in the early seventies I remember the blissful new dawn when everybody from Stevie Wonder to Chicory Tip was using analogue modular synths. But also, I listened to BBC radio talks by producers like George Martin and composers like Thea Musgrave who set the new techniques in the context of a long history of electronic music that embraced the early radio-based instruments like the Theremin and the Ondes Martenot, and included the Musique Concrète school (what we’d now call heavily processed analogue sampling, I suppose).

I’m pretty much tone deaf but I love sound, and having a way to make new sounds, on my own rules, is something I’d like to work towards. I’ve seen the pleasure my adult kids and my wife get from making their music, and I think everybody should have that. Melody and harmony are important, but synthesis has many more dimensions than that. I want to have a go.

I have troubles getting my lfo module to work :-/ Only the left LED (+) lights up when I connect power and it is on constantly. Turning the knobs changes nothing. I have already checked for bad solder connections and I checked, that there is +5 and -5 at the l7805 and l7905.
Any ideas? How can I continue troubleshooting? Next I will check all the resistors, I think…

Obvious stuff first (no disrespect intended): are the ICs, transistors, diodes and polarized capacitors plugged in the right way?

If that all looks OK, can you probe pin 5 of the PIC to see if it is oscillating?
That would split the troubleshooting space in two:

  • if pin 5 is oscillating, the problem is in the analog output filter section
  • if pin 5 is not oscillating, either the PIC is bad, or its inputs are bad

As I don’t have that module, I am basing my analysis only on the schematic on this page:

1 Like

Hej Antoine! thank you for your help! I have checked the things you suggested, they seem to be okay. I have an oscillating signal at pin 5, so the problem is at the stage behind that… I think I will try to track the signal from pin 5 to the output, right?

1 Like

Sounds good. Let us know what you find.

1 Like

I found that I am somewhat stupid :wink: it did work the whole time! I just had to adjust the trimmer poti! Thanks for your help and I would suggest a small note in the description of the LFO project page.


hey Sebastian glad its sorted! I forgot to reply to this, but I made the description of calibration more obvious on the site. hope its working out nicely for you!

1 Like

Mostly finished with mine, testing it out. I have an interesting problem…

Using with the kosmo oscillator I cant get it to modulate anything.

The interesting part is that it works fine plugging it into my behringer pro-1. Also the kosmo osc works great when patched into the pro-1’s LFO. So everything works but not playing nice together I guess

the oscillator right? or the lfo? either way that is very odd! maybe in some weird way the ground is not connectin? or something. maybe check the soldering on the ground lugs on the jack sockets?

Gave up on trying to figure it out and just rehit all the solder and I’m up and running now =]


Can someone please confirm that this is how the jack sockets are wired?

I know there are 7 jack sockets and only 5 power connectors and I see that there are 2 sets of 2 jack sockets that share a single power connector on the bottom of the module. From the photo online it looks like the ground from the power connector wire goes to one jack socket and then from that socket over to the other jack socket ground. I can’t tell if the positive wire from the power connector is wired the same (but to the positive terminal.) I assume so, but wanted to check just in case since I’ve never done this before.

Thanks for the help!

Yes the two jacks labeled “+” at the bottom of the panel (non-inverted outputs) are wired identically: the same black wire goes to the two jacks’ sleeve connections and same white wire goes to the two jacks’ tip connections.
The two jacks labeled “-” (inverted outputs) are similarly wired identically.

1 Like

i’m doing it with the simply version stripboard and add some fonctions

but I have a question about the pin 10 (level)

in the stripboard go it’s going to +5 :

and in the schem to GND :

what can i do with this pin and the difference between the 2 connections please ?

aaah I see. well the lfo has 2 different functions if you look at the data sheet (pin 2 is CV invert), you can invertt the whole chip to respond to inverted response (this reduces the amount of inverting opamps you need

I think you are looking at the full featured schematic which has the mode set to inverted as there is a few pins that are mixed with CV’s check this data sheet and it explains what each of the pins on the chip does

you’ll see in the data sheet if pin 2 is connected to 5v (which it is in the actual module) the cv is inverted, this means I could design the cv inputs with less opamps.

however for the simplified strip board version I haven’t connected pin 2 to 5v, which means it isnt CV inverted which means inputs like level respond like 5v is maximum level and connected to GND would mean the lfo is at minimum level


I hope I made sense in that. haha you could also wire the pin 10 to a knob the same as the other knobs are connected, and it will act as a level control :slight_smile:


thank you but I don’t understand everything, however I tried to read and compare the Data and the different schem …

but no the schem above is the simply one , and the pin 2 go to ground (inverted)
and in the simply stripboard the pin 2 NC (non inverted)

if I understood correctly if pin 2 is on the ground there should be more OP to reverse the signal which is not the case here

I panic :hot_face:

if i don’t connect pin 2 and i don’t want level pot :
pin 10 goes to gnd or to +5 please ?

The inversion setting affects the CV inputs (pins 7-13), not the output signal. There are two stripboard layouts on the LMNC page, and from what I can tell they only differ in the CV direction (so CVs hardwired to GND has been changed to +5V and vice versa in the second one, and (I assume) the pots go backwards relative to the other design if mounted in the same way). There’s no difference in functionality, but the inverted one would make it slightly easier to add more CV inputs (only one opamp needed per input, instead of two).


thanks a lot Fredrik !!!

and with one night it’s more clear in my head this morning

1 Like

i see somethings strange when i compare the Sam complet schemetic and the Datasheet

For the input Sync,

Sam : (go not to ground)

PCB 1.0 VCLFO gros

Datasheet :

datasheet vclfo

when in doubt i’ll do like on data , maybe it’s not important but i wanted to point it out

is it normal / a mistake ?