How to kill LFO bleed-through ?

Ojd · Joined: Feb 22, 2008 Posts: 66 Location: Ua Audio files: 1

Hello. I've built some modules and decided to house them in stompbox format, as it is more suited to gigging. One box i've put together is made of Polyvox filter and LFO (nicolas simple lfo). The problem is that I get "ticking" sound of the LFO even if its not connected to CV in of the filter. I've traced problem back to power supply. I use 12V bipolar for all of my projects (and some commercial stompboxes). So how to kill bleed?

Sebo · Joined: Apr 27, 2007 Posts: 564 Location: Argentina

Hi:
Some things that could work:

1 - Use decuopling in the LFO board (and in every board). A 10uF or 22uF electrolitic bettween +V and GND and other between -V and GND.

2 - Use wires with a biger diameter.

3 - Make sure that your PSU provides enough current.

Hope this helps.

JovianPyx · Posted: Sat Mar 10, 2012 11:51 am Post subject:

If your LFO uses a bipolar 555 timer for it's core - replace it with the CMOS version (number ends in 7555, like ICL7555).

Bipolar 555 timers are well known for crowbarring the powersupply for an instant when pin 3 switches states.

Ojd · Joined: Feb 22, 2008 Posts: 66 Location: Ua Audio files: 1

The LFO is based on 324 opamp. Here the circuit
Posted Image, might have been reduced in size. Click Image to view fullscreen.

The problem is that my wiring is a big mess. Not particularly contributing to s/n ratio. Also when filter is set at max resonance (whistle), LFO at full CCW contributes a slight vibrato.
One way to fight the problem is to send very hot signal, so the ticking is not so apparent. If its a wiring problem I wouldn't be remaking it. If its PSU choking I'll change that one.

Also I want to put mix knob there too, so I could approximate wah pedal sound (which i LOVE), where you can hear clean sound along with filtered one. There might be some phase issues involved, who knows?
Now I might be stupid, but could someone tell me how to use this circuit?
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Where should I connect filtered and unfiltered signal? Maybe I should use another circuit? I think about simple mixer using one FET and dual-gang pot in reverse, the dry-wet control.

Sebo · Joined: Apr 27, 2007 Posts: 564 Location: Argentina

Just re-do the wiring from PSU to the boards...

stewpye · Posted: Sun Mar 11, 2012 7:42 pm Post subject:

Use star wiring from PSU to each module. ie: wire the LFO power wires straight back to PSU and wire the VCF power wires straight back to PSU.

Stew.

creekree · Posted: Sun Mar 11, 2012 10:38 pm Post subject:

I too suggest you redo that wiring.
I´ve been using that LFO design for some time - without any clicking.