Pork Barrel Noisy LFO - FIXED

[wilsona]

Just had an epic tussle getting my Pork Barrel working (it was a dodgy connection on the PCB). Now I have a problem with noise.

The LFO has an audible tick that varies with the the rate - does anyone have any idea on how to get rid of it? It is loud enough to make the pedal unusable. Otherwise it is fine, although it does not like being driven and distorts a bit. Plenty of depth.

I have already tried shielding the pots and signal wires from the PCB with copper tape and checking everything is grounded OK.

Help (again)!

[blearyeyes]

Last guy that had this problem tightened up all of the jacks and such and it went away. Seems like it's always a ground issue.

http://www.madbeanpedals.com/forum/index.php?topic=16495.0

[wilsona]

Well everything on mine is plenty tight... I do notice the case is a bit microphonic, tapping it comes through - what could that be?

[blearyeyes]

The trannies are in sockets, the chips are in sockets. I had a crackling in one pedal that I fixed by bending the transistors leads so they had pressure after being inserted into the sockets. Try tapping on all the components (gently) that's how I found the transistor wasn't seating properly. Some people solder them into the sockets after finishing using a heat sink of course. Not sure if chips can be microphonic.

Did you use plastic jacks?

[wilsona]

Skeleton jacks. I'll open it up and try tapping things.

[RobA]

Ticking from an LFO can come from the changes in power draw at the points where the LFO tops and/or bottoms out. The TL062 should help reduce this because it's a low current draw op-amp. Still, it could be something related to the interaction of your pedal and the power supply. Does it do it with different ways of powering the pedal?

The changes in the current draw can be coming through the audio op-amp because of the changes in available current for its pins. It could be that changing that op-amp to a new type might help. Check to see if all the sections in the power supply filtering look OK too. One thing that might help is to put 100nF ceramic caps across the power rails on the op-amps. Tacking them from pin 8 to pin 4 will get them as close to the rail as possible, and that's what you want. You might be able to test if it'll help just by holding the cap in place while the pedal is running.

[blearyeyes]

Mine sounds 100% better with 15v power, didn't have any ticking though. I bought a road rage to use with it. Really worth it for the 3007 build.

[blearyeyes]

Rob, what could be causing the microphonic case the OP spoke about?
Can chips do that?

[RobA]

Rob, what could be causing the microphonic case the OP spoke about?
Can chips do that?

I've got no idea if chips can do that. I wouldn't say no though. I guess that it would be possible in a case where a lead was not completely attached at a junction with the IC.

My first guess though would be that it was with the connections somewhere or maybe a pot that was a bit screwy. Maybe tap the individual parts and wires to see if it could be narrowed down?

[blearyeyes]

Agree, I guess you learn nothing is impossible with this stuff...except maybe a pedal that does your laundry...  I've fixed more stuff by banging on it in frustration than hours of thinking...8-)) lol.

[wilsona]

Thanks for feedback - I have not had time to open it up and tap around yet. The power supply is 9V from an MXR Brick. I'll try a separate 9V wallwart and see if it is any different.

[wilsona]

Same issue with a different PSU. Will give the capacitor suggestion a try. I do not have one that size around - how close does it have to be to 100nF?

[Scruffie]

It's probably your pot wiring, shorten and tidy the wires, don't braid them together, keep them separate.

You could try a cap anywhere from 100nF to 100uF (negative to pin 4, positive to pin 8 ) on the back of the LFO chip.

Be sure you have all your electrolytics orientated correctly too.

[muddyfox]

anything inherently wrong with braiding the pots? i used to do it all the time back when i was heavily into vero for the sole purpose of spaghetti management. worked wonders for that...

[wilsona]

I've screened the pots from the pcb using copper foil, with only the last cm unshielded, and the I/O wires from the pots and PCB, so I assumed that was sufficient. To braid them I would have to affix longer wires  to the pots but I can try it if you think its worth it. Unfortunately I decided to put the jack sockets at the top of the box, so everything is a bit open up there, and the I/O wires run the whole length of the enclosure under the PCB.

Regarding the cap on the MN3101 - I was just going to use a non-polarised ceramic but I might have a suitable size electrolytic around.