Where to put LFO on a PCB layout

Started by baklavametal, August 10, 2015, 03:35:37 AM

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baklavametal

Hi everybody!
I'm looking for some advice. I'm eagleing a SMD PCB for a Small Clone and I'm wondering where to place the LFO section to eliminate ticking (my current build from etched bajaman board is showing some ticking). I know to put it as far away as possible from signal path. But does it have to be as far away from the power supply section also?
My current layout has pots, 9v and GND pads on the top, then LFO, then PS filtering and finally in/out signals on the bottom. will that be ok? Also, is it ok to put LFO on the other side of PCB, opposite of the PS filtering section?
thanks!

anotherjim

Need to know the precise schematic, but I'm looking at this one...

Generally, I'd say there are 3 distinct power sections.
Audio circuits
LFO
Clock/bbd
I would start by separating the grounds into 3 emanating from a single star point shared with the neg of the 220uF power input cap and the neg supply wire.

The clock/bbd has it's own power decoupling, but the LFO LM358 is sharing with the audio. I would decouple the 358 pin8 feed with a 47R and 100uF feeding the 47R from the pos power wire input. You asked about position of LFO. It's probably going to have to be close to some audio path in most designs, but choose low impedance audio paths such as amp outputs. Inputs tend to have high impedance as well as some gain afterwards, so they're the ones to keep clean.

Belt & braces, I would add 100nF ceramic caps close to the power pins of every chip, across the power input, across the 4.5V and across the clock/bbd supply from Q3. The ceramics do a better job of guarding against Rf interference into the circuit, or out of it into something else.


baklavametal

Thats exactly the one!
Thanks for your input, just one thing still isn't clear to me.
QuoteI would decouple the 358 pin8 feed with a 47R and 100uF feeding the 47R from the pos power wire input.


do you suggest i take the red path or the green path?


thanks!

duck_arse

the green path will draw all IC2 power/noise via the other 47R, putting that junk where you don't want it. the red path means the IC2 currents are not commoned w/ the other parts of the circuit.
don't make me draw another line.

anotherjim