Delay effect - humming - need advise

Started by FastEdTex, August 03, 2016, 01:43:18 AM

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FastEdTex

Building a Mad Bean Cave Dweller2 delay pedal. Link to docs below with layout and schematic.

http://www.madbeanpedals.com/projects/CaveDweller/Cave%20Dweller2015.pdf

I have not boxed it as of yet, but I have rocked it and am getting what I think is a lack of / bad grounding hum in the output.
I have touched up the solder joints on the solder side of the PCB and all the connections at the switch and the daughter card that the POTs are mounted on.
I'm using the enclosed low profile input/output jacks from Small Bearhttp://smallbear-electronics.mybigcommerce.com/stereo-low-profile-pc-mount/
There is continuity between the both sleeve lugs and the pad of the negative side of the power input pad. These jacks have no metal grounding to the case.
On clean channel of the amp the is a very low hum that gets louder when touching the strings or the bridge of the guitar.
On the Overdrive channel it is of course much louder and gets nasty when touching the strings.
The hum also increases when touching the plug housing going into the input jack.
I am hoping to solve the problem before installing in the enclosure. Link to photos of my bad soldering.

http://postimg.org/gallery/syhfd0c8/

I have connected a 9v battery to the leads of the power jack for testing. Reading 8.89v at the +9v pad on the PCB.

IC1 is a PT2399
Pin 1 = 4.94v
Pin 2 = 2.47v
Pin 3 = .1v (meter at 200m - only setting I can get a reading at)
Pin 4 = .1v (meter at 200m - only setting I can get a reading at)
Pin 5 = 2.87v
Pin 6 = 2.47v
Pin 7 = 0.33v
Pin 8 = .065v
Pin 9 thru 16 = 2.47v

Q1 is a 2N5457
D = 5.87v
S =  .99
G = 0.1v (meter at 200m - only setting I can get a reading at)

REG is a LM7805
IN = 7.72
Gnd = 0.1 (meter at 200m - only setting I can get a reading at)
Out = 4.96V

anotherjim

IC1 pin3&4 are 0v so don't be surprised you had trouble finding any volts on them.

I suspect it just needs boxing up. It isn't hard for an unscreened project, particularly guitar fx with their high impedance (sensitive) inputs to pick up radiated electrical noise from lights/air-con/soldering iron - whatever is near.

Box it up in a metal or screened enclosure.

Because I happen have a bag of small gauge screened hook-up wire, I always wire the signal in and out of the pcb with this - it does improve protection from noise on the test bench. But I also start by wiring direct to jacks without the foot-switch for initial testing - the switch body attracts a lot of noise until it's shielded. Switch operation is trivial compared to getting the main circuit working. The switch can be wired & tested after you've proved the rest of it.

FastEdTex


thermionix

If the hum gets louder when you touch the strings, sounds a lot like you have the input jack wired backwards, resulting in a "hot ground" on the guitar.  I can't really tell much looking at the pictures, but the footswitch wiring looks very suspicious to me.