Help: Hum but not when trem is engaged.

[master_wiggins]

Hi,

I'm hoping you can help me, I've been building pedals (from kits) for a a few years (but would still consider myself a beginner).  I have just got to the testing stage with my latest pedal and have come across a problem which I just don't understand.

The pedal is basically an A/B/Y  / loop to go at the centre of by pedal board with a few additions.  My main guitar has a piezo bridge pickup and this pedal sends the piezo signal through one effects loop and the main signal through another loop (actually 2 loops, but that's not relivant to my problem) then they both come back to the A/B switch and then out to the amp.  For the 'Y' switch I have a blender circuit and boost (both built from kits by Fuzz Dog).  Also on the main loop I stuck in an EA tremolo for good measure.

My problem is that when I try the 'Y' circuit I get a really noticeable hum.  I am fairly sure that it is coming from the boost not the blend circuit as I used the blend circuit in a previous pedal.  But here is the weird bit that I don't understand; when I turn on the tremolo the hum just disappears.  I don't understand because these circuits shouldn't have any effect on each other.

So just to clarify:

(Piezo out via EQ pedal) mixed with (humbucker out via distortion pedal) into boost - hum
(Piezo out via EQ pedal) mixed with (humbucker out via distortion pedal and EA trem) into boost - no hum

Anyone have any idea what could be going on here?

David

Ps.  If you'll excuse my shamefully messy wiring I'll post some photos below.

[master_wiggins]

Photo as promised:

http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/IMG_2726.JPG.html?g2_imageViewsIndex=1

[antonis]

Nice tomato & pesto sauce spaghetti...!!! 
(it's almost lunch time here..) 

Don't know much about piezo pickups but, if you use "common" PS for all your pedals (daisy-chain), your tremolo has a 50/60 Hz RC filter in it's individual circuit..


P.S.
Re-arrange that spaghetti and embellish it with some low frequency decoupling caps..

[duck_arse]

as someone much smarter than me once said:

[master_wiggins]

Thanks Antonis,

So would it make sense to try adding a filter to the power supply of the boost cercuit?

Something like this perhaps? :

http://shop.pedalparts.co.uk/Hum_Stop_-_power_supply_hum_reducer/p847124_6807259.aspx

[antonis]

It should be a good idea to place one on every individual circuit..
(if already doesn't exist..)

I don't suggest "one-for-all" for many reasons..
(one of them is the need for a very small series resistor, to avoid high voltage drop due to sum of currents, leading to a big electro capacitor value..)

Note that, you may avoid each circuit's hum but not necessarily the hum due to ground loops..