ANOTHER aby thread :D

[tennisdude]

Hey guys,

The ABY pedal is all boxed up. It hums loudly with my mesa boogie studio 22, but theres no hum with my home-made gilmore jr. amp. what gives? Anyone have comments/suggestions on how to quiet this baby down, or is it just the nature of the beast? Unfortunately, if I kick on the lead channel on the mesa the hum from the box is unbearably loud. It sounds fine loud on the clean channel. Otherwise I'm very pleased, the switching and LED's work fine, and I really like having a stereo setup 

EDIT: It hums from either output.

Thanks
John

[tennisdude]

just found "theundeadelvis" 's suggestion from an old thread:

"I just installed an on/off/on (spdt?) toggle with the center pole going to chasis ground, one pole going to one of the output jacks and the other pole going to both outputs. I can switch between total output isolation, 1, or none. It seems to work pretty and gives me options for other amp and enviroment interactions. Hope this helps!"

This toggle switch has three poles total? Seems like a cool solution to help troubleshoot. Comments anybody?

John

[theundeadelvis]

It has worked great for me. It gives me different ground/isolation options for different amps and enviromwents. When I first built the ABY it hummed lbad but now it's silent.

[tennisdude]

would this do the trick?

http://www.smallbearelec.com/Detail.bok?no=39

it specifies "center off" on the stock list

[theundeadelvis]

Yep. The center position would be total isolation. Then the other 2 positions would be either one jack grounded or both grounded.

[mydementia]

I did a similar thing with a on-off-on SPDT switch (one 'on' pole goes to single output ground, the other 'on' pole goes to both output grounds - middle post to board ground) - while both grounded positions are dramatically less noisy - this circuit is still unusable with my Peavey XXX amp on either dirt channel .  I have had good luck with the fulltone AB switch - really does everything I need.  I also noticed that Radial recently put out an ABY box (Big Shot?) that has a ground lift for ~$60...with all the hours I've spent trying to get the GEO humfree2 working, I should have just bought the Radial!!  ...or started with the fulltone!  I'd really like to get someone (RG?) to chime in on one of these threads to tell us what we're doing wrong...seems to be a recurring theme on this circuit.
Had to add my 2cents.
Mike

[KMS]

Hey stompers!

I built the 1999 GEO ABY 3 months ago without any switching.....just straight out on all channels.

I put 6 channels on it and did not use the "direct out" option.

I tried it on several amps at once and had no problem with all the channels on, but if I lifted any lead that would represent the same switching as the schemo on GEO I got hum (this was before it was boxed up...... on an experimenter board).

For my purpose I did not really want to switch the ABY until after my signal(s) (channels) had gone through various effects so I really never had the intention of using the complete schemo from GEO or GGG layout for my PCB and thus I made my own PCB which is now in this site's archives.

I optioned to do my switching in a diy 10 channel stereo mixer that is now inside my pedal board with the ABY and all my other FX. I found that I could just put an LED/LDR in between each first stage op-amp and the the final summing op-amp in the mixer and turn each channel on and of with no hum.

I'm having good luck making LED/LDRs with .004 amp on the LED I get 400ohm on the LDR and a dark resistance of over 2M. You have to buy several packs of LDRs and cherry pick the pack for the best ones. I also but 220uf cap across the LED to smooth out the on off power surge.

So I can still have stereo with ABY function actually I have ABCY.....and with the switching matrix I built I have a load of different parallel channel output options on the fly which require some preset tasks using some mini toggles but primarily one SPDT MOM operates as a master stomp for the entire matrix.  The beauty of it is that I don't need the expensive stomp switches (that click real loud) to operate the LED/LDRs and none of my audio signal is sent through a physical contact switch anywhere in my pedal board. My switing power supply and all the lights on my pedal board are controlled by a separate 9V power supply (PS).

So lets look at what it took to get no hum without an anti-hum switch waisting board space just to stop the hum.

Inside the pedal board (a big steel box) both of my PS are grounded to the box in one spot call it "ground zero" ( right in the middle of the box) so 0V of my bipolar PS meets the negative of my other PS inside the box.  The two PS(s) are both installed in a separate steel box and for which the PS grounds are isolated in the PS box.

The jacks are all isolated ground both for the PS box and the pedal board.

My guitar signal fist goes into a diy compressor and next a diy noise gate for which both of those circuits are connected to the same negative wire (0V from the bipolar supply but not being used for bipolar on these two circuits) which incidentally is connected to the steel box at "ground zero".  The guitar signal then goes into the ABY which is connected to 0V ground which is the same negative for all of my FX in the box (except my switching matrix circuit which is on another PS). The signal leaves the ABY circuit it then goes into various FX for which each FX is connected to the negative 0V which are all in common with the box at "ground zero".

Call this isolated ground if you like but what it really is partially isolated.  The ground for the guitar signal and the circuitry is isolated up to the point where it is actually put to work and then after that point it is no longer isolated.

I also used shielded cable for the entire routing of the off board guitar signal and I have not yet connect the shielding to ground and perhaps I will if I later get some hum from some future diy hot-ass circuit but for now I don't need that.

I am planning on posting some pics...maybe this Sunday Night...but the box is kind of rough looking and I do not plan on painting the box until I put about 6 to 8 more FX in it. Maybe I will just slap some permanent marker on to give it some color so everyone can get a look at it in the intermediate stage.

I know it sounds like a lot of work to do this..and it is....but zero-hum, zero-pop, and no stomp-click makes it well worth the work.

Hope someone can make use of my grounding methods.

[tennisdude]

very cool advice KMS! I think I'll go the undeadelvis' route to start, because its alot simpler, but if that doesnt kick it ill have to give you technique a try.

[tennisdude]

quick update:

I connected the left output to chassis ground, and left the right output isolated. Poof, hum gone 

I also added a kill switch, so I can leave this baby plugged in all the time and not wear the LED's down, let alone have them keep me up at night.
This is a great pedal! Thanks alot to RG, the undeadelvis, and everyone else who helped me out.

John