GEOFEX Humfree ABY hums............

[Bernardduur]

So I build the Humbfree A/B/Y box from GEOFEX LINK and I tested it with a LOT of different amps but it still hums.....well, not hum. When I plug in my non-humfree ABY it HUMS, but with this unit it is more a high pitched noise....... dunno what it is. All amps I tested it on did the same!

So I checked my build...... but it is still OK. So I touched one of the outputs (isolated) while touching the strings and the noise goes away on BOTH amps.

So I wired ONE of the outputs' ground to the box's ground and now the hum is gone. Weird....... dunno if someone else has noticed this. It is still humfree as one of em is isolated, the other one isn't.

[R.G.]

AC wiring hum is very devious, and there are many different situations. The isolating circuit can only take care of some of these, apparently.

It seems like in your situation, at least one of them has to be grounded to make it be quiet. OK, so connect one side only to signal ground, and then they're both quiet.

You might be able to use a 1M or a 100K instead of a wire there for the single connection.

[morcey2]

I built one also and I love it.  AFTER I un-isolated the 'A' output.  The guitar has to be grounded somewhere.  Without that, you'll pick up all sorts of weird noises.   At some point I'm going to add ground switches to each of the outputs so I can change it as needed. 

Matt.

[Bernardduur]

Hey all!

New question
I tried to build this baby again for my bass needs and now I thought to only use 1 transformer and wire the other output directly to the un-isolated output............
Now I get all kind of weird interference on this channel. Hiss, noise and the guitar signal when turned on.

When I add a transformer the noise and interference is gone and the unit works awesome!

Is there a way to remove the second transformer or should I keep it with 2 of em..............




Edit; nice addition. When I use it with my Baby CIOKS PSU or any run of the mill PSU it is dead quiet (w/ 2 transformers), when I use it with my Dunlop DC brick it hums like a madman............
Shame that DC brick is my main PSU for bass use..........

Edit 2; I solved the DC brick hum; with the other PSU's I don't have to plug in the non-isolated version, with the DC brick I need to plug in the non-isolated output to a grounded amp. Pfoe........ I think the DC brick is isolated or something so the pedal can't use that as a main ground.

[joelap]

Having a similar issue right now.  I built my Hum Free ABY when I had my old poweramp.  I was about to run my rack setup and my AC30 at the same time, no hum.  I put the pedal away for a while, and when I got my new poweramp I took it out again and it was humming like crazy.  Tried a few things, nothign worked, put it away.  Took it out again the other day with the same setup and it was humming.  I noticed when I touched the strings and my foot touched the metal case of the pedal, humming went away.  So I took a wire and soldered it into a screw hole slot (tried to solder it in there) and it worked.  This was 2 days ago.  Went to work, came home, turned it on... hum again!  All my jacks are isolated.  I've read connecting the ground of one of the outputs to the input ground may work... does that mean I am connecting the point where the Ring, Transformer lead, and capacitor meet to ground?  Any other solutions? 

[R.G.]

Try a 100K resistor bypassed with a 0.01uF ceramic cap to "ground" the output jacks. Sometimes you're getting RF buzz and this will "ground" the RF without "grounding" the output jacks. At least ONE output jack needs to be solidly connected to the input jack ground to avoid the open-strings buzz.

... in most cases...


... (mutter) hate hum... 

[trixdropd]

I'd like to hear audio of the issue.

When I built mine, I had the slightest buzz noise in it. I never solved the issue and still have a 5 amp switcher built and collecting dust... I'd love to make her work!!

[doitle]

I'm afraid I can't offer any useful input but I'd like to say that the title of this thread is pretty funny. 

[joelap]

OK so I just connected the sleeve of output 1 to the input sleeve directly via a wire.  The buzz/hum is COMPLETELY GONE .... along with all signal out of output 2!  Checked connections, nothing got messed up during the soldering process, and output 2 is still connected to where it should be (continuity tests).  Removed the wire to the chassis as it was making things act funky.  So now no buzz, but now I've got an A box haha.  Was hoping to use this for a huge gig I have on wednesday... help!?

[Bernardduur]

Huh..... that's weird..... pics?

[R.G.]

All I can imagine is that there was a potential difference lurking between those two points that killed an opamp. Voltages?

[robinbowes]

Try a 100K resistor bypassed with a 0.01uF ceramic cap to "ground" the output jacks. Sometimes you're getting RF buzz and this will "ground" the RF without "grounding" the output jacks. At least ONE output jack needs to be solidly connected to the input jack ground to avoid the open-strings buzz.

So, I'm in the same position as the O.P. - I've built the A/B/Y and it works fine on battery power, but as soon as I power it from a PSU I get loud RF interference.

It is "cured" by grounding the outputs (connecting to input ground) but that kinda takes away the point of the transformer-coupled output.

I'll try using the technique suggested above by R.G. and see how that works. Incidentally, why do you need the cap *and* the resistor? Wouldn't the cap alone ground the RF?

R.

[Bernardduur]

Connect only one of the outputs' ground to the main ground and always use this channel + the other isolated outputs.

[robinbowes]

Hi,

I tried that (connecting input ground to output A ground). output A works fine, but output B still has the same buzz.

Ah, wait a minute - you're saying I should make sure output A is *always* plugged in to an amplifier? That would work, I guess. I'll do some more testing tomorrow.

Thanks,

R.

[Bernardduur]

Yes!

[robinbowes]

That did the trick - input ground to output A ground. It now works great!

Thanks,

R.

[R.G.]

Hum never sleeps.

[robinbowes]

Soundtrack to my youth: