geofex A/B/Y

[Barcode80]

FYI, if you read up on the ggg website, it mentions noise problems when using high gain with this switcher:

http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=16&Itemid=26

[trixdropd]

FYI, if you read up on the ggg website, it mentions noise problems when using high gain with this switcher:

http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=16&Itemid=26

Well that just sucks I guess. I wasted my time and my money. I need to find a solution...

Thanks for your help Barcode...

[Barcode80]

no problem. by the way, never underestimate the merits of a plain ole a/b/y... two switches, three jacks, no mess.

[trixdropd]

no problem. by the way, never underestimate the merits of a plain ole a/b/y... two switches, three jacks, no mess.

I've been there and done that, but the ground loop hum is not usable. I have a morley but it sucks....

[Barcode80]

shouldn't be any ground loops if wired properly in a passive a/b/y...

[trixdropd]

shouldn't be any ground loops if wired properly in a passive a/b/y...

Do you have any examples?? Are we talking about 1 amp mot having the sleeve connected?
I need to build a 5 amp switcher, and I've gotten so close except this little noise issue.

[trixdropd]

R.G., can you help at all?

[R.G.]

Maybe.

1. Do you have this thing mounted in a metal box?
2. What power is being used? Battery? Wall wart adapter?
3. If power comes into the box from an adapter, is the jack a plastic body jack or a metal body one?
3. Is the input jack metal sleeve connected to the box?
4. For each output jack, is it connected to the box?

[trixdropd]

1. Do you have this thing mounted in a metal box?

Have not put it into a box just yet.

2. What power is being used? Battery? Wall wart adapter?

Power pack. Ibanez regulated 9v200ma, I have used with many different pedals with no issues.

3. If power comes into the box from an adapter, is the jack a plastic body jack or a metal body one?

The power jack is plastic and would be isolated from the chassis.

3. Is the input jack metal sleeve connected to the box?

The input jack is plastic But I intend on connecting the ground from it to the chassis.

4. For each output jack, is it connected to the box?

The output would connect to the chassis, but are plastic isolated.

Thanks...

[Andi]

shouldn't be any ground loops if wired properly in a passive a/b/y...

There has to be a ground loop in Y mode. Unless you're just lifting the ground on one or both outputs.

[trixdropd]

shouldn't be any ground loops if wired properly in a passive a/b/y...

There has to be a ground loop in Y mode. Unless you're just lifting the ground on one or both outputs.

I haven't even gotten to "Y" mode yet. This is just one output into my line 6 interface. I've made good and sure my cables are good, and no outside interference is getting in. No crt tv's, no florescent lights, all power through a furman, ect.

If you listen to my audio example its a low lying hum, but in the high gain situation this will be used in, it would be unusable.

I just did some messing around with a 15 watt line 6 spider. it sounds like a low lying 60hz hum. If I connect the two output grounds, the hum seems to almost disappear. I'd estimate it drops by 50%. But, that would defeat the purpose of the design.

I don't know if it matters or not, But I have my input ground connected to the boards ground and the two switch wires "open" going nowhere at the moment. 

[R.G.]

Hook a 10K resistor from each jack ground to a common point.

[trixdropd]

Hook a 10K resistor from each jack ground to a common point.

I will try that fully later. I just tried a 10k resister on the input ground. The noise is much higher.

Another passive question; Wouldn't those resisters set my ground back up to have a loop?

More importantly, This experiment lead me to some insight to what's happening. I don't know the answer, but if the input ground is disconnected, as soon as i connect it, it's silent, then you hear the hum ramp up to its level. This repeats every time. Does that help?   

[Barcode80]

I should note that (correct me if I'm wrong, o great RG) that having a "ground loop" is not the same as having all your grounds connected...

also, the box offers a pretty great deal of shielding from interference. you really ought to box it up before giving up...

[trixdropd]

I should note that (correct me if I'm wrong, o great RG) that having a "ground loop" is not the same as having all your grounds connected...

also, the box offers a pretty great deal of shielding from interference. you really ought to box it up before giving up...

I have and am gonna experiment with that. I've wrapped grounded tinfoil around the entire circuitry with no change. I know the transformers could have hum without great shielding so i'm looking into it.

[R.G.]

Just as a bit of punctuation, there are many ways to get hum.

The air around us is permeated in power-line-frequency electric and magnetic fields. You can pick these up capacitively by having a high impedance input or magnetically by having either a coil (transformers) or a loop of conductor (ground loop). Every electrical outlet has a slightly different AC voltage because the currents and conductor lengths leading to them are different. Every transformer supplying power leaks a little AC into its secondary by capacitive and inductive means.

It is really quite difficult to make large assemblies of equipment be totally hum free, especially if it's got high impedance inputs (like guitar amps), different power supply designs (like guitar amps), old and low-cost design transformers (like guitar amps), two wire power cords (like many guitar amps), and very high gain preamps (like many guitar amps and pedals), plugs into different AC plugs (like many stage setups), and has to be taken apart and reassembled almost nightly (like many stage setups).

It's even worse when the inherent design of the equipment cabling must be high impedance and single ended, like guitar cord, and cannot be changed to shielded twisted pair by the very nature of the equipment, like guitar amps.   

To get a perfectly hum free setup with five amps, you have some *very* tough design and implementation issues to resolve, and while you might get lucky and have it simply go away if there happens to be one major source of hum that you find, it's likely to be more like peeling onions: you remove a layer, cry a little, then remove the next layer.

[trixdropd]

Just as a bit of punctuation, there are many ways to get hum.

The air around us is permeated in power-line-frequency electric and magnetic fields. You can pick these up capacitively by having a high impedance input or magnetically by having either a coil (transformers) or a loop of conductor (ground loop). Every electrical outlet has a slightly different AC voltage because the currents and conductor lengths leading to them are different. Every transformer supplying power leaks a little AC into its secondary by capacitive and inductive means.

It is really quite difficult to make large assemblies of equipment be totally hum free, especially if it's got high impedance inputs (like guitar amps), different power supply designs (like guitar amps), old and low-cost design transformers (like guitar amps), two wire power cords (like many guitar amps), and very high gain preamps (like many guitar amps and pedals), plugs into different AC plugs (like many stage setups), and has to be taken apart and reassembled almost nightly (like many stage setups).

It's even worse when the inherent design of the equipment cabling must be high impedance and single ended, like guitar cord, and cannot be changed to shielded twisted pair by the very nature of the equipment, like guitar amps.   

To get a perfectly hum free setup with five amps, you have some *very* tough design and implementation issues to resolve, and while you might get lucky and have it simply go away if there happens to be one major source of hum that you find, it's likely to be more like peeling onions: you remove a layer, cry a little, then remove the next layer.

All very true. But this is a hum that is induced by this circuit. So far I've only plugged in 1 amp at a time and the hum is unusable with the tight high gain sounds being used. I am gonna try some things to see if I can iron it out. I am determined to get this working right!!

[R.G.]

Here's a thought - is your circuit (with its wound-coil transformers) sitting near any other power line transformer, on an amp, etc? Isolation transformers make good pickups too.

[trixdropd]

Here's a thought - is your circuit (with its wound-coil transformers) sitting near any other power line transformer, on an amp, etc? Isolation transformers make good pickups too.

No, they weren't. That's the first thing I checked. I actually went ahead and killed any power i didn't need to be sure that wasn't the issue.

Some of the things I'm gonna try are having the input grounded to the case, with an unisolated output that is always connected to the input's ground. I will try the 10m resisters on the grounds as well via dipswitch or other switch as to make each isolated output have a choice of 1. ground connected off the transformer as per schematic 2. Ground lifted 3. Ground via 10m resister. Above that, I may make a metal shield around each transformer Like the jensens have and many other brands. I do have a steel enclosure as you recommended on www.geofex.com

So far in my tests I have only run through 1 isolated output at a time without having the inputs ground connected with the amps ground. that may be my problem as well. Thanks for the help. I will attempt these things and when i get 1 to work right, I will tackle the 5!!   

[Andi]

Lifting the ground on a transformer isolated output (if you mean disconnecting the shield at the output) will, I'd think, result in no signal making it out - no complete circuit.