A-B-Y Box Noise:

Lehle Dual SGoS Dual Amplifier Switcher Features at a Glance:
  • Dual amplifier switcher with three sets of outputs
  • Outputs A and B can feed two amplifiers simultaneously
  • Outputs are electrically isolated by the Lehle LTHZ high-end transformer
  • Onboard potentiometers let you adjust the output signal for A and B separately
  • Output T can be used for a tuner or a third amplifier
  • Can be controlled and synchronized with other Lehle SGoS switchers via MIDI
Why this model both A & B outputs are electrically isolated GET IT.......................................:BH:
 
smitty_p said:
Okay…and setting the Transformer Isolate switch to “Isolate” doesn’t help?
Click to expand...
Robert Herndon said:
Nope. I am stumped.

youtube.com

Noise From Two Amps Through Cool Switch Pro A-B-Y Box:

Ground lift feature doesn't cut the noise. I've used both a Blackstar ID-Core 100watt solid state and a Marshall MG50 Solid State with identical results. A g...
youtube.com youtube.com
Click to expand...

To review the operation a little, the Transformer Isolate switch only inserts the isolation transformer into the signal path for Output B. There is no transformer for Output A.

I assume pulling the feed from Output B kills the noise, correct?

Also, I assume you’ve swapped the amps around, correct?

Do you notice ANY change when you flip the Transformer Isolate switch?
 
I think it's time to try another amp switcher box. Maybe jump on Sp8ctre's offer to try his Radial Big Shot AB/Y? Or order the Radial Twin City (AB/Y)... If it doesn't do the trick, just send it back!

No other convenient source to try another AB/Y box from another musician or studio?
 
Robert Herndon said:
Tonight, I bypassed all the FX and just hooked the origin 50 to 'Output A' of the ABY box (Origin Input cable to ABY Box Output A) and I plugged the Blackstar into the 'Output B' of the ABY box. (This is how the instructions say to connect two amps.)

I get really loud 60 cycle hum. Activating the ground lift, transformer isolation and/or phase switch on the ABY box does not stop the noise, but it does change the frequency, as I posted in the video link above.

If I unplug the slave amp from the A-B-Y box, the hum stops, even with the slave amp's volume up

I can turn the Blackstar down enough that the volume drops to zero.
Click to expand...
"Bypassed" all of the effects.
UN-plug all of the effects entirely, take them completely out of the system.
Turn off all of the effects power. UN-plug the effects power from the wall.
Make sure the effects power is completely deactivated, and not powered up anywhere.
Leave it that way for the remainder of the tests.

Hook up the A/B switch to the main amp and to the slave amp.
Is the hum still there?

Lift the ground to the slave amp A/B output. Is the hum still there?

If you turn down the slave amp volume does the hum go away?

Do you have one of these?

1636986140992.jpg Break the tab off, make sure it doesn't touch the power outlet screw.

Plug the slave amp power in, with the ground adapter above.
Is the hum still there?
 
smitty_p said:
To review the operation a little, the Transformer Isolate switch only inserts the isolation transformer into the signal path for Output B. There is no transformer for Output A.

I assume pulling the feed from Output B kills the noise, correct?
Click to expand...

Yes.

smitty_p said:
Also, I assume you’ve swapped the amps around, correct?
Click to expand...

Yes. Several.

smitty_p said:
Do you notice ANY change when you flip the Transformer Isolate switch?
Click to expand...

A slight pitch change.
 
Amp Mad Scientist said:
"Bypassed" all of the effects.
UN-plug all of the effects entirely, take them completely out of the system.
Turn off all of the effects power. UN-plug the effects power from the wall.
Make sure the effects power is completely deactivated, and not powered up anywhere.
Leave it that way for the remainder of the tests.

Hook up the A/B switch to the main amp and to the slave amp.
Is the hum still there?

Lift the ground to the slave amp A/B output. Is the hum still there?

If you turn down the slave amp volume does the hum go away?

Do you have one of these?

View attachment 75825 Break the tab off, make sure it doesn't touch the power outlet screw.

Plug the slave amp power in, with the ground adapter above.
Is the hum still there?
Click to expand...

I've got a full day of recording ahead, so I won't be able to conduct these tests until tonight...but I will report as soon as I have followed those steps precisely.
 
syscokid said:
I think it's time to try another amp switcher box. Maybe jump on Sp8ctre's offer to try his Radial Big Shot AB/Y? Or order the Radial Twin City (AB/Y)... If it doesn't do the trick, just send it back!

No other convenient source to try another AB/Y box from another musician or studio?
Click to expand...

Definitely. I'd like to try @Sp8ctre's unit as we know that his device has worked in real time...
 
Robert Herndon said:
I've got a full day of recording ahead, so I won't be able to conduct these tests until tonight...but I will report as soon as I have followed those steps precisely.
Click to expand...
Narrow down what is causing the hum one step at a time.

I have seen this happen before:
the effect(s) power supply has a magnetic field, which can enter the audio path.

The closer that the audio cables are to the power (supply or power cables etc), the more noise gets into the audio path.

The "power" can be any effects unit (which has internal power), or a multi power supply that supplies several effects pedals.
Ideally the audio wires (patch cables between effects units or to anywhere else)
are separated from the power supply / power wires as far as possible.

And the trouble is that some separation may not be enough to stop the hum or noise completely.
The distance between audio and power needs to be (sometimes) pretty large to stop the hum / noise.

One strategy used is to place power 90 degrees turned from the audio cables....
so that the audio and power are at right angles to each other.
another might be adding shielding to block the magnetic field that radiates from a power supply.
 
Sp8ctre said:
I'm travelling all week for work. I'll be in a hotel in Riverside tonight, then Carlsbad tomorrow night. You are welcome to hunt me down and get it or I can mail it to you...
Click to expand...

Mailing is fine. I've got a full schedule this week myself.
 
Amp Mad Scientist said:
Narrow down what is causing the hum one step at a time.

I have seen this happen before:
the effect(s) power supply has a magnetic field, which can enter the audio path.

The closer that the audio cables are to the power (supply or power cables etc), the more noise gets into the audio path.

The "power" can be any effects unit (which has internal power), or a multi power supply that supplies several effects pedals.
Ideally the audio wires (patch cables between effects units or to anywhere else)
are separated from the power supply / power wires as far as possible.

And the trouble is that some separation may not be enough to stop the hum or noise completely.
The distance between audio and power needs to be (sometimes) pretty large to stop the hum / noise.

One strategy used is to place power 90 degrees turned from the audio cables....
so that the audio and power are at right angles to each other.
another might be adding shielding to block the magnetic field that radiates from a power supply.
Click to expand...

Just a side note here...I've already totally disconnected the FX pedals from the circuit, including removing the power supply and removing the send/return cables from the Origin's FX loop.

There was no change.

I also avoid things like putting a coiled audio cable under the amp head, and creating separate paths for power cables, etc.

More detailed testing to take place tonight.
 
So, much less noise with the Alctron SW-21, but there is still a hum.

The ground lift cable does not eliminate the hum.
 
You must log in or register to reply here.
Back
Top