Hello, while building out my rig, I came across a definite ground loop issue (which is common) and while I was able to solve the issue, I am wondering if there are any alternative solutions. I'll explain in detail.
I have two tube amp heads connected to a single 4x12 cabinet using an Axess Electronics HS-2 head switcher. This works fabulously. (Previously I had a Radial Headbone but it squeals very loudly with my amps and Radial flat out told me that it will not work with high-gain amps...that's another story). With the two heads, one cabinet and the HS-2 everything works great and there is no noise. The I added in my Rack Gizmo to add function switching only (at first). I built two custom control cables which connect to the Amp1 and Amp2 DIN connectors on the back of the Rack Gizmo. The first cable that is connected to Amp1 is wired to pins 1, 2 and 8 only. The second cable is connected to Amp2 is wired to pins 3 and 4 only. The other end of each cable fans out to tip-sleeve 1/4" jacks. The first cable is connected to my first amp via pins 1 and 2 to control channler switching and solo functions. The third plug on cable 1 (Amp1) goes to the footswitch jack on the Axess HS-2 to control which amp head is selected (pin 8, off = Amp1, on = Amp2). The second cable is connected to Amp2 and controls its channel and solo functions. Nothing is connected to any of the audio plugs on the Rack Gizmo. Already you probably will say that there may be a ground loop between Amp1 and the HS-2 because they are connected togther by the ground lead of the custom control cable. The manual for the HS-2 also states that Amp1 is grounded by the Input on Amp1 and that Amp2 is isolated. The HS-2 is powered by a 9VDC power supply (ungrounded). This configuration works great but there is a very noticeable 60Hz hum on Amp1, more noticeable when on the high gain channel (of course).
Here are the things I tried to solve the hum problem that did not make any difference:
1. Minimizing the whole rig. No pedals, no effects loops, etc.
1. I tried 3 different power supplies including a fully isolated MXR/CAR MC-403 with nohting else on it.
2. Routing power and audio cables away from one another.
3. Switching the custom cables between Amp1 and Amp2 (since Amp2 is isolated in the HS-2) - but this did not make a difference and the hum remained in Amp1. This is not what I expected.
What did solve the problem?
When I was troubleshooting, I unplugged the lead in the Amp1 custom cable that controls the HS-2 from the HS-2. The hum completely went away, so I knew that this was indeed the source of the hum. But with the connection removed, I could not switch between amp heads. Then I quickly built a shorting plug from an extra Switchcraft plug a had and a small bit of wire and I connected it into the return jack of independent loop 8 on the Rack Gizmo and then I grabbed a patch cable and plugged one end into the output of loop 8 on the Rack Gizmo and the other end into the footswitch jack of the HS-2 and left the previous cable that went into the HS-2's footswitch jack hanging. I quickly reprogrammed a couple of patches to use loop 8 to control switcing of the HS-2 and this works great and with NO HUM!!!
Now here's my question: Are there any alternatives I could implement in order to not use one of my independent loops on the Rack Gizmo and instead use one of the function switches but without creating a ground loop or introduce hum into the system? I had other plans for that loop and there are only 4 independent loops on a Rack Gizmo (or Effect Gizmo too). One thought I had was to create a custom cable with 4 leads to connect to Amp1 jack to control the functions of Amp1 and Amp2 and use the Amp2 jack to control the HS-2 but I fear that will create a ground loop between the two amp heads. I am trying to avoid using hum eliminators in the audio path, if possible.
Thanks for any feedback and I hope this helps others facing similar issues.
-Wade
I have two tube amp heads connected to a single 4x12 cabinet using an Axess Electronics HS-2 head switcher. This works fabulously. (Previously I had a Radial Headbone but it squeals very loudly with my amps and Radial flat out told me that it will not work with high-gain amps...that's another story). With the two heads, one cabinet and the HS-2 everything works great and there is no noise. The I added in my Rack Gizmo to add function switching only (at first). I built two custom control cables which connect to the Amp1 and Amp2 DIN connectors on the back of the Rack Gizmo. The first cable that is connected to Amp1 is wired to pins 1, 2 and 8 only. The second cable is connected to Amp2 is wired to pins 3 and 4 only. The other end of each cable fans out to tip-sleeve 1/4" jacks. The first cable is connected to my first amp via pins 1 and 2 to control channler switching and solo functions. The third plug on cable 1 (Amp1) goes to the footswitch jack on the Axess HS-2 to control which amp head is selected (pin 8, off = Amp1, on = Amp2). The second cable is connected to Amp2 and controls its channel and solo functions. Nothing is connected to any of the audio plugs on the Rack Gizmo. Already you probably will say that there may be a ground loop between Amp1 and the HS-2 because they are connected togther by the ground lead of the custom control cable. The manual for the HS-2 also states that Amp1 is grounded by the Input on Amp1 and that Amp2 is isolated. The HS-2 is powered by a 9VDC power supply (ungrounded). This configuration works great but there is a very noticeable 60Hz hum on Amp1, more noticeable when on the high gain channel (of course).
Here are the things I tried to solve the hum problem that did not make any difference:
1. Minimizing the whole rig. No pedals, no effects loops, etc.
1. I tried 3 different power supplies including a fully isolated MXR/CAR MC-403 with nohting else on it.
2. Routing power and audio cables away from one another.
3. Switching the custom cables between Amp1 and Amp2 (since Amp2 is isolated in the HS-2) - but this did not make a difference and the hum remained in Amp1. This is not what I expected.
What did solve the problem?
When I was troubleshooting, I unplugged the lead in the Amp1 custom cable that controls the HS-2 from the HS-2. The hum completely went away, so I knew that this was indeed the source of the hum. But with the connection removed, I could not switch between amp heads. Then I quickly built a shorting plug from an extra Switchcraft plug a had and a small bit of wire and I connected it into the return jack of independent loop 8 on the Rack Gizmo and then I grabbed a patch cable and plugged one end into the output of loop 8 on the Rack Gizmo and the other end into the footswitch jack of the HS-2 and left the previous cable that went into the HS-2's footswitch jack hanging. I quickly reprogrammed a couple of patches to use loop 8 to control switcing of the HS-2 and this works great and with NO HUM!!!
Now here's my question: Are there any alternatives I could implement in order to not use one of my independent loops on the Rack Gizmo and instead use one of the function switches but without creating a ground loop or introduce hum into the system? I had other plans for that loop and there are only 4 independent loops on a Rack Gizmo (or Effect Gizmo too). One thought I had was to create a custom cable with 4 leads to connect to Amp1 jack to control the functions of Amp1 and Amp2 and use the Amp2 jack to control the HS-2 but I fear that will create a ground loop between the two amp heads. I am trying to avoid using hum eliminators in the audio path, if possible.
Thanks for any feedback and I hope this helps others facing similar issues.
-Wade
