Hi folks,
I have a Thomann the box 350w powered cabinet the box PA 502 A – Thomann UK that has recently developed a very nasty hum (after having returned from a repair shop that cannot fix it).
The hum is so loud that if I turn the volume to even the first notch it feels like the speaker might blow!
If no XLR cable is plugged in then the hum disappears, and if I plug-in an XLR to minijack cable (which probably has no grounding), there is also no hum. But if I use other XLR cables, the hum returns immediately, even if they are not plugged in.
Any ideas what this is and how to fix it?
Many thanks!
I have a Thomann the box 350w powered cabinet the box PA 502 A – Thomann UK that has recently developed a very nasty hum (after having returned from a repair shop that cannot fix it).
The hum is so loud that if I turn the volume to even the first notch it feels like the speaker might blow!
If no XLR cable is plugged in then the hum disappears, and if I plug-in an XLR to minijack cable (which probably has no grounding), there is also no hum. But if I use other XLR cables, the hum returns immediately, even if they are not plugged in.
Any ideas what this is and how to fix it?
Many thanks!
Measure what contacts of the XLR plug connect to what contacts of the minijack. Usually, such adapters connect 'cold' (negative signal) to ground on the XLR plug.
Does the speaker still hum if the XLR-XLR cable is connected to a sound source?
Does the speaker still hum if the XLR-XLR cable is connected to a sound source?
Hi
Without a diagram it will be guessing - any chance you can find one? (I tried a seach, but did find nothing).
But to give it a try:
I suspect that some connection near the input got broken or even connected the wrong place.
- Did the problem suddenly appear (after the repair shop played with the box)?
- When you write "But if I use other XLR cables, the hum returns immediately, even if they are not plugged in" - you mean "If you plug in any other XLR cable, even if not plugged in at the other end - the hum returns"?
- Could you measure exactly how the XLR-minijack adapter is connected (something like: minijack Tip connected to XLR pin 1, ....) and please include a measurement if any if the XLR pins are connected internally in the adapter.
- Does the box work with XLR-minijack adapter? - as in: can it produce sound?
- If you connect a normal XLR cable and turn up the volume so that you can hear the hum - does the hum change depending on whether you hold the cable or not?
Cheers, Martin
Without a diagram it will be guessing - any chance you can find one? (I tried a seach, but did find nothing).
But to give it a try:
I suspect that some connection near the input got broken or even connected the wrong place.
- Did the problem suddenly appear (after the repair shop played with the box)?
- When you write "But if I use other XLR cables, the hum returns immediately, even if they are not plugged in" - you mean "If you plug in any other XLR cable, even if not plugged in at the other end - the hum returns"?
- Could you measure exactly how the XLR-minijack adapter is connected (something like: minijack Tip connected to XLR pin 1, ....) and please include a measurement if any if the XLR pins are connected internally in the adapter.
- Does the box work with XLR-minijack adapter? - as in: can it produce sound?
- If you connect a normal XLR cable and turn up the volume so that you can hear the hum - does the hum change depending on whether you hold the cable or not?
Cheers, Martin