TOPIC:

Hi guys, I have been using a Minidsp 2x4 between my AVR and 3 subwoofers with great success, however as they require 1.8VRMS for rated power, the MiniDSP 2x4 can only supply 1/4 of rated power.

I have a C-DSP 8x12 from my previous car system. I replaced the 2x4 with the 8x12 and added -10db attenuators to the RCA outputs as this unit outputs 6VRMS, however now I have a bad 50hz hum.

I have tried unplugging almost everything in different combinations, and even using a ground loop isolator on the RCA inputs to the C-DSP and the hum is still present. When I connect the Laptop, the input level is showing -39db so the hum is fairly loud.

If I connect the bare minimum (AVR with no HDMI’s connected, C-DSP and 1 subwoofer) the input level is still around -50db. If I swap back to the 2x4, the hum disappears and the system works perfectly.

In summary, the ONLY change I have made to the entire system is changing a 2x4 for a 8x12 (using same DC power supply) and this introduces a nasty 50hz hum. If anyone has any ideas, that would be greatly appreciated.

Did you manage to find a solution to this issue of yours?

No unfortunately not. I have just put the 2x4 back into the system as it does not suffer this issue. I am limited to -5db from reference before it clips but this is more than adequate 95% of the time

If you have a 12v battery laying around, try powering it with that and see if it makes any difference?

The hum only appears when you use the analogue inputs? If so, have you tried using digital inputs?

Hi All,

i was going to submit a question or ticket to help desk but found this topic on the forums, so i thought i'd chime in here first.

i have literally the exact same problem with ground loop between the 8x12 and my AVR, a denon X3600H. With the RCA cables connected between the AVR sub pre out and the 8x12 analog in, i get the same -30+dB humming input.

i have verified that the same 8x12 has no issues with input ground loop when connected to another device analogue out - a topping D10 usb dac. And also the Denon X3600H subwoofer out works fine when connected directly to a subwoofer analog input or external power amp, no ground loops.

In summary, both the 8x12 and the AVR works fine on their own with other devices, no ground loop. It is only when they are paired, that the massive ground loop is created.

i'm wondering if the 8x12 uses a different type of grounding design, being a car audio device, and is not really meant for use in home audio environment.

Thing is, this ground loop was not always present. i was literally using it in the same configuration, setup and calibrated with no hum. Then when i next switched it on, the ground loop hum was there and wouldn't go away.

In my previous setup, i had struggled with the ground loop quite a bit as well, there was always a lot of sensitivity in the amplifier choice. Some power amps on the 8x12 output does not have the issue, while other power amps causes ground loops. THis particular power amp in using currently didn't use to have the ground loop issue, but now does.

Sorry for the long post. Wanted to provide more details.

Thanks.

Take the cover off the CDSP 8X12. You will see that there is several grounding configurations to choose from.
I think it comes from the factory in "ISOLATE". Try switching it to "GND" by moving the jumper.
There are several other settings available you could try if GND does not work.