I received an email from Goldmund today. Here it is:
Thank you for your email and interest in our product,
I would like to inform you that in analogue system ground loop can be critical and in case you do not respect some conditions a hum can be present on the speaker. The schematics recommended by Job System is known as the "Star System" as used in top measurement laboratories.
In Star System only one central component (usually the pre-amplifier or in digital the acoustic processor) is connected to the building ground (through the AC line connection or directly to an earthing post) and all other unit of the system are not.
I suggest in your case to make some tests to reduce the hum:
1. Use a good coaxial cable for your wiring for sound quality, perfect shielding and speed of transfer.
2. Do not make a physical loop with the coaxial cables from your pre-amplifier to your amplifier, make them arrive at the amplifier input from the same way.
3. The units on the system must respect the Star System. Firstly I invite you to disconnect the amplifier from the preamplifer, put a short-circuit cap on each analog input and turn the amplifier on, the hum must be gone. Is it true than with high efficiency speaker you might be able to have some hiss which is totally normal.
4. Then put back the coaxial cable and power the amplifier with a cable without earth connection. The ground connection will be done through the ground of your coaxial cable and if you use a good coaxial quality the system will be totally shielded.
Be careful that this type of installation must be made and controlled by a qualified technician to provide the perfect safety and quality.
I also wanted to let you know that the noise that you can hear when you flipped the device can be the ferrite bead on the mosfet that moved or it might be that during the transport an internal part was damaged, expect the hum your amplifier works fine ?
Could you please let me know the result of your test, we will then be able to confirm if your unit has a problem and must be return for an exchange/repair.
Best regards
--
Antonio SANNA
Head of Technical Support
Digital Audio SA
www.goldmund.com
Digital Audio SA - 3 Chemin du Pré Fleuri
CH-1228 Plan-Les-Ouates - Geneva
Tel: +41 22 823 05 66 - Fax: +41 22 342 21 20