Yee Ha, an opportunity to use the new reference thread:
Video & Audio: Power, Ground, EMI, Noise in Cables. Can someone explain if 3 circuits are all grounded at the same point as the entire house is ground at how is a ground loop possible?
Mejames, what you have is the classic "pin 1" problem in pro-audio balanced systems. Perhaps I can sum it up by suggesting for *your* system, you use RCA and thereby create an unbalanced system. Trade your nice XLRs. Since you currently have a problem with a balanced line, your distance is 1m and you don't have an extreme environment (EMI, theater, stadium etc.) then there is not much to gain by running a balanced system and a lot to lose. Often, a high end balanced input uses an active (op-amp) circuit to provide a matching virtual impedance for the cable while providing high common mode rejection (CMR) (unlike tubes typically) and all grounds conform to a star ground or better. I don't think you can achieve this without modifying/soldering your current system (either cables, equipment or both).
Try a shielded coaxial cable with foil (for EMI) and braid (for hum) read about them at
Coaxial Cables and Applications (Belden) The most important reference is for you is:
7. Equipment Wiring - Internal to Electronic Equipment
7.1. The "Pin 1 Problem"
The "Pin 1 Problem", refers to a means of EMI pickup in audio equipment related to connections to Pin 1 - the ground pin - of an XLR connector. The reference work on this subject is [2] by Neil Muncy of Toronto, Ontario. Pin 1 of an XLR connector, of course, is the pin used for the cable shield connection. In general, the "Pin 1 Problem", refers to the connection of shields to audio equipment and how connector contact "Pin 1" is internally grounded.
... The "Pin 1 Problem" manifests itself as noise induced into the circuitry of audio and video equipment that then appears on its outputs. In brief, the problem occurs when the circuit grounds are shared with the input and output connector shield grounds. When this occurs, common impedance coupling, as discussed earlier, causes the electrical noise picked up in the shield to be transferred to the electronic circuits.
Why is this so?:
3.3.3. Grounding the Shield
An actual connection to earth plays no part in EMI shielding effectiveness. The ideal EMI shield forms a continuous conductive layer around those items that it protects as shown in Figure 3-3. In the case of twisted shielded pair cable, normally terminated with an XLR, clearly there is an opening in the shield at the connector. By connecting the shield to the ground of the equipment case the continuity of this shield is improved, however, clearly it is far from perfect as the conductors are clearly exposed. In the case of coaxial connectors such as BNCs, the shield makes a circumferential connection to the cable connector and that in turn makes a circumferential connection to the panel mounted connector providing 100% coverage of the inner conductor. In the case of coaxial cable, we have 100% shielding throughout the length of the interconnect and we have a ground loop that is formed between the send and received ends. This has always been one of the difficulties of the single ended transmission system used for video. In the case of audio equipment, the shield is never grounded at both ends to avoid this ground loop problem. At the high operating frequencies of video, maintaining the characteristic impedance of the transmission line (usually 75 ohms) and high frequency shielding are more important than maintaining the ground system integrity.
For your tube equipment with its high input impedance and sensitivity note:
5.4. Separation and Routing
For further reading see:
2.1. The Isolated Star Ground" and the background explanations of
"2.1.1.1. Circuit Ground", "2.1.1.2. Shield Ground", and "2.1.1.3. Equipment Ground"
Followed by:
2.3. Ground Loops
And then before you hire the electrical contractor read:
8. Case Study - Getting the Installation Right
8.1. Power and Ground Systems at The Hamilton Place Theatre
Ignore most concentrate in particular on:
8. Case Study - Getting the Installation Right
8.1. Power and Ground Systems at The Hamilton Place Theatre
When done (whew!) skim the various posts where Subaruguru and others talk about power wiring. Pick cable to match your budget, but at least consider some form of braided 3 or 4 conductor cable or conduit.
One last note, due to power problems I have, I am using GFIs and I'm currently installing a 220VAC feed into a
2000VA Sola constant voltage transformer to create a 110VAC circuit and a virtual isolated ground. This goes to two
Isobar12 with dual EMI/RFI Filtering (40 & 80dB) between equipment outlets. One to supply my MLs, DVD etc. and the other for power amps etc. I think I have found filtering each piece of equipment relieves many noise problems and reduces the need for more exotic power cables, but I do need to test more before getting on a soap box (LOL). One should use at least braided shield power cords to reduce their effects on other equipment.
Ok that is enough *noise* by me!
