On Sat, May 28, 2016 1:17 pm, Martin McCormick wrote: > I am not using XLR's, but I do use 1-to-1 isolation transformers > between the audio sources and sound inputs
Hum in audio systems almost always is a consequence of improper grounding. Although an XLR connector on a piece of apparatus SHOULD BE a guarantee of freedom from hum, such is not always the case; regrettably, not every audio manufacturer has a proper understanding of grounding and shielding, and of the distinction between a signal ground and a chassis ground. Perhaps the best comprehensive collection of application notes is that made available by Rane, at http://www.rane.com/library.html; the notes are: RaneNote "Grounding and Shielding Audio Devices" (updated 7-02) RaneNote "Sound System Interconnection" (RaneNote 110) (updated 7-11) RaneNote "Why Not Wye?" (updated 4-04) RaneNote "Pin 1 Revisited" (8-07) RaneNote "SCIN: Shield Current Induced Noise" (8-07) PDF "Grounding and Shielding Computer-Controlled Audio Devices" Steven Macatee, AES (12-94) PDF "System Problems and Equipment Manufacturers" Bill Whitlock, Systems Contractor News (9-87) PDF Cable Outlook: Is it time to move to shielded category cable? SVC 7-13 (400k) Various manufacturers offer isolation transformers and level converters to enable interconnection of consumer (-10 dBV RCA) and professional (+4 dBu XLR) devices. For example, Rane has the passive "Balance Buddy", and ART has the "CleanBox", which utilizes active circuitry. Such devices are inexpensive, and can be had from most commercial broadcast supply houses. RLH
