[Craig Sawyers]

The RA products that I use are:

SD mains cables. I designed them, and I know from measurement that they work in effectively attenuating differential and common mode RFI up to 1GHz by 20-40dB as compared with a regular "kettle" type lead.

I agree entirely with David that effective broadband RF should be done by design in product, but that is rarely done in domestic audio products. The instrumentation industry goes to great lengths by using multiply shielded mains transformers to reduce primary/secondary capacitance, (in the extreme, using boxed-shielded transformers to reduce capacitance to 0.01pF), but audio. transformers are usually entirely unshielded.

I've recently measured a 120VA 15/15V secondary Block transformer on my HP4275 bridge. Up to 200kHz the primary/secondary is essentially capacitive at 490pF. The phase angle then shifts to increasingly inductive until at 10MHz (the limit of my bridge) it has become inductive with 3.4uH. However it is easy to find papers that show that as the frequency goes up, the impedance goes through a series of LC resonances. So how good is an unshielded transformer at suppressing (in this measurement common-mode) interference? Well not so good. Even a single shield, correctly grounded, reduces winding/winding capacitance to around 5pF - but no-one seems to do this simple thing in the audio world.

Speaker cables. That is essentially for practicality. I use Linkwitz LX521 open baffle speakers. I therefore have 5 channels of power amps on L and 5 on R. Because of the risk of wiring up the bass channel to a tweeter with predictable results, I use Neutrik Speakon connectors - one 8-way and one 2-way, so once the cable connections are made correctly there is no possibility of miswiring the speakers. Of course, the wiring is bundled in expanding sleeving, and preventing crosstalk between drive units is difficult to optimise. However the braided Kimber speaker cable has almost immeasurably low external voltage and magnetic field (by measurement). So I use bundles of braided cables to ensure low drive unit crosstalk.

All other line level connections, of which they are many, are balanced. I use professional grade star-quad balanced cable from Canford at about £1.50 per metre, and Neutrik EMC series XLR's. All colour coded to reduce the possibility of miswiring from the crossover to the power amps.

Craig