On 6/21/2014 12:18 PM, Richard L. Hess wrote:
> In the mid 2000s, I had my last issue with
> RFI. We had installed shielded runs of cable in a church here in Aurora,
> Ontario, for recording mics. The cables had about a 35 foot vertical
> drop from the peak of the ceiling to the mic location and the other end
> went down the same distance at an angle along beams. There was never an
> audible problem with neither AKG C451 nor DPA 4006TL mics hanging there,
> but we bought some low-priced Audio Technica ATM10a omni condenser mics
> that worked with either an AA cell or 48 V phantom, and we could clearly
> hear an AM station in the recordings. These were purchased due to budget
> and their relatively good sound for the price. The AKGs and DPAs are my
> personal mics.
> We finally installed a pair of Shure A15RF In-Line RF Interference
> Attenuators and they worked like magic when installed at the mic.
> The ATAM10a apparently had a reputation for RF sensitivity which, I
> think may come in part from its ability to be dual-powered
Remarkably, I heard similar stories from the engineers at the Ravinia
Festival about Neumann mics. They also went to C451s and some Shure
SM81s, and the problem was solved. The SM81s and C451s had far fewer
problems with humidity than the KM 84s.
> It is all about keeping the RF away from the "diodes"!
Paul (a longtime fan of ferrite beads)