Grounding & Earthing connections

[kgrlee]

I wonder how much gear these days will pass those Tesla tests.

There wasn't much stuff in da old days which passed it either 🙂 The BBC told us, they were the most RFI proof mikes in their inventory. IMHO, things like RFI is what separates the Great Mikes from the merely good.

I suspect things haven't changed much cos there is STILL a lot of expensive 'pro' gear that gives you free added stuff like mobile phone alarms.

Your RFI screenie might be good for RFI immunity, but i'm wondering if it's also best for hum/GL immunity ?

This was a Calrec device which implies certain standards.

I remember a discussion between Ken Farrar, my electronics mentor at Calrec, and a BBC test engineer about the 'new' M-series. He said he could hear hum. Ken replied, 'It's 20dB below the noise and the only reason you can hear it is cos this has noise performance 10dB better than anything you've got.' But we actually modified the prototype 72 channel desk to get rid of this 'audible' hum.

For our simpler devices, again I invite you to suggest situations where the simple scheme I suggest in #12 and Toni follows .. will give problems.

 

[Zero D]

Originally Posted by krglee

IMHO, things like RFI is what separates the Great Mikes from the merely good.

A bit OT, but as it's my thread 😀

I recently discovered you where heavily involved in developing the revered Soundfield Ambisonic Mics 🙂 I know some studios used them for non Ambi purposes due to their clarity etc. One such was PWL. Shame most of their catalogue was crap 😛

But we actually modified the prototype 72 channel desk to get rid of this 'audible' hum.

Did that then affect the RFI specs negatively ?

For our simpler devices, again I invite you to suggest situations where the simple scheme I suggest in #12 and Toni follows .. will give problems.

I'm envisaging Multiple pieces of equipment hooked up together, as in eg Sound Systems. Which is why i posted my wiring screenie solution earlier. I only had time to draw an eg Mixer & one Amp connection. But, these days many people have multiple inputs to their PreAmp, & often 2/3 way, or more, Active Xovers with several Amps. Achieving the lowest possible hum free solution "can" be a problem. As you discovered yourself with the BBC & the 72 CD example, standard grounding/earthing wiring doesn't always achieve this.

Using the "typical" 10R/100n combination between input ground & chassis "can/does" work, but as i mentioned earlier, the more there are = different time constants, from what was i "presume" initially calculated, or not ! So imagine say, 10 units each with 10R/100n, this now = 1R/1uf. That might be fine for RFI intrusion, but the hum "potential" has increased, quite a bit ! It "might" be better to use 100R, or even 1k, & scale the caps proportionately too. I have seen 100R used on some gear, but not 1k. The inclusion of the often used bridge rectifier arrangement in combination is also worthwhile, for safety.

Over the years i've seen some dreadful "supposedly" Pro gear, & Very expensive too, with BAD grounding/earthing issues. I've had to correct each one of them to achieve a satisfactory outcome ! Not only that, even if the circuits where good, the components were cheap & low grade 🙁