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Old 29th June 2018
  #11
Gear Head
 
Hi Brent, I'm Ed, Cranborne's engineering director. I was just mucking about with my audio analyzer when I spotted your post.

I thought "how does the RF rejection compare to a transformer?" was a good question (and I was curious) and I'd do the best comparison I can with the bits I have on hand.

Shoved in the only transformer coupled preamp I have on hand (between 700 and 900 odd quid unit value wise. Won't say the brand as I'm not here to start a fight. Never known it to show any RFI though.) Max gain.

Measured CMRR at 50hz as 88dB, 1kHz = 88dB, 20kHz= 53dB, 100kHz=23dB, 200kHz=12dB.

OK neat, we have a baseline. Time for the Camden, same settings:
50hz = 85dB, 1kHz = 85dB, 20kHz= 83dB, 100kHz=79dB, 200kHz=77dB.

Well now, that's interesting! See the thing about transformers is that unless it's a very expensive unit with an electrostatic shield to minimise capacitance between primary and secondary windings, CMRR falls off rapidly with increasing frequency. As everything in analog audio, it's the implementation not the ingredients that matters. Is the Camden RF rejection better than a world class preamp that has excellent CMRR on it's own right AND a high quality Jensen? Doubt it. Is it very very good and better than a hell of a lot of transformer inputs? Yup.


Also, as I'm mucking around and finally coaxed the sub 5Hz measurements out of my AP... You guy's like bass extension and nice tight linear low ends right? here's a picture that tells a thousand words:
Attached Thumbnails
Cleanest 500 series preamp on the market? - Welcome to Camden 500-camden-low-end.jpg