Rega P3 Helicopter Buzz

Hi Guys

Thanks so much for your reply Graham. It took a few reads for it all to sink it. But, yes, you are right, only one day in and the helicopter buzz is no longer there. I love my Phono Stage by the way, thanks for making such great products. I took a leap without listening to one first, and it's been worth it. I'm looking forward to the day when the rest of my equipment rises to meet the standard of it.

There is always a cause. You aren't alone in this, I discovered the same 45 years ago, mine was a lamp dimmer.

An amplifier will amplify what it is given at its three inputs: the audio input, the audio output, and the power input because it will always find its way to the input.

All semiconductors are based on the diode, and the first-ever radio receiver was the cat's whisker or diode!

Given a choice between a bipolar junction transistor (BJT) and a field-effect transistor (FET), you'd go for the latter where there is the likelihood of radio interference because that's what it is. So that's what all my MM stages use. They used to be BJT, but then the mobile phone became less regulated and more powerful, so I redesigned.

But it isn't the phono stage's fault that strong radio frequencies are breaking-through. There is, for a start, a capacitive filter right at the input - the capacitive load - trying to defeat it. There has to be some form of antenna, and it's called the pick-up arm.

The cartridge assists it because, at radio frequencies, the MM is like an open circuit. It is an inductive device, and its impedance rises with frequency. But, eventually, its winding capacitance comes into play, making it a tuned circuit also.

Therefore, you have two wires inside a metal tube, like Faraday's key in a thunderstorm, waiting to pick up any strong magnetic field that the radio device emits.

But the arm is grounded to the phono stage! At one end! Which means that at some high frequency, the arm offers no protection, and assists in transmission.

RF power density reduces with distance, and if I'd have sited the lamp dimmer the opposite corner of the room, instead of in the lovely fireplace surround, which the turntable was stood on, it would not have been a problem.

The answer, providing you're right about the source of the problem, is distance. Most people can move the turntable away sufficiently to remedy the situation, such that the electromagnetic interference falls below the semiconductors' susceptibility. You're going to have to try.

For some reason, turntables are exempt from EMC legislation, probably because the above facts are known, that they cannot comply, but there is still a good market for them, but insufficiently large to make any real EMC impact.

By making the arm tube the shield such that the cartridge commons attach to the headshell metalwork, and emerge at the arm base as cable shielding, the cartridge signal wires would be effectively shielded at all existing radio frequencies. Also, making the headshell wrap around the cartridge a bit more (like they used to) would assist shielding from RFI.

However, manufacturers don't need to comply. There isn't the legislation. They go the opposite way, with exposed cartridge wires, sexy carbon fibre (which offers no shielding at all), and a tiny flat plate or bit of flattened tube which to attach the cartridge.