Need new MC stage with good RFI suppression

Hi Dave. Quite a Lot has been written to the forum over recent months and others are far better able to give a technical angle on RFI suppression. There has been recent comment from Graham on the contributions from poorly shielded arms -you don't say what arm you have?

I am a little out of step with the majority on the forum in the benefits of upgraded mains cables but to be fair wouldn't have expected that to impact much if anything on actual noise. Good screened interconnects may be of more help?

It sounds like you have focuses on mains led interference from your comments which should benefit the overall sound but perhaps not too much on 'noise'.

When you refer to not quiet enough and you referring to hum, hiss, clicks/pops, radio breakthrough or something else?

I have a dedicated mains feed from a separate consumer unit, earthing rod and feeding a bespoke mains block, heavily screened cables BUT very occasionally suffer radio breakthrough when conditions are right (or perhaps wrong).

On a separate topic I did audition the Diablo I think against the Graham Slee Era gold V and came home with the latter albeit the Dino was well reviewed at the time. Not sure how much Graham's products may resolve your noise issue but Graham prides himself in paying great attention to minimising RFI and similar by meeting all regulations (personally I think one of Graham's little boxes is likely to sound better).

Could always look at the loan scheme to try?

Hi. Is cable management ok, mains and interconnects don't always like close contact? As you have done disconnecting items is a good starting point. I'd dinosaur powered by separate power supply I cannot remember?

Theoretically a metal tonearm gives protection from interference up to 30MHz (based on a 9 inch tonearm).

Above that the arm unravels and opens up like a dog-rose to RFI - the stem being the arm cable - the arm tube being the outer petals and the cartridge wires the stamen. Although there is a cartridge stuck accross the end of the stamen to our eyes, it's inductance (due to its windings) is open circuit to RFI. Therefore you have four nice antennas, two of which go right to the phono amp inputs - the other two chucking their contribution at them through capacitive and inductive coupling in the arm cable.

It could all be different, but arm manufacturers never listen to little old insignificant Graham Slee.

So, the electronics designer must try and stop his design rectifying the RFI.

But where does it all come from? The fridge and all sorts of other mains items? But how?

Spark transmission was the first type of radio transmission and most thermostatically or intermittent supply items are quite good at generating sparks (arcs). Cheap bimetal thermostats arc just before making contact or disconnecting. SCR (thyristor or triac) solid-state switching is better because it is often designed for zero volt switching - but that isn't really true because to latch there has to be some voltage - the result is noise.

Then there is intentional radio transmission of all sorts and kinds, and a lot of that isn't speech or music. It can ride the mains and it floats in the air. It enters shielded enclosures and it "knows" that capacitors are resistors and resistors are capacitors, where the layman simply doesn't.

Whatever the interference, it gets in by rectification at some point. Good shielding should therefore be a concern for us all, but look at all those crazy hi-fi interconnects people buy! It serves them damn well right!

And back to tonearms. Some buzz, some don't. Most rely on a ground connection through their bearings - how silly! But these are world-renowned manufacturers - surely they can't be wrong?...

The only quiet arms are those that use a "fifth wire" connected at the headshell end to conduct the arm tube all the way to the arm base - read Technics! They are quiet, most others buzz (slight hum) because the buzz is generated in the poor contact bearings offer.

Back to rectification - how RFI makes its pressence known. When I was a child there were still cats whisker radio sets and kits. The cats whisker rectified RF to tune a radio station. The cats whisker is a diode. In amplification there are plenty of diode junctions.

The likes of the older designers (EG Doug Self, JLH etc - can't think of that many right now) on which a lot of today's hi-fi is based, didn't have all these extra forms of RFI to worry about. To them a phono input was all about getting hiss levels down which they did by commoning up several bi-polar transistors - and it worked (except the fridge often clicked through).

All those transistors are a number of cats whiskers ready to rectify RFI. But the positioning of a capacitor in the "right" place took that problem away -- not anymore!

Today we have RFI up to 1.5 GHz to contend with. 30MHz (the arm "protection") is useless in this being just a 50th of 1.5 GHz.

The higher frequencies can simply jump all the old RFI precautions, and now we have more interference in the form of computational circuits which work at such high speeds you can forget all about the MHz band because we've now shifted up a gear.

Stability is the thing that counts today. Stability in circuit design now needs to be unshakable. Designers now need to look at how their amplifiers (preamps included) behave well-beyond the old kHz to MHz RFI bands.

My oldest MC design, the Elevator EXP, uses ultra-fast amplifiers meant for video to try and "race" the RFI, but even so, without going back over its design, as I have on several occasions, it would be merrily rectifying today's RFI. Stability is everything.

By far the biggest problem is balancing what the user expects from MC with what can actually be realised. To get rid of interference noise often results in the noise we all know as hiss. What is better? Interference or a bit of hiss? The old circuits were all about achieving the lowest measured noise, but by now they're busily letting in all sorts of RFI noise.

To get the high speed stability to overcome RFI will always result in hiss. With speed comes noise, but that noise is drowned-out once the music is playing - and that music is never (for now anyway) interrupted by RFI disturbances.

There is a way we can overcome both however. The answer is called a moving magnet cartridge...

Provided the preamp still uses the high speed stability techniques.