Fanfare MC stage and telephone noise

Puzzling...

Last week I was on a telephone conversation with Graham and he was talking about the new Accession and how it is the most effectively shielded phono stage in the range. I commented that I have never experienced cell phone or other interference with any of his products and to prove it I took my phone right up to a Reflex M and then Majestic both of which I switched into circuit and turned the volume up pretty high.

No buzzing, humming, crackling or any other audible effect, just silence & this was in a room with two active laptops and two mobile phones, one of which I was using. When I receive or send a text or a call, this has zero audible impact on my system which is only a couple of metres from the listening chair.

- Is it because all the interconnects are GSP Lautus?(with ferrules - but then again, two turntable leads are not).
- Or the fact that I have earth-connected both my phono stages to each other & back to grounded screws in other system components.
- Or that I have switched mode devices on a separate electrical ring?

Or am I just lucky?

Chris Firth wrote: Bingo!

Glad someone with proper technical knowledge knows why I got this right, I did it to avoid hum but this is the bonus !

Tons of hifi wrote: Hi forum Currently I am auditioning (in the Netherlands) a Gran Amp 3 Fanfare. Connected between Mitchell Syncro / ATOC9 cartrigde and Arcam AVR450 (testing that one too with my old Sunfire TGR3)  No other equipment is connected yet Soud is cool. No problem with that. But the phone stage is very sensitive for my cell phone signals. Distortion even at 5 meters is clearly audible. The nearer I come to the phono stage the louder it becomes. Extremely irritating. I even doubt if I am keeping this unit.  Any tips how to handle this??

Hi "Tons of hifi". Firstly let me say I'm not offended by your topic.

Prior to cell phones this was obviously not a problem. Going back in time, music at home was either records, tape or radio, and it was all analogue.

Transistors are needed to amplify tiny signals. MC does the tiniest of all audio signals.

The "smallest" rated output voltage of an OC9 is 0.04mV at 20Hz, but in reality it will be around 0.004mV for most of the music at that frequency.

You might not comprehend (and you'd be in good company if you didn't so don't worry) that 0.004mV is 4 micro-volts.

From an engineering stand-point that is crazy. Crazy because transistor noise isn't much further below it, and hifi guys (and girls) want awesome S/N.

The engineer, accepting that MC is a crazy idea, decides to have a go at making a MC phono preamp anyway.

Lots have tried. One of the most well-known being Doug Self (last heard of designing for International Audio Group - Chinese owned British audio brands).

I have a lot of respect for Doug. His MC input stage schematics can be found on the web, and in his books.

I've tried them and they're "cool" too - but, stick a cell-phone in their vicinity, and the situation is exactly the same.

(by the way, we found Apple products to be the biggest culprit - other "androids" have to be in much-closer proximity - but in other countries that may not be so)

The difficulty is because transistors contain a diode junction, and diode junctions are basically "cats whiskers" which are good at detecting radio frequencies - they "pick them up"!

However, from a cellphone there is an alien signal (the distortion of which you talked), so rather than hearing the taxi-cab firm radio-communications - as it was in the old days - you now have almost-stratospheric high-power interference, which will ripple (rip) through just about any analogue circuit.

Rather than now going into a full technical description about the phenomenon and an explanation as to how each part of the circuit "responds" to the interference - which wouldn't be easy to grasp - I will try and keep it simple.

Filtration:

One would think it relatively easy to filter out the "noise", it being at radio frequencies?

Not so. At these offending frequencies filter capacitors are "invisible". All capacitors, wound or not, are inductive, and the inductance appears in series with the capacitor element. To the UHF frequency that inductance represents a high resistance, so the capacitor represents an easy pass-thru.

Consultation:

In the last year I spent a small sum (£2,000) getting an EMC consultant to work a few hours with me on interference. Famous for his "banana skins" publications at http://www.nutwooduk.co.uk/default.aspx (membership required), Keith Armstrong is the head of Cherry Clough Consultants (http://www.cherryclough.com/home).

We discussed the various options and solutions, and using test gear which operates at frequencies which will make your eyes water (literally perhaps?), such options were tried.

The main one is using rf chokes. Not to be confused with common-or-garden inductors, these are designed to contain the magnetic field and are more effective.

We found we could reduce the effect of mobile phones but, because they are (in my opinion as an analogue engineer) the devil's own work, not even these could effect a complete cure.

Sound Coloration:

Anything that helps however, would be good to implement. But what does it do to the sound!

The degree of coloration was completely unacceptable.

Other Methods:

It is the "speed" of propagation of the offending frequencies which is the problem.

Transistors, as previously shown, are great radio frequency detectors.

But such a circuit as a MC phono preamp requires a low-noise input - which cannot be done with FETs, valves and transformers without introducing noise of one sort or another - so therefore the transistor (bipolar junction transistor that is) is our only choice.

These can be discrete or within op-amps. Discrete layout being more inductive due to PCB traces makes the op-amp a more desirable choice.

It therefore requires a ultra-high speed op-amp in which the interference can flow without being detected.

Those exist at a price.

However, that is not all. What worked in analogue regarding PCB layout isn't any good at thwarting the modern cellphone interference.

A new form of PCB grounding and shielding is needed, along with component segregation, and new case shielding techniques.

These work very well.

But at a price.

Unfortunately £280 doesn't cover it. Let me qualify this. If the £280 product sold in vast quantities it could be cost-effective.

But you MC guys are (excuse me) long in the tooth. Your market is receeding. The demand simply isn't there. The "bigger" manufacturers have more leverage and can - with Chinese production - lever their dealers to sell "big", but dealers are leaving the scene and pursuing different careers.

It reminds me of a Bowie song "We Are The Dead"...

Therefore, already knowing that the cellphone is killing MC, I would have no qualms in dropping the Gram Amp 3 Fanfare from our range. I might well do.

However, our founding principle was to bring great results to a minority audience (you) at reasonably affordable prices.

To some (particularly non-Apple phone owning) customers who recognise that ALL cellphones cause problems - so they leave them in another room - the Fanfare works fine.

Solutions:

Other than "killing" the sound by unsavoury filtration, or you paying more for less of the problem (as in the Elevator EXP used with the Reflex M for example - or the Reflex C as a one-box solution), a lot more could be done by turntable / tonearm makers...

The arm shielding leaves off at 30MHz. This applies to all metal arms which offer "good signal shielding / screening". Carbon fibre? You may ask!

To a cell-phone 30MHz is "nothing". They transmit at frequencies ten times higher.

The tonearm offers zero shielding - IT MAKES A GREAT ANTENNA!

The tonearm picks up the signal like a TV aerial, and induces it (induction is easy at such high frequencies) into the cartridge signal wires - which go to the phono preamp input.

The cartridge inductance is such that the signal sees an open ended antenna - as far as the interfering signal is concerned, the cartridge doesn't exist!

With no loading it can "grow" in amplitude - it is out of control.

The phono preamp detects the alien interference (being so large) and does with it what it would do to an analogue audio signal - the distortion you describe.

A simple - but with costs attached for the arm manufacturer - solution is here - waiting - available - and free (from me). They need only contact me if they wish.

However, the firm you mention no longer has its "creator".

Interconnection cables could be better too!

HiFi is full of sales idiots who either have little conscience or "grey-matter" and peddle badly shielded cables.

These nerds believe that a little bit of RF interference mixed onto the signal add some "quality" - and people fall for it!

It doesn't matter if they're not used to an input. Interference gets to the input from an output dead-easy!

So, let's all get this problem into perspective, and begin to realise we're living in a modern world where cell-phones are top of the list and vinyl isn't.

Where turntable technology ceased in the mid 70s.

Where most cables are BS junk.

And often to get what we want in today's world could cost more than a £280 Fanfare?