COLIN WONFOR’S TECHNICAL CLINIC: Microphony, fact or fiction?

Colin Wonfor

Colin. I appreciate your no-bullshit approach to providing answers. I am counting one now because I cannot get a credible answer elsewhere re microphony in amps. I appreciate that all objects vibrate and each has a fundamental mechanical resonance. So if microphony affects the sonic performance, then how and why – in general? How would I hear the affects by which I mean what should I look out for please? With your designs, do you / can you do anything to affect the effect or is it irrelevant? NW

Hi NW. Microphony in amps is common. Tube/valve have always had problem but any vibration moving a electrode in a stream of electron will be modulated.

Next hate for me is ceramic capacitors, again two plates vibrating just like the old ceramic phono cartridge of the century.

PCB construction and components is another evil source of Microphony, SMD parts are the biggest culprits and cheap paper mush PCB and thin Cu track. I have always used 2oZ Cu track but the but common ones are 0.5oZ - 1oZ tracks and I now never use pin thru but PTH on double sided PCB's and always UL94 Glass Fibre PCB not the nasty brown shit.

This increases the mass of the circuit board and if designed correctly reduces the effects of external vibration i.e. music by the likes of piano.

Now the effects are not irrelevant. This modulation caused by this normal action of moving air is good for hearing, but not so good for the effects it has on components. Components with a voltage applied to it will be affected due to bonding wires on the silicon and/or because it has two charged plates.

Damping or running them in free air is the simple answer. This will improve performance but needless to say, always results in a compromise.

So thick track in depth and width, glue ceramic caps down, and run in a vacuum, ok not the last one. But try and support the PCB with damping. Naim do this very well.

What you hear depends on what part of the circuit and PCB location the naughty vibration is coming form. The audible effect could be a tizz or just a click and even distortion and this depends on the location of the electronics relative to the noise generator. This could be a motor, a speaker or even a phone so it will be observation, analysis, patience and practice I'm afraid to say. That’s it – unless you have very deep pockets to buy laser vibration measuring kits, as used in airplane designs by Boeing.



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