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RE: Hagerman Piccolo Zero Headamp

Posted by 13th Duke of Wymbourne (A) on January 30, 2024 at 14:34:46

In Reply to: RE: Hagerman Piccolo Zero Headamp posted by Tre' on January 30, 2024 at 07:18:42:

Hi Tre'

according to Lenz's Law, if a conductor moves within a magnetic field it will induce a current in the conductor and that induced current will create its own magnetic field that opposes the motion that created the current in the first place. IMHO, that will act to dynamically reduce compliance. I am not sure if, or why, reducing dynamic compliance would be advantageous and it is not clear how small the coil resistance needs to be for Lenz's Law to actually make a difference. Electromagnetism is not my speciality, I once posed this very question to one of my EM-savvy colleagues who had no answer!
In 'normal' voltage mode, very little current flows in the coils as the total resistance is usually >100R. If you took things to the extreme and had zero coil resistance and a true virtual earth transimpedance input then a very large current would flow and generate its own magnetic field that would completely oppose the cantilever movement! Probably, you don't need much resistance to get any benefit while still allowing the thing to work (?).

I had never equated this effect with amplifier damping factor before. In that case the amplifier output voltage creates a field that moves the voice coil and the speaker moves. Considering what I wrote above, in moving a current will be created in the voice coil that opposes the movement - I've never seen that commented on before (at least not explicitly). What I thought advantageous about high damping was if the speaker overshoots and is no longer following the driving signal any 'error' current created due to that extraneous movement will create a magnetic field to compensate for the overshoot. But if there is effective opposition to an overshoot why not effective opposition to the voice coil moving in the first place? Maybe, the current sourced into the voice coil by the driving amplifier swamps out any back emf but when there is overshoot that ratio of back emf to driving current is much higher (because the amplifier isn't driving at that point)?

Enough musing for now, I have some non-EM technical problems to attend to and after that enjoy some LPs without thinking about how they work :)

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