Not sure why you guys don't try using a floating power supply, as originally Hawksford did in the LFD phonostage. That would guarantee a zero current through the cartridge under all conditions.
Sounds like a good idea but you have to generate it - either another trafo or one of those little dc-dc converters.
Is it not just easier to servo the offset out?
Is it not just easier to servo the offset out?
Or one of those little solar cells and some white LEDs 😀.
As you can see, a servo may not cancel the transient currents through the cartridge (it that's a concern, of course). Otherwise, not even a servo is required.
In fact, I believe a servo, while certainly cancelling the offset, may make the transient currents even worse.
P.S. https://linearaudio.nl/sites/linearaudio.net/files/Didden-Hawksford_Part2.pdf page 28
As you can see, a servo may not cancel the transient currents through the cartridge (it that's a concern, of course). Otherwise, not even a servo is required.
In fact, I believe a servo, while certainly cancelling the offset, may make the transient currents even worse.
P.S. https://linearaudio.nl/sites/linearaudio.net/files/Didden-Hawksford_Part2.pdf page 28
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That's the Hawksford LFD phonoamp core. I don't think a more detailed schematic was ever published by himself (I hope I'm wrong).
All kind of implementations can be found on the net, many showing a lack of understanding of his topology advantages.
All kind of implementations can be found on the net, many showing a lack of understanding of his topology advantages.
Not easy to search for. But, found it.
https://www.diyaudio.com/forums/analogue-source/154210-mpp-145.html#post2215423
https://www.diyaudio.com/forums/analogue-source/154210-mpp-145.html#post2215423
Some additions to the original schematic (the servo, the balancing pot) are triggering (transient) cartridge DC currents. Not a big deal, but one of the original schematic features is lost.
Please post the schematic. As I said, there are many variants flying around that are losing this feature in the process of "improving" it. One good example above.
Concerning cartridge dc concerns
On the other hand :
It is frequently claimed that pre-amps with floating supply can
by definition not inject dc into the cartridge coil.
I would love to see a formal explanation for this.
On the other hand :
It is frequently claimed that pre-amps with floating supply can
by definition not inject dc into the cartridge coil.
I would love to see a formal explanation for this.
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