Re: Headphone Amplifier

In article <7f8j24tbsh7grb75t8jpiomohmfo0hvhn2@xxxxxxx>,
flipper <flipper@xxxxxxxx> wrote:

On Tue, 13 May 2008 08:22:52 -0500, John Byrns <byrnsj@xxxxxxxxxxxxx>
wrote:

In article <kk4i24t13io43j65n6jgmbjnpbr7juna56@xxxxxxx>,
flipper <flipper@xxxxxxxx> wrote:


Btw, the OTL doesn't 'require' the 120 ohm resistor and it works just
fine as a 'low impedance' output.

You could just remove the 120 ohm, and then adjust the FB resistor for
the changed Vo, but there's also a nice trick can be played. Instead
of the FB R and blocking cap. as shown, put a 12ohm under the existing
Rk on V2A and take the headphone return to that junction. That
eliminates the DC blocking cap.

If I am following your description of this mod correctly, doesn't that
convert the negative feedback from voltage feedback to current feedback,

Yep

with the expected effect on source impedance?

Yes, but then a moving coil device is actually current driven so I'm
not sure what the 'net effect' would be.

The common "dynamic" loudspeaker is also a moving coil device and people
seem to feel they need to be driven from a voltage source. They talk of
"damping factor" and such. Can I assume that "damping" isn't a factor
with headphones, at least if they are driven from a 120 Ohm source?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/
.

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