The other thing to consider is good old fashioned cross-over
distortion at low audio levels.
This seems to be the reason TT suggested a pad (of a couple of
hundered ohms) in series with the headphones with older equipment. I
would have though the AF output amp was better in a multi kilobuck
Orion but perhaps not.
I also wonder if an AF amp in crossover distortion will rectify stray
RF too?
There was a report of a similar issue (Darth Vader voice on an Argosy
in headphones) in the last month.
Either way I'd try the couple of hundred ohm resistor in series with
the headphones (build a little adaptor it will be hand on other rigs).
Or "ancient" high impedance headphones!
On May 26, 2007, at 9:34 AM, Dr. Gerald N. Johnson wrote:
Could it be that the modern low impedance (4 to 8 ohm) headphones take
so little voltage drive that turning down the DSP headphone drive
leaves
it using so few bits of the digital level that you hear the
granularity
of 4 bit audio? The Trimms would be high impedance and take more
voltage
to give enough power to be heard and so use many more bits at the
digital level, maybe 14 or 15 and so the digital granularity would be
hard to hear.
Could it be that the low impedance headphones need to be driven
through
a 250 ohm resistor? Or a 50L6 output transformer (2K to voice coil)?
--
73 DE N7WIM / G8UDP
Kevin Purcell
kevinpurcell@pobox.com
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