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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