Robert,
It is a misconception that audio devices must be impedance matched.
Audio transducers respond to voltage and current which equates to
power. Normally, audio output drivers are designed as low impedance
sources. That means that they will produce more power into a low
impedance load than into a high impedance load.
A parallel example is the power receptacles in your home. The utility
company strives to provide a very low impedance source (they would like
it to be zero). Here in the US, the voltage is typically 115 volts - a
low impedance device plugged into the power receptacle will draw a lot
of current and power, but a higher impedance device will draw lesser
current (and power).
The major difference between my power line example and an audio power
amplifier is that the maximum voltage available is a less than the
voltage fed to the audio amp output stage. How much less depends on the
device used - and the maximum available current also depends on the
device specs.
I do not have the specific data on the voltage and available current for
the K3 connections.
I also do not understand why some consider it a problem if the AF Gain
control has to be advanced to even the 5 o'clock position to produce
adequate audio for a given application. As long as the audio output
driver is not driven into distortion, that condition is perfectly OK.
There is no rule that says the AF Gain control should not be operated at
the full gain position, or anywhere below that.
Audio transducers vary considerably in sensitivity (efficiency), and the
AF Gain control is there to make the various available transducers
usable. If your headphones are less sensitive than some other ones,
just turn up the AF Gain until you have sufficient audio for your ears.
73,
Don W3FPR
Robert Kirkland wrote:
> We know that to obtain the maximum audio level between two devices we must
> match the impedances between them. The impedance of mono and stereo headsets
> vary widely a good way to tell is if you have to rotate the volume control a
> lot to get a small increase in volume there is a mismatch.The questions are:
> What are the headphone output impedances of the front panel and the rear
> panel jacks and do they vary between modes?.
> Bob,
> w5pvr
>
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