----- Original Message -----
From: <[email protected]>
To: <[email protected]>; <[email protected]>;
<[email protected]>
Sent: Friday, April 01, 2011 4:46 PM
Subject: Re: [Drakelist] My R-4B audio?
In a message dated 4/1/2011 7:31:45 P.M. Eastern Daylight
Time,
[email protected] writes:
Also, just a second thought on the speaker
impedance...based on my
experience in Audio as well as Ham...one should match the
impedance of
the speaker to the impedance designed into the audio
output circuit
While this is generally true, be careful. Some years
ago an attempt
was made to "match" a set of low-Z headphones to the "600
OHM HEADPHONES
ONLY" jack on a commercial audio mixing console using a
600-ohm to 4-ohm audio
transformer. Unfortunately, while the transformer may
have had an AC
*IMPEDANCE* of 600 ohms, the *DC RESISTANCE* of the
winding was too low and,
over time, it burned out the directly-coupled output
transistor in the
console by forcing it to source too much current to the
load.
MORAL: Pay attention to the configuration of the
driving circuit
before you arbitrarily hang something on the output.
73/Paul, K4MSG
Who made this console? Whatever it was the design was
plain incompetent.
Anyway, the Drake receiver has an old fashioned
single-ended pentode amp with transformer coupling. The
headphone jack and loudspeaker jack are essentially paralled
but the headphone jack has a switch to disable the
loudspeaker when headphones are connected. When modern, high
fidelity, low impedance phones are connected they are _very_
loud. A pair of 600 ohm phones is about right and even old
fashioned very high impedance phones work fine. Neither the
amplifier or transformer seem to care about being running
into a short or open circuit.
--
Richard Knoppow
Los Angeles
WB6KBL
[email protected]
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