|
|
Headphone impedance adapter
|
Hi. My main cue system uses 600 ohm phones, but I have some 55 ohm
phones that could be used if I need some more on a session. I was
wondering if anybody knows of a commercially made adapter that I could
plug the 55 ohm phones into so they would effectively become 600 (or
approx.) ohm phones so that the levels of all phones would be about the
same. I'm trying to avoid building these myself.
|
Check the minimum load impedence of the headphone amp. If 55R is OK just
plug it in. If not, to avoid distortion add a series resistor in each
channel to bring it up to the minimum - you'll have to live with the drop in
level, but I've never had a lack of level with an Alto amp with 68R in
series with each channel of each output on 55R-75R phones.
|
|
Impedance and efficiency aren't the same thing.
But what you want is a headphone distro box. Telex makes some cheap ones
that Markertek sells. You can just drive one off a single power amp, and
plug eight sets of phones in with a level control on each one. Be sure to
order the stereo model with the level control as there are some other
variants.
|
Thanks for the reply, Scott. Yes, I realize that impedance and
efficiency aren't the same thing, but given everything else being equal
a low-impedance phone will sound louder for the same amount of power
than a high-impedance one (55 ohm K240M vs. 600 ohm K240M). I've
|
The problem is that everything else isn't equal, and some headphones
are just louder than others. What you need is either more headphones of
the same type or headphone amplifiers with individual volume controls
rather than a single power amplifier to drive the bunch. That's
acutally probalby cheaper than putting stereo L-pads on each output of
your headphone distribution box.
The "impedance conversion device" of which you dream is a transformer
with about a 3:1 turns ratio (that's the square root of the impedance
ratio), which will step up the voltage by that ratio. But one of any
decent quality that will take the power delivered to the headphones
without distortion is probably going to cost as much as a set of
headphones of the sensitivity equal to those that you already own. And
(because all other things aren't equal) it probalby still won't make
your 600 ohm phones loud enough. That's only about a 3 dB step up in
voltage.
|
already been using several distribution boxes such as you mention and
driving them with 60W amplifier since I am sometimes running up to 14
or more phones. But because of the differences in phone impedances I
do have a problem trying to combine the two differenct types of phones
on a session. Thus the need for an impedance conversion device.
|
That sounds more like a need to add some series resistors to some of
the jacks on the distribution panel in order to use more sensitive phones.
|
|
|
|
|