Date:         Mon, 24 Jul 2000 10:22:57 -0400
Reply-To:     David Beierl <dbeierl@attglobal.net>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@attglobal.net>
Subject:      Re: Want tunes through headphones
Comments: To: "Buettner, Peter" <PGB@dolby.com>
In-Reply-To:  <DFF1DE9BFABDD211A6F400A02461FE6F0257B8F5@xsf1.dolby.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 09:39 7/24/2000, Buettner, Peter wrote:
>You should be able to tap right into the speaker wires.  Headphones
>typically have a much higher impedance than speakers (600 Ohms versus 4-8
>Ohms).  The higher impedance will make sure that you won't affect system
>performance and also won't hurt your ears.

Maybe not quite that simple... some phones are 32 ohm, btw...you can often
run into a problem of the amp running into its voltage limits and clipping
even at low volume settings, because of the higher impedance load.  Might
be necessary to use (preferably non-inductive) load resistors in parallel
with phones, which leads to the problem of not burning up the resistors.  I
think the most failure-resistant method would be to tap into the line-level
outputs if the machine has them, and use a separate headphone amplifier
driven from there.  Of course this still doesn't shut off your speakers
unless you have an external booster being driven from the line-outs rather
than the speaker-outs, and can shut it off...

Using a CB with phones (I heartily recommend it, btw -- no blasting the
passengers, and better comprehension.  Traffic noise unaffected or more
audible compared to using a speaker) -- max audio output about 4 w -- I was
using a Midland rig which worked fine with phones and an inline volume
control, plugged into the external spkr jack.  It broke, replaced it with a
Cobra unit, clipping everywhere.  Tried a different set of phones, much better.

david


David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"