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From: dsi@unccvax.UUCP
Newsgroups: net.audio,net.auto
Subject: Re: Connecting CD player to Toyota radio???
Message-ID: <445@unccvax.unccvax.UUCP>
Date: Wed, 19-Feb-86 08:47:40 EST
Article-I.D.: unccvax.445
Posted: Wed Feb 19 08:47:40 1986
Date-Received: Fri, 21-Feb-86 05:33:19 EST
References: <1582@emory.UUCP> <523@eneevax.UUCP>
Distribution: net
Organization: UNC-Charlotte
Lines: 54
Keywords: My AM transmitter is flatter than a Toyota radio....
Xref: watmath net.audio:7693 net.auto:9485

> 
> I saw one of those el-cheapo units on sale here in the DC area last
> weekend (soundesign? one of those) for around $14 (reg. $27, methinks),
> which basically included the cigarette adapter and some peculiar circuit
> you connect to your car antenna.  Wow, does this mean that if I hop up 
> the parts, I can broadcast glorious music to neighboring cars?  :-)
> 

     Not to change the subject (exactly) but we have a peculiar problem
in the Charlotte radio market with respect to FM radios and a desired
station.  When some cars equipped with el-cheapo FM sets are tuned to 96.9
mHz (WLVK) and they pass by you while you are listening to WKZL (107.5)
in many cases, the local oscillator from the WLVK-tuned receiver is able
to completely overtake WKZL.  The effect in many cases is bad multipath
-like interference and the other usual flup-flup noises, with properly
shielded and designed receivers.

     Back to the original point, though: why on earth would anyone want
to play a CD player through a very poorly designed FM or AM modulator. I
doubt seriously that the circuitry exists for either stereophonic FM or
AM in a $27 box; you can be assured that in the FM case, the differential
distortion in the modulator will make CD's sound horrible. (In fact, the
differential distortion in most commercial FM transmitters makes a CD
sound horrible....)

     It is entirely possible that leakage and the right circumstances 
would result in cars around you at a stoplight would receive an interfering
signal of your CD player.

     If I were going to do this, I'd simply open up the Toyota radio and
interrupt the audio at an appropriate place, bring coaxial cable out to
a switch and jacks, etc.  Then again, the last Toyota radio I tried this
with had DC controls for volume and so on, and it was somewhat more
difficult to find the appropriate point in the radio chassis.

     You could always find the "common point" where the AM tuner feeds 
the power amplifier circuitry, and use that; if you aren't committed to
AM radio listening. (The Toyota AM radio in question here wasn't worth
listening to, anyway....)  

     I've played my CD player through the usual 3.5 watt car radio type
amplifier (used as a monitor amp on our earth station) driving BIC Formula
1 (hack, cough, wheeze) speakers.  It wasn't that bad at low volume.
However, most car stereo amplifiers have gross phase distortion (pull out
your Ford factory radio and run a proof on it) as well as a frequency
response similar to that funny thing on your desk with 12 buttons on it....
The Toyota radio I modified (for roughly the same purpose) had more tilt
at 100 Hz than my 1948 Collins 20-T AM transmitter at 100% modulation.

     If you are really interested in doing this, find a decent radio chassis
to start with.  

David Anthony
DataSpan, Inc