Re: Rear amp 5kCST (Long)

[Dave Head <dhead@sundial.sundial.net>]

At 03:21 PM 3/23/96 -0500, you wrote:
>Since I'm going to replace the old Blaupunkt head unit, I always worry about
>the tiny amp/crossover in the back that doesn't compatible with my new 
>head unit. 
>
>In the post you mentioned that the F & R output in the stock head unit 
>are amplified. Is that means they both output the speaker level signal?
>So, that means even the rear speakers have that "amp" things, they still 
>input the speaker level signal? So, when I'm installing the new head unit 
>I probably don't have to convert the Rear speaker level to line level in my 
>new head unit, huh? 
>
>One last things. Actually, is the "amp" thing in the back an amplifier or 
>a crossover? if it's a crossover how come is has power supplied?

The stock stereo puts out a whopping 7.5 Watts per channel. The rear amp is
like the old piggyback add on amps that were around when I was 1st putting
stereos in cars. (I don't know what the amplification factor of the rear amp
is) It incorporates the 'secondary amplification' and crossover for the rear
together - however, power for it also feeds the antenna turn-on/off and booster!
Here are some options for you: 
1) If your new head unit has high level (amped) rear output and you don't
need or want the secondary amplification, buy a pair of two way crossovers,
run a new set of wires to the back, hook up the crossovers to the out wiring
of the rear amp and keep the old rear amp powered via the antenna power wire
of your new unit. You could get three way crossovers out of the front door
of another Audi and add a midrange speaker if you wanted a 12 speaker
system. If you don't want to run new wires, I can send you the wiring
diagrams from the Bentley.
2) If your head unit has amped rear output you should be able to still use
the existing setup - realizing you are now putting a much larger signal into
the 'booster' amp - it could drive it into saturation which would give you
mucho distortion. Then you are either stuck with turning your fader way down
in back to limit the input, or back to 1) above. Most 'better' head units
these days are about 14-25 Watts/channel. The high end ones use that for the
front and go to line outs for the back so people can crank in much rear
power, add subwoofers, etc.
3) If your head unit has line outs (low level) for the back, add an amp and
go to 1) or 2) above. From your post, I would assume it doesn't.

BTW - halfway decent crossovers can be had pretty cheap ($10-20.00).
Blockers (to only allow the tweeter signal, for example) are only a buck or
two - but waste power.

If you're doing this soon - what are your plans for your old unit? I sold
mine to another list member, planning to put in a Nakamichi I bought cheap -
then found out it's microprocessor was bad and it'll cost me $175.00 and 2
weeks turnaround for the repair :-(.  So now I'm looking for a stock unit to
borrow for 6 months or less 'till I can afford it (I still have a brake
accumulator to replace, reflectors to replate, after run cooling to fix...).
This is preferable to me than buying something cheap at a flea market and
carving up my wiring twice!
********************************AUDI FAN******************************
EMCM(SW) Dave Head
87 5KCSTQ 170K miles and counting...
1.8 bar boost - @ 1.3 the shuttle launches
Maitland FL
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