Fordnatics List Archive

This read-only message was archived from a public mail list.
Mail From: (email redacted) (Greg Powers)

I'd like to improve the sound quality of the factory "Premium Sound"
system in my '90 LX hatchback. Specifically, I'd like to boost the
low end performance of the system. Is there a way to add an amp/sub-
woofer and still use the Ford head unit to drive the rest of the
factory speakers? I already have an amp and a subwoofer box, but I'm
pretty much lost from here. Any car stereo gurus out there that can
help?

Greg Powers
((email redacted))

This read-only message was archived from a public mail list.
Mail From: Bryan E Berndt <(email redacted)>

Well, this is right up my alley. I did exactly this to my '88 TC.
However, with only about 95% success, But it works. Here is my story.

The first thing I tried is using a thing called a High Level to
Line Level Step-Down. The Power level of the sound signal from the head
unit is considered to be a lower high level, so you need these; one will
ususally be able to handle two channels. The power after your factory
amplifier is definitly high level.
The first idea I had was to take the wires from the factory
amplifier to the rear deck speakers, and disconnect the speakers, run the
wires to a hi to lo con., then to an electronic crossover, then to two
seperate aftermarket amplifiers, one for a pair of subwoofers, and the
other for the rear deck speakers. This worked for about a week or so.
Soon the factory amplifier realized that there was a decreased load on
the rear channel, and it didn't like it. Factory systems (from what I
hear) are very picky as to what kinds of loads are put on them. The
factory amp was getting very hot, and started cipping on the front
channel. The two aftermarket amps also got hot because the input voltage
from the stepdown wasn't quite right, and the one for the subs was
cutting out at high volumes.
So, I gutted my stuff out of the trunk, and started to look at my
wiring diagrams again. There are only five wires going into the factory
amp. One positive for each channel (the four front speakers are
considered two channels), and one common negative. One the output side of
the factory amp there is a pos. and neg. for each of the four channels,
but each speaker has FOUR wires on it. ??!!!??? go figure. Two pair
of wires, each pair the same color. I don't know why this is, but it
seems to work if you tie each pair together two get two wires. After some
thinking, and playing with all those pretty wires, I finally had another
plan.
I went out and bought another high-to-low-step-down. I cut all
the wires off of the input side of the factory amp. I found the remote
power wire to use to turn on the aftermarket amps when the radio is on. I
ran an 8-gauge wire from the battery to the trunk, witha 40ampere fuse
about 6" from the battery. (have to gaurd against shorts between the
front and rear of the car as well as a fuse for each of the amps and
crossover about 6" from them, although most come with a fuse in the power
cable that they come with.)
One stepdown for the front channel, and one for the rear. I tried
to connect the pos. wires to the pos. leads on the stepdowns, then
connect all the negs. together. This didn't work to well, I'm not sure why.
But when I left all the negs. disconnected it seemed to work fine. so
this is how I left it.
So, in bypassing the factory amp, I had to go to my own. Three of
them; one for the front speakers, one for the rear deck speakers, and one
for the subwoffers in the trunk. One the output side of the stepdowns are
RCA plugs (commenly found on home stereos, but quickly find there way
into the car the last couple of years). The front one went to a small
50watt amp for the front four speakers. *Be careful here* When I went to
see what the impedence of the front channels was, I found it two be 4ohms
on each side. There are two speakers on each side, so I assumed that Ford
used two 8ohm speakers wired in parallel to get 4 ohms. I wanted to
replace these anyway so I pulled them, and put in a pair of Sony satalite
speakers. I don't think I assumed right, and I don't know what Ford did,
because I tested one of the door speakers and it itself was 4ohms. That
50watt amp I had was good for 2-8ohms, so I just hooked up my speakers to
the factory wires and mounted the woofer in the door, and (the dash
speakers are part of this and gone too) the 1" tweeter in the top corner
of the windshield, and called it good. The amp seems fine, so it must be
handleing the four speakers fine, wether their in series or parellel I
don't know.
The rear RCA's went to a two way electronic crossover. This split
up the frequencies and it makes four channel out of two. The high-pass
channels went to an 80watt amp then to the rear deck speakers. The
low-pass channels waent to a 200watt amp and to the subwoofers.

*whew*
The reason I said it was only 95% effective is that in bypassing
the factory, there is also a factory noise filter there, that I bypassed.
Now there is a good amont of alternator noise in the speakers. It is the
infamous engine wine that changes pitch with the engine RPM, and it gets
louder with more accesories on (like lights, A/C, and rear defroster).
I'm still working on that problem. I've tried aftermarket filters, ground
loop isolating RCA cables, and even elaborate grounding of all the
components. I did find out that my head unit wasn't grounded right, and
that did help a little.

Where are you located? Maybe, if your close to me in North
Dakota, I could help do it. I really enjoy tinkering with car stereos.
I've installed three total systems, an alarm, and a CD changer. I hope
you can follow this story. Please feel free to mail me for mre questions.

******************************************************************************
=-->GOOCH<--=
'88 T-bird T forTURBO!
*Alpine*Rockford Fosgate*Coustic*Sony*Audiovox*Jensen*
'93 Trek 9000
(email redacted)
******************************************************************************