Bose Wiring Tips

I just copied this into this section of the tech tips so
it is not lost in the archives…. it is great info that I think should be
placed here… I have dont this without 99HT\’s permission but I hope
that will not be a problem….
Now here you go….
C5 Bose
CD or cassette upgrade wiring notes
Bose CD/Cassette Stereo System
Info:
The C5 Bose stereo system is based on a modified Delco head
unit. The \”Delco/Bose\” head unit, CD or casssette, has four connectors
called C1, C2, C3 and C4 on the rear panel. C1/C2, which is a single
siamese connector, is used for all Delco head units, not just Bose. C1/C2
carry power, ground, BCM data and the front and rear speaker wires.
Connectors C3 and C4, provide interfaces to the head unit front/rear
pre-amp outputs and front/rear power amp inputs. The pre-amp\’s audio
outputs on connector C4 go to the BOSE Signal Processor, BSP, mounted
above the throttle. The BSP \”conditions\” the front/rear audio signals
and then sends them right back to the head unit internal 4 channel power
amp. The basic crossover frequency of the BSP is 1 kHz. The BSP probably
also does ambience and spatial enhancement to the audio signals. The head
unit internal power amp is about 15-18 watt rms/ch and drives the 4 front
and rear Bose midrange/highs speakers called Twiddlers. The rear Twiddlers
are 5.25\” and the fronts are 3.5\”. The Bose system has no true
tweeters. The BCP sums the audio information from all 4 pre-amp input
signals and sends it to the two sub-woofer amplifiers in the doors. The
sub amps have an internal low frequency crossover. These two class D sub
amps feed two reverse cone 8\” \”sub-woofers\” in the door. They are
mounted next to the front 3.5\” Twiddlers behind the door speaker
grills.
Some of the problems with the stock Bose system
are:
1. Speaker placement. The mid/high frequency speakers are
horribly placed. The front Twiddlers radiate at your feet and the rears
radiate at each other. High frequency drivers are very directional like a
flashlight. They need to point directly at the occupants.
2. Lack
of highs. There are no tweeters in the C5 system. The system should have
had pillar mount tweeters. The front Twiddlers are really upper mid-range
drivers.
3. Gain imbalance. The subs level and the mid/highs level
is not ideal. It seems that Bose/Delco is trying to use the bass control
as a subs level control. It does not work correctly. It has a very low
frequency turnover frequency compared to other Delco head units. The
system should have at least three level controls, subs, mids and
highs.
4. Low mids/high power amp gain. The Twiddler power amps in
the Bose/Delco head unit have their gain set very low. I don\’t know
what Bose was thinking. You cannot drive the front and rear Bose Twiddlers
to full level on many CD\’s and certain radio stations, yet you can
drive the Bose subs to full level any time. I modified my head unit to fix
this problem in my hybrid system.
5. Lack of audio power. The
Bose/Delco system has six power amplifier channels. Four channels are in
the head unit and two small class D amps are in the doors. None are more
than 15-20 wrms. The Bose system should have had an external six channel
power amp module with high power. They could have taken the money wasted
on the external Bose Signal Processor and sub amps and put it into an
external amp. Why is it that other GM vehicles like the Camaro have a
seperate power module.
6. No external auxilliary audio input
connector. It this day and age, the head unit should have had a set of RCA
connectors under the dash for a MP3 player or what ever one wanted. The
deck could do this now if it had different software in it.
Audio
interface info:
All low level audio interfaces in the Bose system
are psuedo-differential. These include pre-amp, power amp, signal
processor, subwoofer signals and CD changer. All high level speaker
outputs, head unit and sub-amp, are fully differential. A
psuedo-differential wiring scheme is one that shares one return signal
wire for many signal source wires. A true differential wiring scheme uses
two wires per signal. Using psuedo-differential or true differential
wiring for low level signals improves noise rejection. Pseudo-differential
wiring costs less than differential wiring and does not reject noise as
well. Using differential wiring for high level signals improves voltage
swing by 2x and thus power level. 2x the voltage swing is 4x the power. A
typical single ended power amp powered by +14 volts, will put out 4 watts.
A typical differential or balanced power amp running off +14 volts, will
put out 16 watts. NEVER ground any psuedo-differential or differential
signals to chassis. You may damage the internal differential circuitry.
There is a dedicated floating Common return signal for each low level
interface. DO NOT use the Common signals to interface to any external
equipment. The Common signals in the C5 audio system are non-standard and
should only interface to Delphi or Bose equipment. The 4 Common signals on
the head unit and BSP have a DC offset on them. If you ground any of them
you may do damage to internal circuitry. Only use a high impedance
interface to tap a pre-amp outputs to feed external amps. For a power amp
input signal return, use the shield wires or chassis. Tapping a
differential signal with a single wire is OK, but you will not get the
same noise rejection on long cable runs.
Bench Testing:
The
C5 head units used in the coupe, FRC or vert are under control of the Body
Control Module, BCM. The head unit cannot be tested outside the car
without connecting a spare BCM to the DLC data buss interface of the head
unit. The BCM controls power ON/OFF, illumination, SVC and radio pre-sets
of the head unit.
Modifications:
Replace the rear 5.25\”
Bose Twiddlers with 2 or 3 way speakers. This will improve the highs
slightly. Unfortunately the speakers are poorly placed and do not radiate
at the occupants heads.
Connect real tweeters in parallel with the
front or rear Bose Twiddlers. Point the tweeters at te occupants
heads.
The Bose CD/Cassette head unit can be utilized without the
Bose signal conditioner, Bose sub-woofer amps and speakers by using the
head unit four pre-amp outputs to drive external aftermarket power
amplifiers and speakers. Use the Shield wires or chassis for signal
return. DO NOT USE signals Common on C4(13),LT BLU or Common C4(7),YEL.
These signals are only to interface with the Bose signal
conditioner.
The head unit Radio \”ON\” output can be used to
switch on external power amps. Be safe and use an in-line .5 amp fuse to
protect head unit.
Wiring info:
The following are the Bose
head unit 4 channel pre-amp outputs
Signal CD/Radio Color code
LF
out C4(9) TAN/BLK
RF out C4(10) LT GRN/BLK
LR out C4(11) BRN
RR
out C4(12) DK BLU
Common C4(13) LT BLU, DO NOT USE FOR EXTERNAL POWER
AMP
Shield C4(14) Bare wire
Ground C4(15) BLK
The following
are the Bose head unit 4 channel power amp inputs
Signal CD/Radio Color
code
Common C4(7) YEL, DO NOT USE FOR EXTERNAL POWER AMP
Shield
C4(8) Bare wire
LF in C3(1) DK GRN
RF in C3(2) LT GRN
LR in C3(3)
BRN/WHT
RR in C3(4) BLK
The following are the head unit power
and control signals
Signal CD/Radio connection
SW +12 out C1(8) DK
GRN, Radio \”ON\” signal
Power C1(10) ORG
ground C1(5)
BLK/WHT
The following are inputs to the Bose signal
conditioner
Signal Bose signal processor connection
LF in B5
RF
in B7
LR in B6
RR in B8
Common A4
The following are Bose
\”conditioned\” outputs
fed back to the head unit 4 channel power
amp
Signal Bose signal processor connection
LF out B2
RF out
B12
LR out A2
RR out B10
Common B3
The following are Bose
\”conditioned\” outputs
fed to the front door sub-woofer
amps
Signal Bose signal processor connection
RH out A9
RH return
A11
Drain B9
LH out A3
LH return B11
Drain B4
Bose
signal processor power connections
Power A12
SW +12 in A8, turn on
processor
Ground B1
Bose Bypass info
To bypass the Bose
Signal Processor, make the following jumper using the C3 and C4 connectors
in the wiring harness. Connect the following color wires together. Please
check the wires per the info above.
There is two BLK wires, one is a
signal wire and the other is connected to chassis ground, C3(4) is the one
you want. Solder the connections and tape them up. Do not cut unused
wires, you may want to add a power amp later and you will need these for
signal returns.
C4(9) TAN/BLK connect to C3(1) DK GRN
C4(10) LT
GRN/BLK connect to C3(2) LT GRN
C4(11) BRN connect to C3(3)
BRN/WHT
C4(12) DK BLU connect to C3(4) BLK
C4(13) LT BLU connect to
C4(7) YEL

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