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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

Speed-Racer

Excellent info as usual.

Please if you're trying to do this, see any post here by me on this topic.

I can vouch that the sound is totally unbelievable. The bass is just outa here. The thump is so hard at times it can hurt
I redid one wire last week to have the amp auto turn on with the radio now.
Speed-Racer



[Modified by Speed-Racer, 2:21 PM 8/11/2001]

Abnsteel06vette

any pictures?

gmosley

i cant really follow this thread its seems useful info but it doesnt tell you what is the outcome or why would you want to bypass certain parts of the system
is this referring to aftermarket amps with the factory head unit or something else
please explain it to me
im no audio newb but cant determine exactly what is being accomplished with all the above info
thanks in advance

leolufse

The above info is a bit outdated and not totally correct. What do you want to know? It might be easier to start that way.

gmosley

i want to know what would doing this accomplish
basically what would the benefit be to doing each of the above things bypassing the processor and such basically if i followed the instructions from the post above the end result would yield me the ability to do what
or doing the process in the first post would it improve anything in the factory system

basically if i did a given procedure explained in the first post what would the end result be for each process i do