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 cassette, has four connectors called C1, C2, C3 and C4 on the rear panel. C1/C2, which is a single siamese connector, is used for many Delco head units, not just Bose. The wiring is different though in various cars. C1/C2 carry power, ground, BCM data and the front and rear speaker wires. There is no switched power on the C1/C2 connector, the BCM controls powering up the head unit. 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 BSP in the Coupe is different than in the Vert and FRC. 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" in the Vert and FRC, 6.5" in the Coupe and the fronts are 3.5" in all vehicles. The Bose system has no true tweeters. The BCP also sums the audio information from all 4 pre-amp input signals and sends it unfiltered 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 doors. 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. The 4 channel internal AB power amp in the HU is
about 14 -18 wrms/ch into a 4 ohm speaker. This amp drives the four Bose Twiddlers. The door class D sub amps are about 35 to 45 wrms each into a 2 ohm speaker. Each sub amp drives a 2 ohm Bose reverse cone sub woofer. Since the Bose system has no DC to DC converter like an aftermarket power amp would, the amps are running directly off the alternator's 14 volts. 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.

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.

Simple Modifications:

Replace the rear Bose Twiddlers with 2 or 3 way speakers. This will improve the highs. Unfortunately the speakers are poorly placed and do not radiate at the occupants heads. Buy speakers with swivel tweeters or that have the high frequency drivers angled at 45 degrees.

Connect real tweeters in parallel with the rear Bose Twiddlers. Point the tweeters at the occupants heads. They can be mounted on the car pillars.

Add a subwoofer to the system. Connect the sub amp to the HU rear channel pre-amp outputs.

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
Radio "ON" C1(8) DK GRN, Switched 12v used to turn on power ant and Bose modules
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


Tweeter additions to Bose system

When you add a "4" ohm tweeter and it's crossover in parallel with the front 3.5" Bose Twiddlers, the amplifier will see a more complicated load. The impedance that the amplifier will see will be very low where the two speakers overlap in frequency response. The front 3.5" Bose Twiddler will have a frequency response similar to any add on tweeter. In reality it may be best to put the add on tweeter in parallel with the rear 5.25"/6.5" Bose Twiddler wires. The rear Twiddler is a mid range speaker. Putting a tweeter and crosover in parallel with it will mean very little overlap in the frequency response of the two speakers. The amplifier will not have to supply as much current at a specific frequency to both speakers at once, so it will run cooler and produce less distortion. The rear Bose Twiddler wires are available on the back of the HU.

RR+ C2(18) DK BLU
RR- C2(17) LT BLU

LR+ C2(20) BRN
LR- C2(19) YEL

Delphi/Bose head unit internal improvements:

These mods are not to be done by someone without soldering experience with surface mount components.

The Bose CD deck with the FRC bypass will not drive it's internal 4 ch power amp to clipping on some radio stations or selected CD's. It is not a real problem, but some old CD's were recorded at very low levels. These old CD's usually sound like crap because old tapes were used as the source material and there is a lot of hiss on them. If you like your music loud, then you will need to modify the head unit power amp for more gain. Most head units can overdrive their power amps to clipping for even low level inputs. I have a fix to increase the gain of the internal power amp. You need to replace four chip resistors. The mod requires changing out four 1206 size surface mount chip resistors. The head unit power amp has 4 op-amp based attenuators feeding it. Lower the attenuation and the power amp gain will go up.

The Bose head unit has a modified bass control to work with the subwoofer. When put in a system without a sub-woofer, the control does very little. A normal bass control has a turnover frequency of about 1khz. The Bose HU control is under 200 hz. The stock speakers in the FRC cannot reproduce the sub frequencies. I modified my bass control to work like standard Delco deck. The change requires changing out some surface resistors and capacitors. This mod improves the bass enormously.

I have also gone through the circuitry and improved the low and high frequency response of all the audio circuitry. These changes required increasing the coupling capacitor values by 2x to 10x and eliminating some shunt capacitors from the C3/C4 interface.

Head unit gain and bass control modifications:

The resistors and capacitors I changed are on both sides of the head unit motherboard. I will only describe the gain and bass control mods for now. The other mods I did are too much for most people to attempt. The other mods only enhance the bass and highs more. This is something you will probably not need to do.
DO NOT force anything. Be patient.

To get at one side of the motherboard, you need to remove the radio circuit card, this is easy. To get at the other side requires removing the CD assembly. It is fastened with four screws. This takes more time because you must remove the front panel to get two of the screws. Remove the big ***** only and the nut and washer on the volume control. Be very careful removing the front panel. It is plastic and is clipped onto the metal chassis in many places. Work each "clip" free individually. Be careful removing the CD assy. There is a long ribbon cable attached to it. You must release the tiny compression clamp on the ribbon connector on the CD assy motherboard, to pull out the ribbon cable free.

The four resistors to changed the power amp gain are near the two SO-14 and one SO-8 IC packages used for the pre-amp output and power amp input buffers. The two 14 pin IC's are quad op-amps and the 8 pin IC is a dual op-amp. The resistors are clustered around one of the 14 pin SO-14 package IC's next to the C2/C3 connectors, under one of the RTV blobs. You need to remove the RTV blob on top of the IC. Leave the rest alone. The resistors are labled 5491. This means 5.49K ohm 1%. You need to replace them with four 12K to 27K ohm, 1206 size chip resistors. The larger the resistance value, the higher the power amp gain.

To mod the bass control circuit, locate the small 32 pin PLCC packaged tone control IC near the large Microprocessor IC. The bass control's 2 resistors and 4 caps are on the other side of the motherboard under the tone control IC. Look for two 1206 chip resistors labled 302 that connect to ground. This means 3K ohm 5%. There are four caps connected to these two resistors. It is a "T" network. For the R+L channels, two caps attach to the IC and the resistor hangs between the two caps to ground. The two resistors need to be replaced with 4.3K to 5.1K 1206 size chip resistors and the caps replaced with .1uf 1206 size chip caps.

Be very careful removing the old parts. Heat up both end terminations of a the chip component at once with a soldering iron. Use some extra solder to help transfer heat and work the tip back and forth between the ends. Make a small solder ball if neccessary. Gently push the part off the pads with the soldering iron tip when both terminations are floating free. Clean up the board pads with solder wick. Clean the board with a Q-tip and some alchohol or acetone. Use tweezers to hold the new parts to solder them.

 

Thanks 99HT, once again, great info and I appreciate the research. I don't know if you've seen it, but someone else copied this info a few months ago and quoted/credited it to you, and put it into the Tech Tips section, so it's preserved now.

Thanks
Sam

 

Cool copied it to the harddrive thanks!! :cheers:

 

It would be nice if the latest version was put up. It has a lot more info.

It seems that there is now a PAC solution for replacing the Bose HU and keeping the Bose speakers and subwoofer amps. We need to learn all the pros and cons of this solution and make a Tech Tip out of it.

 

99HT,
I'm going to replace the rear twiddlers.

I'll also be adding a power antenna to the Z06, so looks like

Radio "ON" C1(8) DK GRN, Switched 12v used to turn on power ant and Bose modules

will be a wire I need to tap in to. Is there anything else I should know?

Thanks for all the info (although most is over my head :D ).

 

If you use the stock antenna for the Vert, you should not need to worry about such details. Many FRC and Z06 owners have replaced their antenna and used connected to the existing wiring harness. Do a search on the subject or ask about it in the tech section. I believe Ken Fitchner sells a "kit" of everything you need.

 

Talked to them this morning. Their kit won't include all the standard wiring, so I plan to run one to this wire to activate the antenna.

 

Great info 99HT!! :yesnod: :yesnod: I plan to only replace the rear speakers but if I can find some with a swivel tweeter then that would be great so I could project the highs more toward the passengers. :cheers:

 

Polk & Infinity have models that can be aimed. Found those in the Crutchfield catalog, probably more out there.

 

Great info 99HT... does that info still apply to 2002 C5's?
Thanks!!

An additional Question however, I wish to add an Empeg (RioCar) Mp3 car stereo as an aux player.

How can I get the existing CD head unit with no changer to switch to an Aux mode as if it had a changer but instead use the Empegs output to play from instead of the non-existant CD changer?
Basicly, I'm looking for aux inputs that can be switched on and off from the head unit.

I'm pretty sure it's possible but it sounds like you may have already done the homework on this.

I do have an alternate route if it seems easier to you, My Empeg player has Aux input capability... Could I wire the Empeg into the existing Bose system as the main head and use it's aux switching to flip back to the stock head unit? which method would be easier?

I want to try and squeeze the Empeg player into the bottom tray below the AC controls in addition to the stock unit.

Thanks for your info again!!!

 

Do a search in the archives. This subject has been covered before.

The CD changer/AUX input will not work unless a CD changer or other GM product with an E&C interface communicates with the HU. A sleazey way to go is to record a 1 hour blank CD with a single song on it. You then need to add a cable and switch to bypass the CD changer audio.

Others have opened their HU and added a switch and cables to bypass the internal CD and input and external MP3 player.

 

Great information. Thanks again. :cheers:

 

99HT,
Have you made any progress in decoding the E&C signal??
I was thinking about trying to use the signal to switch my AUX input relay...
If I push the AUX button on the HU, will it send out a burst (to the changer).. then give up when it gets no reply? Do you know what voltage levels the bus uses?
Gary

 

I spent a while looking at the signals. I kinda know how to simulate a CD changer, but operating in that mode is troublesome with an external input. The HU always needs a time code input from the changer. The changer also sends back error messages. I am also not sure if the HU will allow one long song without a ending. It would be a PITA if the HU and black box had to be "reset" every time the time code overflowed.

I need inside info on other modes that the C5 HU will operate in. Since the C5 never came with OnStar or other GM options that use the E&C interface, I don't know if it will be able to operate without the constant time code signals sent from the CD changer now.

 

Yeah, what a pain to reverse engineer everything.
Could you just get it playing and then open the bus and see what happens?
Gary

 

Any interruption of the E&C bus when the CDchanger is playing will cause the HU to display Err and jump back into radio mode. The changer must be in constant communication with the HU when it is in CD changer mode.

I am sure there are other modes that the HU can be commanded into via the E&C bus, but without some inside info, trying to guess would be a wild goose chase.

 

99HT

Thanks for your post, very informative. I'm completely disatisfied with the setup on C5.
My C4 bose was a much better system. Anyway, I have already replaced the rears on my C5 with a set of nice component speakers with optimal tweeter placement, but I'm still not satisfied.

Is it possible to configure the system as follows?

Factory Head Unit and door subs, to remain as configured from the factory. External amp for 4 main speakers and additional sub.

How should I accomplish this?

 

What you want to do has been done many times before, search the archives. The HU has four channel pre-amp outputs. Just tap these signals and feed them to an external amp or amps. Cut the end off two long RCA shielded cables and splice into the wiring harness on the back of the HU.

 

See above. Thanks a lot for ANY help.
P.S. Oh and is the wiring info that was provided by 99HT applicable to an '01 coupe?