donshams

I installed JBL GTO638 3 way 6.5" speaker in the rears using the gm speaker hardness connected by metra part number 72-4568. It feel like the speaker are underpowered. I connected the speakers to a seperate amp 100watt I have lying around and they the speakers work fine... any idea what's going on?

markcz

If you still have the stock radio installed, then they ARE under powered.

jrprich

The rear speakers on a C5 are not connected to the Bose amp, only the door speakers are.
The rears have a very low signal as they were designed to simply provide what Bose would call "proper sound placement"..........they will never have the same volume as the door speakers as they were not designed to by Bose.
When I replaced my door Bose speakers (Twiddlers) with small Kicker coaxials (keeping the BOSE amp and subs in play) I rewired the connection to the rear speakers behind the head unit to disconnect the rear channel and run all speakers (F&R) from the front speaker outputs on the head unit. I also replaced the rear Bose speakers (Twiddlers) with 5.5" Kicker coaxials.
This mod really improved the sound quality in my Vette.............but others may differ. I had my 99 set up this way for 8 years with no issues. I also rewired my new to me 03 in the same way.

Some helpful info from the web:
C5 Bose CD or cassette upgrade wiring notes

Bose CD/Cassette Stereo System Info:

The C5 Bose stereo system is based on a modified Delphi head unit. The "Delpi/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 Delphi head units, not just Bose. C1/C2 carry power, ground, PCM 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 also does ambience and spatial enhancement to the audio signals. The internal power amp is about 15-18 watt rms/ch. The head unit power amp drives the 4 front and rear Bose midrange speakers called Twiddlers. The rear Twiddlers are 5.25" and the fronts are 3.75". The Bose system has no true tweeters. In addition, the BCP extracts the low frequency information from all 4 pre-amp input signals and sends them to the two sub-woofer amplifiers in the doors. These sub amps feed two reverse cone 8" "sub-woofers" in the door. They are mounted next to the front 3.75" Twiddlers behind the door speaker grills.

All low level audio interfaces in the Bose system are psuedo-differential. These include pre-amp, power amp, 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 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.

Modification #1

Replace the rear 5.25" Bose Twiddlers with 2 or 3 way speakers. This will improve the high considerably. Ther are no tweeters in the Bose system.

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.

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