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Heineken's Garage

Speaker

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Introduction
A number of sports cars from the 80s and 90s, were equipped with a BOSE audio system. A popular example, beside the NSX is the Corvette. These systems were specifically tuned to the vehicle to create the typical BOSE sound.

Details
Three specifically tuned amplifiers make up the system. Each one build into the speaker enclosures in the left door, right door and the passenger foot well. Door amplifiers are having six-pin connectors. The foot well amplifier additionally supplies an extra speaker at the rear centre console and is therefore equipped with a 7-pin connector.

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Opened Foot Well Speaker (7-pin)
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Opened Door Speaker
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Door Amplifier Module (6-pin)

Each amplifier module is specifically tuned for its position and therefore only the door speaker amplifiers can be considered exchangeable. Amplifier modules from other cars with a BOSE sound system can be used but their sound tuning won't match exactly.

Speaker Amplifier Module Markings Number of Pins
Left and right Door KAPPA SU FRONT
KAPPA SF FRONT
AMP **** FRNT KAP **
6
Foot Well KAPPA SU REAR
KAPPA SF REAR
7

These amplifiers are Class-D switching amplifiers. They convert the incoming audio signal into very fast pulses that are driving the main output transistors. These pulses cause the transistor to be either full-on or full-off which reduces their internal losses significantly and allows for a small, compact and efficient design (at the expense of sound quality, to some degree).

The speakers inside the housing are of an unusually low impedance of 1 Ω which makes replacements hard to find. Speakers with a higher impedance will strongly affecting the output at a given volume.

Limitations
The radio head unit is supplying a signal ranging from zero to roughly headphone volume level to the speakers which amplify it further. Due to the nature of this system, the amplifiers are permanently running at full amplification and their noise floor at low volume is relatively high. It's normal to hear a slight hissing noise when the engine isn't running and the radio switched-on but no sound is playing.

Checking the rear centre speaker can be difficult due to its comparably low volume.

Known Issues
Similar to many ECUs in the car, the speaker amplifiers suffer from capacitor leakage. Typical symptom are popping, siren or static noise, sudden change in volume or drop-outs.
Leaking capacitors can damage the transistors on the amplifier as well as burn and char the PCB. Preventive capacitor replacement is highly recommended.

Updated 08-02-2021 at 09:10 PM by Heineken

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