JVC head unit alternator noise trouble

[MNBoxster]

Originally Posted by RandallNeighbour

Jim, I've had this noise in every single aftermarket audio system I have installed in cars when the alternator was working just fine or even brand new! To say that xclusivecar needs to have his alternator checked out because there's a little remaining whine is quite speculative and reaching if you ask me.

xclusivecar, if you're happy with your system, drive the car and crank up the tunes while you're at it. I certainly wouldn't spend any money to have an alternator checked out if your battery isn't weak... alternator noise is typical in high powered head units and amps and I always assume it will be there if I don't use a filter.

Jack, I see what you're saying... so what do the high end amp manufacturers do to eliminate the ever-present alternator whine without filtering that "chokes" down the power?

Hi,

Randall, I too have installed several high-end, high power stereos in my cars and friends. Most recently a Nakamichi 400 HU and 4/100 Nakamichi Amp w/ 8 Focal speakers in my Esprit. Being essentially a Plastic car, with few ground points, this was especially tricky. But, I have never had an Alternator whine that I couldn't track down and eliminate.

Whether it's careful routing of the RCA cables away from power lines or harnesses, isolated grounds,. tracking down and eliminating Ground Loops, grounding antennae or failed Alternator Diodes, I have always been able to eliminate any noise even with a high gain setting.

Now, I can't speak with the authority of our esteemed EE, JackG, but I do know these noises can be eliminated, though it can expand your vocabulary getting there...

Happy Motoring!... Jim'99

[JackG]

Originally Posted by RandallNeighbour

Jack, I see what you're saying... so what do the high end amp manufacturers do to eliminate the ever-present alternator whine without filtering that "chokes" down the power?

The "whine" is more of a problem in the head units than in high power amps.

Why, you ask? The head units use the 12vdc as-is to power the unit. Radio tuner, CD player, and amplifier section are all powered by the 12v.

An amplifier that provides, say, 75w RMS per channel to the speakers can't do that using 12vdc. The amplifier uses a DC-DC converter to step up the voltage to something higher internally that allows more power to be delivered to the speakers. The process of converting the 12vdc to an AC voltage, feeding it through a transformer, then converting back to the internal DC voltage very effectively isolates the amplifier from any impurity on the 12v line. That's also why these amps are large, heavy, and expensive... it takes a bit of circuitry and space to do this conversion... and is also why head units, even the high power ones, don't have much power. You just can't cram that much stuff into a DIN sized chassis.