Phatbox versus KEG: Alternative Power Lead

[eddy123]

I would like to know why the PhatBox has an alternative Power connection and the KEG doesn't. I have seen the connections points on the PCB -rev A.

I'm asking this because I suspect some issues I have that power might not be sufficient using the standard cable.

Eddy

[S80_UK]

Hi,

There are different options for powering the main board primariliy because some vehicles will power it from the head-unit, while others don't or can't and so power needs to be brought in seperately.

When the power is brought in on the main head-unit connector, typically it comes in on a few pins (two for the positive supply, and two for ground).  But some people have found that this connection is not that reliable and it could be argued that the head-unit connector is not designed for power use.  On the other hand there can be good reasons for taking power from the head-unit - it can simplify the elimination of electrical noise from the audio in some cases.

Does this help?

[SteveC]

As S80_UK said, it's because with the "generic" phatbox the power source could be different depending on the vehicle. Some would deliver power via the headunit, others wouldn't. The Kenwood box was designed to take power from the headunit, because that's how kenwood changers got their power.

[eddy123]

It does make sense however I was wondering if it doesn't create huge loses over these tiny wires. I'm not sure how much amp the unit needs but there could be a voltage drop at the far end just because of the total resistance, when the KEG is on. The unit by itself gets quite hot after a while so I assume that the power consumption is reasonable high, maybe one amp or so. In my Audi the cable from front to rear is about 4-5 meters. I will try to measure the voltage and voltage drop the coming days.

Thanks.

Eddy

[SteveC]

Remember, the Kenwood's CD interface was designed to deal with a CD changer - including power for all of the mechanical parts that move the CD's around. That is more than enough power for a laptop hard drive. I really believe that the engineers knew what they were doing when they made that choice, and that Phatnoise was aware of the power issues as well.

I'm also pretty sure that Kenwood was pretty clear on what they did and did not want to include on their branded "Music Keg", which led to the elimination of the additional power jack and the RCA inputs as well.

Another thing to note is that using a seperate power source/path opens you up to all kinds of grounding and induced noise issues.

On the other hand, if you are having problems caused by the power feed from the headunit to the phatbox, it will probably be a lot of fun (not) tracking it down.

[S80_UK]

On the other hand, if you are having problems caused by the power feed from the headunit to the phatbox, it will probably be a lot of fun (not) tracking it down.

Yes - eliminating unwanted noise from audio can be one of the trickier areas of in-car electronics.  

Incidentally, except during the initial disc spin-up phase, the current required by the Keg / Phatbox and the hard disc should be pretty low.  One amp would definitely be on the high side.  I would expect to see a figure probably less than half that when running normally.  (Sorry - I would measure mine, but in my installation the power connection is not that accessible).