APX6500/O5 heads: Where is the audio amp(s)?

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buckyswider
Posts: 7
Joined: Tue Nov 06, 2007 8:13 pm

APX6500/O5 heads: Where is the audio amp(s)?

Post by buckyswider »

Hi all, where is the audio amp for an APX6500 with remote heads? Is it within the base unit or in the head itself?

I have (had?) a weird problem. In a two-head config, the front head's volume was turned up too high, the audio would would cut out shortly after audio was heard (either the voice notifications of changing the channel or an actual reception). The level that the front head could be turned to before this started happening seemed to vary based on the setting of the rear head- i.e. the lower the rear head was set, the higher the front head could go before malfunctioning. This behavior was NOT symmetrical- the rear speaker never cut out no matter what.

However, this was noticed with the vehicle's key on "run" without the engine running- we had re-programming done, and I was in the process of re-setting the favorites bank when I noticed the issue. The next day I then set out troubleshooting, still without every starting the vehicle- just turning the key to "on". I swapped out the transceiver with another- same problem. I swapped out the front head with a spare- same problem. Swapped out the rear head with another spare- same problem. I then targeted the headliner-mounted front speaker. Noticed it was soldered in, and drove the vehicle to my house to pick up some lever nuts (boy I love those things!) to cut the wires and make easy work of swapping speaker. However, when I got back to the firehouse (with all original components back in)- and everything was working just fine. Could turn both volume pots up to 10 with no cutting out.

I find it inconceivable that any jostling of that front speaker could've fixed anything- heck, given the symptom, I don't see how that could be attributed to a passive speaker at all. The only thing I can think of is that the voltage supplied by the vehicle battery was just below the threshold needed to allow full operation of the transceiver and both heads.

So that got me wondering- is the audio amp in the base unit or in the heads? The heads get independent power (via the same connector that supplies power coincidentally) but I'm not sure if the control cables pull an amplified signal from the transceiver or it it line-level and then amplified in the head?

And does anyone have any other opinions on what could be causing my audio cutting out (on one speaker only) issue?

Thanks!
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jackhackett
Posts: 1513
Joined: Tue Jun 10, 2003 8:52 am

Re: APX6500/O5 heads: Where is the audio amp(s)?

Post by jackhackett »

There's an audio amplifier in the transceiver, and an amplifier on the CHIB (control head interface board) of each control head.

They are class D amplifier ICs that are spec'd at a supply voltage of 10 - 36 VDC.
buckyswider
Posts: 7
Joined: Tue Nov 06, 2007 8:13 pm

Re: APX6500/O5 heads: Where is the audio amp(s)?

Post by buckyswider »

Thanks much Jack!!

In both the transceiver and the head? Interesting. But given they're specc'd down to 10V, I wouldn't think low battery voltage could be causing this issue then. If the battery was down to 10V, I don't think the vehicle would start!!

Back to the drawing board....
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