Selectable, head amp or outboard amp

Hi all, glad to be a noob here!

I'm trying to do the unusual (as usual), which may be more complex than I'm aware...that's why I'm seeking your pro advice;

I have a '93 Bonneville that I put a new Panasonic CQ-C8403U into. Works as expected, but 18W rms is not impressive through my front 4x7 Boston Acoustics, and rear 6x9 Infinity Kappa's (naturally).

I will be installing a new Infinity 7541a amp (111W rms per (4) channels) =-D
Of course this will be a current hog, and for local hops or parking lot listening, I would like to bypass the beast, and just run the head unit's internal amp.

Clearly, I will have to switch them somehow, and this is where I need advice.
The head unit does have an option to select internal amp on or off, so that part seems simple enough. I'm going to make sure that the blue 12v signal wire that powers up the amp and sub (Infinity Basslink), will for sure be the on-off for those big toys. That should be simple enough also, since I have a switch on the dash to control that signal wire.

My unknown factor: Speaker wiring.
My "guess" is that I can have my speakers wired to BOTH the head unit outputs, AND the 7541a outputs, at the same time. (?)

I can't imagine that the head unit audio outputs could damage the amp while it's off, but I am concerned that the 7541 could fry the head units IC's, from so much power driving into them, though they would be off... I dunno!

I like the idea of being able to select between big or little amp, and there's gotta be a way without complex relays (I hope)?

Any advice is greatly appreciated, thanks!!!

BTW- the 7541 front channels will also be parallel to rear door 6 inch 2-way Blaupunkt's I installed, 6x9 Kappas will get the rear channels.

you could run your speaker wires thru 2 4 contact relays. that would isolate the two units. these relays can be purchassed from a radio shack store. make sure you get the ones with a 12 volt coil.

xs

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expandable sound
south of boston

Personally, I don't think that amp will be too much of a current hog. Especially running mids and highs. But that's just my opinion...take it with a pinch of salt and a shot of Patron!

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The Flakman
I feel strange. I have deja vu and amnesia at the same time.

John | Manteca, CA

If you had an Alpine HU, many of them allow you to turn off the internal amp. Not sure about other brands.

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The Flakman
I feel strange. I have deja vu and amnesia at the same time.

John | Manteca, CA

Thanks to all for your input!

I guess the 4 pole relays would be the safest way to go. Total isolation.
True, the 7541a won't be a "major current hog", but 111 watts compared to 18 watts, is considerable! I'd be forced to run the alternator more often, and with todays gas prices, it would be like throwing quarters into a jukebox...just to play my own system! =P

Well, I'll have to think about this project mod. Lots more potential "points of failure" I'd be adding, plus the added wire length, relays and power lines to add noise, more stuff crammed in the dash...ugh! This idea is getting less appealing as I consider the overhead involved. Then there's that gas pump rearing it's ugly $$$ head!

Maybe I should just add a hand-crank generator to my iPod & earbuds!...
-back to the drawing board. again. grrrr.

You will only be using 111 watts if you have the amp and the head unit at full volume.  Personally I would just use the external amp (better quality sound and cleaner signal).

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Im moving to MEXICO and Im not speaking spanish!

What our non-Spanish speaking friend is getting at, though, is that he won't be using anywhere near 111 watts per channel at lower, normal listening levels.

Nouse, so are you saying if I connect a 300 watt mono amp to a sub, and set the gains correctly, that sub will receive 300 watts when it's barely audible?  If you are, that's just not the case.

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My ex once told me I have a perfect face for radio.

Thanks all!

Besides the 111 wrms per 4 channels from the 7541a, it will ALSO be using the 200 wrms Infinity Basslink sub in the trunk! Though both amps are more efficient than Class A or A/B, that's a ton more than 18 wrms per channel from the HU alone...

I mentioned the Basslink in the original post, but was not very clear, sorry!

It's not worth the effort. If you will be running the headunit at the full 18 watts RMS it isn't going to pull any more power than running the infinity amp at 18 watts RMS. That is the whole idea of the "gain control" setting on the amp. If you don't raise the input voltage from turning up the volume on the headunit then the amp turn itself up (very simple-ized explaination). And like someone else said you will still have the clarity from the amp having all that headroom.

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fiberglass reminds me of peanut brittle... but fiberglass tastes better!

sprawl85 wrote:

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It's not worth the effort. If you will be running the headunit at the full 18 watts RMS it isn't going to pull any more power than running the infinity amp at 18 watts RMS. That is the whole idea of the "gain control" setting on the amp. If you don't raise the input voltage from turning up the volume on the headunit then the amp turn itself up (very simple-ized explaination). And like someone else said you will still have the clarity from the amp having all that headroom.

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Um...I think this got off the topic I'm shooting for...

I'm not concerned with the gains of the main & sub amps. When all of the system is complete & adjusted, I'm confident it will kick serious enough quality sound & volume.

My original post was/is a bit more unusual, which is:

I want to be able to switch audio source completely, for power conservation purposes.

1. With entire system active, (111 wrms x 4, + 200 wrms Basslink sub) I will be required to run my engine, basically full time, or it will put a relatively fast drain on the battery, and my wallet (from fuel cost).

2. If I run only the HU 18 wrms x 4 internal amp, and NOT power up the external amps, it will conserve much more battery power, and be plenty enough for extended parking lot time, or listening to news, etc..

QUESTION SETUP:
- My HU DOES have the ability to turn on/off it's internal amp.
- Blue trigger wire will be manually switchable from dash, to control amp(s) power.
- MY PLAN: Wire front & rear speakers to BOTH the HU audio outs, and the 7541a audio outs.
- (Just FYI) The 7541a will be driving the rear 6x9's, while the front channels will be paralled to the middle & front speakers.
- While speakers will be physically connected to BOTH seperate amp outputs, I feel confident that the audio outputs of the HU will NOT do any damage to the 7541a output circuit (I HOPE!)
- When the HU output is OFF, the external amps will be ON.
- NO concern about the HU pre-amp outs...they're always live...

MAIN CONCERN QUESTION: When on (and HU audio outputs OFF) could the output power of the 7541a, damage the small output transistors and/or whatever circuitry is at the end of the HU audio outs?

I am hoping someone would know if these things have some kind of diode or reverse-current protection? (I understand that they would not engineer for some strange currents coming into their audio outputs when everything is "supposed to be" off...) Yet, I'm also hoping by the nature of the components, that most devices would be safe if a circuit is "off". Applying some power to one lead of many components is moot without a path for current to flow through the device.

So far, the best suggestion I got was to use two double-throw, 4-pole relays to totally isolate the outputs.
That would be PERFECT...except...
(insert cheezy whine here)- All of that would require extra & dedicated speaker wiring, relays, related power wiring, fusing, and stuffing all that into the dash somewhere, besides almost doubling the length for signal-to-speakers (I know, I'm stretching here...consider the whine, of NOT having to add and complicate all this crappy solution...to what I once thought would be a nice idea. geeze.

If anybody is still awake after this - THANKS!!!
If you know what I'm trying to solve, and even have a technical answer thats...not so technical (?) please lemme know!
If I can get away with my first idea, without damaging either units outputs, and you know this, well, you would certainly make my day!!!

Any input is appreciated, thank you all!

nouseforaname wrote:

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mrjc480 wrote:

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You will only be using 111 watts if you have the amp and the head unit at full volume. Personally I would just use the external amp (better quality sound and cleaner signal).

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111 watts is 111 watts reguardless of volume.

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Yes, true, but in this case wrong application. Read on.

If you head unit allows you 18X4, and you can listen to it at a resonable volume, i.e. loud enough for you to listen to it in the parking lot, and an amplifier playing the SAME source, at the SAME volume will pull NO MORE CURRENT THAN THE HEAD UNIT, probably a little less, due to it's eficiency, ESPECIALLY if your 111X4 is Class D!

A deck, producing, lets say, 15 wpc, is significantly less efficient than an amplifier producing the same amount of power. Just because your amp CAN produce 111 wpc, that does not EVER mean that's ALL it puts out, wherever the volume control is. If you have the same source being amplified by the deck, producing a continuous 15 wpc, simply by the fact that the system will be cleaner and SOUND more intelligible, the externally amplified system will probably be making LESS power to the speakers - probably closer to 10 wpc. ALSO, if you implement the high pass crossover (like I know you were going to do ANYWAY, right?) for parking lot listening, the system will run even MORE efficiently, by virtue of not having to amplify low frequencies. A simple switch in the remote lead to the sub will guarantee that the externally amplified version will consume less power, overall, than the deck amplified version.

Stop making it more difficult on yourself than you have to, put the system in, and love life!

Oh, and yes, the HU will take damage, I guarantee it, if you connect it as described above! The outputs have no protection whatsoever (with the possible exception of short circuit) and audio signals are AC, so you CAN'T diode isolate them... Don't even think about following through on that plan, unless you want to go buy a new deck, and soon!

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

haemphyst wrote:

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nouseforaname wrote:

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mrjc480 wrote:

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You will only be using 111 watts if you have the amp and the head unit at full volume. Personally I would just use the external amp (better quality sound and cleaner signal).

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111 watts is 111 watts reguardless of volume.

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Stop making it more difficult on yourself than you have to, put the system in, and love life!

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AHHH! THANK YOU SO MUCH haemphyst !!!

NOW I get it! Everything you said makes sense to me, now I feel comfortable with ditching my "ignorance-is-bliss" idea. I THOUGHT it was a good idea...yours is MUCH better! I'm so happy, another self-made hurdle crossed! Whew, really man, I DO complicate things for myself, from years of modding & fabbing all sorts of projects. Not that I'm not gonna keep complicating this project...I'm looking for a local welder to fab a new passenger seat mount, so I can fit the Infinity 7541a under there... heh.

I sure appreciate your help bro! Pics will be posted when the project gets there...it WILL be unique! (hint: didn't like generic HU mounts for GM, so I made my own with pilots, sockets, switches...) I think you'll get a grin from this 'geezer's' work.

Thanks again to ALL of you! - the12volt ROCKS!