Audio power advice

Mick Rae

Mick Rae

Active Member
Hi, I am planning to fit a small, 120W, Bluetooth amplifier. So nothing crazy, but more than enough for me. It will be fitted such that it's hidden in passenger glove box area, to the inside of the black dash area space between map light and switch. Idea being nothing but a 70s style on/off volume knob that's black and in keeping with car. Plan to use bullets and double connectors to keep tidy so an original bullet connection in the area would nice, but obviously not essential. My question is: What would be the preferred power source (car has no radio currently) to take from such that it's only powered with ignition on?
 
In past, with larger, much more powerful amplifiers I have powered from battery via a relay, meaning the ignition feed only has to switch the relay. I'm thinking now that even for a small amplifier, given its still a wee bit more powerful than a std radio/cd player, I'd be better doing that, just a bit of a pain when battery is in the boot. But then I can take off the relay power from any ignition live I guess, as a relay has very minor draw. I could get battery direct from fuse box feed pre-fuse box? I know, look at the circuit diagram, and I will once I get to it, just pondering of an evening......
 
Relay off the terminal post or shunt if you have the round instruments - i.e. not through the ignition switch as a power source. In line blade fuse. No need for a run to the battery.
 
Thanks Peter. Round instruments, so shunt it is. At risk of appearing dim, what is the shunt? Assuming it's something to do with the ammeter, but only as I've seen the word used in ammeter threads, but no experience with ammeters, hence daft question.
 
Me again Peter. Having googled a bit, the shunt looks pretty involved to get to. Do you know if any more accessible battery live points up front? When you mentioned terminal post, what was that? Apologies, my issue us usually not knowing all the terminology so may well be staring at stuff without knowing it's correct name.
 
It's behind the dashboard "wood" trim. I don't think models with the round instruments have the post, it's in the footwell which would work great for you. I changed from the strip speedo to the round dials which is why I know this. I have several shunts with the intension of fitting them but decided not to for safety. Here's the post in my LH D car. As the battery cable always runs down the RHS I assume it's the same. The new cables are for my uprated alternator. The AC11 being crap.

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Interesting, as my car has also been converted from strip to round dials (I think, as an sc car would have been strip apparently). So I may also have this post, I will look and see. What I am looking at in your picture is right hand footwell yeah, up under dash? Or am I disoriented! Sure would be handy if I have one. That said, if the shunt is just behind the wood, easy enough I'd think (but freely admit I fear the ammeter and its associated parts having never had one before, but see nothing but scary stories online:eek:). Thanks for you time and help Peter, really appreciated.
 
That's the floor under the carpet... Transmission tunnel to the left (white sealant), wheel arch intrusion carpet on the right.
 
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Home at last, had a spy under carpet. Yes, I have the post, excellent, much easier now. Peter, thanks so much for your time and advice today, that been really helpful......if there was such a thing as an online pint I'd be buying you one.
 
Mick Rae said:
Home at last, had a spy under carpet. Yes, I have the post, excellent, much easier now. Peter, thanks so much for your time and advice today, that been really helpful......if there was such a thing as an online pint I'd be buying you one.
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Easy job now with a ring crimp and you can simply cable tie a feed to those brown cables and run it to the center console through a fuse. I think this is a much safer method than hacking around the keyswitch etc. Car radios didn't run to 120W in those days and the accessory wiring isn't going to be up to it or at best very marginal. I always work on the principle that any change or additionis "better than OEM" even if it means overkill. If anything goes wrong and it's your handiwork, the insurance people might take a dim view.

Saying that, there are options with the keyswitch but I'd onlyuse that for switching on your amp. I took this reference when I took the dash apart. Anything white or white/something is an ignition circuit. The ones marked "X" were unused in my case.

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Incidentally did whoever change your dashboard wire in the ammeter? These are sketchy things as the whole electrical load goes through the shunt. If these fail and you are lucky, they act like a fuse and the car dies on the spot. If you are unlucky they become an electrical fire starter.
 
As regards the change from strip to round dials, I presume the previous owner did it. Ammeter works, so must have had shunt added. The chap was an electronics professional, so have to presume he did it right, the rest of his wiring was good standard though. I'd love to know why it was done, guessing back in the day it was sportier looking. Funnily enough, I'd have quite liked a strip for the novelty of it, but happy enough that what's there works. I'm undecided about my original relay activated by ignition to switch on the battery to the amp idea now, would mean another switch, and all to make the amp isolated, might in future, but for now think I'll just wire directly off the area you showed me, and always remember to switch off amp (I'd have to remember to switch off relay, so no different). I'm with you on using new wires, this way I am really pleased to not be messing around cutting into the loom. Had an old mk 2 escort a long time back, and after two days ownership turned the lights on, promptly melted an area of wiring as previous owner had fitted super strong lights to unfused, thin wires. Lesson learned! But damn, wish I had kept that car given the prices now......
 
Small is good. I hope! Just arrived, can remember when such a thing was size of a couple of bricks.
 

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I'd be astonished if you got 120w RMS out of that. Bear in mind a class B amp can only be 78% efficient at best. It has no heastsink....
 
Mick Rae said:
Small is good. I hope! Just arrived, can remember when such a thing was size of a couple of bricks.
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Hmmm looks like it say's DC in 5.2W so I am guessing no more than about 2 watts max unless its a digital amplifier in which case maybe 4 ( but I doubt it).
I am also surmising that its made in China where I have seen a 5 watt amplifier rated as 1200 Watts, the level of exaggeration seems similar for sure.

Graeme


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Well, we will see. Reviews seem to indicate it's fine enough for cars, but yeah, reviews. They do returns, so worth a go I reckon. I'm not looking for anything more than what an old radio can put out (certainly not booming bass!). Will report back good or bad, and will hook up to test prior to installation, then if useless, back it goes!
 
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