Amp& sub help def 90.

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MaxyMan

MaxyMan

Well-Known Member
Posts
2,540
Location
Hampshire
Hi all,
Been having abit of a nightmare with my sound set up in my wagon.
Basically one day the subwoofer just randomly cut out.
The amp decided not to power up at all and I got fed up so got another amp.
Put new amp in and worked spot on for 1day then cut out like the old did.

I've tested the subwoofer all is fine
Tested both amps now, both work hooked upto small speaker and with 12v converter from mains
RCA leads all fine.

I changed the amps about a few more times and both worked for about 10secs then when deep bass they cut off again.

All fuses are fine.

This is where I get confused, the switched live from headunit to amp is randomly sending from 6-12v. But the amp is on ok it's not getting lack of power.

Once the sub cuts out it will not work at all until the amp is disconnected from live and earth and all wires taken off.
I can re connect it, run it on very low volume so no bass when I turn it up it cuts off.
The amp will remain on but no output??? This is the same on two different amps but one stays powerd on and the other will just remain dead.

Any ideas??
Cheers
 
Ok cheers, will have a fiddle with it. Works fine with a small speaker but just dies on the big sub guess could be underpowered and getting hot?
 
davesdisco said:
try turning the bass all the way down and run it for a while then slowly turn the bass back up on the amp to see if it cuts out.
Click to expand...

The bass was right down when volume was low, ran fine. When I turned volume up it cut out like it did randomly to start with.
 
Haha I said in the thread title "Def 90" - land rover defender 90. Engine etc is irrelivent as it just electrical radio problems.
 
Rattlegun said:
Might be going into protection because of impedance mismatch. Check output impedance limit spec of amp vs speaker.
Click to expand...

Cheers will give it a go.
But it's not going into protection as there's a separate led light that should come on for going into that mode and it's not?
 
I have heard of this kind of thing happening in the past, particularly with high power aftermarket ICE systems.

The electrical supply system in a vehicle is happiest when it's delivering a medium to high(ish) steady or near steady current. High power amplifiers especially those with what might be called "over-generous" levels of bass can cause extremely heavy spikes in the current being drawn from the vehicle system. If the supply system can't meet those spikes in demand then the amplifier might see that as a failure in the power supply and close down. So getting the power supply which will do the job is essential.

The first thing to check is obviously is the earth connection, but seeing as you say you've done that the next thing to look at is the size of the power cables. These should be something like about 10 square mil for both pos and neg and taken straight back to the battery, through a suitable fuse of course. The amplifier is going to draw quite high current as you damage your eardrums while you drive along.

The next thing to try is to fit a very large capacitor, something like 1 Farad as close as you can to the amplifier power input; this will act as a back-up battery designed specifically to meet the demand of those sudden high current spikes which the vehicle supply can't.

Maplins do big capacitors specially for the job.
 
Thanks fella, the cables are both suitable so that's somthing else ticked off. Will see if can get a capacitor and see what it does!
 
What are the models & specs of the amps you are running? Never been convinced with capacitors as an aid to power supply for ICE but like anything there'll always be people who are for and people who are against them. Have you tried the amps or sub in anyone else's cars?
 
I know you said its connected straight to the battery, but are the connections good? doesnt take much to annoy an amp.
what size is the amp, got a 900W (stupid car 900W sub, prolly about 150/200W RMS) sub in mine, power feed if from bat, but its earthed to the body volt-gauge ticks a fraction with it wound right up but barely noticable, moves more when towing with indicators on.
 
Good conections on the batty. The amp that first died was a 1200w. Replaced with a 450w one and the sub I'm not sure but it's only a 12" diameter alpine think around 400w.

The original amp and sub worked in my mates car ok. There is a crack in the ANL in line fuse live from the battery but still sends out 14v from alternator ok.

I've got another fuse on order so might be that but I wouldn't of thaught so.
 
just to try it, bypass the fuse but dont leave it like that.
or, leave landy running and collect it to another car thats also running with jump leads, more power. i remember i had a 3000W rms systen in a 1.0 corsa b before, even with a huuge battery it couldnt keep up. connected it to disco and had both running, worked not too bad. ended up with 3 disco tdi batterys in the boot and one under the bonnet and 2 100A altenators. worked fine, much better than the standard 50 amp one haha.
used to set off car alarms and broke a few boot windows on the corsa haha. :D
 
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