Amp cutting out


New member
Username: Clio14

Post Number: 3
Registered: Nov-04
well no one has posted a reply to my last q so ill keep it short. Bought a JBL amp new (gt 766.5) when i turn it up it keeps cutting off. Ive got a constant 12.5v supply even when the low bass kicks in so it isnt a power issue i dont think,any ideas???

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 5620
Registered: Dec-03
where is the gain set on the amplifier?
what load is the amp seeing?
is it bridged?

New member
Username: Clio14

Post Number: 4
Registered: Nov-04
Gain is up 1/2
4 ohm over each channel
not bridged, not using the 2 sub channels, just two front and two back.

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 5656
Registered: Dec-03
not sure why this is happening.
could be a bad connection somewhere, like a faulty ground point

Silver Member
Username: Carguy

Post Number: 181
Registered: Nov-04
Hey Martin, I can't find any info on your JBL amp. What is the spec? What HU are you using it with? Are you using rca or speaker wire to rca converter with the amp?
Is that your first amp in the car or did you have one before?
Did you do the wiring yourself? How/where is your ground connected to?
I find that most problems are related to bad ground.
When an amp cuts off, something is overloading it or it could just be a bad amp.

New member
Username: Clio14

Post Number: 6
Registered: Nov-04
Thnx for all your posts,

My Amp

6/5/4/3 channel
Power Output: 60 watts RMS x 4 channels + 107 watts RMS x 2 channels at 4 ohms and U 1% THD
RMS Power into 3 channels: 160 watts x 2 + 300 watts x 1 at 4 ohms, 14.4V supply and U 1% THD
MAX Power: 4 x 120W max + 2 x 200max (or 4x120W + 500W max)
Signal-to-Noise Ratio: 79 dBA (reference 1 watt into 4 ohms)
Dynamic Power: 117 watts (channels 1,2,3,4); 163 watts (channels 5,6)
Effective Damping Factor: 6.392 at 4 ohms
Frequency Response (C3dB): 10Hz - 47kHz (channels 1,2,3,4); 10Hz - 302Hz (channels 5,6)
Maximum Input Signal: 6V
Maximum Sensitivity: 250mV
Output Regulation: .042 dB at 4 ohms

my head unit

Max. output power (watts) MOSFET 4 x 50 Watt

DIN output power (DIN45324, +B=14.4 V) 4 x 27 Watt

Max. preout voltage (V / Ohms) 2,2


5-mode preset equaliser Yes

Custom preset equaliser Yes

3-band parametric equaliser Yes

Source Equalisation Memory Yes

Selectable Loudness Yes

Selectable FIE (Front Image Enhancer) Yes

Loudness Yes

Source level adjuster Yes

Fader Yes

RCA Preout 2 (F + R)

I have ground the amp underneath my back seats. It is a heavy bolt and all the paint has been scratched off, has always been a good grnd point.

Using RCA leads from my HU and Have used splitters to feed both channels on the amp.

Have done the wiring myself, think ive done all the right bits e.g. 4 guage power line with fuse next to the batt, run power lead on the seperate side to my rca/speaker/rem leads. Short ground wires. I also have a rockford fosgate mono amp and vibe sub and these are fine, have checked the voltage at the batt, distribution block and all the amp terminals and the voltage is 12.5v+.

I am also using a audioleads 1.5 farad power cap, could this be the problem???

thanks for all your help guys, it is appriciated.


Silver Member
Username: Carguy

Post Number: 189
Registered: Nov-04
Hey Martin, it sounds like you have a weird problem so let's test each channel separetly. Connect one rca cable to one channel and turn up the volume. See if it cuts off. If not, move on to the next channel etc.
BTW, you mentioned that your level is set at half way, what exactly is that? Some have mid level as 1V. Your HU is putting out 2V. You really should try and match that.
There's a chance that one of your rca cable could be bad. Someone else had a similar problem.
Oh make sure you test the rca cable first.

New member
Username: Clio14

Post Number: 8
Registered: Nov-04
k i will do. i figured out that my gain was set slightly too high on my amp, about 3 volts. set it too 2 and it held 4 a short while longer before cutting out again. i will test each channel and get back to you with the results.

I only wired in my system last week so i hope that all the cabling is ok, (all new). thnx for your reply, at least some of us know where to look for the problem.
thnx again
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