Alpine amp plays fine but needs lots of signal input? - diyAudio
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Old 20th January 2007, 12:27 AM   #1
spooney is offline spooney  United States
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Join Date: Dec 2006
Default Alpine amp plays fine but needs lots of signal input?

The amp I'm referring to is an alpine MRV-F300 4 channel amp(The same amp I recently replaced an output transistor in).For testing purposes I hooked it up in my car bridged into 2 channels to drive a pair of ten inch subwoofers.It does get loud and seems to have plenty of output but it takes a lot more signal to drive this amp than any other amp I've ever had in this car or any other car for that matter. It took me maxing out the amplifiers gains as well as my subwoofer output from the headunit to get decent output from this amp.Does anyone know if this is just characteristic of these amps or does it sound like there may be a problem with the preamp section of this amp?I know all is well with the rest of the system as i just swapped out another amp today that was playing fine with much less gain and input.
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Old 20th January 2007, 04:23 AM   #2
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Join Date: Dec 2005
Location: Northern California
Sounds like a blown input RCA ground trace. I have seen them flash like fuses, or maybe a cracked circuit board, or broken RCA shield connection to the board , try looking at all the solders for the RCAs.

Check the + - 15 volt rails to the input chips... Good luck, it sounds like a easy fix, just a drag to take aprt to find the issue
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Old 20th January 2007, 08:20 AM   #3
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The amp is supposed to make rated power with only 200mv (0.2v) at max gain. If you're driving it with a standard head unit, there should be at least 1 volt getting to the amp. If the amp isn't being driven into clipping at full volume, there may be a problem with the muting circuit in the amp. If the output is clean but low, the muting circuit is one of the few things that can affect all channels at once.

If you have a test tone disc or a tone generator, drive a signal into the amp and measure the AC voltage at the RCA jacks AND at the output terminals. At max gain, with 200mv in, the output should be ~11 volts AC (calculated from the power specs of 30w into 4 ohms). Do this at a relatively low frequency (20-100Hz to insure that the meter is going to be accurate.

It's possible that the amp is simply not very powerful (80 watts RMS/ch bridged to 2 chanels) and is not going to be very loud.
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