# Old Rockford Power 300 has scratchy channel



## SUX 2BU (Oct 27, 2008)

I have a 1988-vintage Power 300 I bought from an electronics repair place about 8 years ago and I just decided to install it in my system to replace a RF 4080 that blew up one of it's rear channels. I found that after installing the Power 300 one of the front channels has a distorted, scratchy output. I know it's the output section and not the input. Any idea what this is? I'm hoping possibly for a dirty gain pot but that might be too easy. I'm bummed


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## ChrisB (Jul 3, 2008)

If it were a dirty gain pot, you'd generally hear the scratchy noise as you turned the gain. I have an Orion 280 GX that has noisy gains, yet you don't hear the noise when the amplifier is playing.

I also had an amplifier with some dried out input filtering caps that produced a distorted, scratchy, output at low volume but it went away as I increased the volume.


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## SUX 2BU (Oct 27, 2008)

Hmm interesting. I might have to play around with it some more then. I'm wondering if I bridged those channels to a sub, if the noise would either disappear or be discernable.....


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## Sarthos (Oct 29, 2010)

I had a rockford amp that had some major noise on a channel due to a bad ground. But I'm not sure what you mean by "scratchy"


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## SUX 2BU (Oct 27, 2008)

It plays distorted. You can hear the music, but it's distorted. Like a staticy radio channel.


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## Sarthos (Oct 29, 2010)

Okay. So it's not adding extra noise (like static) more like as though you throw the signal through a screwed up equalizer?

I'm assuming you tested inputs by swapping a working RCA from another channel and tested outputs by swapping to another working speaker?

If the gain on the amp has problems, a line driver or higher voltage pre-outs on your stereo might help.


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## chauss (Sep 20, 2009)

Will it play at lower volume levels w/o the scratchy sound? If so - Did you swap channels to make sure it is only that 1 channel? If you swap channels and the same one still has the "scratchy" sound it could be the amp does not have enough power to drive the speakers at that level...(left and right signals are usually not equal) If so try bridging it for more power. Is it volume related? ie: more volume = more scratchy sound?


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## SUX 2BU (Oct 27, 2008)

I didn't try it at too high a volume level yet but I got to about 50% volume on my deck and it was the same. I first swapped RCA inputs and the scratchy sound stayed at the same speaker. I was hoping for a blown speaker! Then I swapped speaker output leads and the sound changed to the other speaker  So I figure something is not right in my right-front output channel. I wonder though if bridging the front 2 channels on to say a subwoofer would net me clean sound.....


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## chauss (Sep 20, 2009)

Definitely sounds like an output channel on the amp- sorry bro! Maybe worth getting it fixed if it is just a transistor? Good luck in finding the "cure"- if nothing else....a good excuse to upgrade!


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## SUX 2BU (Oct 27, 2008)

Well my upgrade though is to using an even older amp than before lol I love old skool audio but repairs are unfortunately a part of that game. Thanks for the info!


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## envisionelec (Dec 14, 2005)

SUX 2BU said:


> I didn't try it at too high a volume level yet but I got to about 50% volume on my deck and it was the same. I first swapped RCA inputs and the scratchy sound stayed at the same speaker. I was hoping for a blown speaker! Then I swapped speaker output leads and the sound changed to the other speaker  So I figure something is not right in my right-front output channel. I wonder though if bridging the front 2 channels on to say a subwoofer would net me clean sound.....


The problem is that only half of the channel is actually functioning - so you get a half-wave rectified output. You can get the same sound out of your other channels by wiring a diode in series with the speaker.

It's a repair job, because it is likely that one of the channel's fuses are blown. When replaced, it will blow again due to an issue with the channel: shorted output FETs (and their corresponding drivers) are extremely common.


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