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Old 27th July 2009, 12:24 PM   #1
chemhaz is offline chemhaz  Australia
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Default Squealing lil'pig, a PPI PPI4240

I have a PPI 4240 whcih gives off a constant high pitch squeal when powered on. The sound is coming from the inside of the amp. It sounds like an old camera flash charging. I'm guessing it's a cap.

The squeal is constant and at the same pitch when given a signal all 4 ch work OK, the sound is undistorted, the squealing continues even without a signal, moving the gain makes no difference.

Any assistance would be apreciated.

I can do basics like change caps etc if that's all that is needed... but if it's more complicated, off the repair it will go.

I also have a Rockford Fosgate 150s which thinks it's an AM tuner as you can clearly hear a radio station without a source input, but that's another story.
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Mitsubishi Magna.
Pioneer DEH 7650 hu, PPI PC4800 running front Boston Acoustic Pro 6.5's and rear Kenwood HQ 6x9's. RF POWER 250x2 running 2 Perless 12's (aka VDO HPS12)
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Old 27th July 2009, 12:41 PM   #2
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For the PPI, try touching the windings of the transformer and twisting the transformer. Does either make a difference?

Does the squealing get into the audio?


Are you close to an AM transmitter tower?
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Old 27th July 2009, 01:51 PM   #3
Dealer is offline Dealer  United States
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Default Radio amps

The powersupply is either a heavy load or there is some harmonic not filtering correctly. What you hear is the powersupply oscillation frequency (heavy load)or harmonic of that frequency (filter failure).


As to the 150 playing AM, yes i believe it in AM, but I have a much more interesting situation that I would not have believed unless I saw it for myself. Kenwood KAC-821 playing FM without any signal on the input.
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Old 27th July 2009, 01:51 PM   #4
Dealer is offline Dealer  United States
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Default Radio amps

The powersupply is either under a heavy load or there is some harmonic not filtering correctly. What you hear is the powersupply oscillation frequency (heavy load)or harmonic of that frequency (filter failure).


As to the 150 playing AM, yes i believe it in AM, but I have a much more interesting situation that I would not have believed unless I saw it for myself. Kenwood KAC-821 playing FM without any signal on the input.
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Old 27th July 2009, 02:01 PM   #5
chemhaz is offline chemhaz  Australia
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Perry, - PPI , I've tried running my fingers over it and twisting it.. with little success as it's pretty tight. The noise is only coming from the amp transformer, it does not go through the speakers.

I think I need to send it to a repaier

RF 150s I don't believe they have put up any new AM towers around my home, I found some info online about Radio Frequency Intererance (RFI) breakthrough on home and guitar amps which expains it, the RCA leads act as an aerial.. IT has not happend to any other amp before.. or after.
__________________
Mitsubishi Magna.
Pioneer DEH 7650 hu, PPI PC4800 running front Boston Acoustic Pro 6.5's and rear Kenwood HQ 6x9's. RF POWER 250x2 running 2 Perless 12's (aka VDO HPS12)
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Old 27th July 2009, 04:35 PM   #6
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If the squealing is only in the amp and the amp is working properly otherwise, it doesn't need to be repaired unless the amp is going to be mounted in the passenger compartment of the vehicle. Some transformers/supplies are noisy.

I've never had a Rockford amp picking up AM radio. Does it do it with and without RCAs plugged in?
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Old 28th July 2009, 09:53 AM   #7
chemhaz is offline chemhaz  Australia
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Join Date: Apr 2008
Perry,

With the PPI, I took you advice one step further; I started tapping the transformer with the handle of a screw driver. With each tap the squealing changed frequency and I noticed it got quieter when I hit it on a side, so i kept tapping until it the squeal was barely audible. I turned it of and one several times and let it run for 2 hours.. It seems to have worked, so when all else fails, use brute force..

Rockford Fosgate 150s - I've noted the following,
It picks up the radio station (Sydney ABC 702 am) better with one RCA lead plugged in. When no leads are plugged in it dos not work( radio reception)
The gain control seems to act like a volume and also tuner, reception is best in the mid gain setting
Depending where I stand, also affects the quality of the radio reception.
It only picks up the station in stereo mode, HPF and full range setting
IT does NOT pick up the radio on LPF setting

I took a video of it on my phone, I donít think this can be fixed so Iíll use it on LPF bridged.. it seems to work fine, probably because AM does not go to under 80hz.
Check out the video here if your interested

http://www.youtube.com/watch?v=no1yBFSw4ns

Thanks guys.
__________________
Mitsubishi Magna.
Pioneer DEH 7650 hu, PPI PC4800 running front Boston Acoustic Pro 6.5's and rear Kenwood HQ 6x9's. RF POWER 250x2 running 2 Perless 12's (aka VDO HPS12)
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