# Two PPI Powerclass amps with same problem, Buzz Noise



## Unclemeaty (Oct 17, 2010)

Let me start by saying that I've got a certain nostalgia for Precision Power, and in the 90s I loved using thair PC450 and PC1400 (Big boy). I regret seeing them, but alas theres enough even now to go around. Unfortunatly time must be getting the best of two amps I ust picked up, as I have what appears to be a common problem between both... Two amps are experiencing the same issues. 

The amps are both the Charcoal Grey Precision Power Powerclass amps, one is a model PC2150 (150x2 4ohm / 600x1) and the other is a PC275 (75x2 4 ohm / 300x1).

The setup:
I'm powering a single sub with the PC2150. The sub is 4 Ohm and the amp is running 4Ohm bridged (600w). The PC275 is running 4 Ohm door speakers. Amps are running seperate RCA cables from a Pioneer HU.

The problem:
PC275
Left channel is Fine / Perfect sounding quality. This one is the model I go by for the rest of the problems as this channel sounds totally better than any other over both amplifiers. *THIS IS THE GOOD CHANNEL*

Right channel has a distinguished noise or buzzing sound, most audible when turning off the HP crossover (Playing full range) and playing a sin wave from CD in the 100 - 2000hz range.

PC2150
Both the left AND right channels are playing the same noise or buzzing sound as the other amp! Because this is a SUB amp its really hard to tell from the sub but is apparent at very low volumes listening very close to the sub. For a more acurate test I swapped plugs with the PC275 and ran the door speakers off my PC2150. Indeed both door speakers make an exact buzz like the PC275's Right channel.

In-Car troubleshooting: With the engine off... I've eliminated any RCA cabling issues because I have two seperate cables of different type; both sets do exactly the same things. I've also tried flipping the speaker-out plugs up-side down, and the problem at least on the PC275 follows the bad Right channel. If I unplug the left (good) channel's RCA, the right channel's buzzing gets about 20% less noticable. If I half pull out the right (Bad) channel's RCA - leaving only the inner connector attached - the problem gets another 25% better. If I leave both RCAs half-way pushed on and almost hanging then the problem gets about 75% better at a cost of overall sound quality - I think the PPI's internal noise reduction system starts eating into musical sound at this point.


On-Bench troubleshooting: Neither of these amplifiers had been opened before me; the original warrantee sticker was still on them when I got the amps off Craigslist. I'm fair to good with a soldering iron so I started going to town on re-soldering mostly resistors and some capacitors. I probably resoldered only about 15% of the PC275's PCB, and very very little on the PC2150. It didnt help, and I think it may have actually made the PC275's bad channel a little worse. There are no burned up or noticable problems with the PCBs on these boards. I've vaccumed, brushed, and checked most of the 3w resistors with my Fluke DVM. Unfortunately thats about the extent of my knowledge of these things. I wish I had an osiliscope. 

After searching google and this forum all I came up with was a very similar problem from anoter member with a PPI Art A600 amp:
Noise on one channel of PPI A600 - diyAudio

Please help, I hope I didnt buy these in vein. If you know how to fix please post, PM, email, or even give me a call

[email protected]
Cell 678-778-5533


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