Old School PPI problem

Audio Head

Member
2013-05-21 9:49 am
Hello everybody. I have been lurking for a long time on this site and this is my first post. No I didn't join just to ask for help, but I could sure use it. I have a PPI PC4800 that doesn't seem to turn on by itself. If I turn the car on, I get a strange pulsing sound and an eerie noise that sounds like a mumbling voice. If I unplug one of the RCAs and plug it back in, the amp kicks on. It will turn on every time I unplug and replug the RCA. It is a new install so I am open to the fact that it may be user error. I am feeding the amp a variable balanced signal from a stock head unit. I don't know if this is the problem as I think the ground is floating. The rear channels are bridged, and the front is set to high pass at around 70. When I first connected the amp one side would turn on but the other side wouldn't. When I unplugged and replugged the RCA the other side came on. I tried a Y cable to plug into both the front and rear inputs, but then both sides would not kick on until I unplug and replug an RCA into an input. I would appreciate any insight anyone can give me.
 
Have you tried a hand held source like a Ipod or something ? This would rule out weather or not the amp is the issue, or if its the install or the head unit setup.

" I am feeding the amp a variable balanced signal from a stock head unit."

balanced signal drive in my mind means something, are you sure the term "balanced" is correct in the description ? RCA signals are un-balanced as I recall, and balanced line driver signals require receivers to bring them back to RCA proper level to be used. I am sure this amp does not accept balanced line drive signals on its RCA inputs. So this is why I tag that description for clarification. And ask if you have tried another source like some hand held device to drive the amp with.


next step would be to see if you have any DC voltages present on your RCAs and or on the speaker terminals with NO RCAs hooked up and No Speakers connected but the amp turned on and idling. oh and ground for your black probe would be the 12 volt ground and on second test common speaker ground < amps power supply secondary side > Amp testing only at this point...
 
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Audio Head

Member
2013-05-21 9:49 am
Have you tried a hand held source like a Ipod or something ? This would rule out weather or not the amp is the issue, or if its the install or the head unit setup.

" I am feeding the amp a variable balanced signal from a stock head unit."

balanced signal drive in my mind means something, are you sure the term "balanced" is correct in the description ? RCA signals are un-balanced as I recall, and balanced line driver signals require receivers to bring them back to RCA proper level to be used. I am sure this amp does not accept balanced line drive signals on its RCA inputs. So this is why I tag that description for clarification. And ask if you have tried another source like some hand held device to drive the amp with.


next step would be to see if you have any DC voltages present on your RCAs and or on the speaker terminals with NO RCAs hooked up and No Speakers connected but the amp turned on and idling. oh and ground for your black probe would be the 12 volt ground and on second test common speaker ground < amps power supply secondary side > Amp testing only at this point...

Thanks for the reply.
Yes balanced means something else to me as well. Some car stereos (in my case a stock BMW unit) choose strange ways to send their signals. It is actually called Differential balanced. Here is a description.

This circuitry reduces noise radiated into your signal cables by up to 40dB. This is equivalent to a noise reduction of approximately one hundred times what the noise level would be without this circuitry.
It provides all the benefits of a true 'balanced' line without the need of any special cables (see diagram below). This type of input works with any conventional RCA cable.

Many modern amplifiers such as JL accept the Differential Balanced inputs, and the PPI manual mentions it as well, but it also says it is not compatible with floating ground speaker outputs. I think Differential Balanced is floating ground.


To answer your question I did test it on a bench with an iPod and it did seem to work fine. The sound seems fine, it is just the problem of the amp not turning on unless I unplug and replug the RCA cable. It is almost as if a relay is not activating unless the it gets a jar from the RCA being plugged in. I am still trying to get my head around the whole PPI concept of how their channels interact. The amp does sound great by the way. Lots of detail. However trying to integrate anything with the stock BMW system is a nightmare. I had the idea of hooking up a JL amp which takes the inputs fine and running from the RCA outs of that into the PPI and see if that triggers the amp any better. I am out of town at the moment, however I thought of yanking the amp out of the car and giving it a good clean. Thanks again for your insight.
 

Audio Head

Member
2013-05-21 9:49 am
I will go buy an inexpensive multimeter tomorrow to check for DC voltages.I actually forgot to mention that at one point I started the car and I could hear engine whining in the speakers. However when I disconnected the second set of RCAs the noise went away and has not come back. Is it appropriate to put the probe through the center of the RCA to check for voltages? It has to be done in the car, but I will gladly follow your advice.
 
Thanks for the reply.
Yes balanced means something else to me as well. Some car stereos (in my case a stock BMW unit) choose strange ways to send their signals. It is actually called Differential balanced. Here is a description.

This circuitry reduces noise radiated into your signal cables by up to 40dB. This is equivalent to a noise reduction of approximately one hundred times what the noise level would be without this circuitry.
It provides all the benefits of a true 'balanced' line without the need of any special cables (see diagram below). This type of input works with any conventional RCA cable.

Many modern amplifiers such as JL accept the Differential Balanced inputs, and the PPI manual mentions it as well, but it also says it is not compatible with floating ground speaker outputs. I think Differential Balanced is floating ground.

I am interested as well. Audio Head, where did you get that quoted text about the differential output of BMW head unit? I am preparing to connect a BMW CD43 business radio to my old school ESX amplifier but am planning on using the ESX's balanced inputs instead of the RCAs. I also do not know about PPI but your description sounds like there may be some sort of automatic signal sensing used to turn the amp on that is not working properly in one channel.
 

Audio Head

Member
2013-05-21 9:49 am
Hi. The quote was from the PPI site. Does the ESX accept differential balanced? I think 1moreamp is suggesting it has something to do with voltage on the inputs of the amp. I will be back home in a couple of days and check it. I was going to buy a cheap multimeter but decided to wait