I have already searched for info on this site and found a very informative thread from a PDX V9 owner but it falls short of explaining now to remove and replace ribbon cable.
Recently purchased a used PDX F4 and one channel is not working properly. I suspect it is the preamp ribbon cable but I have not worked on one of these before and I am afraid to force the 15 year old plastic connectors. I have attached pics of the bad channel and a good one on my scope and the connector I am looking for help with. I don’t know how to release the ribbon cable connectors.
Thanks @Perry Babin I did not want to force anything. I have broken enough old plastic connectors on my 90s era BMWs by forcing them before I understood how to release the retainers. Didn’t want to do that here. All 4 channels are working again but still not quite right. Channels 1 and 2 do not show the same voltage on my scope at 1 Khz as channels 3 and 4 even though the input gains are set the same. I am feeding the signal from an old Zapco DSP6. Output gains are the same for all four channels.
Output gains?
Did you try sweeping the entire frequency range to see if the problem may be frequency related?
Did you try sweeping the entire frequency range to see if the problem may be frequency related?
Not yet but I will. I was using test signals from an old Sheffield Labs test disc for the first testing. My plan is to setup a poor man’s test suite using Room EQ Wizard and a Focusrite USB audio interface. There is a YouTube creator named RAWCAT that has some videos explaining how to do that.
Test suite?
Why not use audacity to make a sweep? Attached is a 20 second sweep. If you use it, set the volume very low initially. It's recorded at just under 0dBfs.
Why not use audacity to make a sweep? Attached is a 20 second sweep. If you use it, set the volume very low initially. It's recorded at just under 0dBfs.
Thanks @Perry Babin for the sweep file. I tried playing it using audacity and that worked fine. The problem I have run into is really excessive noise on the outputs of the Alpine that are a combination of AC line noise from my laptop and the high frequency switching frequency of the Class D amp, I ran the laptop on battery and that cleaned things up a bit but the high frequency noise is still there and it is much worse than it was in the scope pictures above. Makes it very difficult to measure output voltage of the amplifier with the sweep or single tones. I believe something i am doing wrong is causing the problem becuase the amp sounds fine when playing music. The little OWON digital scope is having a difficult time synching with the sine wave tones or sweeps. I can see the voltage envelope but that is about it. I think I have an old analog scope with a CRT screen in storage. I am wondering if that will do a better job as it has a much lower bandwidth that covers the audio range and not much above it.
I did figure out how to use REW wtth the Focusrite 2i2 audio inhterface but the noise riding on the sine waves was just as bad and drive the 2i2 into clipping many times while running sweeps. I found multiple threads on this forum and Audio Science Review discussing how a low pass filter must be used to measure most Class D amplifiers.
It appears that the Alpine PDX amp is OK but I do want to figure out what I am doing wrong.
I did figure out how to use REW wtth the Focusrite 2i2 audio inhterface but the noise riding on the sine waves was just as bad and drive the 2i2 into clipping many times while running sweeps. I found multiple threads on this forum and Audio Science Review discussing how a low pass filter must be used to measure most Class D amplifiers.
It appears that the Alpine PDX amp is OK but I do want to figure out what I am doing wrong.
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If you connect a jumper from the RCA shields to the amp's ground terminal, does that clean things up?
You have a CRT based scope and you're not using it?!?!? Most people can't afford a nice analog scope with a CRT so they're forced to use something else.
You don't need storage. Audio is 20k, the lowest rated analog scope is generally 1000 times higher than that.
If you want a specific tone, produce the waveform in Audacity. I'd suggest -1dBfs but any level will work. I'd recommend saving in .wav format.
As a side note, Alpine amps do not completely filter out the carrier in all of their amplifiers.
You have a CRT based scope and you're not using it?!?!? Most people can't afford a nice analog scope with a CRT so they're forced to use something else.
You don't need storage. Audio is 20k, the lowest rated analog scope is generally 1000 times higher than that.
If you want a specific tone, produce the waveform in Audacity. I'd suggest -1dBfs but any level will work. I'd recommend saving in .wav format.
As a side note, Alpine amps do not completely filter out the carrier in all of their amplifiers.
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LOL My analog scope is a 45 year old Hitachi I bought when I was in school studying engineering. I wanted a Techtronix but in those days, even used ones were way beyond my means. The last time I powered up the Hitachi, it still worked so I will dust it off and give it a try. 😀. It has been a long time since I did any hands on work with electronics so I also dusting off old memories and learning new things.
I just realized you questioned what I meant by output gains. The output gain on the Zapco DSP is adjustable. I made sure all 4 channels coming out of the Zapco were at -6 db. I also made sure the Alpine input gains were in the center detent. The cleanest measurement I got so far was when using optical connection between an Android head unit and the Zapco and not connecting my laptop to anything - just using the OWON scope. I am going to try copying the wav file to the Android head unit and see if that gets a better result.