PPI PC2400 not turning on

[Perry Babin]

Single-ended signal sources are not a problem.

Are you getting the same 'noise' in the non-bridging speaker terminals as you are on the bridging terminals?

If you set the crossover to low pass, is the signal clean?

Is the shield ground for the generator intact?

The signal generator should be grounded to the negative terminal of the 12v power supply. If you measure the resistance between the shield ground for the generator and the negative terminal of the 12v power supply, you should read ~0 ohms.

[midnightg35x]

Originally Posted by Perry Babin

Single-ended signal sources are not a problem.

Are you getting the same 'noise' in the non-bridging speaker terminals as you are on the bridging terminals?

If you set the crossover to low pass, is the signal clean?

Is the shield ground for the generator intact?

The signal generator should be grounded to the negative terminal of the 12v power supply. If you measure the resistance between the shield ground for the generator and the negative terminal of the 12v power supply, you should read ~0 ohms.

I'm not sure how check just the bridging/non bridging terminals. I am using differential voltage probes to measure my voltage, so I always have one probe on a bridging terminal, the other on a non-bridging one.

The shield ground for the generator is good, it measures 0.7 ohm when I have the negative terminal of the +12V supply and generator shield ground connected.

For whatever reason, didn't even think to try the crossover. When put in low pass mode (crossover point well about my test frequency, function generator off) the signal is clean. When put in high pass mode the signal gets dirty again. For all the previous testing I just turned the crossover off completely.

When I disconnect the function generator from the input completely, there is no noise. When I plug in the MP3 player with no output on the MP3, there is no noise either. I use the same 2x RCA to 3.5mm cable for both the MP3 player and function generator.

What would you suggest trying next?

Is it also possible I'm worrying about nothing because when I use the function generator, I have bare wires and alligator clips running around that are just picking up noise that isn't there with the MP3 player?

[Perry Babin]

I don't think you'll get a completely clean signal with this amp but the noise isn't audible so, in my opinion, it's not a problem. Virtually all of the PPI amps I've seen have had a bit of noise when viewed on the scope.

[midnightg35x]

Originally Posted by Perry Babin

I don't think you'll get a completely clean signal with this amp but the noise isn't audible so, in my opinion, it's not a problem. Virtually all of the PPI amps I've seen have had a bit of noise when viewed on the scope.

OK. I'll try with a real speaker and some music and see what I can hear. It wasn't really the noise that was causing me all the concern, it was the associated additional current draw. At idle, with no "noise" on the input, I idle at 1.1A. With just a little noise it goes up to 1.5A. When it was really bad, I've seen it idle at 3A.

The other issue was when the noise was there and I still put in a signal, the noise would modulation along with the intended signal.

On a side note, I just tested both channels to >100W average out with no issue. So other than the high noise issue, I think it is mostly fixed.

Edit:
After hooking a speaker up to it, I can audibly hear a slight hiss with the high pass mode with the MP3 player and no input at all. It does not grow with volume, so I'm guessing it is the bit of noise you're talking about. It is only noticable with my ear right next to the speaker.