PPI PC2400 technical questions..

[MatthewS]

Hey guys, first time poster over here and fellow tech. I stumbled across the site looking for information on a PPI amp I have been love-laboring over. There appears to be a great wealth of peers here with PPI experience (to-3, perry, etc)

I took in a PPI PC2400 for free and it was totaled. Burnt traces, blown MOSFETS, a BIG hole in the board where the torridal secondary ground was soldered down, the torridal was shot and so was one of the channels along with a hole burnt through the PCB where a current sharing resistor was in that channel. This amp took a beating from hell and I brought it back! Hand wrapping a new torridal and epoxy dipping it is the most relaxing thing! At any rate all features and function are working properly, but I have some issues. So enough of the small talk, and onto the questions.

1) I am getting a clipped 50hz sine on the outputs around 120watts on a 2 ohm dummy load (stereo) This seems a bit weak for this amplifier. In fact I should get about 200 watts RMS on a 2ohm load without clipping. I tried 1khz too and it clipped out around 110 watts. Can anyone share some thoughts on this?

2) I have no refrence on the rail voltages to go by. I matched the turns/ga on the torridal of the OEM I removed, and in fact reused the same core. I installed irfZ46N's and adjusted everything accordingly. The results I have are a peak idle voltage of 58v/total (29v +/-) and it never sinks below 50v/total under heavy clip (25v +/-). Is this correct? or is this why I'm clipping so early in the game?

3) Adjacent to each Driver module in a 2 pin header labeled as a jumper. What are these for?

4) There is a RED LED center of the PCB, explain this please.

5) There are a total of FOUR trimpots center of the PCB. I am assuming two of them are BIAS adjustments. Can anyone elaborate on these?

I put a lot of love into this thing, and really bolstered the power supply. I seem to recall these amplifiers having a dispicable amount of headroom and it seems as if none of it's potential is being realized at this point. Thanks guys!

- Matt

PS. it's the chrome model, if that makes any revisionary difference.

[Perry Babin]

I'll try to fill in a few of the blanks...

1/2. For the supply voltage you have, the output is about what I'd expect. For 120 watts into 2 ohms, you'd need ~21v DC. Since the outputs can't drive the output to the rails, there will be some loss of voltage. If the supply is dropping to 25v, 120w is about all you can expect. If you want more power, you'll have to determine the reason the voltage is dropping. If it's an unregulated supply, you'll need a higher ratio on the transformer. I'm assuming that the B+ voltage feeding the amp is remaining near or above 13v. If it's dropping below that, that could explain the low power output.



3. If the plns are connected to the bias compensation circuit, they are to kill the biasing so the amp can be serviced with no chance that the outputs will overheat/fail from thermal avalanche. I could be wrong on this.

4. No clue.

5. Two of the pots are for biasing. The other two are for DC offset.

[MatthewS]

Thanks Perry.

The calculations make sense, but did you only take one rail into consideration? because I have 50 volts total. The amplifier is rumored to be unregulated and produce more power if you feed it more voltage. However I made no attempts to confirm that before I left for the day. I fed it a steady 12 volts and the supply is good for 100 amps regulated. I did rewrap the torridal secondary to spec, I guess I could tear it out and wind a custom one to get me up to 35v/rail. Not sure how much of the extra 10 volts will be of use to the outputs. Worth a try? If I go any higher I'll have to start changing caps, etc. I also changed the MOSFETS so I'll need to recheck the duty cycle as well.

Thanks for the answers on the other stuff. Would still love to know about the red LED. At one point it started flashing. I think I was adjusting the Q-bass. I think I need to take a closer look at the board tomorrow, I'm sure I can trace it back to a component or two and make sense of the whole thing.

- Matt

[Perry Babin]

I was only looking at the positive rail voltage. That's all that's necessary for the calculations unless you were calculating power for a bridged load.

You stated you had a 12v supply. Was the power rating (from PPI) at 12v or at 14.4v?

If you have trouble tracing it and can take good, sharp photos of the board, send them to me and I'll try to help.

The following schematic may be similar enough to your amp to be of some help. It probably has some errors. I didn't have the amp long enough to check the schematic thoroughly. Right-click to zoom in.

http://bcae1.com/temp/ppipc420002.swf

[EnvisionAudio]

Originally posted by MatthewS

4) There is a RED LED center of the PCB, explain this please.

[/B]

Used as a 2V diode. Doesn't light up - don't worry about it.

Byyy the way. Did you use the original toroid core? It could have gotten so hot that it no longer functions correctly ie: permeability changed. I have a SoundStream REF 500 that couldn't carry a load above about 35 watts. Replaced the core, rewound new and all was well again.

[MatthewS]

Originally posted by EnvisionAudio


Used as a 2V diode. Doesn't light up - don't worry about it.

Byyy the way. Did you use the original toroid core? It could have gotten so hot that it no longer functions correctly ie: permeability changed. I have a SoundStream REF 500 that couldn't carry a load above about 35 watts. Replaced the core, rewound new and all was well again.

Thanks for you input.

I want to believe every word of that, but I seen the LED light several times.. Can you explain it's exact function so I can understand why I seen it light?

On the torridal issue a cold joint on a secondary leg caused enough arcing to cause some enamel damage. I don't know if you were aware but this amp has a thermal mounted center of the torrid (as well as several other places) that would usually shut things down. However heat just wasn't the reason one way or the other anyway. I saw it as an opportunity to make a nice twisted set of strands for the secondary. I'm a big fan of stranded anyways. I'm also a big fan of epoxy, so I did that as well. The problem seems to be a loss of voltage, it will dump plenty of current.

The PS appears to be true unregulated. I managed to up my output to 13.16 volts input and got 59.17 volts on the rails. It already does RMS ratings, I just recall a lot more headroom from these amps. Maybe my memory fails me. I load tested it into 1 ohm mono (.5 ohm stereo) and it held up accordingly and took it's share of current. The calculations I made tell me it will deliver rated RMS into a load without clip if fed at least 13.5volts. It feels a little low, but close enough for usage.

I think I'm just expecting too much from this thing. Good thing it's going into wifey's car. She will be just thrilled with it. I myself have not had a system under 1kw in many, many years...

- Matt

[EnvisionAudio]

Originally posted by MatthewS


Thanks for you input.

I want to believe every word of that, but I seen the LED light several times.. Can you explain it's exact function so I can understand why I seen it light?

On the torridal issue a cold joint on a secondary leg caused enough arcing to cause some enamel damage. I don't know if you were aware but this amp has a thermal mounted center of the torrid (as well as several other places) that would usually shut things down. However heat just wasn't the reason one way or the other anyway. I saw it as an opportunity to make a nice twisted set of strands for the secondary. I'm a big fan of stranded anyways. I'm also a big fan of epoxy, so I did that as well. The problem seems to be a loss of voltage, it will dump plenty of current.

The PS appears to be true unregulated. I managed to up my output to 13.16 volts input and got 59.17 volts on the rails. It already does RMS ratings, I just recall a lot more headroom from these amps. Maybe my memory fails me. I load tested it into 1 ohm mono (.5 ohm stereo) and it held up accordingly and took it's share of current. The calculations I made tell me it will deliver rated RMS into a load without clip if fed at least 13.5volts. It feels a little low, but close enough for usage.

I think I'm just expecting too much from this thing. Good thing it's going into wifey's car. She will be just thrilled with it. I myself have not had a system under 1kw in many, many years...

- Matt

I should have made myself more clear. It lights up, but that it likely isn't for any indication/purpose. Similar to LEDs used in current regulators in the LTP of Phoenix Gold amplifiers. They provide a triple diode drop without using triple diodes. The side benefit is they light up.

I believe it's in the protection circuit - maybe in the latch(?) It's been a while since I've seen that amp...

Seems odd that they would throw a big common mode core in there after the toroid if it wasn't regulated...all the Power Class amps I worked on *were* regulated. Maybe you still have problems...

It can draw lots of current and not output its rated voltage if the core was killed. The toroid loses inductance and cannot support the amount of magnetic flux it once had.

So, rewind that transformer with a new core....