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Old 24th August 2007, 04:54 AM   #1
ppia600 is offline ppia600  United States
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Default precision power pro mos 50, good stuff?

I just got one on egay for pretty cheap, I needed something to match the A600 I'm running my mids on. The guy told me it was .5ohm stable and ran 800wrms at 1 ohm mono. I don't believe it can do that with one 60 amp fuse (that's what my A600 has) but I do believe it could put 600 clean watts out at that load. The deal is I opened it to see if there are any differences from the A600 (because the shell is exactly the same, only black and a different model name) and I noticed the power supply filter caps are 50v on either rail, I believe the A600 is the same. It also uses the same model number and quantity of output transistors and power supply mosfets. In fact it looks the same except for the power resistors, this one has them for the collector and emitter apparently. Is that the only reason it is .5 ohm stable, because there are some extra resistors to soften the load on the output transistors? I would think the power supply rail voltages would be lower and there would be more output and power supply transistors. Is this amp good for 600 well damped watts, or what? Any opinions welcome, thanks.
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Old 24th August 2007, 05:32 AM   #2
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hi ppia600,

wow .5ohm stable!..i'd expect a lot of mosfet switchers & output tranies for that to be realistic..unless the mosfets & tranies used are so powerful...

i don't know the specs of that amp though

what are the supply rails @ that rated load?
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Old 24th August 2007, 06:57 AM   #3
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It's common for PPI to use multiple parallel 0.68 ohm emitter resistors. There are no resistors in series with the collectors.

I have an art series a600 here now and it has two parallel 0.68 ohm resistors on each emitter.

The rail voltage is likely much less in the promos amp. That alone would allow it to drive a lower ohm load than the a600.
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Old 24th August 2007, 01:54 PM   #4
ppia600 is offline ppia600  United States
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Thats why I'm wondering why there are 50V caps on each side of the rail That would seem like a waste, wouldn't it be better to use a lower voltage/higher microfarad cap instead? It has evidence of being repaired too, there is a thin solid strand wire soldered from the channel closest to the speaker terminals directly to one of the terminals. Maybe one of the tiny fusible resistor/jumpers blew and they didn't feel like pulling the entire board to replace it. Everything else looks oem like its never been touched though. I'll be putting it in today hopefully, to see how it compares with the earthquake D2. Maybe the woofers and the mids will be more in phase with eachother now that I have two of basically the same amps and the crossover is built into the deck.
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Old 24th August 2007, 10:06 PM   #5
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It's possible that they use the same exact board as another amp but install a different transformer.

Lower voltage, higher value caps may be marginally better but would not make an audible difference.
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Old 24th August 2007, 11:56 PM   #6
ppia600 is offline ppia600  United States
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Well, I got it installed today and..

-WAY less power than the earthquake phd2
-Distorts WAY sooner than I'd expect (the phd2 had almost none)
-Runs SUPER hot even at low volume levels, the A600.2 I have running my four mids and tweets runs cool compared to the mos50

I'm running the mos50 at 2 ohms bridged, using two mtx t7500's that are rated at 400wrms each. I guess they are kind of heavy for the ppi, but sheesh I didn't expect such a drop in spl and rise in distortion

Would running it at 1 ohms bridged make it substantially louder and also maybe magically make it run a little cooler since the output voltage will be lower??? I mean I know I've been griping about the phd2 dropping volume at a certain level, but I'm almost contemplating putting it back in.
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Old 25th August 2007, 12:39 AM   #7
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Running it a 1 ohm is going to make it run hotter. If it's getting really hot really quickly at 2 ohms, 1 ohm will likely cause it to fail.

Does the amp get hot at idle? If so, the biasing may be too high or the amp could have other problems (leaking outputs, defective drivers...)

If you ever have the two amps apart, you should measure the rail voltage to see how much they differ.

The distortion is likely because you were running it to clipping. Below clipping, the distortion levels will be below audibility unless the amp is damaged.
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Old 25th August 2007, 03:26 AM   #8
ppia600 is offline ppia600  United States
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Yeah, I realize it is clipping. It just happens way earlier than I would expect. I'm just used to the phd2 I guess. And the phd2 having such a steep slope on the built in crossover really helps the crossover from midwoofers to subs. The ppi doesn't have one and I'm using the internal one on my Kenwood deck which supposedly has an 18db slope but doesn't sound like it.
What I will do in a few minutes (just finished completely lowering my car and changing several mounts) is take a ride for about thirty minutes with the radio on and volume turned way down, I will check and see if the amp gets hot. If it does I will check to see if the bias setting has been tampered with next time I get a chance to remove the amp from under the seat. I guess I'll also remove the board from the sink and check underneath to see if there are any problems with cracked joints or bad transistors. The low impedance light never comes on so I don't see any bad problems with the power supply transistors or outputs but maybe a driver in between isn't working or one of the vertical ceramic boards has a problem. I did try both channels independently in the house before installing it and they both played clearly and sounded like both sides of the sound wave were there.
My next goal will be to find a manual with specs and see if I'm running it correctly. I've had the other pro mos amps with the white heat sinks and fins, and I know they are stable into 1 ohm each channel, but I've never seen an art pro mos in person so I don't know how I should be running it. Either way I will pull it apart next time I get a chance, I was just anxious to see how it sounded. Thanks for the replies

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Old 26th August 2007, 04:05 AM   #9
ppia600 is offline ppia600  United States
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Default Need to find the actual specs, picture..

Does anyone know where I could get actual specs on this amp? I contacted a person who buys and sells amps on ebay, he sells manuals for ppi as well. (Didn't get my amp from him) Of course he didn't have a manual for the amp I have. He told me he is suspicious of my amp because he says they didn't make any pro mos 50 in the art style housing. Mine is obviously genuine, down to the worn silk screening. Here's a pic from the ebay listing. It actually has all of the schematic silk screening still, just can't see it from this angle:

Click the image to open in full size.
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Old 26th August 2007, 09:41 PM   #10
ppia600 is offline ppia600  United States
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Wow, I just went to ampguts.com and they have pics of pretty much every amp you can think of, inside and out. The only amp that is the same is the A600.2, it looks exactly the same on the inside as my "pro mos 50" except mine is all black. I am going to go take it out of the car now and take it apart completely. Maybe this one is modded to not protect because I know neither my old A600 or my current A600.2 will run 2ohms mono without making horrible noise and making the low impedance light come on. Maybe I will be able to find out how the low impedance function has been bypassed or modified, I have a feeling its the jumper wire I wrote about previously. Wow, this is weird, the amp appears to be un molested on the outside.


?????????????????????
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