difference in PG MS-2125 and MPS-2500 - diyAudio
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Old 14th December 2008, 04:41 AM   #1
damage is offline damage  United States
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Join Date: May 2006
Default difference in PG MS-2125 and MPS-2500

What is the circuit difference between these two amps? It seems the MPS-2500 is just a "high current" version of the MS-2125.

I just bought one of the MPS-2500 off epay and planned to use it 1 ohm bridged into my subs.
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Old 14th December 2008, 10:54 AM   #2
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Join Date: Dec 2005
Location: Northern California
I'll take the floor on this one if no one else minds ?

Yes all of the MS-2XXX series are on the same sink, and on the same PC board layout and design. BUT, There are significant circuitry differences starting at the power toroid, and extending into the supply control circuits.
Then there are the very different rail supply voltages for each model dictated by the prescribed load consideration of each amp and each amps specified output power range.

Then there is the third stage op-amps gain factor variable that is also predicated by the model design. This sets and controls the main amp drive curve so the amp does what its model number designated it to do.

There are also some resistors different in each model inside each channel due to the rail supply differences. Different rail supply's need different resistor values to maintain proper circuitry operation.

You would either need all three sets of schematics or have all three set side by side to preform a direct comparison of each model to actually see the different value components, resistors mostly, and a few caps in certain sections controlling the amps stability and DC filtering.

Now, I know this is fairly wide range info but I have a MS project on another forum where I am completing 5 each MS-2250 TA's but I am converting them to "Original MS-2250's.

The "Original MS-2250 in black or Nickle were built in the mid 90's and they were tested at 3 DB's above there spec'ed power ratings by independent magazines. That's just at 500 watts RMS unclipped at rated distortion spec per channel at 4 ohm's load. Or 1 Kilo-watt stereo unclipped at 4 ohm's stereo.

Not too shabby for a mid-90's amp I would say.

I also have a mint 1991 employee accommodation MS-2125 < the very first MS amp I ever worked on>, it came back to me about two years ago for free>, and a very badly blown original black sink MS-2250 that just arrived to be completely restored to spec as templates for comparison.

I sold my 2500 I had about three years ago along with my 2250 TA edition. Ah the things we do when we need money

And yes the 2500 with its significantly reduced rails is a high current version of the venerable MS-2125, and the monstrous MS-2250. The 2250 has +&- 63 volt DC rails, so with 120 VDC inside this big boy you really need to run the amp with the custom fan shroud they built for them back then or fabricate a custom forced air system to cool the bad boy down, as the 2250 does run very hot for its small size.

The main power limitation on ANY of these three models in the sink size versus the raw RMS power output. I have been meaning to do a thermal power curve for the basic sink for each model so everybody would realize the sink is actually setting the max power this amp can dissipate before thermal cycling to protect itself. Maybe later this coming year, I'll get time for that test before I send all these amps on there way back home.....PG truly did engineer each model exactly for it purpose,..... Hope this info was of help to you, as these are sort of pet hobby of mine....
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Old 14th December 2008, 01:22 PM   #3
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Can I have the MPS 2500 after you fry it?

I would never run that at 1ohm bridged.
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Old 14th December 2008, 01:55 PM   #4
damage is offline damage  United States
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Why would you not run it 1 om bridged? My understanding was that the MPS series where stable to 1/4-ohm stereo. At least that's what I remember.

I could run it 2-ohm stereo, but wasn't sure if that would be enough power for the ID subs.
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Old 14th December 2008, 01:58 PM   #5
damage is offline damage  United States
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Join Date: May 2006
Originally posted by 1moreamp
Hope this info was of help to you, as these are sort of pet hobby of mine.... [/B]
Very useful. I knew it had to be more than just a switch. They look so similar from pictures that it prompted me to wonder "just how different could they be?"
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Old 14th December 2008, 02:43 PM   #6
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IMHO, anything below 1 ohm stereo is abusive. Especially on a classic like that.

1/4 ohm stability was a marketing ploy by the likes of PG, Orion, Soundstream, etc. Sounds like it was a great way to sell more amps.

That MPS should belt it out at 4ohm bridged. Try both configs, and see what you like better.
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Old 14th December 2008, 06:01 PM   #7
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Morning All,
The MPS-2500 was rated to IASCA standards for a reason, it was there low ohm standard. PG came to market in the low ohm IASCA competition days of the 1990's, So they had to splash big when they started selling amps or they would be sunk back then.
I remember a VW Jetta that got two of them in the trunk. It was rated at a meager 50 watts per at 4 ohms stereo. It was one heck of a 100 watt rated amp.
It had a 3 DB headroom as with all PG amps from back then, so at 4 ohm stereo it really was about a 200 watt amp un-clipped at 4 ohms stereo.

PG designed it with really low rail supplies of 25 volts DC typically, and a driver stage voltage about 8 volts higher. So at best it would only swing 40 volts out to any load you hooked up to it. But at 4 ohms that's over 100 watts possible.

As for its low ohm rating, well I think they stopped at one ohm stereo in print at least.
I will add that there are two little red LED's located on the connection panel and that you should pay attention to these as there are true clipping indicators. And if clipped on a constant basis they tend to fail a transistor in the circuit and the LED's get turned on constantly. A fairly common issue, I have repaired a couple of these over the last few years including yesterday for a friend in Holland that uses all MS amps in his home stereo.

Also I would look at the 12 battery side capacitors located at the rear side panel. They with age tend to fail and leak electrolyte on the PC board. Once this occurs the liquid which is conductive will short between the 12 volt power feed and ground underneath the caps and the electro-chemical reactions will cause the board to become damaged. I suggest strongly that you have the amp serviced and get these and the 4 main rail caps in blue replaced as a standard.
PG charges $50.00 for the 4 large rail caps if you wish to buy PG exact parts, they will sell them to you and install them for a flat service rate + the caps cost.
ANY new cap will be better then the original old used caps in these amps. Caps have impressively improved over the years since this amp was built. So think about this fact when contemplating usage of ANY amp of this era and age.

A simple thing is to look at the caps and read the date code on them. It will look like a 5 digit code similar to this 9315L. The 93 being there manufacture date back in 1993. Caps of this age are pretty beat by any standard, so it will improve the SQ and power of the amp by replacing these.
The 12 volt side caps are Panasonic FC standard with a 5000 hour rated life at 105 C temperature. Please use only the best grade of cap possible, and at least 105 C rated as these see all the heat the amp does.

The last set of rail caps i replaced measured upon removal about 40% of there original rating and this is way out of spec for a competition amp like this being run at low ohm loads.
Low ohm loads will need new caps in the amp for best performance. I do this all the time for folks. Plus after 12 + years of service any brand of amp could use a refresh inside, So PG used the right parts, and the amp has long useful history, but even with the best parts of the day, somethings need to refreshed for best performance. I strongly recommend you don't over look this last suggestion.

The original MPS-2500 had 15,000ufd 35 volt DC caps in the supply, but later on they went to 10,000ufd at 40 volts DC rating. I suggest the original parts as they store more energy.

You can goggle about the capacitor failure issue. There are several good pictorials on the web showing how to replace these and with what. Even I have a few posts located elsewhere about this so folks can do there own if they want. It does require good soldering skills, so if soldering at a pro level is not your bag of tricks them please have it done by someone qualified. Its not something to skimp on IMO.

If your truly going to run it at low loads please buy and keep the correct fuses on hand for the amp. This will keep you running and relieve you of the search for 5 by 20 MM fuses used inside the amp on the rails. Also buy good 12 volt fuses not the cheap ones that are imported from far off lands and are very poorly manufactured and have a failure rate of 3 out of 5 right out of the Chinese packaging. For some reason soldering skills used on these cheap fuses allow then to be pulled apart just by grasping then at the ends and tugging firmly. Such good quality control does not bode well for high current draw applications like your usage.

Well I have bored most of you to tears by now, and some to sleep also. SO I will cut this long winded post off and just say that I can be reached by PM email if you need more support related info and such....

Oh here is a link to some MS and other PG amp repair posts on a small board. Not trying to promote another board, but all the info most need can be had here:

Also here is a RARE fan shroud for your MS amp on sale on flea-bay right now. These can be hen's teeth to find when you want one...

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Old 14th December 2008, 08:21 PM   #8
damage is offline damage  United States
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Join Date: May 2006
I was about to ask whether I should recap. I imagine I have plenty of Nichicons to do the job.

Mine came with 10000uf rail caps. You say that it should handle 15000uf ok? No problem with damaging the rectifiers?

The input torrid is damaged. Looks like a poor soldiering job. Wire looks ok but the board is burnt through. I doubt the seller knew this because the unit still works. But it appears someone has at least opened it up and looked at it cause I saw some tool scratches on the gold trace.

There are two power fuses, but there are no rail fuses. Instead, they have some sort of rolled steel connector. Manual does not mention to rating needed. I am wondering if these are original as they look it.

Lastly, the manual states the MPS-2500 is stable into 1/4 ohm stereo. So that should mean it's fine 1 ohm bridged right?
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Old 15th December 2008, 12:46 AM   #9
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Yeah 15,000ufd was the original value by spec, but i think they started using the 2125 caps in later recaps and releases. I have 15.000ufd caps at 35 volts DC they are nothing special to find. I would use the original spec, as this amp could use all the stored energy it can get at the low rail volts it runs. The rectifiers used by PG rarely failed, and the only reason I ever replaced one was because someone had taken the amp apart and broken the leads of the devices.

On the input filter toroid PG made a bigger one for the 2250. Its Green in wire color, but it has twice the windings for twice the current handling. ( about $9.00 US from PG) Also just pull the input wires forward till they reach where the bars tie down and just use slightly longer screws to direct connect them. Again this was done in the 2250.

Rail fuses were 10 amps typically 15 and 20's were available and until the TA anniversary issue they all used fuses. Yours has been modified to bypass the fuses it seems. I have the fuse holders in silver plate they are also nothing special to find just about everywhere if you decide to go back to original spec.
On the TA version PG just used simple wire jumpers. I use toroidal inductors to lower any hash noise coming of the supply side. They also look nicer then jumper wires.

1/4 ohm stability has nothing to do with 1/4 ohm thermal loading of the sink. As I said before PG made a forced air cooling shroud for these and I completely recommend it for harsh duty for any amp being pushed as far as this amp can go. This sink needs to be able to dissipate the heat load of a 1000 watts of audio power in harsh duty and most installs of these amps has them upside down with no ventilation on the sink. This is a recipe for disaster and thermal shutdown issues if you run this amp to its limits all the time or even in shows.
I personally have never seen ANY load this amp would not run. But I have seen them run so hard that they got hot and cut off mid music. PG's protection circuitry works very well, and all the time from my experience.

I have seen a whole system run off just one of these amps back in the 100 watt category long long ago. and it had loads of speakers hooked up to it. And it played music, so 1 ohm mono or 1/2 ohm stereo I think would be just fine as long as you make efforts to deal with all the heat this amp will make at those loads, and are able to send it ton's of current from the battery. The internal 12 volt fuses start at 40 amps each and go up according to the load your driving. 80 amps at 12 volts is lot of current and should give you about 500 watts audio power to your speaker load using simple ohm's law math.....
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