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  • AB Precedent 900A opinions

    Hey Guys, any good or bad stories on these. I bought a clean one for 200. The specs are good but I'm not happy about the lack of a fan and may add one where the frame allows. The 1100A is the same frame and it has a fan. I repaired a 600 for a friend a few years ago and recall it only had 6 outputs per channel yet it was a simple amp to work on. Thanks for any thoughts, Paul.
    http://www.ameranouche.com/
    http://www.youtube.com/watch?v=thl46...eature=related

  • #2
    Great amps just as good as QSC, I bought a 1100a for same amount as your 900a, 200$ and works great for powering my subs. Their sleeper amp most folks never heard of them because they went out of biz. But Aged horse from this forum can give you the low down on these amp he mentioned something working for them or something like that might PM him if you need more info.

    Comment


    • #3
      The 900A was significantly different than the 600 in that the 900 is a 2 tier class H amp that switches between Vlow and Vhigh as required to increase efficiency and reduce waste heat. It's a great amp, heavy duty with a 3 rack space chassis but quite shallow. It's chief drawback for heavy duty cycle and 2 ohm loads is the location of the air inlet and the air circulation pattern (side to back).

      The 1100A is essentially the same thing, except an added tier switch that switches between 0volts, Vlow and Vhigh. This does nothing for resistive load efficiency but improves reactive (speaker) load efficiency. All of the AB amps were designed to drive reactive loads well.

      Most of the 900's and 1100's were shipped with the fan kit (notice the slot below the heatsink for air flow) but also require a small diverter that screws to the bottom of the chassis. It looks like a little "V" and insures the air passes up through the heatsink. There will also be a piece of sheet metal across the back of the heatsink that helps with the chimney effect.

      The fan mounts to the left side of the chassis and blows IN. There is a fan header marked J6 on the power supply PCB, but the fan control components (Q1-Q3, R1-R7, D1 and the fan thermal switch) must be installed for the fan to work.

      At one time, I owned several dozen 1100's and 900's. Both are excellent amps when racked with an understanding of the thermal management required. The 400 and 600 were class AB versions of the 900 and 1100. I was also involved with the original AB Systems & AB International.

      If you are interested, I have a quantity of 710C's in average condition (biamp w/ 600 watts on the LF and 100 watts on the HF w/ crossover cards) and a quantity of 900A's in dead-mint condition.

      There were about 4 versions of the 900's. Most of the differences were due to different output and driver transistors. I stock most of the parts. Don't be put off that there's only 6 outputs (plus 2 drivers and 2 rail switches) per channel. The class H circuitry reduces the requirement for SOA hence a smaller number of transistors are required. The 1100 also has 6 outputs per channel, (plus 2 drivers, 4 rail switches) but the 3 tier design reduces the requirements even more, making up for the higher operating voltages.

      Older versions used 2SB554/2SD424's, later versions used MJ15022 and 23's, and even later units used MJL21193 & 94's. I also thought they used some MJ15024's and 25's, and MJ21193 and 94's but that's not shown on my docs.

      Hope this helps.
      -------------------------------------------------------------------------------------------------------------------------------------------------------------------
      Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

      Currently product development engineer: Mesa Boogie

      Comment


      • crizzy
        crizzy commented
        Editing a comment

        I know this is an old thread but you had mentioned that you had a "quantity" of 900a's in dead mint condition and I was wondering if you had any lying around still.  It is a long shot but I have one and would like 2 more and I have a friend that would likely buy 2 if you still had some.  Thanks!!


    • #4
      Hi agedhorse, Thanks for the info. I'm familliar with the MJ15024s from working with the CS 800s, BGWs and other quasi amps which are bassically PL 400s. I think the 2SBs and Ds were only 10 amps, hopefully it's got 15s. I put the amp on layaway and won't have a look at it for a few weeks. Is it a good sounding amp? It won't see 2 ohms, only 4 or 8. Thanks for your wealth of info, I think we'll be chatting a lot in the future, Paul.
      http://www.ameranouche.com/
      http://www.youtube.com/watch?v=thl46...eature=related

      Comment


      • #5
        The BGW's are very different from the Phase Linear 400's, except that both were quasi-comp. The BGW's (I'm comparing to like era of course) were based on an integrated op-amp diff-amp where the PL400 was fully descrete. I've also got some PL parts avail. y the way.

        Transoistor current is not the problem, it's the safe operating area. 30 amps worth of output is plenty provided it;s within the bounds of the transistors thermal SOA. The 2SD424's (& B554's) were a very fast, high gain audio device and of very high quality.

        The AB amps were very good sounding with no obvious flaws. The class H switch is pretty transparent. It's a bi-polar switch rather than a FET switch like QSC and most others these days.
        -------------------------------------------------------------------------------------------------------------------------------------------------------------------
        Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

        Currently product development engineer: Mesa Boogie

        Comment


        • #6
          Hi agedhorse, Thanks for the reply. Whats your opinion on the best trans for the early CS 800s, SJ6343B or MJ15024. I have one amp of each. The SJ one is currently running minus two outputs. Can the SJ amp take the MJs without changes, I know they can't be mixed in a channel.. I would be interested in a few XPL909s as I have been running a PL400 in one of my home systems minus two for about ten years now. I keep the bias on the low side and can abuse it for hours on my DQ 10s without any overheating problems. The BGWs I have are the 7000 models, on paper they look like a PL 400 in the output stages almost to the penny. What do I know I'm just a hack, I'll be picking your brain a lot in the near future, Thanks for you time, Paul.
          http://www.ameranouche.com/
          http://www.youtube.com/watch?v=thl46...eature=related

          Comment


          • #7
            The 15024's are a lot faster and may be nore prone to oscillation, but other than that should work just fine. Maybe a little more compensation will be necessary though. Hard to tell. They were pretty heavily compensated to begin with.

            I don't think I have any XPL's, probably just FPL's. Can't mix them.

            I'm not familiar with the 7000 schematic.
            -------------------------------------------------------------------------------------------------------------------------------------------------------------------
            Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

            Currently product development engineer: Mesa Boogie

            Comment


            • #8
              The 900A was significantly different than the 600 in that the 900 is a 2 tier class H amp that switches between Vlow and Vhigh as required to increase efficiency and reduce waste heat. It's a great amp, heavy duty with a 3 rack space chassis but quite shallow. It's chief drawback for heavy duty cycle and 2 ohm loads is the location of the air inlet and the air circulation pattern (side to back).

              The 1100A is essentially the same thing, except an added tier switch that switches between 0volts, Vlow and Vhigh. This does nothing for resistive load efficiency but improves reactive (speaker) load efficiency. All of the AB amps were designed to drive reactive loads well.

              Most of the 900's and 1100's were shipped with the fan kit (notice the slot below the heatsink for air flow) but also require a small diverter that screws to the bottom of the chassis. It looks like a little "V" and insures the air passes up through the heatsink. There will also be a piece of sheet metal across the back of the heatsink that helps with the chimney effect.

              The fan mounts to the left side of the chassis and blows IN. There is a fan header marked J6 on the power supply PCB, but the fan control components (Q1-Q3, R1-R7, D1 and the fan thermal switch) must be installed for the fan to work.

              At one time, I owned several dozen 1100's and 900's. Both are excellent amps when racked with an understanding of the thermal management required. The 400 and 600 were class AB versions of the 900 and 1100. I was also involved with the original AB Systems & AB International.

              If you are interested, I have a quantity of 710C's in average condition (biamp w/ 600 watts on the LF and 100 watts on the HF w/ crossover cards) and a quantity of 900A's in dead-mint condition.

              There were about 4 versions of the 900's. Most of the differences were due to different output and driver transistors. I stock most of the parts. Don't be put off that there's only 6 outputs (plus 2 drivers and 2 rail switches) per channel. The class H circuitry reduces the requirement for SOA hence a smaller number of transistors are required. The 1100 also has 6 outputs per channel, (plus 2 drivers, 4 rail switches) but the 3 tier design reduces the requirements even more, making up for the higher operating voltages.

              Older versions used 2SB554/2SD424's, later versions used MJ15022 and 23's, and even later units used MJL21193 & 94's. I also thought they used some MJ15024's and 25's, and MJ21193 and 94's but that's not shown on my docs.

              Hope this helps.


              hello i just recently started using ab amps in my HT ive used several home type amps denon, sony,yamaha just to name a few. I believe these amps to be some of the best ive used, anyway ive just purchased a 900A and its in bad shape. i noticed right away that the 2 resistors located at the far right just bto the right of the circuit board part number are fried. i removed them and checked them they read 4.7-5.0 ohms, they got so hot they burnt the circuit board. I took a physical look at the rest of the circuits and everything look fine, after checking the resistors against another 900A it have I decided to cleak the circuit board and solder them back in. I turned the amp on it started up and there was a noticable electrical noise and it blew the fuse. i by no means am a electronics expert but I have been toying with electronics for many years. Is there any low cost info you can help me with to get this amp running again thank you for your time regards

              Comment


              • #9
                No low cost way to get the amp running. They are very complicated amps and really require experienced service folks. Folks experienced with this circuit too since it works differently than most.

                Blowing fuses is a generally bad sign for this amp, Usually (though not always) it's some outputs, possibly a rail switch, maybe drivers, and other parts. It's unlikely to be anything in the power supply though, they were very troublefree.

                These amps, when properly serviced, are very reliable. I am currently configuring 5 of the 900A's into a new rack to drive a compact line array system for a client. All 5 are in perfect shape and meet original factory spec with no work necessary.
                -------------------------------------------------------------------------------------------------------------------------------------------------------------------
                Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

                Currently product development engineer: Mesa Boogie

                Comment


                • #10
                  Aged Horse,

                  Can you tell me how they rated these amps? Let me be more specific... did they use a sine wave or burst/peak to rate the watts? It seems like these amps were rather conservatively rated on their specs. In use, they've had more headroom than I would have expected from their specs on paper. I've heard a number of companies use "burst" power (milliseconds) to boost their perfomance specs where as others used more real world numbers.

                  p.s. I'm a recording guy converted to a live audio guy. I'm still very much in the learning stage about this stuff, so please be gentle if my terminology is not quite correct.

                  Thanks!

                  Comment


                  • #11
                    They used the RMS rating, "continuous", that's in part why they are so heavy. The power transformers are really oversized for general purpose audio use. They are conservative.

                    Anybody want a set of 4 biamped 710C's, I'll let them go cheap. Low channel 500W at 4 ohms and high channel 75 watts at 8 ohms. Great for biamping top boxes or monitors.
                    -------------------------------------------------------------------------------------------------------------------------------------------------------------------
                    Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

                    Currently product development engineer: Mesa Boogie

                    Comment


                    • #12
                      Funny how things change. I'm sure that those old ABs were sine wave rated as was just about every "professional" power amp.

                      I submit that a proper burst test is more real world that sine/RMS/average rated amps because music IS a series of bursts and almost never continuous. And a burst test would be closer to describing the "sound" of a power amp.

                      I am assuming you do not need to drive a shaker table
                      Don Boomer

                      Comment


                      • #13
                        Funny how things change. I'm sure that those old ABs were sine wave rated as was just about every "professional" power amp.

                        I submit that a proper burst test is more real world that sine/RMS/average rated amps because music IS a series of bursts and almost never continuous. And a burst test would be closer to describing the "sound" of a power amp.

                        I am assuming you do not need to drive a shaker table


                        I agree. The AB amps had a pretty impressive burst spec too, which is why they sounded bigger than they rated at but this has become non-competative in today's marketing market.

                        In all of my amp designs, I am hyper-aware of the "burts versus time" rating, as this has a direct corrolation to how big an amp sounds and performs in the real world. The industry has traditionally used 20mSec for the burst period, I typically use 200 mSec which is much better representative of low frequency signals.
                        -------------------------------------------------------------------------------------------------------------------------------------------------------------------
                        Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

                        Currently product development engineer: Mesa Boogie

                        Comment


                        • #14
                          No, I'm looking to power some JTR Growlers (1 per sub- bridged). Jeff @ JTR recommends 1,000 watts going to the each box. As this is an install (i.e. weight doesn't matter), I thought I might try a couple the 900A's on the subs. As the AB 900 amp is rated 925 watts @ 8 ohms, they seem like a good fit. I guess my original questions was focused on an amp that is conservative and matched to the sub on paper versus an amp that has hyped up specs that might be slightly underpowering the subs.

                          wouldn't you rather have a conservative rating on your amps knowing they've got a little reserve than pushing your amp full tilt to get the rated output? Again, I'm still new to this and just want to be a sponge for knowledge.

                          Comment


                          • #15
                            "I am assuming you do not need to drive a shaker table"

                            I just realized that I gave you a serious answer to a rhetorical question

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