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  • Class A amps

    I have a 4-way system with DSP crossover and quad amplification. The AMTPRO-4 tweeters are driven by an Adcom GFA-535II, I think it is about 80W per channel into 4 ohms, class A/B. Not that I listen to it all that loud. I have been thinking about trying a class A amp on the tweeter. More specifically, either a used Pass Labs Aleph 30, or a new Schiit Aegir (?), which is class A/AB, and supposedly stays in class A for the first 10 watts. But the analytical side of me says I wouldn't really notice a difference compared to my Adcom, which is supposed to be a 'high bias' amp, which minimizes crossover distortion.

    So does anyone out there have experience with class A amps, and do they make a difference or not? Or is it just audiophile nonsense?
    Are there other Class A amps that are more reasonably priced? TIA.
    "She don't love my speakers anymore..."

  • #2
    Class-A amps are often quite simple devices, the cost comes from heatsink and power supply requirements due to the fact that they work 99% as a space heater, and 1% as an audio device. FWIW I use my AMTPRO's with a Class-D amp from Hypex, which is also a topology devoid of crossover distortion, but I also need to use a furnace to heat my house so there are downsides ;)
    "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
    exactly a Fc 3K for both drivers, anybody can do it." -Xmax

    Comment


    • #3
      If you are good with solder, the net has many diy builds/designs/kits based on Nelson Pass's Aleph (and probably others) line of class A amps.
      http://techtalk.parts-express.com/fo...khanspires-but
      http://techtalk.parts-express.com/fo...pico-neo-build
      http://techtalk.parts-express.com/fo...ensation-build

      Comment


      • #4
        Originally posted by wavefunction View Post
        I have a 4-way system with DSP crossover and quad amplification. The AMTPRO-4 tweeters are driven by an Adcom GFA-535II, I think it is about 80W per channel into 4 ohms, class A/B. Not that I listen to it all that loud. I have been thinking about trying a class A amp on the tweeter. More specifically, either a used Pass Labs Aleph 30, or a new Schiit Aegir (?), which is class A/AB, and supposedly stays in class A for the first 10 watts. But the analytical side of me says I wouldn't really notice a difference compared to my Adcom, which is supposed to be a 'high bias' amp, which minimizes crossover distortion.

        So does anyone out there have experience with class A amps, and do they make a difference or not? Or is it just audiophile nonsense?
        Are there other Class A amps that are more reasonably priced? TIA.
        The Adcom is likely class A for the first few watts of output. There may be something out there that discusses the Adcom bias current. Once you know that, you know how many watts into 4 Ohms you'll get before you exceed bias and move into class B. I doubt you'd ever exceed 5W going to the tweeter, even under very loud conditions. There's just not much music power above 2KHz.

        A 10W Class A amp module should be all you'd need for your AMT.

        Comment


        • #5
          Originally posted by dcibel View Post
          Class-A amps are often quite simple devices, the cost comes from heatsink and power supply requirements due to the fact that they work 99% as a space heater, and 1% as an audio device. FWIW I use my AMTPRO's with a Class-D amp from Hypex, which is also a topology devoid of crossover distortion, but I also need to use a furnace to heat my house so there are downsides ;)
          LOL! I looked up Hypex, it didn't seem like they had any distribution in the US. They had a link to their diy site, but prices were quoted in Euros, and their one complete kit wasn't all that cheap. What model do you have and where did you get it? Seems counter-intuitive to use class D on a tweeter!
          "She don't love my speakers anymore..."

          Comment


          • #6
            Originally posted by Kornbread View Post
            If you are good with solder, the net has many diy builds/designs/kits based on Nelson Pass's Aleph (and probably others) line of class A amps.
            I did some poking around on ebay the other day (something I rarely do), and saw bare boards and stuffed boards for Pass designs. I think they came from China. I downloaded the manual for the Pass Aleph 30 from the Pass Labs site, also watched an interview of Nelson Pass by the Audiophiliac (does he bleed audio?). Somewhere in that info dump was the fact that they use International Rectifier Hexfets and hand match them to get the lowest noise and best performance (distortion?). So I think some kit with parts from unknown sources may not quite equal the real thing. Plus if it doesn't sound better than what I have now is it due to Class A being BS, or just my execution of it?
            "She don't love my speakers anymore..."

            Comment


            • #7
              Originally posted by JST_NTHR_SPKR_GY View Post

              The Adcom is likely class A for the first few watts of output. There may be something out there that discusses the Adcom bias current. Once you know that, you know how many watts into 4 Ohms you'll get before you exceed bias and move into class B. I doubt you'd ever exceed 5W going to the tweeter, even under very loud conditions. There's just not much music power above 2KHz.

              A 10W Class A amp module should be all you'd need for your AMT.
              A lot has been made about Nelson Pass designing the Adcom amps, but my guess is that he did the design of one of the original amps, maybe the big GFA-555, and then people at Adcom made lower power versions of it, such as the GFA-545 and GFA-535. These are the 'Mark 1' versions I am talking about. Some years later, they came out with the 'Mark II' versions, that used double-darlington output transistors. I don't think Nelson Pass had anything to do with those designs, but I could be wrong. I just recall my user manual for my Mark II had a page explaining the design change and how it resulted in less influence from load impedance variations. That page was 'signed' by someone other than Nelson Pass. Then years later, they brought out another new set that have 4 digit numbers, based on FETs.

              So the mark II version I have on my tweeters may not have the Class A performance for the first few watts the originals have. I have a mark I version on my mids, maybe I will swap them and listen for a difference. But many years ago I tried both on some JBL studio monitors I have and preferred the sound of the mark II on the highs. It was subtle, but it seemed more 'polite' sounding. Maybe just confirmation bias.
              "She don't love my speakers anymore..."

              Comment


              • #8
                Originally posted by wavefunction View Post

                LOL! I looked up Hypex, it didn't seem like they had any distribution in the US. They had a link to their diy site, but prices were quoted in Euros, and their one complete kit wasn't all that cheap. What model do you have and where did you get it? Seems counter-intuitive to use class D on a tweeter!
                I'm currently using a AS2.100D plate amp with DSP, but would like to eventually upgrade to the new Fusion FA123. No, I don't think it's counter intuitive. Efficiency and light weight is always good and performance is performance.

                You can buy the Hypex plate amps at PE's competition, not hard to find, the individual amp modules and such you can order from the Netherlands directly, I've ordered there before and the shipping cost was fair. They're not cheap but of the best class-D amps you can get. The top end nCore stuff are of the best amps available period, and the monoblock kits you can buy from the Hypex store are still a lot cheaper than a commercial nCore amp like NAD M22 for example.
                "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
                exactly a Fc 3K for both drivers, anybody can do it." -Xmax

                Comment


                • #9
                  Originally posted by dcibel View Post

                  I'm currently using a AS2.100D plate amp with DSP, but would like to eventually upgrade to the new Fusion FA123. No, I don't think it's counter intuitive. Efficiency and light weight is always good and performance is performance.

                  You can buy the Hypex plate amps at PE's competition, not hard to find, the individual amp modules and such you can order from the Netherlands directly, I've ordered there before and the shipping cost was fair. They're not cheap but of the best class-D amps you can get. The top end nCore stuff are of the best amps available period, and the monoblock kits you can buy from the Hypex store are still a lot cheaper than a commercial nCore amp like NAD M22 for example.
                  Thanks, I'll check it out when I can.
                  "She don't love my speakers anymore..."

                  Comment


                  • #10
                    Originally posted by JST_NTHR_SPKR_GY View Post

                    The Adcom is likely class A for the first few watts of output. There may be something out there that discusses the Adcom bias current. Once you know that, you know how many watts into 4 Ohms you'll get before you exceed bias and move into class B. I doubt you'd ever exceed 5W going to the tweeter, even under very loud conditions. There's just not much music power above 2KHz.

                    A 10W Class A amp module should be all you'd need for your AMT.
                    This is almost exactly what I was going to say.

                    For the frequencies that the Adcom is reproducing, does it ever get out of class A?

                    Comment


                    • #11
                      Originally posted by wavefunction View Post

                      A lot has been made about Nelson Pass designing the Adcom amps, but my guess is that he did the design of one of the original amps, maybe the big GFA-555, and then people at Adcom made lower power versions of it, such as the GFA-545 and GFA-535. These are the 'Mark 1' versions I am talking about. Some years later, they came out with the 'Mark II' versions, that used double-darlington output transistors. I don't think Nelson Pass had anything to do with those designs, but I could be wrong. I just recall my user manual for my Mark II had a page explaining the design change and how it resulted in less influence from load impedance variations. That page was 'signed' by someone other than Nelson Pass. Then years later, they brought out another new set that have 4 digit numbers, based on FETs.

                      So the mark II version I have on my tweeters may not have the Class A performance for the first few watts the originals have. I have a mark I version on my mids, maybe I will swap them and listen for a difference. But many years ago I tried both on some JBL studio monitors I have and preferred the sound of the mark II on the highs. It was subtle, but it seemed more 'polite' sounding. Maybe just confirmation bias.
                      your guess is wrong. i am not sure why people have such a hard time accepting that Pass designed the early ADcom line of amps.

                      https://www.audioxpress.com/article/...th-Nelson-Pass
                      craigk

                      " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

                      Comment


                      • #12
                        Originally posted by craigk View Post

                        your guess is wrong. i am not sure why people have such a hard time accepting that Pass designed the early ADcom line of amps.

                        https://www.audioxpress.com/article/...th-Nelson-Pass
                        Thanks a lot for clearing that up! I also have an Adcom GFA-5300 (all FET) that I got for $125 about 18 months ago. The online reviews that I could find for it range from just OK to lousy. None that I found were 'glowing'. So I stuck it on my woofers (80 Hz to 330 Hz). Maybe if I tried it on my tweeters it would be great! It runs very hot, so probably remains in Class A for a while.
                        "She don't love my speakers anymore..."

                        Comment


                        • #13
                          IIRC, Rod Elliott had a class A board available. However I am at work and cannot check the website because it is blocked here. Elliott Sound Products.

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