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  • Small measurement amp

    I have read that inexpensive class d amps are not good to do measurements with due to the impedance causing varied frequency response. Right now I use a big full size class ab amp, but am looking for something more practical.

    What is a good small inexpensive amp that I can reliably take fr measurements with?

    Thanks
    Projects:

    transcenD: http://techtalk.parts-express.com/fo...5035-transcend
    Summits: http://techtalk.parts-express.com/sh...75-The-Summits
    References: http://techtalk.parts-express.com/sh...-My-References
    Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

  • #2
    Pretty much any class-AB amp will do the trick. Like this one:

    https://www.parts-express.com/dayton...ifier--300-812

    An option for a cheap solution is to buy something used from your local classifieds (kijiji, craigslist, etc).
    Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

    Comment


    • #3
      Originally posted by dynamo View Post
      I have read that inexpensive class d amps are not good to do measurements with due to the impedance causing varied frequency response. Right now I use a big full size class ab amp, but am looking for something more practical.

      What is a good small inexpensive amp that I can reliably take fr measurements with?

      Thanks
      Not all class-D amps have a high output impedance. Many tube amps are affected as well. Look for an amp that specifies the output impedance or a class-AB as suggested above.

      Comment


      • #4
        Originally posted by rickcraig View Post
        Not all class-D amps have a high output impedance.
        It's not the output impedance that is an issue with class-D (its usually very low), but interaction of the output filter of class-D amps that use pre-filter feedback topologies. The output filter interacts with the complex speaker impedance which can create some change to the frequency response at the top octave. Newer technologies such as Hypex UcD implement a post-filter feedback to overcome this.
        Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

        Comment


        • #5
          That Dayton is nice, but I'm looking for cheaper. Used on CL or feebay are an option but is there anything else small and cheap?

          What about alternative class (t, etc)? I'm thinking along the lines of a lepai type amp.
          Projects:

          transcenD: http://techtalk.parts-express.com/fo...5035-transcend
          Summits: http://techtalk.parts-express.com/sh...75-The-Summits
          References: http://techtalk.parts-express.com/sh...-My-References
          Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

          Comment


          • #6
            maybe look for used older car amps, i got a Altec Lansing ALA25, 2x25watts along time ago of the ebay. think i paid around 20-30 bucks for it, find a pre amp and a 12volt power supply, good to go.

            *edit- or you could check one of these out if you dont mind building your own case or finding one to put them in.*
            https://www.parts-express.com/pam861...board--320-604
            https://www.parts-express.com/dayton...odule--300-385


            personally i wouldnt go to cheap on the amp since you dont know how cheap the internals are. i would more suggest this amp, if you cant find any good car/home amps that fit your needs of CL
            https://www.parts-express.com/dayton...5-wpc--300-380

            Comment


            • #7
              Class-T is a trademark for a specific type of class-D made by Tripath. They'll have all the same problems. Really if you're not concerned with being a dB or two off in the top octave response, they'll work just fine.
              Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

              Comment


              • #8
                instead of editing my post agian, another option is building a DIY LM1875 amp. it wont need a big heatsink but agian you would need a preamp/case. chipamp.com has some kits, i think he might have even added a passive pre as an option.

                Comment


                • #9
                  Cool, thanks for the suggestions and clarification guys!
                  Projects:

                  transcenD: http://techtalk.parts-express.com/fo...5035-transcend
                  Summits: http://techtalk.parts-express.com/sh...75-The-Summits
                  References: http://techtalk.parts-express.com/sh...-My-References
                  Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

                  Comment


                  • #10
                    I've compared FR plots taken with my Lepai 2020 vs a vintage ADVE\T Model (B?)300 receiver. Not sure what class it is, but curves looked awfully similar. Could they have been off by a dB above 10kHz? Maybe . . . but at least the top half of that octave is lost to me anyhow (but not my wife - and I didn't ask her if they sounded different, maybe next time).

                    Comment


                    • #11
                      The top octave response will be load (speaker) dependent. And yes I agree to not put much importance in the response above about 12-15kHz.
                      Don't waste your money on a new set of speakers, You get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

                      Comment


                      • #12
                        Originally posted by Chris Roemer View Post
                        I've compared FR plots taken with my Lepai 2020 vs a vintage ADVE\T Model (B?)300 receiver. Not sure what class it is, but curves looked awfully similar. Could they have been off by a dB above 10kHz? Maybe . . . but at least the top half of that octave is lost to me anyhow (but not my wife - and I didn't ask her if they sounded different, maybe next time).
                        Thanks Chris. I happen to have a 2020 so perhaps that is what I will use then.
                        Projects:

                        transcenD: http://techtalk.parts-express.com/fo...5035-transcend
                        Summits: http://techtalk.parts-express.com/sh...75-The-Summits
                        References: http://techtalk.parts-express.com/sh...-My-References
                        Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

                        Comment


                        • #13
                          Originally posted by dcibel View Post
                          It's not the output impedance that is an issue with class-D (its usually very low), but interaction of the output filter of class-D amps that use pre-filter feedback topologies. The output filter interacts with the complex speaker impedance which can create some change to the frequency response at the top octave. Newer technologies such as Hypex UcD implement a post-filter feedback to overcome this.

                          Thanks for the clarification - it seems I read about a Peavey? amp that had a high output impedance.

                          Comment


                          • #14
                            Crown Drivecore, Pascal, Hypex, and ICEpower are class D amps with no change in HF due to impedance.

                            That said- I like the sound of the 2020Ti amp. I placed it in the chain when I removed the Crowns for InDIYana, and was pleasantly surprised! I've used it for breaking in woofers too, and use a 19VDC floor-wart.
                            I'd have to see if the top-octave changes though...
                            Wolf
                            "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                            "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                            "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                            "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                            *InDIYana event website*

                            Photobucket pages:
                            http://photobucket.com/Wolf-Speakers_and_more

                            My blog/writeups/thoughts here at PE:
                            http://techtalk.parts-express.com/blog.php?u=4102

                            Comment


                            • #15
                              I had the same issue a while ago and depending on the speaker impedance, you could be off by 2-3dB in the top octave. Not an acceptable compromise for me. So I picked up a used Parasound Z amp for $75. Not the cheapest option, but a really solid 30 watt class AB amp and really small for what it is. It's got enough oomph to give the speakers a little workout once I'm done testing them too.

                              Dan
                              _____________________________
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