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Why so few higher powered Class D stereo amp boards?

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  • #16
    Originally posted by Simon Moon View Post
    Class D Audio makes some great sounding, high powered class d amp boards.

    http://classdaudio.com/

    Their lowest power board (CDA-120) is 60 watts RMS X 2 into 8 ohms, 120 watts into 4 ohms. Their most powerful (SDS-500) is 250 watts RMS X 2 into 8 ohms.

    Some are bridgeble into mono. For example, the CDA-120 is 240 in mono.




    Not to be picky, but class D amps are not digital amps.

    All the amp boards by Class D Audio are better than .02%.

    Typical Class D Audio amp board specs look like this:
    Model SDS-250
    Number Of Channels 2
    RMS Power Per Channel 8 Ohms 125W RMS X 2
    RMS Power Per Channel 4 Ohms 250W RMS X 2
    RMS Power in Bridge Mode 500W Into 8 Ohm Only. Single Channel
    Input Sensitivity 2V
    Total Harmonic Distortion (THD) Better than .02% (normal listening is about .003%)
    Frequency Response 10hZ to 35KHz
    Input Impedance RCA 30K
    Input Impedance XLR 45K
    Actually the specs listed are incomplete, a lot of marketing and borderline misleading. Go and take a look at how much power the boards produce at .02% distortion, the graphs that TI publishes is from 1 to 10 watts single ended and only an occasional dip below .02% in bridged mode, nowhere near close to the RMS values listed. I base this assumption on taking a look at the spec sheet for the amp chip they are using and looking at the graphs. A good well written amplifier spec will have the distortion listed along with a frequency range and the power range.

    Never believe what they say, dig deep and then dig deeper.......

    Comment


    • #17
      Originally posted by tomzarbo View Post
      ... my intended use is really for my bantam table radio, which could probably use just a few more watts than the little 50 watt board I've been using. T

      TomZ
      Your max volume problem is not the amp, it's your supply voltage.

      The nominal Wrms out is a function of two things: (1) DC supply voltage and (2) speaker impedance. If you've been running at 12 V, your not getting "50 W" per channel out of any amp. My ROT for these class D amps is Wrms = (Vs-1)2 / (2 * Rs) where Vs is the DC supply voltage and R is the speaker impedance.

      Examples: 12 V supply and 8 ohm speaker = ~7.5 Wrms; 12 V supply and 4 ohm speaker = ~15 Wrms.

      To get more watts you need to up the supply voltage. An 18 V laptop brick will put out 18 Wrms into 8 ohms and 36 Wrms into 4 ohms. With a 24 V brick its 33 W at 8 ohms and 66 W at 4 ohms.

      I use a 2.1 TPA3116 class D board at 24 V via an Li-Ion battery pack. I'm getting 66 Wrms into the ".1" 4 ohm woofer. On the beach, 500 people rise, over 200+ hundred yards, when I play the National Anthem in the morning. They love it

      Being a table radio, your not dealing with batteries. So it's easy to pick a DC PS with higher voltage. Now your only problem will integrating the fancy display electronics that run at 12 V or less.

      BTW: all the class D boards we've been using operate in BTL mode with the "100W" 2.1 output boards configured in PBTL (parallel BTL) for the sub channel. With my calculations above, the only way tp get a 100 W is to use a 2 ohm sub.

      Comment


      • #18
        Originally posted by westrock2000 View Post
        I’d like to see more digital amps that are rated, even at 50 watts, but with less than 1% distortion. Many of these digital amps are rated at at 10% for their advertised power output.
        Derate the power to non clipping levels and the big mfg "2 x 50w" chips are maxing out at 0.2 or .3% THD, worst case. Your correct about the advertised power - they must compete with their rivals in the marketing arena. So THD, a lesser understood spec, suffers.

        My ROT for these popular class D boards (e.g., TPA3116): Per channel Wrms = (Vps -1)2 / (2 * Rsp) where Vps is the power supply voltage and Rsp is the driver's nominal impedance.

        At 24 V into a 4 ohm driver, your output ist 66 Wrms @ < 1% THD. That's a fair amount power for medium sized speakers/enviroments. Huge towers, big subs, HT, they all need a lot more power.

        I'm running the original 8 ohm Advents (modified) with a TPA3116 class D amp and a 24 V brick. That's 33 Wrms per channel and it easily overwelms the 22' x 18' man cave.

        Comment


        • #19
          Thanks again for all the info guys. A sleepless night has yielded some good information for me to delve into.

          With all the parts/components, veneer, etc. using PE's 50 watt board, I'm around $240 all in for one of these Bantam Table Radios at this point, so adding another $60-$100 to the price is getting into dangerous territory cost-wise.

          Maybe this amp would be suitable for my needs: https://www.parts-express.com/sure-e...ogy)--320-3340

          It's similar to the one a4eaudio suggested, but this one looks to like 4 ohm loads a bit better than the other TDA7498 board. It looks like I may be able to fenagle it into the middle opening of the radio as well. If I could power it with a 24v brick, it may provide enough of a wattage improvement over the little PE 50w board to drive the Bantams louder and cleaner enough to make a difference. That would make life easier as a few of the other components I'm using are 24v max as well.

          I may order one up this weekend and see how it compares.

          I looked at all the suggested options and I appreciate the help everyone. I'm thinking of the amp for this project: http://techtalk.parts-express.com/fo...91#post1419991

          It's basically the Bantam speakers in a table radio format. Here is the Bantam thread: http://techtalk.parts-express.com/fo...speaker-system

          I've listened to them with the little PE 50 watt amp board and though it did work pretty well, I think a little more clean power wouldn't be a bad thing either.

          Thanks again for all the great ideas and input. I'll keep looking at your suggestions.

          TomZ
          *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
          *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

          *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

          Comment


          • #20
            Tom, keep in mind that all these boards will produce the same amount of power with the same voltage power supply. So, if you power your 50W amplifier with a 24V brick and you power your 100W amplifier with a 24V brick, you're going to get the same power out. You would have to step up to a 30V supply to get the increase to 100W. Also, even if you truly go from 50W to 100W, you're only going to gain a maximum of 3 dB out of your system. So make sure you ask yourself if the cost increase is worth 3 dB more output from your radio. Of course, this all assumes there are no quality differences between the 50W and 100W amplifiers you are looking at.

            Comment


            • #21
              Originally posted by 1100xxben View Post
              Tom, keep in mind that all these boards will produce the same amount of power with the same voltage power supply. So, if you power your 50W amplifier with a 24V brick and you power your 100W amplifier with a 24V brick, you're going to get the same power out. You would have to step up to a 30V supply to get the increase to 100W. Also, even if you truly go from 50W to 100W, you're only going to gain a maximum of 3 dB out of your system. So make sure you ask yourself if the cost increase is worth 3 dB more output from your radio. Of course, this all assumes there are no quality differences between the 50W and 100W amplifiers you are looking at.
              Good point Ben.
              in the case of the little 50 watt board, the max recommended voltage is 18v and I had been using 16v as I had some good ps units that were good quality. If I went to the full 24v with the more powerful board I'm thinking it may provide enough of a benefit to matter volume- and quality-wise. Sounds like the benefit may be negligible though.
              the sound quality of the little amp is pretty good though.
              I think the sure board may also have adjustable gain on the input as well, that may bump up the output a bit as well?
              Just thinking out loud, I obviously don't know what I'm talking about .

              TomZ
              *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
              *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

              *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

              Comment


              • #22
                Originally posted by tomzarbo View Post

                Good point Ben.
                in the case of the little 50 watt board, the max recommended voltage is 18v and I had been using 16v as I had some good ps units that were good quality.

                TomZ
                Tom, the "2x50W" designation is the max thermal dissipation the chip can handle referenced to output power (with proper heat sinking). The TDA7492 is rated for 2 x 50 W. The PE/mfg spec's for voltage vis'-a-vis' speaker impedance, reflect that limit. For example; they spec 18 V for 4 for ohm drivers. That's because maximum output is 48 W rms.

                There's no issue running at 24 V with a 4 ohm speaker, if ... , your not exceeding 50 W per channel output power (Note: max W at 24V @ 4 ohm is 66 Wrms). Unless empircal results prove otherwise, I'd go with common 24 V bricks and 4 ohm drivers. Remember, all these spec.'s are referenced to a sine-wave as the signal. Music is never as power dense as a sine wave, maybe 1/3 to 1/2 per my casual observations. And that greatly reduced power denisty also greatly reduces the thermal dissipation demand on the chip.

                If your running at 16 V with 4 ohm drivers, the max power output is 28 W rms. That's a lot for a table radio, no? Even if your using 8 ohm drivers, @ 24 V with the TDA7492, your getting 33 Wrms per channel. That has to be the loudest table radio ever built.

                SO, SO SO, why do you need more watts for your table radios? I bet youi're not getting anywhere near 10 W or more per channel. It may be the signal into the amp. If the source signal doesn't have sufficient amplitude vis'-a-vis' the chips gain setting, you'll never get the calculated watts. output. It's like having the the volume control knob turned down low all the time.

                Test the for a difference in output with the current source(s) versus a PC/laptop headphone output with the volume controls up full.

                Comment


                • #23
                  Glad to see mention of the TI TPA3255/51/45 has finally made its way here. You are not going to find a better price performance contender. They don't need a beefy toroid power supply like the ClassDAudio amps (which I used to own but the TPA is better), just a SMPS. The 3255 gets you 315W, the 3251 175W. These amps excel at lower impedances so go ahead and build that 2ohm digging MTM, the 3251 and 45 can handle it. I did. The sound quality is exceptional, like Class A.

                  Comment


                  • #24
                    The best way to get more useful power is to use more amps in an active setup. Use a small DSP crossover with EQ and BSC and Bass Enhancement, and use separate amps for each driver. Rod Elliot has a nice article on the benefits of using separate amps, but the bottom line is that a 50W/50W bi-amp system can offer the same peak capacity as a 200W amp.

                    For example, the amp below is for a computer monitor stand project that uses a low-cost 6-channel TPA3116 board. This isn't an ideal setup because the power supply is only 70W, but that's sufficient for the application. The stereo 3-way DSP board is in the middle. It's got a Bluetooth board hanging off to the left that allows you to tweak the crossover and EQ from your phone. There is a new version of this board that is getting tested now that uses the $18 ADAU1701 Learning Module, so there is no SMD soldering involved. But the new board requires software changes, and it might be a few weeks...

                    Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

                    Comment


                    • #25
                      Originally posted by Millstonemike View Post

                      Tom, the "2x50W" designation is the max thermal dissipation the chip can handle referenced to output power (with proper heat sinking). The TDA7492 is rated for 2 x 50 W. The PE/mfg spec's for voltage vis'-a-vis' speaker impedance, reflect that limit. For example; they spec 18 V for 4 for ohm drivers. That's because maximum output is 48 W rms.

                      There's no issue running at 24 V with a 4 ohm speaker, if ... , your not exceeding 50 W per channel output power (Note: max W at 24V @ 4 ohm is 66 Wrms). Unless empircal results prove otherwise, I'd go with common 24 V bricks and 4 ohm drivers. Remember, all these spec.'s are referenced to a sine-wave as the signal. Music is never as power dense as a sine wave, maybe 1/3 to 1/2 per my casual observations. And that greatly reduced power denisty also greatly reduces the thermal dissipation demand on the chip.

                      If your running at 16 V with 4 ohm drivers, the max power output is 28 W rms. That's a lot for a table radio, no? Even if your using 8 ohm drivers, @ 24 V with the TDA7492, your getting 33 Wrms per channel. That has to be the loudest table radio ever built.

                      SO, SO SO, why do you need more watts for your table radios? I bet youi're not getting anywhere near 10 W or more per channel. It may be the signal into the amp. If the source signal doesn't have sufficient amplitude vis'-a-vis' the chips gain setting, you'll never get the calculated watts. output. It's like having the the volume control knob turned down low all the time.

                      Test the for a difference in output with the current source(s) versus a PC/laptop headphone output with the volume controls up full.
                      Mike,
                      Are you saying it's okay to use a 24V brick with the TDA7492 50 watt amp that I've used before because they use sine waves to generate the specs, and music is never that 'dense' signal wise?
                      Well if that's the case, then I may just be able to use that little amp anyway. It always did run cool with the 16v brick I've usually used with them. I'll test that out on the bench maybe this weekend.

                      28 watts is a lot for a radio, but for example, my Onkyo receiver is rated at 80 watts and with most music, I can turn the volume knob up to the upper 60's or so on the digital readout while driving my 'Bantams' speakers, (it only goes to 80 which is MAX) so I figure that I'm getting around 50 watts or so to the speakers at that point? Just a guess on my part, but those last several digits on the volume doesn't generate much louder music. This radio I'm working on is basically the 'Bantams' speakers in a table radio format, so same drivers, probably almost the same crossover, etc.

                      The faceplate isn't as loud as a laptop is for example, I realize that because I've used both on the amp. When I speak of watts, I'm doing so understanding that the source, or the faceplate in this case, is output limited, and I realize that limits the volume the amp is able to generate, but ultimately to keep apples to apples in this conversation, I'm using the term 'watts' and saying I wouldn't mind more of them just to have something to reference the output level to so I can keep the discussion about what I'd like to upgrade so to speak, the amp. I hope that made a little sense.

                      Basically, I know that because the faceplate preamp doesn't generate full 'line level' output like a CD player or laptop turned up would, the amp can't generate it's full output either, but that's what I have to work with, so the amp is the only thing that I can really change, unless the power supply can be 'upped' thus generating more power without burning it out.

                      Honestly, the little PE 50 watt amp did fine and it did play loud, but I know they're louder when hooked up to the Onkyo stereo so I'd just like to leave a little less 'volume' on the table so to speak. The Bantams are not efficient speakers, they need some watts to really get moving in my experience.

                      Thanks for the help guys,
                      Mike, I'll hook up the faceplate to the PE 50 watt amp with a 24v brick to the bantams and see what it does with that.

                      TomZ




                      *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                      *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                      *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                      Comment


                      • #26
                        Hi Tom,

                        I have used that same little TDA7492 amp board in 3 different projects, everytime with 24Vdc power supplies. They work and sound great with the higher voltage. The heatsink barely gets warm even after several hours with the volume cranked way up and 4 ohm speakers. Heck, one of them I shoe horned into a small cigar box along with the power supply brick and it's working great after about 4 years.

                        I noticed an improvement in dynamic headroom switching from a Dell 19 Volt brick to the 24 Volt brick. I think you will too.
                        Craig

                        Comment


                        • #27
                          Originally posted by PWR RYD View Post
                          Hi Tom,

                          I have used that same little TDA7492 amp board in 3 different projects, everytime with 24Vdc power supplies. They work and sound great with the higher voltage. The heatsink barely gets warm even after several hours with the volume cranked way up and 4 ohm speakers. Heck, one of them I shoe horned into a small cigar box along with the power supply brick and it's working great after about 4 years.

                          I noticed an improvement in dynamic headroom switching from a Dell 19 Volt brick to the 24 Volt brick. I think you will too.
                          Thanks for the reaffirmation and first hand info Craig. I'm definitely going to give it a run this weekend and see what it does.

                          Really a nice little board I guess for the price. 24 volts, here I come!
                          TOMZ
                          *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                          *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                          *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                          Comment


                          • #28
                            Hypex ST180. Plenty of power and slam.

                            Comment


                            • #29
                              Originally posted by tomzarbo View Post

                              Mike,
                              Are you saying it's okay to use a 24V brick with the TDA7492 50 watt amp that I've used before because they use sine waves to generate the specs, and music is never that 'dense' signal wise?
                              Well if that's the case, then I may just be able to use that little amp anyway. It always did run cool with the 16v brick I've usually used with them. I'll test that out on the bench maybe this weekend.

                              28 watts is a lot for a radio, but for example, my Onkyo receiver is rated at 80 watts and with most music, I can turn the volume knob up to the upper 60's or so on the digital readout while driving my 'Bantams' speakers, (it only goes to 80 which is MAX) so I figure that I'm getting around 50 watts or so to the speakers at that point? Just a guess on my part, but those last several digits on the volume doesn't generate much louder music. This radio I'm working on is basically the 'Bantams' speakers in a table radio format, so same drivers, probably almost the same crossover, etc.

                              The faceplate isn't as loud as a laptop is for example, I realize that because I've used both on the amp. When I speak of watts, I'm doing so understanding that the source, or the faceplate in this case, is output limited, and I realize that limits the volume the amp is able to generate, but ultimately to keep apples to apples in this conversation, I'm using the term 'watts' and saying I wouldn't mind more of them just to have something to reference the output level to so I can keep the discussion about what I'd like to upgrade so to speak, the amp. I hope that made a little sense.

                              Basically, I know that because the faceplate preamp doesn't generate full 'line level' output like a CD player or laptop turned up would, the amp can't generate it's full output either, but that's what I have to work with, so the amp is the only thing that I can really change, unless the power supply can be 'upped' thus generating more power without burning it out.

                              Honestly, the little PE 50 watt amp did fine and it did play loud, but I know they're louder when hooked up to the Onkyo stereo so I'd just like to leave a little less 'volume' on the table so to speak. The Bantams are not efficient speakers, they need some watts to really get moving in my experience.

                              Thanks for the help guys,
                              Mike, I'll hook up the faceplate to the PE 50 watt amp with a 24v brick to the bantams and see what it does with that.

                              TomZ



                              Yes, 24 V PS is fine with the TDA792 module.

                              The TDA7492 module: If the chip is set to 20 dB gain, then that's a problem for all are common sources, receivers, phones, etc. Then you only option is to move onto a different module (or do surgery on a couble of SMD resistors that set the amp gain).

                              The ND 91-4 is fairly inefficient. But 50 W is a lot of power for it. Is it really getting that much power from the Onkyo?

                              You can easily measure power by measuiring voltage at a speaker output. Use a 60 Hz signal (remember the signal generator PC app) and a cheap HF meter set to AC.. With a 24 V PS, if you can turn up the source to get 14+ V at the output, your getting 50 Wrms into the ND91-4.

                              Comment


                              • #30
                                So I gave the amp 24v and ran it from the intended preamp. The difference between 16v and 24v is pretty substantial.

                                Louder and cleaner... it will work for sure. Now I'm even more impressed with that amp!
                                with bass heavy music playing for 5 or 6 min I only registered 90 degrees max on the heatsink. Seemed to be coasting heat wise.

                                Not to toot my own horn, but this radio is going to be pretty awesome if I do say so.

                                Thanks again all for the guidance.
                                TomZ
                                *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                                *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                                *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                                Comment

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