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A DIY audio amplifier design

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  • #16
    An even simpler 'super-integrated' design ....

    Originally posted by jr_41 View Post
    Interesting stuff, particularly the 'integration' concept...
    I was rooting around in the garage this morning and I found what is surely the last word in 'integration'.

    ILP, a British company, took an audio amplifier idea not dissimilar to the kit (previous posts) and potted it into a cavity in an enlarged die-cast heat sink. That means, after they tested the assembled circuit board, they poured a thermo-setting epoxy over it to completely seal it from the atmosphere. So what we have here is an even more highly 'integrated' power amplifier. I'm not sure if it's still available, but I believe that they sold tens of thousands of these over the years. We considered using some in active speakers but the heat sink protruded too far from the back panel of the speaker and would have been damaged in transit or use.

    All we need is to provide a safe mains input socket which we solder directly to the transformer's brown and blue wires (the mains switch built into the IEC socket which also has a non-essential mains filter) and solder the red, black, yellow and orange transformer wires directly to pins on the 'pod'. The smoothing capacitors are now 'potted' inside the pod.

    We just need a volume control, a phono input and a speaker connector (and ideally a case) and we have a complete mono amp. Not one single additional part is required.

    I have no idea if this amp (or indeed the kit) would pass the A-B instantaneous switch over test. It may or it may not; it is most likely to depend on the acuity of the listener. But whether or not, what will come out of the kit or this super-integrated amp will be recognisably good music. The objective of this exercise is to re-emphasise that whilst this sort of DIY solution will 'do the job' there is surely no pride of ownership, and when the audiophile has the funds available, he'd be better to invest in something with a decent cosmetic and above all, minimum risk that it will expectedly fail and destroy his expensive speakers.

    That durability, whilst not an attractive marketing buzz word, is IMHO the most important parameter of any power amplifier capable of destroying expensive speakers - as they all are.

    >
    Attached Files
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

    Comment


    • #17
      Audiophile components?

      Now that's what I call a black box solution!

      A fear of damaging expensive equipment (or yourself!) through tinkering with DIY if you're not completely confident is an issue. I think a pair of cheap speakers - to at least check the amplifier is basically working - is a good idea, not to mention a basic understanding of mains electricity and safety best practice.

      Returning to my previous argument for a moment, I note that in your cross over designs you use a very high quality PCB (with gold/gold plated tracing?), high quality film capacitors, etc., and in the P3ESR SE, oxygen free copper wiring. Am I correct in understanding these high quality variants were chosen because they're in the signal path and provide an audible improvement? In the kits listed above only the cheapest variants are used (that potentiometer is a far cry from the Alps Blue Velvet you typically find in a hifi amplifier). Given an amplifier is also in the signal path, is the use of higher quality components and wiring not justified there as well?

      I'm not sure which if any of the caps in the kit are actually in the signal path (as opposed to the large capacity electrolytic caps which are used in the PSU section and entirely appropriate), but I've read on a number of occasions that electrolytic and ceramic caps are a noticeable degradation vs film caps.

      Comment


      • #18
        Mosfet modules

        Not nearly as tightly "integrated" as the ILP module shown above, but have you seen these modules? Top notch British design and manufacture, brilliant value for money.

        And they seem to sound rather good too...(OK, I'll get my coat...)

        Comment


        • #19
          Exotic parts?

          Originally posted by jr_41 View Post
          ...I note that in your cross over designs you use a very high quality PCB (with gold/gold plated tracing?), high quality film capacitors, etc., and in the P3ESR SE, oxygen free copper wiring. Am I correct in understanding these high quality variants were chosen because they're in the signal path and provide an audible improvement? In the kits listed above only the cheapest variants are used (that potentiometer is a far cry from the Alps Blue Velvet you typically find in a hifi amplifier). Given an amplifier is also in the signal path, is the use of higher quality components and wiring not justified there as well?
          Er ..... never crossed my mind to use, or even bother to investigate the use of 'exotic components'. I'm far too experienced in the art of the marketeer to be sucked into that bog! Needless cost for no benefit = bad engineering.

          Our philosophy here is simple: We do not see the provision of spare parts/servicing as profit centre in our company (as most companies do) - we see it as a cost centre. This is a subtle difference.

          Profit centre
          : After care/upgrades are run as a for profit activity and they can be the most profitable department in a company, far more than first-time sales as the amp upgraders know.

          Cost centre
          : The company does not have a dedicated service/upgrade department with expensive staff waiting like vulture. It supplies service parts and takes the hit against general overheads.

          We absolutely do not want to be diverting time from hard-pressed production staff to resolving avoidable* customer issues. Every second that is taken off production can never be compensated by the meagre profit on spares (when they are processed at normal prices, not as a super-profitable activity), so we over-engineer to virtually guarantee that what we sell never comes back. We do not plan to get two bites at the cherry. That's the primary thought behind designs here: we never set cost minimisation as a goal: the speaker will cost what it costs and that not negotiable internally. You would be horrified if you could see what we discard (I am) to keep up the standard.

          Electrolytics: you may have seen my analysis of these elsewhere here (where???). I'm on a mission to eliminate them.

          'Exotic' parts in amplifiers: do the electrons flowing around know that they are in a piece of fancy cable or a swish capacitor? I don't believe that they do. As I've said here before, the use of fancy cable is entirely for marketing demands. Despite our well known position, many markets insist on exotic cable in their speakers and they are willing to pay for it.

          *Some customer issues (amplifier failure, child crushes supertweeter) are not avoidable, they are bad luck: we must get those customers up and running as soon as possible. But what we make and leaves our door we have responsibility over and can minimise the risk of failure due to parts/manufacturing by using best quality materials and careful selection and testing.
          Alan A. Shaw
          Designer, owner
          Harbeth Audio UK

          Comment


          • #20
            DIY Chip Amps!

            I'm very pleased to see this thread on the Harbeth User Group. Building your own audio gear is a lot of fun and very rewarding. Believe it or not, with little more than a good multimeter, a soldering station and some basic tools, you can easily build a great-sounding amplifier. If you're looking for a way to get off the audio nervosa merry-go-round, DIY is a good way to do it. And as a side benefit, you get to learn something new! How cool is that?

            This is my DIY chip amp based on the National LM3876 using only 12 components per channel, including the power supply. It's built onto an old cutting board for now, using a piece of aluminum stock for the chassis and heat sink. I've ordered some proper heat sinks for it and am building a nice aluminum chassis for it using scraps from a local metal supplier. Sounds very nice with the Harbeth P3ESR and took just a few hours to assemble.

            http://gallery.me.com/jplaurel/10015...13339172430001

            Here's the chip amp hooked up to the Harbeth P3ESR speakers, using the Bel Canto integrated above as a preamp. I'm sure Alan will be pleased to note the zip cord speaker cable!
            http://gallery.me.com/jplaurel/10015...13339172550001

            One thing I should mention is that when you build these things, be sure to test them on some old speakers before you connect them to you valuable Harbeths. I keep an old pair of Radio Shack Minimus 5 speakers in my shop for just this purpose.

            Comment


            • #21
              Potted poweramps

              Ahh yes, ILP modules... that sure brings back memories of the days when I
              had more hair and reading Everyday Electronics magazine. It is now "EPE", I understand. I would have bought a few in the whole line if funds permitted then, but student pocket money was never going to be adequate.

              The first diy amplifier I made used a plastic molded part instead of the potted one, with the venerable LM380. It made a nice racket with the crystal set and transistor radio, with an open-baffled, paper-cone Sanyo speaker

              tinears

              Alan wrote :
              "I was rooting around in the garage this morning and I found what is surely the last word in 'integration'.

              ILP, a British company, took an audio amplifier idea not dissimilar to the kit (previous posts) and potted it into a cavity in an enlarged die-cast heat sink. That means, after they tested the assembled circuit board, they poured a thermo-setting epoxy over it to completely seal it from the atmosphere. So what we have here is an even more highly 'integrated' power amplifier. I'm not sure if it's still available, but I believe that they sold tens of thousands of these over the years. We considered using some in active speakers but the heat sink protruded too far from the back panel of the speaker and would have been damaged in transit or use."

              Comment


              • #22
                Perfect example

                Originally posted by jplaurel View Post
                This is my DIY chip amp based on the National LM3876 using only 12 components per channel, including the power supply. It's built onto an old cutting board for now, using a piece of aluminum stock for the chassis and heat sink. I've ordered some proper heat sinks for it and am building a nice aluminum chassis for it using scraps from a local metal supplier. Sounds very nice with the Harbeth P3ESR and took just a few hours to assemble.
                Very nice jplaurel! A perfect example for this thread I'd say.

                Comment


                • #23
                  Job well done!

                  That's a really lovely amp assembly. Perhaps I've been to hard on myself dismissing my little kit and not considering taking it to the next stage and mounting in in an attractive case/stand. Very well done to you.

                  It's making me think .... should I assemble my kit or not?!
                  Alan A. Shaw
                  Designer, owner
                  Harbeth Audio UK

                  Comment


                  • #24
                    Yes, build that amplifier kit!

                    Thanks Alan. Yes, you should certainly build your amp and share your impressions here. I plan to build a case for mine, but I do enjoy peoples' reactions to it as it is. No one can believe the P3ESRs sounding so beautiful driven by an amp built onto an old wooden cutting board!

                    Decades ago, it was common for hi fi enthusiasts to build amps and speakers. Now that's what I call a hobby - creating, experimenting, learning. The hi-fi "hobby" today seems like just endless... buying. Speakers are tough. There's practically no way a DIY hobbyist could build a loudspeaker as good as the Harbeth without access to all the research, materials and tooling and even then, you'd have to be incredibly brilliant or incredibly lucky to get even remotely close. But it is possible to build your own amplifier and end up with something that sounds world class.

                    This thread must give you some pause because I'm sure you don't want to start seeing RADIAL drivers coming back to the factory with burned out voice coils because of improperly designed DIY amps that sent too much DC down the speaker wire.

                    Originally posted by A.S. View Post
                    That's a really lovely amp assembly. Perhaps I've been to hard on myself dismissing my little kit and not considering taking it to the next stage and mounting in in an attractive case/stand. Very well done to you.

                    It's making me think .... should I assemble my kit or not?!

                    Comment


                    • #25
                      'Class D' DIY monoblocks amplifiers

                      Here are a pair of DIY Class D amplifiers that I just finished assembling. These are a good option for those of you who'd like to dabble a little in amp construction, but don't want to go to the extent of building an amp out of discrete components. All you have to do is install the module into a chassis and wire it up. Each amp took me about 4 hours to assemble.

                      These little amplifiers use the Bang & Olufsen ICEpower 125ASX2 module. These modules are used by a number of well-regarded manufacturers, such as Bel Canto Design, Wyred4Sound and Jeff Rowland. Each amp supports two channel operation and produces 120 watts per channel into 4 ohms (115v). The two channels in the 125ASX2 can be bridged, a mode that ICEpower calls "BTL" mode. In that mode, each amp module supports a single channel and produces 450 watts per channel into 4 ohms with 115v. I don't know how they accomplish this and I barely understand the operating concept of Class D, but those numbers are from the spec sheet.

                      How do they sound? Well, they sound pretty much like Class D amps, which nowadays are very good indeed! The Bel Canto integrated amplifier in my previous post also uses the same 125ASX2 module, so of course the sound is very similar. I've noticed that Harbeths seem to work very well with the new Class D amps. And another benefit of Class D is that they are very efficient (over 80%). Each of these monoblocks only consumes around 15w of power - about as much as a hallway night light.

                      http://gallery.me.com/jplaurel/10015...13348007740001

                      And here they are in my test system with the Harbeth P3ESRs. The Squeezebox Touch is feeding a Wyred4Sound DAC2, which is connected to the two ICEpower monoblocks via balanced XLR.

                      http://gallery.me.com/jplaurel/10015...13348007520001

                      The modules are normally only sold to audio equipment manufacturers, but I was able to source this pair from a very nice gentleman in Shanghai, who offers them in kit form, complete with the chassis and all the hardware you'll need. And all for a very reasonable price under USD $300 shipped. PM me privately if you would like his contact information.

                      {Moderator's comment: Harbeth cannot warrant this very interesting experiment. You should also investigate after-care and remember that DIY is never a substitute for a long term relationship with an experienced audio dealer in your area.}

                      Comment


                      • #26
                        DIY: You're on your own

                        While the risk of something going with these particular modules is low, since they are supplied completely built from ICEpower, you can do serious damage to your speakers or even associated equipment if you get the wiring wrong. As the Moderator implies, you are on your own in the DIY world, with no support from anyone. I would like to restate that when you are building your own amps, be sure to carry out the proper measurements before connecting any valuable speakers. I have an old pair of speakers that I use for testing purposes. Many DIYers use salvaged car speakers and things like that.

                        Also be aware that there is a risk of personal injury. On an amp like the Class D project above, the risk is limited to potential exposure to the mains leads. But if, like me, you enjoy building tube amplifiers, always be aware that the extremely high voltages in those things are instantly lethal. And they can continue to be lethal even hours after the amp has been powered down. So please get some training and follow the proper precautions before you start fooling around with this stuff.

                        The upside is that you will get immense satisfaction from building your own audio gear and learning new things.

                        Comment


                        • #27
                          More info please ...

                          Originally posted by jplaurel View Post
                          While the risk of something going with these particular modules is low, since they are supplied completely built from ICEpower, you can do serious damage to your speakers or even associated equipment if you get the wiring wrong. As the Moderator implies, you are on your own in the DIY world, with no support from anyone. I would like to restate that when you are building your own amps, be sure to carry out the proper measurements before connecting any valuable speakers. I have an old pair of speakers that I use for testing purposes. Many DIYers use salvaged car speakers and things like that.

                          Also be aware that there is a risk of personal injury. On an amp like the Class D project above, the risk is limited to potential exposure to the mains leads. But if, like me, you enjoy building tube amplifiers, always be aware that the extremely high voltages in those things are instantly lethal. And they can continue to be lethal even hours after the amp has been powered down. So please get some training and follow the proper precautions before you start fooling around with this stuff.

                          The upside is that you will get immense satisfaction from building your own audio gear and learning new things.
                          Hi jplaurel,

                          could you elaborate on the three RCA- and double XLR inputs per chassis? Perhaps a photo of the rear?

                          Am I correct in assuming that this supplier makes an input board for balanced sources with psu for the lit on/off switch?

                          Bel Canto also uses an input board, with XLR option and a groundswitch (to short pin 1 to 3 in single-ended mode). I'm not too convinced of XLR inputs on domestic amplifiers but some swear by them.

                          Comment


                          • #28
                            More details of the amp

                            Originally posted by Spindrift View Post
                            Hi jplaurel,

                            could you elaborate on the three RCA- and double XLR inputs per chassis? Perhaps a photo of the rear?

                            Am I correct in assuming that this supplier makes an input board for balanced sources with psu for the lit on/off switch?

                            Bel Canto also uses an input board, with XLR option and a groundswitch (to short pin 1 to 3 in single-ended mode). I'm not too convinced of XLR inputs on domestic amplifiers but some swear by them.
                            Hi Spindrift-
                            Here is a shot of the back panel. The B&O ICEpower 125ASX2 supports single ended inputs via RCA jacks in stereo mode, but if you bridge the two channels ("BTL" mode), it supports a single balanced XLR input. To enter BTL mode, you short two terminals on the board. You can see the switch on my amp that accomplishes this. Note that when you bridge the two channels of a 125ASX2 in BTL mode, you must connect the speaker like this:

                            positive right channel amp output -> negative speaker input
                            positive left channel amp output -> positive speaker input

                            You can imagine that there is a lot of room for user error here. Further reinforcing the Moderator's point above, idiot-proofing is a big part of the added value that manufacturers like Bel Canto and Wyred4Sound offer when they integrate these modules into their products.

                            Full into on the 125ASX2 with specs and detail on its various operating modes here:
                            http://www.icepower.bang-olufsen.com...ns/125asx2.pdf

                            On the far left of the panel, you can see an XLR output and another RCA input. The purpose of these is to facilitate single ended input when the amp is in BTL mode. In BTL mode, the 125ASX2 is a monoblock, but the only natively supported input in this mode is balanced via the XLR. So if you want to use the amp in BTL mode as a monoblock but with RCA input, you need a transformer, which the kit supplier provides. To use it, you simply connect your input to the RCA jack, then run a short XLR patch cable between the transformer board's XLR output to the 125ASX2's XLR input. Now you have a monoblock that accepts single ended input.

                            The transformer adds a tiny bit of background noise that can be heard a few inches from the speaker drivers. In native stereo or BTL mono mode, the 125ASX2 is completely silent at idle.

                            The RCA-XLR transformer board uses the 125ASX2's 24V auxiliary power supply. The LEDs get their power from the transformer board, but if you omit the transformer, you could just connect them to the 125ASX2's aux power supply.

                            Balanced connections generally have less noise than single ended, even more so if the back of your equipment rack is a tangle of wires. Whether they will make a big difference in your system will depend on where you live, the wiring in your house, other active devices nearby, etc. I use balanced whenever possible and in my case, it does make a difference on certain systems. But it's hard to know whether that has to do with the balanced connection rejecting common mode interference or the implementation of the inputs. For example, when I connect my McIntosh C22 preamp to the MC275 amp via single ended outputs/inputs, you can put your ear to the speaker and hear just a little hiss starting from around 6 inches away. With balanced connections, it is dead silent, but on the MC275 the single ended inputs pass through an additional 12AX7 tube which could account for the additional noise. On the other hand, the single ended and balanced connections on my C50 and MC452 are indistinguishable from one another. Then again, it's in a different part of the house... As you can see, a lot of variables are involved.

                            http://gallery.me.com/jplaurel/10015...13348007370001
                            Last edited by jplaurel; 20-04-2012, 09:01 PM. Reason: additional detail

                            Comment


                            • #29
                              Information about the DIY Amplifier Kit

                              Alan, can you please post information about the small DIY Amplifier that you showed in the picture? Where can I locate this so I can build one? Thanks.

                              Comment


                              • #30
                                Costs add up ....

                                I think it's a Gainclone type of amp and there is loads of info on DIYaudio about these. For you in the US, this company might make a good start -

                                http://www.audiosector.com/lm3875.shtml

                                and also -

                                http://www.decdun.me.uk/gaincloneindex.html

                                These amps look to be dirt cheap on the surface, but it's the transformers and casework that cost the real money, as in real-world amplifiers. "Don't skimp on the transformer" is my advice...

                                Listening.

                                By now I have come to expect something quite special from these little chip amplifiers and once again I was not disappointed. This time I have used just one 120VA transformer and a single rectifier bridge but the amount of bass produced by this amplifier is astounding! Clarity is one area definitely improved from the old Arcam circuit and the impression overall is that a new lease of life has been breathed into this 22 year old amplifier. A successful project, and given the small outlay, I am very satisfied with the result.

                                Comment

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