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A DIY audio amplifier design

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  • A DIY audio amplifier design

    Want to learn about electronic components? Want to have the pride of owning something entirely unique, customised exactly as you want it? This thread concerns the making of a DIY (power) amplifier, how it should perform and what to realistically expect for small money.

  • #2
    One question asked repeatedly is 'will amplifier X work with Harbeth speakers Y?' You know the answer is 'yes, if the amplifier is competently designed and working within original specification'.
    How good does the amp have to be? How little or how much should it cost? How big or how small? How many component parts? Are all amplifiers basically the same under the lid (yes)?

    Old habits die hard. The habit of believing that the amp is supremely important (it isn't) will not die. We hope that this thread will give you a grip on the reality of audio amplifiers. They are about as simple an electronic device as you can imagine ....

    Comment


    • #3
      Opening statement

      Interesting idea! OK, where to start. Let's start with a bold statement, which if you can disprove, you can win FOC a pair of brand new M40.1 (see here).

      1) "We absolutely agree (and hear for ourselves) that if you randomly select any competently designed stereo audio amplifiers working within their original performance specification* (and obviously of enough power output**), and hook them to your Harbeth speakers you will hear a difference between them. That's absolutely assured and expected..."

      2) "When precautions are taken to turn down the more 'gainy' (that is, sounds louder) amplifier to match the gain of the quieter amplifier, the big differences that you truly could hear under 1) above diminish or disappear on an instantaneous A-B switchover."

      3) As there are no standards for the gain (loudness) of amplifiers at the loudspeakers relating to the marking of the volume control knob on the front panel, you cannot be sure how many volts any amp is producing for any volume control position on the front panel. For example, amp A at volume setting 8 produces 18w output; amplifier B produces 41w at volume setting 8 and amp C, which doesn't have a volume control, produces 110w from a fully driven input stage. It is impossible to compare the sound of these without reducing (in this example) amp B to volume setting 3 (to match A's 18w output) and measuring the output of amp C. Who would think to do that?

      Can amplifiers be level matched by ear? Absolutely not! That's why this debate will not die. The failure of the ear as a precision instrument is the source of the problem! You can't use your ear to validate your ear!

      Maybe the conclusion of this thread will be that whilst it is entirely possible to make a perfectly functional, perfectly reliable power amp that will drive any Harbeth speaker for the cost of a meal out - and of adequate sonic performance - all of us would prefer the pride of ownership of a professionally made amplifier sitting with our audio equipment, not a DIY lash up. And that is all the excuse you need to invest in a really well made amp, not any considerations of 'audio quality'. Who would want a kit-car when they could own a Bentley?

      * Obviously the design has to be thorough and professional. If the design was poor and the amp is unstable, has whistles or distortion issues, and has a frequency response which is not basically flat then it is not a competent audio design or it has slipped out of original specification and needs servicing.

      ** It's clear that a flea cannot pull a horse. We cannot meaningfully compare a 7W tube amp with a 100W solid state amp when driving a real loudspeaker.
      Alan A. Shaw
      Designer, owner
      Harbeth Audio UK

      Comment


      • #4
        Why ask unanswerable questions about amplifiers - or blondes?

        Originally posted by A.S. View Post
        ...Maybe the conclusion of this thread will be that whilst it is entirely possible to make a perfectly functional, perfectly reliable power amp that will drive any Harbeth speaker for the cost of a meal out - and of adequate sonic performance - all of us would prefer the pride of ownership of a professionally made amplifier sitting with our audio equipment, not a DIY lash up....
        We should consider the beginner audiophile. Someone like me when I started out. I had the choice of DIY (that was my only choice due to fund issues), or daydreaming of Leak, Quad, Ferrograph etc.. My first three amps were kits - I wish I'd kept them - but one I found pinned up in a museum display (picture to follow).

        I stress again .... in my opinion there are much more relevant and important factors in the selection of a hifi amplifier than any claims you will read about 'sound quality'. You are far better to select on the basis of styling, power, brand image and reputation, after-care, user facilities and value for money. These factors are important.

        Nobody here can ever factually answer the question 'does amp A sound better than amp B' so why ask that question? The answer will be as vague and personal as asking 'do blondes make better lovers?'. No one can answer that objectively: they can only answer subjectively and that is not an answer, it's merely an opinion. They can answer the question 'is amp A reliable? What after care did you receive from amp B's maker? Can you comment on the styling of amp C? What's the remote control on amp D like? How hot does amp E run? Does F have enough inputs? How heavy is it? Does it hum?'

        So, what does today's DIYer have available as an amp kit? Well, for the price of a few beers, an extremely well presented little amp kit ....

        More follows
        Alan A. Shaw
        Designer, owner
        Harbeth Audio UK

        Comment


        • #5
          Zen and the Art of DIY: 2W tube amp

          Originally posted by A.S. View Post

          So, what does today's DIYer have available as an amp kit? Well, for the price of a few beers, an extremely well presented little amp kit ....

          More follows
          My recommendations are:

          1. the Zen:circuit by Nelson Pass, comprising single gain stage and easy to construct but a beast of a heat sink. Pictures will follow (not so much a DIY kit but a set of plans)

          2. The 46 SET Tube Amp using Tungsol 46s. Comes as a kit from Thomas Mayer, but you need to be aware you are dealing with high voltage!! Ouch. For the fainthearted it comes fully assembled (I am definitely in latter category) In finished form it weighs around 25kg and delivers no more than 2W per channel.

          P3ESRs and the 46 SET are magical.

          Comment


          • #6
            Pride of ownership - zero

            Here is an excellent little kit amp. Everything you need to make a complete and very high quality monoblock power amp (two needed for stereo). 100W output (with suitable cooling). Flat frequency response. Inaudible hiss. Very low distortion.

            It works. Who would take any pride in owning such a DIY box when they could buy a beautifully made amp in a hifi store with proper after care? And that's all the justification you need to buy a proper amp. But in sonic performance terms, can this amp actually be distinguished?

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

            Comment


            • #7
              AMB Laboratories is a popular site with DIY headphone enthusiasts. Many of Ti's designs can be adapted to drive speakers instead (though the output is on the low side), and he does provide a power amplifier design.

              http://www.amb.org/audio/

              I built the AMB M amplifier and σ11 PSU to drive headphones, but it can be configured as a 6Wrms per channel (into 8Ω) power amplifier instead. The designs are all free.

              Building this project taught me a lot about analogue electronics!

              Comment


              • #8
                Originally posted by A.S. View Post
                Here is an excellent little kit amp. Everything you need to make a complete and very high quality monoblock power amp (two needed for stereo). 100W output (with suitable cooling). Flat frequency response. Inaudible hiss. Very low distortion.

                It works. Who would take any pride in owning such a DIY box when they could buy a beautifully made amp in a hifi store with proper after care? And that's all the justification you need to buy a proper amp. But in sonic performance terms, can this amp actually be distinguished?

                >
                Interesting.
                I see no issue in using a DIY amp if it performs well, is reliable and built with care (esp. the solderings and internal fixtures). In fact, a tiny mono amp (as it appears to be) can easily be hidden behind the curtains or amongst furniture.

                Is it for sale as such or is it a collection of selected parts/units from Farnell, RS or a similar parts supplier?

                Comment


                • #9
                  Enough parts?

                  Originally posted by A.S. View Post
                  Here is an excellent little kit amp. Everything you need to make a complete and very high quality monoblock power amp (two needed for stereo). 100W output (with suitable cooling). Flat frequency response. Inaudible hiss. Very low distortion.
                  >
                  On second examination of that photo there doesn't seem quite enough to build an amplifier, at least safely. Also, why is there a lemon in the photo? Am I missing something - is this a joke?

                  Comment


                  • #10
                    Amp kit - part count

                    To reply to the previous two posts:

                    1) The complete amp kit is available on the internet as a stereo pair not including the metal box.
                    2) I count 22 electrical components plus one pcb plus three connectors. The pcb is highly recommended but not essential. The three connectors (blue, green) are sensible for testing. Not shown is a mains input socket. The speaker can be directly wired to the blue socket or a pair of proper speaker sockets connected to the blue socket (or wired directly to the pcb).

                    The only electrical component that is optional is the LED. Deleting the LED means that there would be 21 essential electrical components. If you reduce the count to 20, the amp will not function at all. If you add one, two, ten, one hundred more components the amp will not function any better. There are no circuit places that would benefit from the addition of even one component. It might look fancier and more sophisticated, but for this all-in-one IC chip, this is really all you need. The mains toroidal transformer (right) and the two black capacitors and the 4-wire rectifier (total 4 parts) could be common to a stereo amp.

                    Note: If you were to make a stereo kit with single LED, you would need 21 + (21-4) + 1 (LED) = 39 components and not one more. None of these electrical parts have a 'personality' and this circuit could (as a generalisation) be found in a UPS or printer.

                    Photographed on the kitchen table, the lemon is for scale.
                    Alan A. Shaw
                    Designer, owner
                    Harbeth Audio UK

                    Comment


                    • #11
                      Complexity?

                      It was the lack of a mains connector, fuse (though one is usually built into the mains cable, but probably not of a rating suitable to protect the amplifier from overload) and means of earthing the metal case which I was alarmed to find missing from a kit, but in the context of your argument this is being picky.

                      One thing though, although toroidal transformers are better at reducing EMF, would having the AC section (i.e. the PSU) so close to the signal input in that single, small case not introduce an audible 50hz hum/noise floor? Although again, this could potentially be argued as not relevant to this argument, is it not these kind of considerations which is increase the complexity and cost of an amplifier, at least to a degree?

                      Comment


                      • #12
                        Quick answer:

                        Picture attached of a very successful active speaker module we made some years ago using this IC power amp. The bass section was driven as push-pull; >100W power output.

                        Marked IEC connector with external user replaceable fuse - star electrical and safety earth - and very close proximity of toroidal transformer to the 3 ICs. Even much closer than shown here, there was no audible hum induction on the output to the woofer (it was extremely quiet to my surprise).

                        First rate power amps do not need to be complex, heavy or expensive. Nor can they be 'voiced' except by deliberately tweaking the frequency response and/or poor layout design and/or degrading the feedback or temperature stability - all bad practice. Power amps are extremely simple devices: when they work they work.

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

                        Comment


                        • #13
                          So simple amp?

                          Impressively simple! If this is all that's required to take on any power amplifier, disregarding power output (though perhaps additional complexity is required to achieve satisfactory signal reproduction at > 100W?), and render the listener unable to distinguish A or B - assuming the levels are matched - then this is genuinely a revelation (at least to people like me - who may have at least a degree of understanding of the theory, but don't have the experience or a true grasp), not to mention you are doing our wallets a great service!

                          Are we talking purely about power amplifiers here? In point 3 of your post above you mention volume control. If we're talking about volume control etc. then are we not into the realm of integrated or pre/power amplifiers? To continue in the vein of keeping things simple, shall we say that an integrated or pre/power amp adds signal gain control and perhaps input selection? A power amplifier alone is of limited value in the real world, and in my experience, when audio amplification is mentioned it usually infers both. In what way do you consider the addition of these features impacts your argument?

                          I also note you mention an instantaneous A-B switchover, is there a particular reason for this?

                          Comment


                          • #14
                            Adding a volume control

                            Originally posted by jr_41 View Post
                            Impressively simple! If this is all that's required to take on any power amplifier, disregarding power output (though perhaps additional complexity is required to achieve satisfactory signal reproduction at > 100W?), and render the listener unable to distinguish A or B - assuming the levels are matched - then this is genuinely a revelation (at least to people like me ...
                            Thanks for the feedback. To answer you ...

                            1.) Yes, it really is that simple. But it can be even simpler. If the sales volume of the amplifier is expected to be sufficiently high, you as the manufacturer could approach the chip maker and ask them if they would 'sweep-up' as many of those twenty-odd electrical components into the chip itself. There would be a trade-off. Those blue and orange two-legged capacitors are, as you can see, rather large proportionate to the IC itself. They would be difficult to embed into the IC package unless it was made much bigger, which would add more cost than the deletion of the external capacitors themselves; that's a no-no. So, most likely, the IC people would offer a compromise where the power output was down rated from, say, 100W to 50W, some restrictions on how hot it could get (etc. etc.) and the super-integrated result would be available.

                            If you look inside any modern miniature audio equipment (MP3 player, iPod etc.) you will see that there is a very high degree of 'integration', which is a fancy way of saying that there are ICs but not much 'glue' (external components) like capacitors, resistors and so on. This saves cost, saves assembly time and above all, increases reliability. IC are fantastically reliable and will work for decades as we know. Capacitors are dirt cheap and have a very short (and temperature related) lifespan counted in thousands of hours. Getting rid of capacitors in any (high powered) electronic circuit is the first step to improving reliability. The primary durability-limiting component in a power amplifier is the power supply capacitors (the big black cans) as they are working hard, in a hot environment.

                            2.) The limiting parameter for the power IC is - perhaps surprisingly - simply that of heat dissipation. 100w means 100w - would you want to hold a 100w light bulb just turned off? It's a lot of heat. It melts plastic. So if the heat sink (attached) is big enough, or force cooled (noisy fan? popular with PA stage amplifiers) can carry that heat from the chip it will run at 100W day in, day out.

                            3.) Yes, that little kit is all you need for a power amplifier. If you only intend to drive it from a 'high level' source such as a typical CD player (2v output) then you could directly connect the CD to the input of the kit. If the CD player has a (remote) volume control, then that's all you need to adjust loudness.

                            If the CD player does not have a volume control then you have three choices:

                            A) By a Passive Volume Control and connect the CD to its input and the output to the amp. This is what I use. It is nothing more than a volume control (see picture, it's green) in a nice box: no other components at all.

                            B) Obtain a Pre-Amplifier with multiple inputs, volume control, ideally tone controls and connect its output to the input of the kit. This may also have a phono input. It may have adjustable in/out gains, as the QUAD 44 does.

                            c) Add your own volume control and/or input selector to the kit amp! The picture shows what's needed: a volume control and knob, and a switch (rather ugly) to change between two input sources (which in this really fancy arrangement operates the two yellow relays). Finish the kit off with a pair of speaker connectors and some nice quality phono inputs.

                            Personally, at this stage of my audio life, I would far rather go and buy a well made amplifier with a first-class after care "buy once and forget" than make my own. Under the lid it may be the very same components but what I'm willing to pay for is someone else to take responsibility for servicing it - and something that looks well made - rather than having to roll-up my own sleeves. I'm sure you feel the same. The essential issue is that none of these basic parts have or can have a 'personality'.

                            The A-B question has been covered at length here I think.

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

                            Comment


                            • #15
                              Tempting to build

                              Interesting stuff, particularly the 'integration' concept. Thanks. I hope someone takes up your challenge and that you're able to prove your point. It is tempting to build one of these amplifiers and see how it compares to one of the 'Hi-Fi' offerings, and whether it's possible to distinguish them. You have demonstrated how simple an amplifier is at it's fundamental level with the use of ICs, which in itself is an eye opener.

                              Comment

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