Announcement

Collapse

HUG - here for all audio enthusiasts

Since its inception ten years ago, the Harbeth User Group's ambition has been to create a lasting knowledge archive. Knowledge is based on facts and observations. Knowledge is timeless. Knowledge is human independent and replicatable. However, we live in new world where thanks to social media, 'facts' have become flexible and personal. HUG operates in that real world.

HUG has two approaches to contributor's Posts. If you have, like us, a scientific mind and are curious about how the ear works, how it can lead us to make the right - and wrong - decisions, and about the technical ins and outs of audio equipment, how it's designed and what choices the designer makes, then the factual area of HUG is for you. The objective methods of comparing audio equipment under controlled conditions has been thoroughly examined here on HUG and elsewhere and can be easily understood and tried with negligible technical knowledge.

Alternatively, if you just like chatting about audio and subjectivity rules for you, then the Subjective Soundings sub-forum is you. If upon examination we think that Posts are better suited to one sub-forum than than the other, they will be redirected during Moderation, which is applied throughout the site.

Questions and Posts about, for example, 'does amplifier A sounds better than amplifier B' or 'which speaker stands or cables are best' are suitable for the Subjective Soundings area.

The Moderators' decision is final in all matters regarding what appears here. That said, very few Posts are rejected. HUG Moderation individually spell and layout checks Posts for clarity but due to the workload, Posts in the Subjective Soundings area, from Oct. 2016 will not be. We regret that but we are unable to accept Posts that present what we consider to be free advertising for products that Harbeth does not make.

That's it! Enjoy!

{Updated Nov. 2016A}
See more
See less

Refurbish capacitors inside speaker crossovers?

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Refurbish capacitors inside speaker crossovers?

    The manufacturer of my audio (electronics) equipment advices to refurbish the capacitors inside the amplifier every ten years or so. To let the amplifier sound again just like "new-recap" they call it-

    Now I wonder since there are caps to be find inside the crossover filter of Harbeth speakers -I guess-is it wise to change these caps also once in a? Or does this not apply to speaker crossover filters?

  • #2
    Refurbish capacitors...?

    I would not advice it at all.

    Comment


    • #3
      And that"s because?

      Comment


      • #4
        Capacitors in Speakers do Less Work than Amplifier Caps

        Possibly something to do with the fact that amplifier caps tend to be large and, particularly, do a lot of work. They get warm, which limits life due to electrolyte loss. I don't think speaker crossover caps do nearly so much work.
        Ben from UK. Harbeth Super HL5 owner.

        Comment


        • #5
          We need some background on capacitors

          Before we can begin to give a worthwhile answer to this question, we have to understand something about how a capacitor is constructed. Otherwise we may become a victim of half-truth and spend good money "upgrading" what cannot be upgraded.

          Almost all references to 'capacitors' on the internet dive in with lots of complex maths (which I don't understand or need to know) such as here. Forget all of that stuff and just skim down the article, note that capacitors come in many shapes and sizes (and colours and voltage ratings too). The key words to look out for concerning how they are constructed are plates and dielectric.

          Then have a look at this much more digestible article here.

          Now with those two crucial words plates and dielectric we can see from this article that there are many types of capacitors made from different combinations of plates and dielectric, each with particular advantages (and disadvantages) such as size, cost, availability, case style, voltage capability, ageing, tolerance etc. etc.. There is no perfect capacitor and the equipment designer must balance cost v. size v. those other factors in deciding what exact type of capacitor to use and in what capacitance value.

          As a general rule, the physically larger the capacitor the more difficult it is for the manufacturer to control the exact capacitance value hence the tolerance becomes greater. For example, as new a small thumbnail capacitor may be supplied as +/- 5% tolerance either side of the value printed on the case. A new big power supply capacitor the size of a yoghurt pot may be +/- 50% of the value printed on the case. If the true value is +50% that's probably a good thing as the capacitor will have more reserve and smooth out power supply hum better. But if the true value is -50% that particular amplifier will (perhaps) have a weaker bass and more audible psu hum.
          Alan A. Shaw
          Designer, owner
          Harbeth Audio UK

          Comment


          • #6
            Capacitors

            And another answer...: the electrolitic capacitors in the power supply of an amplifier are prone to deterioration over the years, because they are that: electrolitic.

            Any 'dry' capacitor does not really need to be swapped out, just the electrolitics in power amplifiers and then only after 20 years (or 10 years if the equipment is always on, like NAIM). Still a NAIM amplifier will still work after 20 years, but possibly slightly below spec.

            Comment


            • #7
              Ok, that may be so but you've jumped ahead a little. Most of our readers are non-technical and you need to work progressively towards the answer you gave to carry the audience with you. We only want to be covering this subject once here on the HUG so our explanation should be comprehensive for all, yet simple. So if I may suggest a step back ...

              I mentioned in my previous post the key words of plates and dielectric. That's all you need to make a capacitor. You can make one on the kitchen table, and indeed, the first capacitors were nothing more that two metal plates separated by an air gap - or technically, an air dielectric. The plates have to be something which will conduct electricity but the dielectric absolutely must not conduct electricity otherwise the opposite charges that builds up on the two plates will leak through the dielectric and cancel themselves out: the capacitor will become a resistor. Air is an excellent dielectric even up to frighteningly high voltages - which is why our mains supply carried overhead on pylons doesn't short together.

              Anyone want to take up the explanation of exactly what dry and wet dielectric means and why capacitor inventors moved from the air dielectric of the early capacitors to the modern types?
              Alan A. Shaw
              Designer, owner
              Harbeth Audio UK

              Comment


              • #8
                Request

                Originally posted by fred40 View Post
                The manufacturer of my audio (electronics) equipment advices to refurbish the capacitors inside the amplifier every ten years or so. To let the amplifier sound again just like "new-recap" they call it-

                Now I wonder since there are caps to be find inside the crossover filter of Harbeth speakers -I guess-is it wise to change these caps also once in a? Or does this not apply to speaker crossover filters?
                Shall we please return to the original question and have a qualified person answer it directly without delving through matters of design?
                Alan, as the manufacturer of Harbeth speakers "is it wise to change (Harbeth capacitors) once in a?"

                Comment


                • #9
                  I've been directly asked a reasonable and serious question. I have freely given up my time to build up to an answer which, in the spirit of this Harbeth User Group will stand the test of time i.e. only needs to be asked and answered once.

                  If you think it can be answered with a simple yes/no answer then you better look elsewhere. Nothing in audio is black/white, yes/no. Everything is in the grey areas. Unless you appreciate the variables that operate in the grey areas, you may as well flip a coin.

                  Is your need for an instant answer so pressing that the knowledge that would enable you to make your own decision (not take my word for it) just too much bother?
                  Alan A. Shaw
                  Designer, owner
                  Harbeth Audio UK

                  Comment


                  • #10
                    Knowledge = power

                    I agree with Alan.

                    Look, we have here a well-respected and experienced speaker designer who is taking time he does not need to take in order to answer a question in a detailed and serious way, and in such a way that people will not only know the answer, but will (hopefully) understand it.

                    I'm sure it would be the easiest thing in the world for him to say "yes it matters" or "no it doesn't" and leave it at that. But how would that advance anyone's knowledge or understanding one bit? All you know at that point is what somebody else thinks, without any idea of why they think so. And it's that type of "knowledge" that renders us all vulnerable to the agendas of those who speak not because they want to impart truth, but because they have something they want, and their communication is intended to manipulate people in that direction. Alan Shaw may be someone you can rely on, but others will not be, and how will you tell the difference? Unless, of course, they go step by step and tell you why what they believe is the truth.

                    So I for one am grateful for Alan's time and energy and will do my best to follow the discussion however he wants to present it.

                    Comment


                    • #11
                      OK, back on the subject of capacitors, and how this relates to crossovers. Shortly, you will be able to identify the various types yourself and make your own decision about this issue just by physical examination of a speaker crossover.

                      Capacitors come in many shapes, sizes and colours. The next think we should dismiss to avoid confusion is colour. The case colour of the capacitor has no technical correlation with its construction, usage, durability or longevity. It does seem to have a connection with its marketability, since certain colours (yellow, purple, red) seem to add more perceived value in audio circuits. But if you are a big enough customer you can have any case colour you want: sparkly pink if you think that will add some value to your product and you order a million or two pieces. So forget colour.

                      We have to make a solder connection to the two plates of the capacitor, so the fixed value capacitor must have two solderable wires. The next issue is how those two wires exit the capacitor's body. There are a few alternative methods. The super-miniature capacitors used in mobile phones are a special case, but for normal consumer electronics, and certainly all speaker crossovers, there really are only two choices: the capacitor will be either the so-called radial or axial construction. The significance of this will become apparent later.
                      >

                      P.S. The choice of either the radial case (wires coming out of the bottom) or axial case (wires coming out of opposite ends) is down to the equipment designer. For a given capacitance value, axial cases are physically larger. This means that for a given area of circuit board, you can fit far more radial cased capacitors than axial ones. We prefer radial cased capacitors for that reason.
                      Attached Files
                      Alan A. Shaw
                      Designer, owner
                      Harbeth Audio UK

                      Comment


                      • #12
                        Happy Birthday Alan!

                        Comment


                        • #13
                          Originally posted by A.S. View Post
                          OK, birthday morning and back on the subject of capacitors, and how this relates to crossovers. Shortly, you will be able to identify the various types yourself and make your own decision about this issue just by physical examination of a speaker crossover.
                          ...

                          Hear Hear!
                          After reading your latest installment you've made me a devotee of your splendid exposition Alan.

                          Comment


                          • #14
                            Happy 54th birthday Alan!

                            Comment


                            • #15
                              The case sealing issue ...

                              Before we try and crack open a capacitor or two, I'd like to think about how a capacitor can fail, be it a slow gradual degradation or an instantaneous one. We know that electronic systems are generally very reliable. There are electronic circuits in space probes hundreds of millions of miles away from earth sent many years ago which are still working perfectly. My guess is that those circuits, designed for longevity and reliability as the primary requirements (regardless of cost) resulted from one or two key decisions at the design stage. And undoubtedly one of those decisions would have been to use as few capacitors as possible in the circuitry because capacitors do fail.

                              Before we look inside one, I want to show you some macro photographs I took today of the point at which the metal solder-leg actually enters the body of the capacitor. The quality of the junction between the tinned-wire and the case material is extremely critical and all-important to a reliable long service life. The reason is that with time the wire will, under the microscope, reveal that it has tarnished (a layer of oxide build-up) and as it oxidises it swells. That swelling will prize-open a very small air-hole in the case around the lead wire. And that microscopic hole, vastly bigger than an air molecule will allow the atmosphere to penetrate the inside of the capacitor's body - and conversely, for whatever is in the capacitor to slowly escape. Remember that we said in an earlier post that the capacitor is made of two conductive metal plates. And metals, just like the copper lead wires, corrode. So if there is even the tiniest air leak in the case - and the most likely place is around the lead-out wires, not only with the leads tarnish but the plates too. And given enough time the oxide build-up on the plates will grow towards the opposite plate and bang! The end of the capacitor.

                              From the attached pictures you should be able to identify radial and axial capacitor bodies. Attached are some close-up pictures of the point that the lead-wires actually enter the case. The outer case is a hard material cylinder or box: the ends of the case are open to permit assembly of the capacitor. The final assembly operation is to seal the open ends of the case. In these four examples, a thermosetting liquid has been poured into the open end(s), and this then dries to seal the lead wire. The pictures shows the resulting seal.

                              As we will see later, sealing the case ends with a runny and expensive liquid is the most expensive way of making a quality capacitor. There are far cheaper and faster curing methods in common use ....

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

                              Comment

                              Working...
                              X