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Switching power supply for audio amp query

Discussion in 'Electronics & Electrics' started by Nick the Knife, Mar 9, 2022.

  1. Nick the Knife

    Nick the Knife Member

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    Hi All,
    Recently had my amplifier die - and due to limited finances I thought I'd replace it on the cheap with a well regarded entry level D class amp, an Aiyima A07. Was much cheaper delivered without the factory supply - and oddly the makers RECOMMENDED buyers get a 48v@7.5A supply instead of the 32v@5A one they would have supplied.

    So figured this was a win-win - and I sourced a local 48v@7.5A switching power supply - it's near identical to this.

    I don't pretend to be an expert with electrical componentry - so hoped I could get some feedback on a few (I am sure stupid) questions:

    1) I will have both the amp and the finished/wired up PSU in a home theatre type cabinet - should the PSU be placed within a plastic 'hobby box' or similar or is it perfectly fine to have it sitting as it is (bare metal and wires)? Thankfully it's a childfree home - but just wondered would best practice would be?

    2) Should I ensure that a ferric bead/ring is placed on the power input into the device just before the DC barrel adapter?

    3) I'm going to cut up an old 'kettle' cord or similar for the AC to the PSU - for the DC output is there any particular sized 2 core cable I should use?

    Thank you in advance for your assistance. :)
    PS> FWIW I believe the amp has a 5.5/2.5mm barrel DC input - so figured on grabbing one of these from Jaycar and soldering that on to the DC input wire.
     
    Last edited: Mar 9, 2022
  2. HSV_Enigma

    HSV_Enigma Member

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    1) You should make an effort to shield the terminals so that no one can accident pick it up and come in contact with terminals, a piece of perspex shaped and well attached to it will work
    2) You can, see how you go with noise
    3) Make sure the earth actually has continuity to the chassis of the PSU when connected. Use the biggest cable you can reasonably fit into the barrel jack and keep the run short, it'll be fine.
     
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  3. ernie

    ernie Member

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    The earth is the most important thing. Test it with a multi-meter to make sure the case is well earthed.
    The switching frequency should be ultrasonic. If you think there is switching noise getting to the amplifier and causing some sort of distortion, you will need to borrow an oscilloscope to verify it. It would surprise me if the amp didn't have some sort of DC input filter.

    You won't need special cable for the DC just cut up an old computer power cord.

    Those power supply fans are noisy, that might be a problem.

    - Ernie.
     
    Last edited: Mar 10, 2022
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  4. OP
    OP
    Nick the Knife

    Nick the Knife Member

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    Thanks for the replies - wired up the AC input part of it yesterday, pretty straight forward. Read that while the amp puts out most power with 48v input folks perceive it a tad happier with lower voltage input - so used the variable voltage screw and dialed it back to 32v - tested with multimeter to confirm this.

    Just addressing the great replies to those questions:
    - yes it has a flip up-down clear perspex cover over the top of the terminals, I've screwed the N,L +Earth wires in after adding 'spade' type clips onto the end of them. You'd have to make a real effort to put something in there now but still might put either some tape around these or just get some spare tupperware and mod into a ghetto box for it - will be out of site so looks not hugely important to me (within reason).

    - I will go and find a tutorial on how to check the earthing via a multimeter

    - good idea on the PSU fan - I don't plan to crank it for long periods so might disconnect this now or down the line, seems a 50mm yumcha and I am sure it's quite loud though didn't come on in very limited testing yesterday.

    FWIW I also did some very minor mods on the amp. Surprisingly well made, quite thick aluminium case around it - I opened it and drilled some holes in the bottom of the case (for cool air to enter) and then holes in the top of the case, above where it has a large internal heatsink for heat to exit the case. I also cut some small rectangles of a silicon baking mat and placed these in between the large heatsink and multiple capacitors that are either side of it. They are very close and on one side they were literally touching the heatsink - I didn't think this was a good thing, the silicon seemed the safest insulating material to use.
     
  5. OP
    OP
    Nick the Knife

    Nick the Knife Member

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    Hmmmmm sorry to ask but I've checked a bunch of searches and I can't find a proper guide/info on earth testing a PSU via a multimeter. If anyone could advise or point me in the right direction I'd appreciate it - thanks in advance.
     
  6. Supplanter

    Supplanter Member

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    Measure the resistance between the earth pin on the power plug and the metal case of the power supply. It should be close to 0 ohms.
     
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  7. OP
    OP
    Nick the Knife

    Nick the Knife Member

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    Thank you for that. As you stated I set the multimeter to the resistance mode - used the 200 and 2k sub-settings of this. Connect the leads to the earth pin of the PSU;s AC input power lead - and to the aluminium case of the PSU - read 0 on 2k, very close to it on 200. So based on whats stated that should be correctly earthed.

    Much thanks - glad for the assistacne in doing that check.
     
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  8. darkanjel

    darkanjel Member

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    Plug replacement must be done by a suitably qualified person under the Electricity Safety Act (NSW link), e.g. a qualified electrician, someone who has completed a certified plug replacement course, etc. Risk of huge fines, fire and death etc.
     
  9. HSV_Enigma

    HSV_Enigma Member

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    The act you linked is listed as historical and has no mention of 'suitably qualified', got a supporting link?
     
  10. Technics

    Technics Member

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    It usually refers to a competent person. Except in Queensland where we're all quite rightly assumed to be incompetent. In some ways that competency is a bit like the swimming test for witches. If you electrocute someone then you definitely weren't competent. Ideally you should be trained and/or experienced.

    In terms of the power supply. There are many IEC standard (with corresponding AS/NS standard) including the 60335* series of standards and many others. Some of the standards outline how to perform tests for isolation using special probes that are designed to be like a small child's finger. Given you probably don't have access to the standards, experience or equipment to carry out the battery of tests involved (or the capital sitting around to invest in having someone else do it) you should probably err on the side of caution and enclose that supply. The other aspects of the standards consider safety in both normal operating and fault conditions. As is, even with the terminal cover the bare wire running out of the screw terminal aren't double insulated or in an earthed enclosure are they. The site you linked to shows it wired up without an earth and given it doesn't seem to be double insulated you probably don't want to use that as an example of the gold standard when it comes to electrical safety. You need to satisfy yourself that is is safe and you can never be sure who will visit your home in future.
     
  11. OP
    OP
    Nick the Knife

    Nick the Knife Member

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    Yes, technically you're likely right - that said like many things in life I prefer to apply a little common sense rather than blindly following whatever legislation is in place - especially where it pertains exclusively to within my own home.

    I don't want to go offtopic - but I do wish we were a bit more like NZ, where folks can do such things themselves legally. So your point is noted but is moot to me. :-/

    I never said I was using an image of the PSU as the 'gold standard of electrical safety' - why make such silly comments? If I felt that was the case I'd not have been posting here to seek guidance of persons who I knew were far more learned.

    With all due respect, I know EXACTLY who comes into my home - so again you're making a huge assumption - not really sure why.
     
    Last edited: Mar 11, 2022
  12. JSmithDTV

    JSmithDTV Member

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    Isn't that a bit high on the current? I thought the recommended higher voltage supply for the Aiyima A07 is 48V@3A.

    If you're confident, aware of mitigating risk and happy doing these things DIY, go for it. This is a great DIY forum if it helps at all;

    https://www.diyaudio.com/community/ :)



    JSmith
     
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  13. OP
    OP
    Nick the Knife

    Nick the Knife Member

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    Hi,
    See the original factory link I provided in the OP - as it states: "Recommended power supply:DC48V 7.5A Power Supply "

    As mentioned I read on I think Audio Scienece Review forums that folks felt the sound was better at lower voltage - hence I dialed the PSU back to 32V at present - amazed these have such a range on them.

    Appreciate the link - thank you. :)
     
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  14. Technics

    Technics Member

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    You did mention two core cable in the original post. It wasn't intended to suggest you did consider it the gold standard but was simply a comment on how bad the source material was as an example.

    Because you can't be sure you won't be incapacitated or many other possible events (or changes of circumstance) that could happen, even if unlikely. It's not really an assumption.
     
    Last edited: Mar 11, 2022
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  15. HSV_Enigma

    HSV_Enigma Member

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    Having a higher current supply is better, it will only draw whats it needs.
     
  16. darkanjel

    darkanjel Member

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    You're right, dug myself a rabbit hole. That Act was superseded and consolidated with others into the Gas and Electricity (Consumer Safety) Act 2017. Major changes were made between 2003 and 2017 as it became consumer-oriented around the marketplace, however DIY for personal use is not a marketplace. Within the Gas and Electricity Act, you'll find links to the Work Health and Safety Act (and Regulations). You'll find that the Act links itself synonymously with the applicable AU/NZS Standards (as opposed to NZ).

    Fair Trading regulates electrician licensing and electrical articles sold in NSW. They do state that "Every householder in NSW is legally obliged to keep their home safe, including the way it uses electricity.". They might be referencing duty of care. Generally, duty of care is applicable to everyone under the Civil Liability Act.

    Regarding electrical work:
    "Electrical wiring" is explicit, you must be licensed (electrician or limited). Plugs don't fall into this definition.
    "Electrical articles" are all based on the marketplace; you can't sell/dispose (as in asset dispose, like gift, trade, sell) import (for sale) or hire them unless they are approved.

    What is "suitably qualified"?
    For electrical wiring:
    Under Gas and Electricity, competent person means:
    (a) for electrical work on energised electrical equipment or energised electrical installations (other than testing referred to in clauses 150 and 165)—a person who is authorised under the Home Building Act 1989 to do electrical wiring work.
    Under the Home Building Act Part 2 Division 2, you'll find who is "competent" to do electrical wiring work.

    For electrical articles:
    The Standards might contain definitions, but I can't access them (paywall). OHSRep.org.au cites that under AS/NZS 3760 (In-Service Safety Inspection and Testing of Electrical Equipment), a competent person is defined as someone who: "has the necessary practical and theoretical skills, acquired through training, qualification, experience or a combination of these, to correctly undertake the required tasks".

    From an AQTF perspective, the training competency looks like: UEERL0001. Therefore if one can RPL the competency, one is likely to be deemed competent.

    Non-exhaustive list of AS/NZS Standards that may be applicable:
    3100 Approval and test specification - General requirements for electrical equipment
    3112 Approval and test specification - Plugs and socket-outlets
    3350 Safety of household and similar electrical appliances
    3760 In-Service Safety Inspection and Testing of Electrical Equipment
    3820 Essential safety requirements for low voltage electrical equipment
    4417 Marking of electrical products to indicate compliance with regulations
    60335.1 Household and similar electrical appliances – Safety

    Therefore:
    • If you work from home, have an office at home, are an employer/self-employed, or do anything commercial at home such as renting out, then you would automatically fall under WHS (duty, compliance) or applicable tenancy Acts.
    • If you dispose of the article, you fall under Gas and Electricity.
    • If any of the applicable Standards mentions who can (or cannot) make repairs/modifications and/or how, that would axiomatically apply.
    • If none of the above apply, duty of care still applies.
    In sum, is it explicit that one cannot replace the (240v) plug without qualifications/experience? Doesn't seem so, unless it says so in any of the applicable Standards. Would then need to cross-reference whether the Standards mean for sale or generically, i.e. in normal use. It is only implicit, for example, duty of care.

    Funny enough, this also means every single used PSU sold here is subject to the (relevant state) law, and requires either a test tag or label not to connect (when sold by someone in NSW).

    The adapter above would fall under declared articles, but presumably importing for personal use only so naturally exempt (again, unless Standards say otherwise).
     
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  17. Technics

    Technics Member

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    I would consider commissioning a piece of equipment to be quite a different scenario to replacing a plug. Simply because the plug can be replaced in such a way as to closely approximate the original, presumably tested design. Fitting a lead to the PSU may not be illegal in some states. But it would not be considered safe according to the relevant standards (nor in my opinion) to operate the PSU without an earthed enclosure and/or a way to prevent contact with the terminals or the part of the flex where the outer jacket was removed (being able to touch the single layer of insulation on the inner conductors is not considered safe). The legal requirement to meet the standards may or may not be there but it would fall under duty of care as you mentioned in any case. I'd wouldn't want to be the one arguing that I'd met my duty of care with a device that clearly didn't meet the relevant standards in the event of an accident.

    I have actually seen these type of supplies used with a 3D printed cover/IEC C14 socket arrangement over the terminals. It prevented any possibility of contact with the wiring or the terminals. I can't unequivocally state that it would meet the relevant standards or guarantee it would be safe in any given circumstance but it's certainly looks better then just running a cutting the end off of kettle cord in and screwing in the bare ends.

    Edit: Found an example https://www.thingiverse.com/thing:3884166
     
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  18. HSV_Enigma

    HSV_Enigma Member

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    Pretty much sums up my understanding, anything that is sold, commerical or forms part of a fixed installation (that includes downlight replacement Bunnings staff) requires someone suitably qualified, for fixed wiring thats an electrician.
     
  19. darkanjel

    darkanjel Member

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    The question would be, is it manufacturing? Particularly if it isn't for resale/distribution. Broadly, manufacturing generally means large-scale.

    Same, but that is our personal risk tolerance given our scenarios.

    The domestic importer or seller is responsible to ensuring it complies with Australian Standards (if it will be "disposed"). If it has gone through the process, it will have an RCM marking on it (triangle + tick). Anyone can check the registration status via ERAC. This unit only has a CE marking, which for Europe and not accepted here.

    It doesn't meet Standards unless it goes through the process, which includes lab testing, certification, application fees and markings applied.
    It probably would be able to meet Standards, if someone bothered and paid for the process.

    That is, the Standards include conforming to safety PLUS an Australian bureaucratic process. The product probably conforms to safety since it is CE certified. One can personally import it and use it, but cannot dispose of it.

    As a practical outcome of this research, I was able to call out a power supply in some gear I just bought. Has CE markings but no RCM, which is our requirement. I think it'll be an interesting response...

    Just to be clear:
    1. That was NSW focused. QLD is definitely slightly different. SA from memory is aligned with VIC/WA/TAS.
    2. Instead of "sold", think of it as "asset dispose", which includes sell, trade, gift, donate, etc, but not destruction, recycle, etc.
    3. Pandemic means many had to work from home, which means automatic catch of higher duty.
     
  20. darkanjel

    darkanjel Member

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    If you like finding exceptions to the rules... RCM marking isn't the be-all of certification.

    The Standards can be pretty complex. Personally, I'd source fit-for-purpose power supplies locally. I would delegate responsibility of being competent to somebody else :lol:
     

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