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Excuse for a class A DIY AMP build?

Discussion in 'd.i.y.' started by Dowser, Sep 3, 2019.

  1. Dowser

    Dowser Learning to bodge again..

    I'm probably doing this ass about face... I just bought this for £10 - well, £25, shipping was more expensive (it weighs 14kg without electronics or transformer!). Casualty of a lightening strike apparently. It comes with the cover, binding posts, power inlet and transformer cover;


    I have always fancied trying a really simple DIY class A transistor amp - so which should I choose? I have ESL63s, so would like 15W plus (my current DIY valve hybrid SEs are 18-20W) - any recommendations? So far I quickly reviewed Passlabs, JLH and Hiraga designs - I'd really like it to have as few components as possible (I run SE valve hybrid today, some say I must like distortion :)).

    Many thanks, Richard
  2. john.luckins

    john.luckins pfm Member

    By coincidence I'm in the process of building my first Class A amp, only to use to fill in behind my Hackernap when I upgrade it. I've ordered and built up boards of the DLH Amp over on DIY Audio. It's not a Pass design and relatively new. If you search "DLH Amplifier Trilogy" you will find the thread there. I have spare boards if you want to give it a try as the min order from PCB Way was 10. No exotic components an unusual input stage, no VAS stage and a trimmer to adjust between single ended and push pull. I'm using two boards per channel eventually in bridged mode which will give at least 24W into 8 ohms, but with more than 100W of waste heat!

    I'll post a thread about it here when its up and running later this month. Let me know if you want more details in the mean time.

  3. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Rush cascode eh... you don't see those very often! NAD 3020 anyone...
    New one on me is that there DLH and looks interesting.
  4. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    You're a bit lacking in heatsinking there for any more than 15-20W by the look of it but plenty of space inside so could go the way of the Krell KSA50 and use an internal fan cooled heatsink if wanting more power... so may as well build a KSA50 clone!?
  5. Dowser

    Dowser Learning to bodge again..

    Thanks John, I check the DLH out. Anyone have experience of Hiraga 20W circuit?
  6. Dowser

    Dowser Learning to bodge again..

    Hey Jez - I’d assume the KSA50 is not a minimum component kind of design though?

    Agree on the heatsink area - I tempted to try just 10W, but am concerned my ESL63s would prefer more.
  7. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    No it's not minimum component but not hugely complicated either... much more straightforward than the Hiraga designs though as rigorously matched devices not as important. There's an earlier thread I posted on Hirage "Le Monstre" but I haven't heard the 20W version.
  8. stevec67

    stevec67 pfm Member

    I'm building a JLH 1969, it's on hold while the weather is good and I've been working away but I now find myself back home with the odd drizzly evening. I toyed with some of the more oddball Pass designs, I fancied a Hiraga but Jez's comments have put me off, so I'm plodding on with the JLH because there are PCBs available, it's known good, easy to build, no unobtanium parts or exotic setup, so a novice like me out to be able to pull it off. You're an experienced builder, you can be more ambitious. What do you fancy?
  9. sam_cat

    sam_cat C'est Crounchifique!

    If using fans get something decent, Noctua or similar.. They do a low noise version thats designed to run on 12v, drop it to 7-8v and its inaudible.
  10. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Again not as minimal component as it's possible to get (maybe the Zen, son of Zen etc for that) but the Pass Aleph 3 is a design which I would like to try myself... it got mega rave reviews for the factory version!
  11. James Evans

    James Evans Bedroom Bodger

    Colin Wonfor offers his SECA amps in kit form - might be worth having a look at.
  12. Marra

    Marra pfm Member

    Having built one of Colin's SECA amps I think that far bigger heatsinks would be needed even with fans.
  13. russel

    russel ./_dazed_and_confused

    Here’s one I designed that isn’t that complicated.


    I lucked into to a 2SJ18 for a tenner the other day so I am now looking for another one to make two low power single ended class A amps, most likely spend a small fortune getting the other one, some transformers or inductors as a load for it and then some horn loudspeakers that are sensitive enough to be driven by them but that’s diy for you.
  14. toprepairman

    toprepairman pfm Member

    You could do a copy of the MF A1, as designed by Tim de Paravicini. There are circuit boards available and not too complicated.
  15. stevec67

    stevec67 pfm Member

    They're nice, but I don't think that I would spend time building something that you can easily buy for modest money. For me, if you are going to go to the time and not trivial expense of building something, it needs to be a bit unusual.
  16. Dowser

    Dowser Learning to bodge again..

    Thanks all - lots to research. I’m not an accomplished builder, just an OK bodger- frankly power amps scare me for their ability to destroy everything when something goes wrong :)

    But ai need a winter project, so...
    CJ14 likes this.
  17. russel

    russel ./_dazed_and_confused

    If you are not too sure then a Pass project is a safe bet, quite simple and loads of help available as they are popular, plus Nelson Pass is a respected designer.
  18. sq225917

    sq225917 Bit of this, bit of that

    Winter, class a amp, itll be finished by mid summer....
  19. davidjt

    davidjt pfm Member

    The case layout suggests you need a design with a separate board for each channel: the best Pass design for a beginner imo is the ACA - excellent build guide, great sound, your heatsinks would cope and the ready-made power supply would fit inside the case. But maybe incompatible with ESLs. As noted above, that chassis (great bargain, by the way) won't do 25W of ClassA by itself.

    I've not built anything that requires the output Mosfets to be off-board, which is presumably the other layout option. IIRC there are potential rfi/oscillation issues unless the 'flying leads' are short. Others (Jez, sq?) will know far more about this than I.
  20. sq225917

    sq225917 Bit of this, bit of that

    Flying leads for output devices, nope.
    CJ14 likes this.

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