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Hackernap parallel output transistors

Discussion in 'd.i.y.' started by Pete MB&D, Jun 10, 2018.

  1. david ellwood

    david ellwood Kirabosi Kognoscente

    For each doubling of output devices you halve the output impedance, its kind of the opposite of bridging.

    So there are benefits by increasing the damping factor.
    bugbear likes this.
  2. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    It could be a more liner part of the curve it certainly looks that way from the data sheet, and Arcs are current hungry beasts I doubled the smoothing caps once and they sounded better afterwards.

  3. timH

    timH Senior Moment Member

    I might give this a go then. On a practical note I can see the need for the extra emitter resister but not sure why we don’t need an extra 100r from base to emitter
  4. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    The 100ohm is from the driver transistors emitters and you only have one (per side)

  5. timH

    timH Senior Moment Member

  6. bugbear

    bugbear pfm Member

    Whilst my Sugden was poorly, I was vaguely looking on eBay for a spare power amp. The Rotel RB-850 looked quite appealing. Very simple, reputed to sound OK, 50 WPC.

    But with the Sugden now working, I stopped looking. (The Sugden has gert big parallel output trannies, BTW).

    But I had downloaded the technical manual for the Rotel.


    [​IMG]parallel by plybench, on Flickr

    A pair of 2SD1047 (with their friends, the 2SB817 on the other side of the 0v rail)


    (datasheet at link)

    The power handling of a single 2SD1047 is 100W (and it's only taking half the waveform) so you (or at least I) might have thought that a single 2SD1047/2SB817 pair would suffice.

    But, no, they've used a parallel pair.

  7. demotivated

    demotivated pfm Member

    4 sources of heat is far more reliable than 2. Power ratings of bipolar transistors are often for bursts of power or at 25C or at low supply voltage etc. It is also easier to turn off a big power BJT that is passing less current. Most turn on easier than they turn off, so the standing current is often a bit signal and temperature dependent.
  8. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

  9. bugbear

    bugbear pfm Member

    100W output? (check)
    Parallel Output devices (Sanken, I think)? (12 off, check)
    Sugden? (check)
    Class A? (check)
    £12,000 for a mono-block? (check)



  10. demotivated

    demotivated pfm Member

    What is ridiculous with the hifi brigade is that the pro audio brigade embraced fan cooling in the 70s. Now admittedly fans in PA amps are probably chosen to be noisy, so you can hear they work, [I have used a few pro amps] but the IT industry has produced plenty of very quiet DC fans which can be run slower and still lose domestic amounts of heat from a power amp.
  11. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    Did some more testing last night, the bass is so much deeper and cleaner its well worth doing.

  12. martin clark

    martin clark pinko bodger

    Quite apart from the SOA issues noted, it's likely that a pair sharing a nominal load current are ach working in an area of greater current-gain (hfe on the datasheet - there's often a graph on a good datasheet) - which means the VAS/driver stage 'sees' less of a load, even though it is now driving two pairs not one. And in addition, the effective base drive input capacitance (which can be really quite large with BJT outputs when a pair is pushed, c.10nF in some circs) is so reduced.

    Together these are a good thing - less open-loop distortion, a hair more forward gain, and so - being a feedback-defined amp - a more accurate output is possible.

    Edit to add: 'if some is good, is more better..?' Not really for amps like this: adding a third pair will be down in the mud, because the big step is going from one to two well-driven output pairs. If your application needs more output current than that - you probably need to re-think the preceeding stage to take advantage of it / or simply put - a 'bigger' amp in the first place.
    bugbear likes this.
  13. timH

    timH Senior Moment Member

    Indeed it is
  14. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    Oooo have you done it?

  15. timH

    timH Senior Moment Member

    Yes indeed. Improvement’s not just in the bass is it. Can’t stop listening to music now - always a good sign - lots of foot tapping too :)
  16. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!


    It makes a surprising difference doesn't it.

    What voltage are you running your output stage at?

    I did mine as I have recycled my 135 clone transformers so 56v on the output stage and its a bit to much for a pair on their own.

  17. timH

    timH Senior Moment Member

    I’m running mine at 50v but I decided to give it a go after you were so positive about it plus all the comments on Les’s NCC300. Well worth it. The SBLs are singing now oh yes
  18. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    It was the NCC300 that spurred me on.

  19. 337alant

    337alant Negatively Biased

    Sounds like a great idea Pete
    I still love my hackernap amp, I used it again recently whilst I was building my NCC300 amps and it never put a foot wrong

  20. hacker

    hacker Delicious and nutritious

    Oh you bunch of bastards, as if I don't already have a big enough backlog of projects waiting for bench time.... :D

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