DIY Power Amplifier Advice Thread

Discussion in 'DIY' started by Vansen, Sep 10, 2017.

  1. Vansen

    Vansen Gear Master (retiring)

    Staff Member Pyrate
    Joined:
    Nov 19, 2016
    Likes Received:
    3,893
    Trophy Points:
    93
    Location:
    Seattle
    Since we don't have a thread dedicated to general DIY power amplifier discussions, I figured I would start one...

    Some time next year, I'm moving back west and I'll be far closer to my father. Following my move, I plan to build a set of speakers and an amp. For the speakers, I'm heavily considering the Nagaoka D-37 mkIII plan that @JK47 and @struggles used. Regardless of whether or not I use Nagaoka D-37 mkIII plan, my speaker requirements will be as follows: minimum of 94.5 dB/w/m, highly resolving at low volume levels, plays nice in a small room (regular den/ bedroom).

    I'm looking for suggestions on DIY amp designs that will play nice with those speaker requirements. I don't have the electrical knowledge to spearhead a project like this on my own, but my father spent most of his career as an electronics R&D engineer, and certainly does. This'll be a nice learning experience for me and will give me solid quality time with my father.

    The basis of what I'm looking for are:

    Low watt output is preferred
    BJT amplification, no FETs
    No coupling capacitors
    20 to 20kHz response: -0.1 db
    2 to >= 45kHz response: -3.01 db
    Constant phase shift over 20-20kHz (provided phase shift is listed)

    ...these specs look a fair bit like the new Vidar out there. Also, banning MOSFETs from the design eliminates Nelson Pass designs.
     
  2. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

    Pyrate
    Joined:
    Sep 28, 2015
    Likes Received:
    4,276
    Trophy Points:
    113
  3. peef

    peef Friend

    Pyrate
    Joined:
    Oct 5, 2015
    Likes Received:
    311
    Trophy Points:
    63
    Location:
    Montreal
    You can build some of NP's designs with BJTs, if you really like. MOSFETs and BJTs and JFETs and tubes are usually interchangeable with a little creativity.

    A Zeus could be fun. If using BJTs in lieu of darlingtons, you probably want to use a CFP or a Darlington to keep the input impedance high. Since you won't need much gain, you can use some step-down on the output transformer and run the active devices at a lower current.
     
  4. Grahad2

    Grahad2 Red eyes from too much anime

    Pyrate
    Joined:
    Jan 26, 2017
    Likes Received:
    1,162
    Trophy Points:
    113
    Location:
    Singapore
  5. JeffYoung

    JeffYoung Friend

    Pyrate
    Joined:
    Apr 11, 2017
    Likes Received:
    714
    Trophy Points:
    93
    Location:
    Ireland
  6. Cspirou

    Cspirou They call me Sparky

    Pyrate
    Joined:
    Sep 27, 2015
    Likes Received:
    8,200
    Trophy Points:
    113
    Location:
    Northwest France
    @Vansen - Are you still looking?

    I believe the SuSy Dynahi is all BJT, no capacitors and can power speakers. There's no real central location for all the information but from what I can piece together it can do 30w Class A per channel. Gain is 20dB which is speaker territory.

    It's a difficult build though and will require large heatsinks and either a separate chassis for the power supply or one huge 4U chassis to contain everything. But it seems like your father is fairly technical and would like something like this.
     
  7. Telstar

    Telstar Bottom 1% of posters on SBAF

    Joined:
    Mar 28, 2018
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Italy
    Let’s add another class A classic, Hiraga Le Monstre. 20 or 25W. Don’t remember anout coupling.

    Btw, if u build a dc-coupled amp it most likely will have a dc servo which has an impact on sound more or less (usually less) than the coupling cap.
     
  8. Cspirou

    Cspirou They call me Sparky

    Pyrate
    Joined:
    Sep 27, 2015
    Likes Received:
    8,200
    Trophy Points:
    113
    Location:
    Northwest France
    Not usually. Most designs have adjustment pots to eliminate DC even without capacitors. For example, the First Watt F5 has no capacitor and no servo.
     
  9. Telstar

    Telstar Bottom 1% of posters on SBAF

    Joined:
    Mar 28, 2018
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Italy
    The modulus cited above has a dc servo.
    I definitely agree with you that without is better. The Op doesn’t want mosfets, but I believe there is a F5 version with bjt somewhere in diyaudio ocean.
     
  10. Priidik

    Priidik MOT: Estelon

    Pyrate BWC
    Joined:
    Sep 27, 2015
    Likes Received:
    2,153
    Trophy Points:
    113
    Location:
    Estonia
    These guidelines are not getting you far in quest for sound quality.
    Output transformers have some phase shift, they are not linear in fr by that spec, no matter how god mode.
    Yet they are still the champ to beat with high eff speakers.
    My point is that these specs suggest almost any high feedback amp with dc servo which can sound terribly dull.
    I had a POS Marantz amp, full bjt design that must have met your quoted requirements.
    It was quite the opposite to good sound.

    With your choice of speakers of >94dB/W I'd concentrate on class A.
    In case of Class A mosfet is not some diabolical creature to be afraid of.
    I takes high competence to design good sounding AB amp with either device,
    so class A is relatively safe for diy experiments, for whichever device type.

    Sometimes for bjt input stage input cap is required and a bjt is imo better choice for this
    (what is Schiit using for input stages? I bet it's all bjt or tube).

    Unless you are really tight on money (or time), I'd try different cheap options out.
    A chip amp, like the Modulus, a few simple Class-As like JLHood and why not this thing.
    Proper SET with OT-s would be my recommendation above all else, but I suggest trying it out first,
    as this is going to cost 10x more than a JLHood.
     
    Last edited: Apr 1, 2018
  11. Telstar

    Telstar Bottom 1% of posters on SBAF

    Joined:
    Mar 28, 2018
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Italy
    Some of those reqs are a bit silly, like the last two:
    "2 to >= 45kHz response: -3.01 db
    Constant phase shift over 20-20kHz"

    To not have phase shifts within audio band -3dB will extend way over 45khz, more like 500khz, which only very few power bjt can achieve.

    The OP needs to experiment with the many options available and understand what he likes and then why.
     
  12. peranders

    peranders New

    Joined:
    May 3, 2018
    Likes Received:
    6
    Trophy Points:
    3
    Location:
    Sweden
    Home Page:
    Is SMD your thing? If yes, then you will have some design to build.
     
  13. Cspirou

    Cspirou They call me Sparky

    Pyrate
    Joined:
    Sep 27, 2015
    Likes Received:
    8,200
    Trophy Points:
    113
    Location:
    Northwest France
    Are you the same Per-Anders from Sjöström Audio?

    http://sjostromaudio.net/
     
  14. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

    Pyrate
    Joined:
    Sep 28, 2015
    Likes Received:
    4,276
    Trophy Points:
    113
    He is.
     
  15. bobboxbody

    bobboxbody Friend

    Pyrate BWC Contributor
    Joined:
    Sep 6, 2016
    Likes Received:
    1,465
    Trophy Points:
    93
    Location:
    GR, MI
    Doesn't fit @Vansen's requirements other than being low watts, but there's a preorder going for the Pass ACA at diyaudiostore. Has anyone heard one of these?
     
  16. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

    Pyrate
    Joined:
    Sep 28, 2015
    Likes Received:
    4,276
    Trophy Points:
    113
    The ACA is a nice (yet expensive) training kit. Pretty sure there are better options.
     
  17. gepardcv

    gepardcv Almost "Made"

    Contributor
    Joined:
    Nov 20, 2015
    Likes Received:
    408
    Trophy Points:
    63
    Location:
    Terra, Sol System
    @Hrodulf: What makes it just a training kit? Low power? I guess I think 20Wpc in class A in dual monoblock configuration isn't shabby — particularly with all the casework already done and reasonably nice.
     
  18. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

    Pyrate
    Joined:
    Sep 28, 2015
    Likes Received:
    4,276
    Trophy Points:
    113
    To quote Pass himself: "Remember, the whole idea is for you first-timers to get your feet wet in the shallow end of the pool. Put on some sun screen, and come on in."

    The distortion figures doesn't seem to promising either. 2W and up goes above 1%, which is high, even for a Pass amp.

    For that kind of money, I'd get a Lindsey-Hood from the East.
     
  19. peranders

    peranders New

    Joined:
    May 3, 2018
    Likes Received:
    6
    Trophy Points:
    3
    Location:
    Sweden
    Home Page:
    Yes :) I noticed also a misspelling. I ment that I have design which the thread starter can build but especially the QRV08 amp needs a very special mindset to build. It takes many hours to solder.
     

Share This Page