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Hackernap help - progress

Discussion in 'd.i.y.' started by chrisn, Jan 24, 2019.

  1. chrisn

    chrisn pfm Member

    https://www.dropbox.com/s/e53u9si2au0j8ir/Input and feedback caps.JPG?dl=0

    This is where I am up to now. The front ends tested ok so I went ahead and built the output stage on one board. I used what I had and bought the rest of the components which were cheap individually but quickly add up!
    Main question is which to use as the input cap? I really wanted to use the BC128 10uf 25v as I have a whole bag I never used. The big grey box is the feedback cap, recycled. I also have x4 mmk 47uk white boxed I could use.
    Second question is, can I use a 40-0-40 front end transformer with a x2 28-0-28 output stage transformer I have? The plan to start is to use a single front end transformer with x2 small homemade cap banks pictured which I know is not ideal but a start.
    Finally I was a bit concerned that some of the Dale resistors were 1/10 watt. Mostly the were kR values but one was 100R is this OK?
    Any help would be appreciated.
  2. Pete MB&D

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

    You should have 2 100R near the drivers.

    It will work with those voltages, it would be better if they where closer.

  3. timH

    timH Senior Moment Member

    I’ve got two mmk 47uf paralleled as feedback capz fitted underneath the board and hot glued , but you could use just one if you don’t want the faff
  4. hacker

    hacker Delicious and nutritious

    The resistors will be fine, no worries.

    As Pete said, it would be nice if the voltages were closer (higher output stage). Ideally you're looking for 42-0-42 and 35-0-35. But what you've got will work.

    BC128 will work just fine for input caps, but it's been so long since I tried them that I can't remember if I liked them or not. If I recall correctly, LesW used to (sill does?) use them for input coupling caps, and if they're good enough for Avondale they're good enough for this. The 47uF MMKs are waaay overkill for input caps. A 10uF tant would be fine, too.

    I never liked the 68uF AVXs you have for feedback - they sounded thin and lacking deep bass to my ears, but of course your mileage may vary. 2x 47uF axial tants are great in this location. Positive ends to ground.
  5. Pete MB&D

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

    +1 on the MMK's I found the big gray ones bass light, they do make good decouplers for the output stages if you have 4.

  6. chrisn

    chrisn pfm Member

    Thanks for the advice:-
    I am sort of reserving the MMKs x4 for trying as decouplers instead of the tall electrolytics next to the output transistors unfitted as yet (those are the decouplers?). Can I switch the input and output transformers separately. Don't know why really apart from less wire (Velleman too).
    Thanks again, Chris
  7. hacker

    hacker Delicious and nutritious

    The MMKs work well for decoupling the output transistors, but after running both 47uF MMKs and 470uF Panasonic FCs for a while, I settled on the FCs. The MMKs have a tight, punchy sound that was amazing for electronica, drum and bass, hip-hop, etc music, but for almost everything else I preferred the FCs because they weren't as lean as the MMKs; there was a bigger, richer presentation that I preferred for my music through my speakers in my house. Try both if you've got 'em, see what you like.

    To make life easier when swapping caps, I suggest soldering a pair of short flying leads (twisted together reasonably tightly) from the PCB to the caps so that you can swap caps easily before making a decision. Then remove the flying leads and permanently install your caps on the PCB. Same for feedback caps and input caps.

    With regard to switching, there isn't an input transformer so I'll assume you mean the front-end transformer. Do you mean to have separate individual power switches for front-end and output stage supplies? No good can come from that, please don't do it. Just wire the transformers up to a nice beefy power switch or a soft start circuit (Avondale sell a couple of models and so do Connexelectronic. I'm sure there are others). Keep wiring simple, use the shortest runs you can, and keep things tightly held together with cable ties - minimize the distance between power cables and their respective grounds.
    337alant and john.luckins like this.
  8. chrisn

    chrisn pfm Member

    Thanks again your help especially for the comment about feedback cap polarity. After much research I think I have finally worked this out correctly. There must be many the wrong way round which may be why non polarised capacitors might sound better. Acoustica.org is not always right.
    Input cap positive to signal in and Feedback cap positive to ground!

    Avondale SSMs seem to offer a good solution for two transformers. Can you point me to a suitable switch for the module?
  9. hacker

    hacker Delicious and nutritious

    Given that the SSM takes the inrush load, this 16A DPST rocker switch fits the bill nicely: https://uk.rs-online.com/web/p/rocker-switches/2789828/

    Note that if you get Avondale's SSM1 it comes with a fuse. If you get the SSM2, it doesn't have a fuse and you'll need to sort that out yourself.
  10. chrisn

    chrisn pfm Member

    I am about ready to switch on and test the R side

    Using Build Manual v1.2 and following it closely (thanks to the author)
    Looks a mess at present
    No soft start, but Velleman DC protection with 10k x2 resistors for the grounds
    https://www.dropbox.com/s/k2wwvjbc1lvmvi8/Hacker test1.JPG?dl=0
    https://www.dropbox.com/s/ym90gyag7q9czg8/Hacker test2.JPG?dl=0
    To take this forward:-
    I am using a decent 40-0-40v from Canterbury for the front end and a lesser quality Talema Nuvotem 35-0-35v for the OP. Hopefully the front end is the most important and the plan is to use the Canterbury to power both FEs. I have a second identical OP transformer and I could use this
    Not sure what is best, my preference would be a 2 channel enclosure. Any thoughts? Any spare Hacker transformers out there?

  11. chrisn

    chrisn pfm Member

    Well, it works on the channel I have completed
    Testing as per build manual points A and B +- 57.5V, D and E +- 55V
    Bias steady at 3.2mV
    Offset is a bit disappointing at 65mV - do I need to look at the transistor matching of TR1 and TR2?
    Plays music through a stunt speaker

    I will complete and test the other board
    Last edited: Apr 11, 2019
  12. martin clark

    martin clark pinko bodger

    65mV isn't anything to worry about; into even a 4ohm speaker, it's 1.0mW
    It cannot damage the speaker: you might like it to be lower, but frankly it's not going to cause any issues at that.

    Get the other channel built, get the lot in a case and running, checked, and in-use.
    And then come back and check the DC offsets once settled, warm, and run for a day or so: see where it has drifted-to longer-term, and then fix what you see - if you think you want to.
  13. chrisn

    chrisn pfm Member

    Left channel tests ok with a better offset of 43mV
    Next step is to decide on wether to go for a quick completion with shared transformers and a single case to see how it sounds
    Or the expensive option with a full set of transformers in two cases
  14. 337alant

    337alant Negatively Biased

    My Hakernap works fine sounds excellent in one case with a shared Canterbury windings dual output transformer
    If you go for the cheeper quicker option for now you will be up and running and you wont be dissapointed and you can also go for the dual mono block amps at a later date

    [​IMG]Hackernap Star by Alan Towell, on Flickr

  15. BowerHinton

    BowerHinton Active Member

    I have some half-finished boards and most of the components from some years ago and thought I would try and finish them. I'd prefer to not invest too much at this stage so my question is can I test the boards with output transformers I already have of 22-0-22 (and then if it works buy the correct size)?

  16. Pete MB&D

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

    Yes, that will work fine.

  17. martin clark

    martin clark pinko bodger

    +1 Yes, you certainly can; bias and set-up advice reamisn exactly the same (as it does not depend on supply voltage); and supply transformer of 20-0-22VAC will yield about 40-45watt output into 8ohm - so still an entirely-useful and likely very nice amp in its own right. Depending on your listening habits and the speakers you have in use, could well be all you need :)
  18. BowerHinton

    BowerHinton Active Member

    Thanks for the advice - I'll press on then.

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