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Colin Wonfor's SECA amp build

Discussion in 'd.i.y.' started by Marra, Oct 17, 2015.

  1. shoom

    shoom open ears and mind

    And all was well in the end. :rolleyes:


    Biased up to 1.5A

    Just the other one to finish now.:cool:
  2. Marra

    Marra pfm Member

    Thanks for posting pics Shaun I think I might have fitted a few to many components:eek:
  3. shoom

    shoom open ears and mind

    Hi Keith

    The other bits on the side and back of the board are for switching the relay so not needed unless you are going to use it.

    ummmm even the stripped down version had me making with the nubee error but hay ho 3 weeks without a fag and counting.:rolleyes: should have quit after the build.

    the second mono is biasing up as we speak.:cool:
  4. CJ14

    CJ14 Retired

    Spot on GO MAN GO, and quitting smoking is shit hard for me too. :mad:
  5. CJ14

    CJ14 Retired

    Nice work, if it is running warm to the hand try 1.7 - 1.9 Amps
  6. shoom

    shoom open ears and mind

    Hi Colin

    Important things first:D

    Giving up smoking wellllll

    I’ve resorted to one of those new fangled Vaping gizmo’s which is really helping. Makes a good halfway house and very few of the nasties.

    My lungs feel so much better but my head feels worse.

    I’ve been 5 weeks now without a ciggy but I still have those ‘’magic moments’’ of utter confusion.

    Vaping works for me and makes it slightly more comfortable.


    I’m planning to slowly turn the wick up in steps of 10mV so I can monitor the heat.

    Santa is bringing me a pair of 0.19 Heat sinks and some 300x40x4mm copper bars so I’ll be transferring to those after Xmas.:D

    then I'll be playing with some fans to see if things can be pushed further but 1.7 is my first stop just tickling into the sweet zone.

    give me a day or so to warm things up a little and I'll report back.

    those E lines

    I've built more than a few amps/pre/pre,pre in my time but when ever those E lines come up I nearly always reverse at least one.

    they seem so counter intuitive to me.

    the SMD where a breeze BTW but I've had a little practice with other projects.

    any one wondering if the SECA is a good first time build project?

    Well IMHO maybe not the full build but the ready made boards are ideal with just the metal work/wiring to do.

    I know for sure that is possible as Bens (Audiochews) build proved. great work Ben and helpers.
  7. Sovereign

    Sovereign pfm Member

    Fantastic work shoom !!
  8. shoom

    shoom open ears and mind

    Thanks but it's not quite up to the chews builds which are superb.

    I turned the bias up to 1.7A last night just to test the heat thing.

    whilst the temperature @ idle seems to be not much different to 1.5A. With the new PSU the amp actually seems to run cooler in use and that's despite having the PSU’s regs and transistors bolted to the same heat sink. It does run warm but not as hot as the Musical Fidelity A1 (George Forman (sorry Tim hard to resist):D design original 18W version) I used to own.

    I’m also really surprised that adding 200ma of bias had a noticeable effect on the sound which was pretty obvious to my ears. When Colin recommended the tweak up to between 1.7-1.9A TBH I though yep I’ll do that but it can’t make so much difference to the sound can it?

    Well it seems to make a noticeable difference.:D

    Put's it into the sweeeeeet zone:)

    Looks like 1.7- 2.7A is where the real amp (fun) takes over.

    I’ll report back on the sound once things have settled but I’m more than happy.

    Has anyone done a direct comparison with the Iridium? I remember buying a copy of HFW just to read the review. Never did get to hear one but it was well liked and seems to have more than a few things in common with the one4 which looks to be a simplified variant.

    Just curious.:cool:

    Looking forward to the new sinks and spreaders and extra bias current which they will allow.
  9. Marra

    Marra pfm Member

    Good news indeed Shaun:cool:

    I am currently running my basic amp at 1.7A so looking forward to installing the p/s boards which I seem to remember Paul(quickie) saying only dissipate an extra 10 watts.

    Did you need to add a small heatsink to the BD139/140 transistors?
  10. CJ14

    CJ14 Retired

    Yes I have and it is OK as you need no insulators, as the Collectors of the BD's are common to the case or back plate and are connected in the circuit. About 1mm thick 50mm square works well.
  11. shoom

    shoom open ears and mind

    Hi Keith

    yes the PSU Dissipate 10W from what I've read but it's running cooler in use (not idle) that when I had the raw supply and 1.5A.

    at the end of the music session the sinks used to be noticeably warmer than with the PSU fitted. at least that was my recollection (which can be a little hazy right now).

    nope no heatsinks fitted on the BD until 5 mins ago when the scrap box challenge commenced. :eek:

    now yes but I'm going to re-bias just to be sure all is good.

    the new heat sinks are up to my usual cut and slash scruffyness:eek: but seem to be working.

    I did read that they where used but have not noticed them fitted to any of the other builds that I've seen so errrr forgot to fit them..

    so good question Keith.:cool:


    is it worth thermo-coupling Q5-6 just for good measure? tricky in terms of board position but a little heat shrink goes a long way.:)
  12. CJ14

    CJ14 Retired

    "is it worth thermo-coupling Q5-6 just for good measure? tricky in terms of board position but a little heat shrink goes a long way."

    It is, I did and it worked well.
    I also fitted some Cu foil around their plastic bodies no shorting wires, then heat shrinked.
    I also tried matching HFE that was good DC offset was 100uV.

    But all these is OK if this is not your first project, so to make things a KISS I left them off and waited for comment, and yours is the first yipeee.
    Dowser likes this.
  13. shoom

    shoom open ears and mind

    Hi Colin

    Thanks for the info.:cool:

    I have transistors matched for HFE from board to board on all of the 337 and also matched pairs for Q5-6 Q7-8.

    I did wonder about putting a little heat shrink around Q5-6 for just a little more stability.

    I'll do that when I transplant the boards to the larger sinks.:cool:
  14. Marra

    Marra pfm Member

    Thanks for confirming that Colin:cool:

    I knew that I had read it somewhere but couldn't remember on which forum.

    Hopefully I will finish soldering up the p/s boards tomorrow and with any luck tested as well.
  15. shoom

    shoom open ears and mind

    Nice one Keith:)
  16. CJ14

    CJ14 Retired

  17. shoom

    shoom open ears and mind

    Hi Colin

    I've been playing with Your SECA's for a while now but was wondering about the 0.7V sensitivity quoted in one of you previous posts.

    I’ve been using a DCB1 to drive my SECA with my Buffalo DAC which has a DC coupled discrete (almost) OP stage. It has 1.5V OP and TBH I think (to my ears) that the DCB1 has been struggling to drive the SECA’s relatively low IP Impedance.

    So I’ve been experimenting a little.:D

    The Buffalo can deliver quite a punch on its OP (up to 100Ma) and did sound better driving the SECA direct.

    Next I wheeled out my Shunted Ventus Balsie which is set to have gain of around 10db and the same 100ma on its OP.(both the Buffalo and Ventus are capable of driving very low loads)

    It’s sounding really good with my 93db 1W 8ohm PMC with the last (gain and current drive) combination (like really, really good) which seemed to grow the soundstage wider deeper and deliver a bigger punch bass wise.

    I’m wondering what others are using PRE and speaker wise?:)

    I've read your thoughts on Digital but do bear with me. paradise is approaching.:D:D

    I've also found some Black Gate 10uf 50V N series that I'm going to try the next time that I have the bonnet up on the SECA's

    Any news of the new arrivals Keith?:cool:
  18. Marra

    Marra pfm Member

    The boards are fully stuffed apart from the output transistors and 317/337's. I need to drill out a heatsink so that I can test without stripping the amp out.

    It would all have been completed this afternoon but SWMBO was sent home from working feeling unwell so I felt compelled to pamper her:)

    The Blackgates should prove interesting on the input.
  19. shoom

    shoom open ears and mind

    ''It would all have been completed this afternoon but SWMBO was sent home from working feeling unwell so I felt compelled to pamper her''

    Always a good move:cool:
  20. CJ14

    CJ14 Retired

    A wise and a very good move, if you want to eat. But I have no such worries mine left me to join the TQ twats.

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