The Christiansen "DG" 300B Amplifier Build Thread

Discussion in 'DIY (Do-It-Yourself) Discussions' started by sceleratus, May 21, 2013.

  1. sceleratus
    Festool Domino 500 arrived and the music room shelf is complete. Soon l will tackle the amp cabinet.
    I came up with a very unique design based on an iconic shape.  I hope I can pull it off.  It will be wild.
    The room will be painted a different color as well.
  2. sceleratus
    Been gone for a while.
    During which I made a set of Bob Brines M10-A10 Mass Loaded Transmission line speakers using the MarkAudio Alpair 10M driver.
    I am very pleased with how they sound with the 300B.  I built them on a leaf-of-faith and I’m very surprised with the results.  The bass far exceeded my expectations.  Naturally I’m not going around listening to other speakers.  Ignorance is bliss and easy on the wallet.
    Currently building a preamp and phono preamp.
  3. DejanM
    Hi Sceleratus,
    I like very much what you have done here. Using 300B in SET seems to be ultimate solution for a headphone amp. I am trying to read through your posts here but somewhere I've got stuck .... What I am interested is to find out what changes to the original scheme of Damn Good 300B you've made in order to make a headphone amp ? Did you used the original DG PCBs and then did some modifications ?
    I am thinking of going the same path you did but I would like to find out first what I can expect in terms of already existing DG PCBs ... ?
  4. Misterrogers
    Not Sceleratus, but I'm pretty confident he (and Tom, the designer provider of this information) wouldn't mind. I've built the same amp, and Sceleratus and I but implemented the same basic 'LPAD' circuit that Tom provided. I've attached it below. This allows us to switch between speaker taps and headphone out. I've been running mine with Mills resistors, but just yesterday rolled in Path Audio resistors. The mills sounded great, but these PA resistors are ridiculous. Clean, smooth, fast, better macro / micro detail (less phase shift / smear) and better separation. Not cheap, but they're not coming out.
  5. sceleratus

    Hi Dejan,
    Misterrogers is spot on.  Has nothing to do with the PCB.  It's all about the output transformers.  The windings and resistor values you specify to match your headphone and speaker specs.  If you only want to use HP's have the OPT's made to match.  Mine are  Audeze LCD2 and  MTL speakers with Alpair drivers.
    I'm building a case for Misterrogers DG300B. Why?   Cuz I didn't build my case and I wanted to see if I could build a better one.  Unfinished woodworking business.  Being an insufferable show-off here's where it stands.  We are finalizing the top and back plates.  We've also come up with some cool tricks which will be revealed if they actually work. [​IMG]  Gotta update my other thread.
    jh4db536 likes this.
  6. Misterrogers
    ^ What he said :)
    Glad you mentioned the case - didn't want to 'out' your efforts; cause if I was reading this, building this amp, and you weren't making it for me.... I'd be dogging ya! 
  7. DejanM
  8. Misterrogers
    There are a handful of things that can be swapped or upgraded (output resistors / caps come to mind). You don't need to (the amp is well designed, and the BOM is solid), but you can if you want to squeeze more out of it. I went with custom Silk power and output transformers - c-core. Don't have experience with LL2765.
  9. tomchr
    If you use the circuit shown in Post #634, you won't need to change the output transformer either. Just build according to the instructions and you'll be fine.
  10. Heffa
    DejanM - did you build the DG300B using the Lundahl LL2765?

    I'm really interested in building a DG300B for powering my Audeze LCD-2 as well, and beeing Swedish I would like to use the Lundahl OPT if possible. As far as my very limited understanding tells me the LL2765 would work...
  11. tomchr
    As far as I can tell from the data sheet, the LL2765 should work.
  12. Heffa
    Thanks for the feedback Tom!
  13. jh4db536
    Dropping by to give Tom the well deserved praise for designing such a wonderful amp. It fired up on first try and sounds great, worked out perfectly to power my high efficiency system. I configured the amp to run 6DJ8/PCC88 driver tubes, 300b output tubes, mundorf and jantzen superior coupling caps, and electraprint silver output transformers. Driver tubes are Siemens PCC88 and Genalex 300b.

    The speakers are BK20 BLH with 8" F208EZ sigmas. Approx 97dB/w.

    Last edited: Jun 2, 2017
    raybone0566 likes this.
  14. Heffa
    Wow, that looks sweet! :)
  15. jh4db536
    A little more on the 300B build and BK20
    Initial check and biasing
    I think this is possibly understated

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