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JoaMat

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Posts posted by JoaMat

  4. DIY mini T2 Build Thread

    in Do It Yourself

    Posted

    18 hours ago, yabba235 said:

    Did you run it with lsa389? What did you change in the schematic?

    Have you considered using the SOIC version instead of the TO-71 transistors?

    Not much (nothing) has happened since my post 11 months ago.

    Here is a schematic, original to the left and lsk389 version to the right.
    mini t2 input 6922 vs lsk389_1.jpg
    My idea was to replace 6922 tubes with lsk389 and just make necessary changes and else keep the board unchanged. This is a draft - more work is needed.

    Of course you can use SOIC lsk389, but I prefer TO-71 since I think it fits better in the layout.

  5. finally an electrostatic transportable

    in Do It Yourself

    Posted

    20 hours ago, kevin gilmore said:

    all three power supplies a total of $80.62 with shipping from china.

    fully regulated 12v to 18v input.

    i could not build these things for that price, no way.

    DSC_1055.JPG

    DSC_1057.JPG

    Nice, great news!

     

    Did this in 2019 and it has been in sleep mode since then. Maybe UHV-POWER bricks will wake it up. Power transistors plus a few other components on one side and the rest on the other side.
    Screenshot_35.jpg

  9. and now for something completely different part 3

    in Do It Yourself

    Posted · Edited by JoaMat

    Have had a new bias servo working with my CFA3smd something for a few days. Schematically it looks like this,

    Screenshot_30.jpg

    and the new thing is in red square. Now I get a good reference point to the servos. Don’t understand why I didn’t figure this out earlier – slow brain perhaps. All four servos are fed from the same point. So, one trimmer and full control over the BIAS of all channels.

    Diagram for new servo - 6 minutes from cold.
    Screenshot_29.jpg

    and diagram for old servo (in mA for the first 40 minutes from power on)

    Snapshot_22-09-14_12-51-54.thumb.jpg.c24c02fe9a2f09719b5d264d745b728c.jpg

    Please have in mind that the graph for no servo is for my CFAsmd something. I guess the original CFA3 have a different and better behavior – where all tripple Darlington and vbe transistors are mounted on heat sink.

     

    • Like 6

  10. and now for something completely different part 3

    in Do It Yourself

    Posted

    On 7/17/2024 at 12:13 AM, justin said:

    Last year I ordered a lot of different boards of KG's amps/PSUs and had someone here put them together as a project. One of them was this 6DJ8 hybrid that uses the triple output buffer of the CFA3. Single-ended output only. There was 1 missing trace on the board that prevented it from working, found and fixed that, so possibly nobody had assembled one of these before. Problem is there's a substantial hiss (very easily audible with even sensitive planars, something like 0.3mV rms of 'white noise'. The +100V is coming from a TL783 regulator, tried AC, DC, batteries for heater, different grounding, gate stopper resistors, feedback caps, w/out servo..exhausted a lot of stuff but couldn't get more than a few % improvement on the noise. Anyone have ideas?

     

    th.PDF 51.92 kB · 23 downloads

    gilmore-liquid-legend.jpg

    What dual op amp are you using?

  25. The ultimate DIY? A Stax SRM-T2!

    in Do It Yourself

    Posted

    1 hour ago, jokerman777 said:

    For left channel, output offset are both around -40V, point C and D both measures -3.5V.

    For right channel, output offset are about -4 and -10V, point C and D both measures -0.65V.

    Seems your balance servos are working since C and D have same readings. As for right channel where you have unbalance – investigate the R88 – R91, C8 and C9.

    • Thanks 1
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