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ang728

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Posts posted by ang728

  1. Here to bump the thread up.

    Does anybody knows the spec of SRM-007T transformer?

    I am currently working on a SRM-007T repair and the transformer showing signs of leakage on one secondary HV rail. Measured about 160VAC w/o load and showing some magic smokes... also DCR on corrupted rail is lower than normal ones (79ohms vs 50ohms).so I feel theres some insulation breakdown in the sec side.

     

    I ask some workshop to see if they can rewind the transformer.they ask me detail about specs of all the rails.

    from schematics KG kindly provided me.I am sure HV should be two 270VAC ,filament is 12.6V CT (6.3-0-6.3).but I still need:

    AC Voltage on LV side (I assumed  30VAC CT)

    current rating on all secondary side rails

    thanks!

  2. so after some fiddling around , now my CFA3 working perfectly.I replaced all my old stock BC546/556 to newer parts with roughly matching,offset still 40mV w/o Servo but no big difference switching back to 300ohm 

    maybe my problem comes from some crooked old BC parts...? I dunno but fixed anyway lol

    BE3mY9Ll.jpg

    On 5/13/2023 at 1:54 AM, ang728 said:

    Finished building CFA3 Ver1.21 recently.But offset reading seems off ,about 0.8V relative to gnd and 0.2V  after solving oscillating issue ,VO+ to  VO- also high as 0.2V

    and bias went huge bump when switching ss to zf with oscillation on scope.I was quickly solving the problem by pulling 600pf,20pf caps form the mentions in this thread.

    After some wild goose chase then I noticed a slight difference between schematic and board silkscreen.R211,R222,161,R262 value at current mirror is 680ohms but showing 300ohm on PCB.

    now I have about 40mV offset w/o servo at each side with 680ohm resistor,haven't done any further test but I think I can have a good sleep tonight ;)

    Scrolling through the thread and it seems nobody mentioned .Not sure if that's a issue but just a heads up

     

    • Like 2
  3. On 5/13/2023 at 5:47 AM, Pars said:

    There are posts in this thread that discuss some problems between ZF/SS as well. Like this one:

     

    I hate to recommend this, but there might be some posts in the HF thread as well, if you can wade thru the bullshit.

    Yes , I solve this problem from this post , a big help.but still need more fiddling to find out

    and that's why I like HC more than HF 😭

  4. Finished building CFA3 Ver1.21 recently.But offset reading seems off ,about 0.8V relative to gnd and 0.2V  after solving oscillating issue ,VO+ to  VO- also high as 0.2V

    and bias went huge bump when switching ss to zf with oscillation on scope.I was quickly solving the problem by pulling 600pf,20pf caps form the mentions in this thread.

    After some wild goose chase then I noticed a slight difference between schematic and board silkscreen.R211,R222,161,R262 value at current mirror is 680ohms but showing 300ohm on PCB.

    now I have about 40mV offset w/o servo at each side with 680ohm resistor,haven't done any further test but I think I can have a good sleep tonight ;)

    Scrolling through the thread and it seems nobody mentioned .Not sure if that's a issue but just a heads up

    • Like 1
    • Thanks 1
  5. 6 minutes ago, Pars said:

    Wire gauge: I'm wiring up the PSUs to the Carbon boards, but wanted to get an opinion on AWG to use. I had bought a bunch of 22ga teflon jacketed 600V wire from ebay seller skip malley. Since I don't think the HV supplies are sourcing much current, I think this should be fine but want to get any input if you think it is too light of gauge? Usually I've used 18 or 20 for other amps.

    Thanks.

    I used 22AWG before,they worked fine.

  6. 45 minutes ago, simmconn said:

    I'm glad to report that both the GeneSiC G2R1000MT17D and the Microsemi MSC750SMA170B work well on the KGSSHV Carbon. 

     

    But I have different results here 

    do you have other changes on the board like zener diode that KG mentioned ?

  7. On 10/20/2021 at 12:12 PM, johnwmclean said:

     

    I used the C3M0350120D in both the Carbon and GRHV.

    On the bench I tested the amp boards separately and they worked fine along with the GRHV.
    In the final build with 2 amp boards connected there was oscillation which caused all sorts of odd voltages, namely 400V over the outputs and a GRHV + rail that read 8V. Funnily enough I could get the amp working with the capacitive load of a dvm killing the oscillation when probing over the GRHV outputs and I had music.

    I replaced everything back to C2M1000170D and all was stable. To be honest I haven’t done enough testing to know whether the GRHV with the C3M0350120D would be ok in the field or not. But hopefully you can gain some insight from my experience with it.

     

    Some similar experiences here,but microchip MSC750SMA170B instead.

    Was using it on my GRHVs, same issue when PSU was measuring normal under no load (both rail measured around 401V),but dropping to about -180V on B- and B+ also seems a bit off (about 391V) as powering carbon amp which is using now precious C2M100070D.

    Everything back to normal as I swapped microchip SiCs back to C2Ms...

    but I would continue trying any alternative option on GRHV.

     

    • Like 3
  8. contgats !

    6 hours ago, mwl168 said:

    It took 5 months but my Dynahi is making music now.

    This one uses matched 2SK170/2SJ74 in place of the THAT340. PSTA06/56 in place of MPSW06/56. Gain is set at 5 and running 30VDC rails.

    Aside from matching the sands, the most challenging part for me was to figure out how to adjust the amp which I will document in a separate post.The build took a long time for various reasons but was relatively uneventful. It helps that I read this thread back and forth and took notes along the way.

    Many thanks to Kevin and to those that have contributed much valuable and crucial information. 

     

    Dynahi.JPG

     

    • Like 1
  9.  

    2 hours ago, belt250 said:

    Hi everyone, I'm a newbie here :D

    Thank you all for this great project, I just finish my first KSA5 amp, The sound is absolutely crazy good. 

    I use a small case for my ksa5 mainboard. 10k pot.

    To reduce power case depth, I raise the power board and let the transformer under the power board.

    cch0gqI.jpg

    ZTgXHoK.jpg

    hReqRZ8.jpg

    fVaP1FG.jpg

     

     

    nice.

    恭喜台灣 DIYer 再+1名

  10. digging up this thread ...

    has anyone build smd version of ubal and buffer? 

    I built mine ,when firing it up , leds did lit up and  smoked instantly

    picture as attached .not quiet sure whats going on yet.

    31mbsg3.jpg

     

    I use diffinput3smtd and  dbuf3 gerber files to make curcuit boards

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