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Posts posted by Helium

  1. On 5/3/2024 at 9:57 AM, MLA said:

    Working on a BH at the moment, and given what you found regarding Cob for 2690; do you think it would be worthwhile to use TTC004b instead, or is the difference too small? I guess you may have checked it but discarded it as an option?  

    Seems that KSA1220AYS may also be replaced with TTA004B,Q? The latter also seems better.

  2. Yep, I myself had to scroll this thread again as Im in the process of building one.

    I think the mod is referred to this post:

    But I dont see what resistors were XXohm value in the original design and became 33kohm in the updated design as Im building the latest rev of PS PCB (speaking of original DIY T2).

  3. On 1/8/2011 at 1:50 AM, Craig Sawyers said:

    (1) The power supply mod developed by Kevin and Inu to make it stable

    Can anyone please point this mod for me?

    I can't find it reflected in the (latest?) schematic or PS PCB.

    R14, R29, R41 and R53 resistors are all 2.2k, or am I looking at wrong locations?

  4. 8 hours ago, demonkuro said:

    Thank you for your concern, before connecting the PSU to AMP, I let it work independently for several hours, all the output voltages are right, the drift is very small, and it looks very stable. So I confidently linked it to AMP, but nothing good happened... Just like the carbon I made 8 years ago, the PSU also exploded, and that time I replaced the damaged part and it worked fine. Thanks to your advice, I will go find an insulation tester to test each power supply. I should be more cautious.The PSU was tested today and luckily all worked fine except for -500V and +500V.Waiting for new parts and replace the wire with a higher withstand voltage rating.

    Did you trim snap-in capacitors leads underneath PCB? Seems that PCB is quite low and may be touching bottom cover. Once I made same stupid mistake. Without load PSU was OK, but when I connected amp section, it exploded quite spectacularly.

  5. On 5/14/2023 at 5:01 AM, Satyrnine said:

    Welp after all that work trying to stuff a quad cfa into a 3U, I think I'm going to add a ubaltobaltubeschem2 and grhv100, and go split chassis. Anyone have any ubaltobaltube or grhv100 boards?

    Any specific reason why you would put tube unbal-bal converter in front of CFA? Just to make it as complicated as possible? There will be ~100 more parts in signal path, hardly they will make amplifier sound better.

    • Like 1
  6. I would use different layout.

    Move transformers and grlvs to the front. Move cfa to the rear. Keep DC protection board where it is at the front. Use extension shaft to mount volume pot at the rear close to inputs.

    Side notes: move ac inlet to the left or right, it doesn't have to be on the center, it gives nothing. Stack the upper cfa higher so that transistors are distributed more evenly over heatsinks area. Move inputs closer to center (and to the pot) and move speaker terminals to outer edge of the chassis. Cause your speakers will be placed to the left and right and maybe quite far away from the amp.

    Consider stacking transformers on top of each other, you have 120mm clearance if you don't use steel chassis.

    That way you will have space to mount grlvs horizontally.

    After all I don't think that amp with bjt output transistors is good to drive speakers. I would consider omitting speaker terminals completely.

    • Like 1
  7. 1 hour ago, Satyrnine said:

    I haven’t, thanks for the heads up, definitely the reason I posted here before finalizing/ordering. Thank You! That said, Dukei is the one who suggested it, sounding like it was possible. I’ll touch base with him on those concerns and either redesign or report back with a possible solution. 

    As far as the steel floor chassis add on, this is good to know too. The trafo covers i ordered through antek are nice and beefy and support/clamp to the bottom plate around the edge of the cover as well as via the thicker/wider center support which maybe would prevent/reduce any rigidity related issues vs bare toroid? Def open to the add on support, but prefer not to if possible, if only for aesthetics. Since I’ll be assembling myself I don’t have to worry about shipping with trafos installed at least.

    Well, I myself don't like mounting trafos on aluminum plate. Dissipante comes with 3mm anodized top and bottom plates, mounted with 4 small screws m3. For me this structure is not very good to sustain weight of trafos.

    Moreover, if you use steel chassis to mount everything inside, you can do without any holes in bottom plate (except those for feet).

  8. 4 hours ago, Satyrnine said:

    Almost ready to start building my CFA2/3! 

    • Dual Mono, 2x GRLV, 4x CFA2 boards, and maybe a bal/unbal down the road. I plan to use this with my LCD-2's (orig), and my desk monitors via added speaker outs. I have all the components on hand but the chassis so far.
    • Details: Dissipante 3U chassis. Mounting boards directly to heatsink.
    • 2x Antek 100VA 30V trafos with steel covers
    • MUR820 Ultra Fast diodes on daughterboards vs standard GBU4 package rectifiers for GRLV boards
    • Goldpoint quad/balanced stepped attenuator
    • KG Headphone Protector Board (just had a set made at Oshpark)
    • Options for Bal and SE in
    • Bal and Unbal outs (unbal out only works with se ins in CFA2 mode obv)
    • Dale RN60 resistors throughout, Used Pars's BOM

    Here's what I have drawn up so far for Front/Rear panels I'm having made at Modushop, as well as internal layout plan thus far. Getting panels engraved/machined, with the "CFA" cut deeply at a bevel. Large circle where vol knob is is just a placeholder for the largest possible size knob. Dotted line around headphone/speaker switch is a rear recess since front panel is 10mm thick.


    Many Thanks to the infamous Dukei/Miroslav and Pars for guidance, as well as arteom from diyaudio for generously supplying boards, and of course the man himself for this awesome design.

    I used modushop dissipante quite a few times. I doubt that you will be able to mount boards on side heatsinks this way. Have you accounted for steel support brackets that take up significant area of the heatsinks, and use of steel chassis on the floor? Since you are mounting transformers on the floor it's good practice to use steel chassis (sold separately) to get extra rigidity.

    • Thanks 1
  9. 10 hours ago, johnwmclean said:

    One channel of my latest build has little to no drift at all (no servos installed), which is odd behaviour from my experience.
    After 45 minutes warmup offset and balance can be trimmed to under 1VDC.
    From a cold start everything is now under 1 volt and stays that way. I’m curious as to the reason, do I need fix or leave as is? 

    Wait a minute, are you telling that no drift is something wrong?

    From my experience there is some drift (0.5~1VDC without servo, and ~200mVDC with optoservo installed, both balance and offset), and I wish it wasn't there.

  10. Did anyone experience how vulnerable DN2540N5 are?

    They are damaged so easily that I had to scratch my head.

    E.g. desolder it from a donor known good GRHV, actually new (don't ask why, I had to get spares) and it's detected OK in circuit as N-Ch depletion mosfet.

    I desolder it, test it and BAM it's no longer depletion mosfet, it turns into kind of Voltage regulator. And doesn't work of course. I spoiled 4 pcs already, despite the fact that I know how to desolder and handle components. And only one out of 5 was OK after desoldering.

    • Sad 2
  11. 17 minutes ago, Beefy said:

    Would the phase of the transformer secondary windings be an issue here? There doesn't seem to be anything indicating the start of a winding, both wires of each winding are the same color.

    I know that getting the phase wrong can cause issues when tying windings together to create your own centre tap.

    I checked phase of all windings prior to connecting. Yes, they are not marked, I marked them by myself. And connected both HVs in phase.

    4 minutes ago, jamesmking said:

    can I ask a possibly dumb question, I see the grlv with fully populated + and - sections,

    the board attached to the side wall seems to be a grhv but it only looks like a single rail grhv which would mean its either +400V or -400V i does not look like a dual output board to me..... ???


    Yes, it's single -400 board. The other one (+400) is dismounted ATM and waiting for a part for replacement.

  12. 9 minutes ago, jamesmking said:

    since the grlv and grhv have separate transformer windings they are floating with respect to each other.

    with only one amp being grounded through the grhv that amp board is tied to that psu but would have no idea what the LV voltage is since the LV floating with respect to the hv psu and nto referenced to it. The other amp board being grounded through the LV only would have no idea what the hv voltage is in relation to the lv voltage....

    you would see this by measuring the voltages on one amp board with the multimeter neg on that amps ground and then measure the voltages on the that amp board with the multimeter neg on that amp boards ground.

    Another way to think of it is electricity flows in a circle, for the amp connected to the hv board the electricity comes out of the hv board goes into the amp board and returns to the hv board through the ground wire, The Lv electricity enters the amp board BUT has no return path direct or indirect to the LV board... and visa versa for the amp board connected to the lv ground only....

    This is why I check the psu voltages of a fully built amp at the amp board using the amp boards ground and not at the psu using the psu ground....





    Wait a minute please. I see what you mean.

    Is the transfotmer up to the task? That's most unfortunate if it's not. Is Star ground of everything a cure?

  13. Thank you folks.

    4 hours ago, jamesmking said:

    0. make sure there is continuity between the grounds on the amp boards, hv psu and low voltage psu. HV psu ground -> amp ground       LV psu ground to -> another amp board with no ground connection between the LV and HV boards is not going to work. All 4 pcbs needs to share a common ground.


    2 hours ago, audiostar said:

    This is no good!
    Connect all grounds (LV, HV+, HV-, all amp boards) together to a single (star) point.

    Yes, currently GRLV has no ground connection with HV ground.

    Didn't know that non-tying LV and HV grounds is so critical. Usually it ends up with hum/noise, such sort of things.

    I will fix that and see.

    I the mean time I adjusted CSS with GRLV 15VDC to 18mA, so AMP boards are presumably good. Currently amp is almost done, need to replace DN2540N5 on +400 PS.




  14. I've ran into an issue building Carbon.

    I'm using split PS boards + separate GRLV.

    When I connect PS boards to transformer (without AMP boards) everything is fine, and voltage is +405/-406VDC (bias is a bit low at 563 but that's non-relevant issue and a matter of zener tolerances).

    But as soon as I connect AMP boards, transformer starts to heat up a lot (I didn't risk to leave it connected for more that 15 sec). Maybe it will start melting.

    Here is my connection:

    +400 goes to each AMP's B+ terminal, -400 goes to each AMP's B- terminal (obviously). However GND from each PS from goes to nearest AMP board only and are not tied together or by a sort of star terminal, therefore GNDs are not shorted.

    Am I missing a point here? Should connecting GNDs of each split boards remedy the transformer heating problem?

    Easy to check by yourself, one must say, but one of my DN2540N5 went bad and I cannot check it right now.

    This is my transformer spec (must be plenty of power, so insufficient VA rating must not be a reason?):

    PRI:230V SEC:
    > 2x 330V under load (350mA) (separate windings)
    > 2x 18V under load (500mA) (separate windings)
    - VA rating around 300VA


    • Sad 2
  15. Wow Soviet) A good old wine)

    Correct me if I'm wrong, but like AMP series, thread all the way down to gasket (rarely beautifully looking) implies that the gasket is left outside the panel. I usually like to put connector inside the case (this is low voltage Neutrik Speakon, but same idea).



    • Like 1
  16. On 6/21/2021 at 3:43 PM, starcat said:

    Yeah, they take a long time but are fun to make 🙂 I just completed the umbilical for the BHSE I am building (with original HeadAmp boards) and it took long as well despite using an AMP connector with crimp type pins. To be honest, I liked that connector much more than the Amphenol we use for the T2. It is like cutting wires, crimp pins on both sides and insert into the connector housing and voila. The pins are automatically isolated within the connector housing as well, so no fiddling with shrink tubing or soldering into the connector and the pins are available for different AWG sizes as well. A very nice system. 

    Craig, do you have any part number for that special glass fiber insulation and how long are your umbilicals? I am planning for 90cm, 3ft. 




    Hi starcat. What are P/N of the connectors and housings and pins you are using?

    I'm tempted to try these. As far as my quick search revealed, pins and wire entry seals don't come in bundle and are sold separately, aren't they?

    My concerns is that CPC series seems to be rated for 250VDC/VAC only, and that there is no space between the thread and the gasket, which means that the gasket itself will be outside the panel/case. Any considerations?

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