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Skooby

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  5. Balanced to unbalanced board

    in Do It Yourself

    Posted · Edited by Skooby
    parts updates

    I took a stab at Mouser BOMs for the diamond_buffer and unbal_2_bal SMD boards.  Can someone kindly enough to check and correct the BOMs?  Many thanks!

    **** Edit ****
    The below lists hadd these changes (thanks to mypasswordis!):
    LED from 2V to 1.9V
    300-Ohm LED resistors from 250-Ohm
    0.1uf C2/C3/C7/C8 caps to 0603 package
    10uF C1/C4 to X7R
    Other note: OP27G U1/U2 can be changed to other op-amp
    **************

    Unbal_2_bal SMD
    Mouser #                            Description                                                                                                  Order Qty.
    757-2SC3324BLTE85LF   Bipolar Transistors - BJT Audio Freq Low Audio Freq Low                      7
    757-2SA1312BLTE85LF    Bipolar Transistors - BJT PNP Trans -0.1A LN -120V VCEO                     7
    284-APC1206B1K00N       Thin Film Resistors - SMD 1KOhm 0.1% 1206 25 PPM                             4
    667-ERA-8AEB103V           Thin Film Resistors - SMD 1206 10Kohm 0.1% 25ppm                             12
    667-ERA-8AEB132V           Thin Film Resistors - SMD 1206 1.3Kohm 0.1% 25ppm                            2
    647-UWX1E101MCL1        Aluminum Electrolytic Capacitors - SMD 25volts 100uF 8x5.4 20%        2
    584-OP27GSZ-R                  Precision Amplifiers LOW-NOISE PREC IC 2.8V/uS                                    2
    581-06033C104K4T4A      Multilayer Ceramic Capacitors MLCC - SMD/SMT 25V .1uF X7R             4
    710-885012209028            Multilayer Ceramic Capacitors MLCC - SMD/SMT                                      2
    710-150120SS75000         Standard LEDs - SMD WL-SMCW SMDMono TpVw Waterclr 1206           4
    603-RT1206BRD07300RL Thin Film Resistors - SMD 1/4W 300 ohm .1% 25ppm                                6

    Diamond_buffer SMD

    Mouser #                             Description                                                                                                    Order Qty.
    649-68016-404HLF            Headers & Wire Housings 4POS R/A HDR SnPb                                           1
    279-CPF1206B10RE1        Thin Film Resistors - SMD CPF 1206 10R 0.1% 25PPM 1K RL                   4
    279-CPF1206B24R9E1      Thin Film Resistors - SMD CPF 1206 24R9 0.1% 25PPM 1K RL                 2
    756-PCF1206R-20KBT1     Thin Film Resistors - SMD .125W 20K ohm 0.1% 25ppm                            1
    757-2SC3324BLTE85LF     Bipolar Transistors - BJT Audio Freq Low Audio Freq Low                        4
    757-2SA1312BLTE85LF      Bipolar Transistors - BJT PNP Trans -0.1A LN -120V VCEO                       4
    710-150120SS75000          Standard LEDs - SMD WL-SMCW SMDMono TpVw Waterclr 1206            2
    603-RT1206BRD07300RL   Thin Film Resistors - SMD 1/4W 300 ohm .1% 25ppm                                6

    • Like 1

  9. The Multi Amp aka Dynalo Mk2

    in Do It Yourself

    Posted · Edited by Skooby

    That's one fine soldering work on the QNF chip, sir!  Ruined two boards, getting 3rd and 4th boards for another attempts.  Damnit, this ain't rocket science!

    (*** if you can't get the QFN on.  No sweat, just get the AMB Lab off-board/pre-soldered regulators! ***)

    My problem is getting just the "right amount" of solder on pins and pad.

     

  11. The Multi Amp aka Dynalo Mk2

    in Do It Yourself

    Posted

    I refer a mechanical mean to keep the heatsinks on, easier for serviceability.  I modified mine a bit with an extra heatsink to provide a conductive mean to transfer the heat to the chassis.  The extra heatsink contacts the top plate once it's screwed on.  The BJTs get real hot (John said of 74C sounds right).  Radiative/convective heat transfer via the heatsinks in the small chassis space may not be enough.  Try someway to get the heat to the chassis... 

    inside5.thumb.jpg.d6b82308733864d8876e8d3781475f53.jpg    

    • Like 1

  12. KG Balanced Dynahi build discussion thread

    in Do It Yourself

    Posted · Edited by Skooby

     

    27 minutes ago, gepardcv said:

    AC buzz or hum sounds different from gain-related hiss, at least in my experience. What does your noise sound like? If it's more AC-like, then try to rearrange your wires, as Pars suggested. Sometimes trying to keep AC wires at right angles to all other wiring helps. Also, how did you connect the front panel switch? If you're running AC to the switch and back out into the transformers or PSUs, that might extend the resulting EM field.

    I have had tube amps with the 60Hz buzz due to AC heater and OPT interference.  This is more of gain hiss, pretty sure it's not AC hum. 

    I will have to move the 32VAC wires to the GRLV boards away from the signal wires.  Right now, the heatsinks are at 42-47C after 30-min on (nominal from what I've read?).

    Thanks Dr. KG and Steve for setting up the GB!       

     

  13. KG Balanced Dynahi build discussion thread

    in Do It Yourself

    Posted

    Got 0.75V bias with strapped 500R parallel to 1K to get a new floor of 200R; 5-min job...

    1 hour ago, Pars said:

    Having the transformer(s) that close to the audio boards/pot probably isn't helping your noise floor at all. AC wiring also appears to be right over the input wiring to the left side of the pic.

    Two chassis was my initial plan; however, a simple single chassis with small footprint/stack would be nice.  I did try the amp out with the trafos off the chassis (a foot or so away).  No noticeable improvement on the noise floor with trafos on-board.  

    Yes, the AC/signal wiring is sloppy (so excited to get the thing humming into life).  Will  have to clean-up the wiring...:D      

    • Like 1

  14. KG Balanced Dynahi build discussion thread

    in Do It Yourself

    Posted

    Good point...didn't think about safety issue; being a cheapass, I was just thought to save some resistors for other projects :)

    The 500R is nestled pretty tight in against the pot and 5K, so 1K is easier to replace/mod with.  Will work out what needs to get lower floor (~200R or so?).

    I'll run it at 0.75V bias; the heat was ok, just warm, not hot.  Though, my heat sink is smaller than yours, so may be keep it low (will test it out and decide).  Yours is so beautiful, mine is so bland and ugly! :(  So jelly...

    inside.thumb.jpg.c1b3d495304ebf4970cd73242906edd4.jpg

     

        

    • Like 1

  15. KG Balanced Dynahi build discussion thread

    in Do It Yourself

    Posted

    Alright, thanks guys for clarifying the high noise floor.  That dual Dynalo/hi combo is a great solution for that problem, nicely thought out!  LCD-3 definitely sounds better on the Dynahi.

    On 4/10/2017 at 11:28 AM, gepardcv said:

    I was thinking of replacing the 500ohm resistors next to the outer trimpots with 300ohm or 390ohm parts (I think they're R1 and R4 on the circuit diagram), since I have both values lying around, and try to get 0.75V bias. Is that a good idea?

    So took on this idea last night, I strapped 750R parallel to R1/500R (300R equiv.) and adjusted RV1, I was able to get the bias up to 0.75V.  The resultant resistance across R1 was about 250R.  Look back at the schematic, the 1K/R50 and R51 are there to keep the resistance from getting below 333R.  So, thinking of shorting R50/51 out;  just have to remember to set RV1/2 to max before power up.  No problem right?           

     

  16. KG Balanced Dynahi build discussion thread

    in Do It Yourself

    Posted

    On 4/10/2017 at 11:28 AM, gepardcv said:

    The highest bias I can manage is just around 0.42V. If I get it higher across one set of devices (the outer four on each side), it plummets to 0V on the other set (the inner eight). 0.42V is the best I managed so they're all the same (give or take a couple mV), with offset hovering at 30mV (I could probably get it lower, but it didn't seem worthwhile trying yet)

    I was thinking of replacing the 500ohm resistors next to the outer trimpots with 300ohm or 390ohm parts (I think they're R1 and R4 on the circuit diagram), since I have both values lying around, and try to get 0.75V bias. Is that a good idea?

    Super build!

    I am having the same problem of biasing my Dynahi (ver1.5).  I can only manage to get one set (inboard or outboard) of transistors to 0.75V but zero for the other; around 0.402V for both sets.  Would like to know a solution to this problem too.

    Also, on low impedance/high sensitive cans (D7K notably), I hear quite a bit of floor noise (running at 0.4V bias).  But no noise for high impedance cans, LCD3/HD800.  The way it is?  MiniDynalo were dead quiet though...   

  18. silver plated copper wire from navships

    in Do It Yourself

    Posted

    I usually search on eBay for MIL-16878 for silver plated wires (same stuffs navships sells).  Some sellers sell bulk rolls (500ft-1000ft) at steep discount prices.  There are spec sheets for MIL-16878 wires somewhere on the web.  There are listed voltage ratings which handy as a reference for HV hookups.  I use this stripper for teflon, works fine even for 16 awg:

    https://www.amazon.com/gp/product/B000IBOP70/    

  21. The Multi Amp aka Dynalo Mk2

    in Do It Yourself

    Posted

    Finally gave up on getting the QFN regulators on the board (even with Amtech flux).  Getting shorts probably due too much solder.  Ordered these instead:

    http://www.ebay.com/itm/TPS7A4700-Ultralow-noise-4-VRMS-low-dropout-linear-regulators-3-5PIN-1-4V-20-5V-/252348749037

    Any chance that we can have gerber files for these boards (positive and negative regulators) for the group buy?  I would like to practice some more but not on the dynalo mini board and ruin more.  

     

  24. The Multi Amp aka Dynalo Mk2

    in Do It Yourself

    Posted

    Thanks Kerry, for the clarification and providing us the board design.

    Any advice on the best way to solder the TI 7A4700?  That thing's tiny, I ruined one board doing this already.  I'm thinking melt some solder first on the pins and then put the chip on.  I got a rework air gun, not sure it's the best way though. 

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