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Millett "Starving Student" hybrid amp

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  1. Entropy1
    Unfortunately I'm still having issues. The pin on the volume pot actually didn't change anything to my surprise. Would it be bad to check voltages to the tubes when it's running? Someone mentioned that one of the tubes wasn't getting the same voltage as the other. Other than that I don't know what could be the problem as I've checked the resistances in both channels everywhere but each yields different results.
     
  2. UKToecutter
    Quote:

    Originally Posted by Dunceiam /img/forum/go_quote.gif
    Still having trouble with the SSMH P2P I'm building,

    Symptoms:

    One tube lights up as expected, the other is VERY dim.
    Zero audio coming out of the amp. Not even crackling.
    When you flick the switch, the LED flashes three times at the same rate in this video. But then stops, and the tube's begin to glow after it stops.

    I've been checking and reflowing all the connections, the MOSFET's do indeed heat up now that I've used the Bergquist pads/mounting kit.

    Any ideas? (Old, but largely the same) photos are here.
    http://www.head-fi.org/forums/f6/mil...ml#post6380448

    Thanks!

    Also, is this the correct pin placement for the pot? With the shaft pointing away from you, pins pointing down, the left row is ground, middle row is input, right row is the output?




    Looking from behind the pot the right hand pins are ground.

    The initial flashing is the PS collapsing. That should settle after some seconds.

    There is a mod (mentioned earlier in this thread) that resolves that issue
     
  3. UKToecutter
    .
     
  4. UKToecutter
  5. Dunceiam
    Quote:

    Originally Posted by UKToecutter /img/forum/go_quote.gif
    I think the mod was increasing C1 to 680uF 63V

    Have a look at http://www.diyforums.org/SSMH/schema...origPCB-sm.gif




    C1 already is 680uF 63v [​IMG]. However, if it's not harmful at all to the PSU, I kind of like it's effect.
     
  6. UKToecutter
    Dunceiam,

    Sorry if I missed it, but are you using the 'standard' Cisco 48V PS?
     
  7. skkhai
    Quote:

    Originally Posted by iPoodz /img/forum/go_quote.gif
    How pretty! Are those white or blue LEDs?



    Those are white LEDs, guess my camera's white balance was a little off.
     
  8. Dunceiam
    Using the exact one in the BOM.
     
  9. getllamasfast
    Pics of my second 12AU7 build:

    I did this one on this radioshack board.

    [​IMG]

    [​IMG]

    [​IMG]

    ^ the tubes are actually a little brighter than they seem in this pic ^
     
  10. Narwhalius
    I went back and checked my soldering joints on the inputs and everything looked good. Turned the amp on when it wasn't fully in the case and I was getting sound out of both ears. Then I put the amp back in completely and was back to just the right ear getting sound. Took it completely apart again and touched every joint on the bottom and now I'm getting very little sound out of the left ear and full sound out of the right ear. Any ideas?
     
  11. tomb
    Quote:

    Originally Posted by Narwhalius /img/forum/go_quote.gif
    I went back and checked my soldering joints on the inputs and everything looked good. Turned the amp on when it wasn't fully in the case and I was getting sound out of both ears. Then I put the amp back in completely and was back to just the right ear getting sound. Took it completely apart again and touched every joint on the bottom and now I'm getting very little sound out of the left ear and full sound out of the right ear. Any ideas?



    These things happen when you assemble a case and then disassemble. It's all because of the wire leads. They get torqued or twisted, which puts stress on the connections or terminal blocks. A dodgey solder joint gives way, or a partially cut lead becomes fully broken.

    First thing I'd look at would the be the terminal blocks. Make certain the screws are all tight and are clamped down on good wire. After repeated tightening, you can compress the wire ends so much that the screw is no longer able to grip them. At the very least, a little wiggling back and forth - which will happen when wire is folded into and out of a case under pressure - and the screws will start to loosen.[​IMG]
     
  12. Narwhalius
    I tried some configurations with the terminal block. Switched the wire that I had in the right spot with the wire I had in the left spot thinking maybe the left wire is faulty but I got no sound from either channel EDIT: I get no sound from the left channel. So the left spot doesn't work even with the wire from the right spot which I know works. So something with my left spot is wrong? Also I'm hearing a beeping noise, very faint, and constant. Idk if its my computer or what.

    EDIT: Made some changes to clarifiy
     
  13. the_equalizer
    Quote:

    Originally Posted by getllamasfast /img/forum/go_quote.gif
    Pics of my second 12AU7 build:

    I did this one on this radioshack board.
    <snip>

    ^ the tubes are actually a little brighter than they seem in this pic ^




    Beautiful pics my friend ! Nice to see another 12AU7 build [​IMG] So, did you solve the noise issue you were having?

    cheers!
     
  14. the_equalizer
    Hello all,

    Some months ago, I posted in this thread about a 'drawing board' version of the SSMH using a 30 volt HP printer supply and 12AE6 tubes. Today I finally got around to building the circuit and can happily report that it works [​IMG]. I'm listening to it as I type and it sounds wonderful. [​IMG]

    My original idea was to use the C2175A HP printer supply, since a friend in the US told me they were cheap and plentiful (and it uses the same connector as the Cisco 48 V supply). Unfortunately I couldn't manage to get a hold of one where I live and I was forced to use my own HP printer supply which provides 32 volts @ 350 mA and would be good to build the prototype in spite of it's weird proprietary connector.

    Back in october I drew a load line for the 12AE6 with a 22 Kohm plate load and a 2 Kohm cathode resistor. According to my calculations these values would result in a quiescent point of 20 v plate voltage and .42 mA plate current.

    Considering what Dsavitsk posted about load line drawing (try to choose a plate resistor that halves the supply voltage) today I redid the load line and the calculations resulted in 35 Kohm plate load resistor and 1.6 Kohm cathode resistor. These values would yield a 15 v plate voltage @ .42 mA plate current. Looking in my parts box I only managed to find 33 Kohms and 1.7 Kohms which I figured would do for the purposes of the prototype.

    This is the first time I've actually 'designed' a common cathode triode amplifier of any kind and so the quiescent current I chose could probably be considered far from optimal for the 12AE6. I kindly ask the help of more experienced electronic designers here to choose a better quiescent current if that is the case.

    The values measured in the actual circuit are 10 volts plate to cathode and -.97 volts grid to ground, which considering a 1784 ohm resistor results in a .54 mA plate current. The value for the plate voltage baffles me a bit... tube variance maybe ?... I guess using a 27 Kohm plate resistor would be a good idea.

    So summarizing the only component changes in my prototype were R5, R11 = 1.7 Kohms, 12AE6 tubes and the HP 30 volts supply!! Incredible how adaptable this elegantly simple circuit is.

    As with the 12AU7 version, please note that the 12AE6 while using the same 7-pin mini tube socket as the 19J6, has a different pinout. You must change the socket wiring accordingly. You can find the 12AE6 pinout in its datasheet.


    Some pics now [​IMG]

    Going through the parts box
    [​IMG]


    Proto-board wiring, one channel done, one to go
    [​IMG]


    First time turn-on. The heaters took about 30 seconds to start glowing... but to me it felt like half an hour!!
    [​IMG]


    After measuring DC offset at the inputs and outputs, (0 v at the input, 4~5 mV at the outputs); ready to plug the cheap earbuds and listen to Yes' "Drama"
    [​IMG]

    The weird HP printer supply connector.
    [​IMG]


    cheers!
     
  15. iPoodz
    Excellent work, equalizer! I don't understand all the details, but it's great that you are able to adapt the amp to whatever parts are available to you. I jumped on the kit because I don't think I'd be able to do that [​IMG]

    getllamasfast, what case are you using? Did you get the holes precut?
     
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