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Millett "Starving Student" hybrid amp

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  1. hellomoto
    Thanks ArtemF and Beftus!
    Could you just describe a little bit more how to differenciate the pins of the power jack, using the multimeter?
    I also would like to know what would be a good wire setup for the amp: which material, which gauge (inside the amp, not for the link between the amp and the source)? What about that:
    or that:
    About the LED, i already bought the ones describe in the BOM from DIYForums, it show how to put it in the PCB, but not how to put it when you haven't a PCB.

  2. the_equalizer


    That's perfectly normal. When cold, the heaters look like a short circuit to the PSU; which then starts, dumps a bit of current into the heaters and shuts down. It then re-starts, dumps some more current into the heaters and shuts down again.  The tube heaters start increasing their temperature with the current dumps until eventually they no longer look like a short circuit to the PSU which is then able to sustain the required current; so the tubes start glowing and the amp comes on normally.
    As to the increasing turn on time, I'd monitor it for a few days but 30 seconds is really OK.
  3. c12mech
    Thanks for the quick reply.  That's what I thought was going on from reading some of the early posts in this thread.  I just was not sure if it would hurt the PSU. 
    As for the amp itself, it has made a huge difference in the way my DT880's sound.  I can hear peoples conversations in the background during one live performance that I listen to regularly.  I think I'm just going to keep listening to this thing for a while before I decide to upgrade.  I'm thinking Bijou or CK²III, I know they are both completely different animals, but isn't that the fun of diying.  Right now though for the money I don't think the SSMH can be beat.
  4. hellomoto
    Double post error, sorry!
  5. wiisus
    Thanks for the pics!  Those are exactly what I needed.
  6. wiisus
    Just wondering, how difficult would it be to add a S/PDIF-in to this?
  7. FallenAngel Contributor
  8. the_equalizer


    Glad to hear you're enjoying it with your Beyers. I agree, for the money, it's a really great little amp.
  9. c12mech
    I got home tonight and tried to turn on my amp and it does not seem to want to come on.  The PSU cycled for more than 2 minutes and still the tubes did not light up.  I pulled out my dmm and took some measurements.  The PSU reads 48V at the output.  When I plug it into the amp, where I should get 48V I'm getting 5~6V.  At pin 6 on both tubes I get ~3V.  At pin 4 I get 0V. 
    I checked the grounds and they are good.  Nothing is burned and all the other checks with the meter read good.  I'm at a loss here.  Did both mosfets die at the same time?  They are both isolated from the heat sinks and have heat shrink around all the pins.  It worked fine last night and now nothing.  Any help would be appreciated.
  10. ArtemF
    It looks like your power supply units do not like the cold heaters. I mean they do not withstand the
    initial current. There are two solutions: 1) buy a more powerful PSU. 2) Install a switch (or two switches)
    that will allow you first to start one channel, then the second one.
  11. ArtemF
    add-on - if the mosfets die they can do it in two ways: always open and completely burnt when there's no conductivity at all.
    In the second case there will be no load so the PSU voltage will not drop. If we're dealing with the first case then they will
    not act as current limiters and the PSU will not be able to feed the heaters with 48V because of high current.
    Put 1K resistor instead of one of the heaters so you'll be able to check if the problem is in the
    weak PSU that doesn't want to feed two cold heaters.
  12. Beftus
    Connect the LEDs right after the on/off switch like this: 
  13. c12mech

    I'm thinking it is the PSU.  When I turn it on now it does not cycle.  It still reads 48V with no load but only ~5V with a load.  If I pull out one tube and put in a 1K resistor and it works I'll know that is the problem.  I assume that is what you meant by that.  At that point I'll just add a switch inline to start one and then the other.  If that does not work I may just build a power supply for it that can handle the load. 
  14. ArtemF
    that's exactly what I meant. If the PSU can power one channel and if you do the same test for the second channel
    (just to make sure they are identical and there are no surprises to expect) then you know for sure that you need
    either a more powerful PSU or separate power switches for the channels.
  15. the_equalizer

    Wow, that's certainly new. I agree with ArtemF's suggestion about inserting a 1K resistor in series with the tube filament. There are 1A Cisco PSU's out there that might help solve your problem, in case it's the PSU.
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