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Millett "Starving Student" hybrid amp

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  1. Wiljen
    If you own a drill press, it is something that can be done at home as really no complex machining is involved, just punching a couple holes for tubes and a couple smaller one for volume knob and connections.
     
  2. drabina
    Anybody made a Starving Student amp with a built-in source (i.e. Raspberry Pi + DAC running volumio)? Few years back, I have built SS amp but it is not being used much because I always forget to either charge my Sansa Clip ZIP or load new music on it. I would like to put Raspberry Pi Zero W with PhatDAC as a source for the amp. Then I can pull all my music from the NAS and control all via phone. I am just not sure what to use for the power supply as the Cisco brick is only 380mA or so. Can't really squeeze much more out of it to power the RPi.
     
  3. Nathan P
    I bet if you used a little switched mode step down converter you could use the Cisco to power both. Remember, the Cisco is running at ~48v (IIRC) * 380mA = 18.24W of power. With an efficient switched dc-dc converter the Rpi would take 5v * 250mA = 1.25W. Should easily be within the power budget once the tubes are warmed up at least.

    The power brick only cares how much wattage it sees, the current rating is at it's output voltage. Since the Rpi runs at a much lower voltage if you're smart about it it shouldn't be an issue.

    If you tried to use a linear regulator to do the voltage drop, yeah you'd have a problem. But modern switched regs can be extremely efficient.
     
    Last edited: May 3, 2018
  4. drabina
    Would something like that work?
    https://www.ebay.com/itm/DC-DC-Buck...988244?hash=item2cd3717194:g:3vkAAOSwuxFYyQyb

    I guess with the step down converter, I can move the two LEDs that light up the tubes from the 48V to 5V.
     
  5. Nathan P
    That looks reasonable. Buck converters are generally efficient, they're a type of switching power supply. I was looking into DC-DC switchmode regs on Digikey/mouser. You might find one that's monolithic (a single part) that's preset to 5v output.
     
  6. viivo
    I'm really interested in this and have been wanting to take on a DIY project. Would it pair well with low impedence and high sensitivity/high power handling headphones? Also, it seems some of the parts have increased in price over the years - a preliminary list I put together has the cost over $75 and that doesn't include buttons and connectors.
     
  7. Wiljen
    Your cost figures sound about right unless you are building an 19j6 variety and then a pair of tubes may cost you something ridiculous as they have become very scarce. The 12Au7 variant is much more realistic these days as tubes are cheap and plentiful. If memory serves, the original design with the 19J6 tubes had an output impedance of roughly 3 ohm so using the standard rule of thumb would be best suited for headphones above 24 Ohm. So if by low impedance you mean 32 or 50 ohm designs, you should be fine, if you mean 16 ohm it might be a bit on the low side for optimal performance.
     
  8. drabina
  9. Nathan P
    That's exactly the type of thing I was thinking of.
     
  10. tomb
    There will be another round of Starving Student kits available in about a month on beezar.com. This includes the Dsavitsk-designed PCB and custom-machined Hammond case. As before, they will be based on the original 19J6 tubes. I have enough for about 40 kits. Details on the SSMH kit and how to build it are in my signature below and on the SSMH website.
     
  11. JImmye00
    Tom, will there be an option to buy only the case?
     
  12. tomb
    Probably not initially, but it will depend on how things go. Everything is predicated on the number of tubes. I have 90 tested, but some will still end up bad in the long run or microphonic. I will try to replace them for a customer if that happens. So, if I end up with less tubes, then there will be some cases left over.
     
  13. Wiljen
    Will you have a kit of the necessary parts for those wanting to build the 12au7 variant to go with the package? Not a ton of changes, but would be nice to see it all in one place rather than having to hunt them down.
     
  14. tomb
    The 19J6 is a 7-pin tube, whereas the 12AU7 is 9-pin. Unfortunately, when considering tube sockets and PCB-based circuitry, that's about as big a change as it can get. So no, there will be no provisions for 9-pin tubes.
     
  15. WhiteSpyder
    I've actually been thinking about offering a pcb and/or parts kit for a 12au7 SSMH for well over a year now. Offering a full kit including the enclosure would get costly because of shipping and the initial cost for ready-made enclosures, but a parts kit with international shipping would definitely be possible if there's demand for it. Making a custom enclosure is part of the project for many anyway. I'd be able to include some new production tubes too. My pcb design includes a power input tweak to make the amp more compatible with different switch mode power supplies as well as built-in optional tube leds.

    I know myself how great it is to build something from a good kit without having to worry about the pcb or getting all parts so I'll make it happen if there's enough interest in it!
     
    Last edited: Jun 7, 2018
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