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Millett "Starving Student" hybrid amp

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  1. JamesL
    Tube microphonics - I have the same problem on one of my tubes.
    Unfortunately, the 19j6 aren't easy to come by.
    I've never had a problem with microphonics traveling up from the desk, but I've used a cloth mousepad under a amplifier before which was very effective at preventing vibrations in my PC-case making its way up to the amp.
    Clamping down part of the cable from your ipod to the amplifier to something solid helps to dampen any microphonics going up that way.  
    I still experience microphonics when touching any part of the case, but I haven't been bothered enough to do something about it yet.

  2. Ikarios
    Are there any good repositories of info for new builds of the SSMH with replacement tubes and PtP wiring? I've been wanting to build a starving student for so long but the lack of availability of the original 19J6 tubes (and thus, kits) has deterred me. I'm not good with schematics and I don't really trust myself to be able to read one without screwing up a connection and having to redo the whole thing. However, I'm itching to build something, and I just remembered I had some Alien DAC boards down in my basement from way back, so I'm thinking about populating those this summer as well. Does someone want to hold my hand through this process? :D
  3. tomb


    I hate to put a hole in your enthusiasm, but the SSMH will blow an Alien DAC if you're not very, very careful.  Search the thread and read the warnings on the SSMH PCB website.[​IMG]
    As for P2P designs with replacement tubes, I put a page that was generously donated by the Equalizer on the SSMH website.  He has supported many design changes using other tubes.  Just reading the last couple of dozen pages in this thread can clue you in to the numerous possibilities.[​IMG]
  4. Ikarios
    Okay, so I spent most of my time at work today reading the last 50 pages of this thread (read: slacking off). From the looks of it, I'll probably be making a 17EW8 variant with the modified 220Kohm bias resistors (which, if I'm not mistaken, results in the heaters glowing a little brighter.... right?). I'm not a very adventurous DIYer and I hated physics, so I'm going to stick as closely to the BOM as possible, with exceptions being made if I can buy a bunch of components at the same place, like beezar. I have a couple extra pots sitting around from my first cmoy (a panny evj-c20 that tangent recommended, and an alps RK097). I can just wire these in without modifications, right?
    also, the possibility of killing some DACs is a little worrying to me. however, if I'm not mistaken, it most likely happens when you touch connections between the DAC and the amp, right? What if I wired an alien or a bantam/grub directly to the SSMH? In that case the only IC I'd be changing would be the USB. Hmm, but now that I think about it, that might not be the best solution...
    is there an inexpensive USB DAC (DIY or otherwise) that will not suffer from this death charge on the SSMH? I have a "hotrodded" X-Fi but I'd rather not connect an amp that is known for killing some DACs to my beloved desktop; I'd also like to keep my speakers connected to the X-Fi and not have to change a bunch of connections every time I want to use the amp.
    Anyway, over the next week or so I'll study the 12AU7 variant schematic and draw it out on paper with components and all just to make sure I understand it. I'll report back soon, hopefully :)
  5. tomb
    There are only a few DACs that the SSMH will potentially kill - those with little to no output protection or buffer.  The AlienDAC, the BantamDAC, and I believe the Gamma 1 apply.  There's not a sound card that I know of that would be vulnerable to the SSMH - neither would almost any DAC that provides a secondary buffer or opamp at its output.
    Where you'd need to be careful is with a DAC design that outputs directly to a voltage signal right from the DAC chip and no additional buffer is used inbetween.
    EDIT: You are correct that it appears the danger occurs if the DAC is connected when the amp is running.  Due to the SSMH Cisco switching power supply, a charge may develop on the RCA jacks.  If you touch the output of the DAC to the RCA jacks when that charge exists, that's when the damage occurs.  Again, most commercial equipment and high-level DACs use extensive output circuitry that insulates the DAC from this scenario.
  6. Ikarios
    Well, in my case, since this will be my only amp (if I get another one it will most likely be a Carrie amp + grub/bantam combo), I will probably leave the DAC connected 24/7. Since the Alien and the Bantam/Grub are the two DACs I'm most interested in, mostly due to cost and simplicity, I think I'll build one or two anyway and just be careful about connecting it while the amp is running.
    EDIT: I'm assuming there's no way to simply "add" the output protection, as the problem lies in the way the circuit is designed, right? If not, is it a simple fix or something?
  7. Beftus
    Fire in the hole! No magic blue smoke. The heatsinks heat up nicely, the 12AU7 tubes too. Uh-oh, I'd better check my work again. I get ~12.5 VDC on the left and right outputs... Aha, forgot to add the last two 2K resistors near the outputs. [​IMG]
    With both resistors added I measure ~3mV DC offset left and right. Plugged in my PX-100's... It works! Woohoo! On top of the 2" tall heatsinks I measure ~50°C (122°F), the IRF510 metal tab clocks in at ~63° (145°F). This thing gets bloody HOT! [​IMG]
    It sounds great already. Plenty of punch, lovely highs. Gotta do some burning in but I really like what I'm hearing. No hum. Veeeery slight hiss, hardly worth mentioning. Touching the aluminium volume knob introduces hum. Should I ground the pot casing to get rid of it?
    I'm a bit disappointed in the tubes: no tube glow as the heaters are enclosed. I might install orange LEDs to light up the tubes. I did prepare the tube sockets for that.
    Specs for the nerds among us (you know what you are):
    1. 4x Panasonic FC 470µF 63V
    2. 2x Panasonic FC 220µF 25V
    3. 6x MKP1837 0.1µF
    4. 2x Electro-Harmonix 12AU7
    5. Alps 50K pot
    6. resistors 0.6W metal film
    7. 2"tall heatsinks
    8. really cheap wood box
    Many thanks to:
    • Pete Millett for the design
    • Dsavitsk & the_equalizer for making the the conversion to 12AU7 tubes
    • others who have contributed to the enormous Starving Student thread
  8. ArtemF
    Hi everybody and many thanks to the author of the thread for simple yet effective design.
    I tried to reproduce the scheme but it's next to impossible to find the 19J6 tubes nowadays.
    So, I ended up with slight modification of the original circuit diagram to fit it to 6J6 tubes that
    are exactly the same as 19J6 except for the heater voltages.
    (May be somebody has done the same, I just don't have patience to scroll through 300+ pages :)  )
    To do this mod one will need 2 150Ohm resistors (mouser part # 286-150-RC ) that will serve as
    heaters replacements in the MOSFET circuit and two powerful 10W 39 Ohm resistors that
    are connected in series with two heaters (all 4 elements in this circuit are in series - 2 x 39Ohm
    and two heaters).
    An obvious drawback of this approach is more heat that is dissipated due to Ohmic voltage divider
    and two extra resistors that replace the heaters. An advantage is also obvious - 6J6 are easy to find
    and the price is ~$2 a piece.
    I also added diodes protection to the outputs to eliminate the headphones load problem.
    I took 8 blue LEDs (they are said to have higher opening voltage but in reality they open at ~1.2V so
    I put two in series to get ~2.4V threshold). They flash nice when the power is on and they glow a bit
    when it's off.
    Now about the sound: it's pleasant, with a good bass and gives good details. I tested it switching from
    the headphones output of Harman Kardon 75  (optical input from the player) to the Millet's amplifier and to
    the headphones output of the player itself. The volume levels were adjusted to get more or less the same
    sound volume. All frequency corrections were turned off. The new amp definitely outperforms the Harman Kardon
    though the latter gives a good sound on the speakers. To my surprise, the internal headphones amp of the
    player gives almost the same quality as the new amp. The frequency response is a bit different and the tube amp
    is a bit softer but these are the peculiarities and one has to make a blind test to identify what is really better.
    Of course, I can make the tube amp sound much louder and it performs great but if one compares apples to apples
    (same volume levels) then they are comparable. Perhaps, the internal one is just very well designed :)
    Summarizing, it was a nice experience, I recalled my young years when the tube amplifiers were still around (though rare).
    Here's the picture. Everything except the tubes sits inside (and is getting hot - I think of changing the design but the box
    is metal and it serves as a big radiator so I'll keep it for a while as is).
  9. Yaka
    very nice build there mate
  10. Beftus
    Thanks, though I know it's nothing special in terms of layout. Seen plenty like this one, but hey it's mine and I made it myself and above all it works bloody well! [​IMG]
    I still gotta do some minor improvements, like hot glueing the large caps to the inside of the case. I did ground the pot casing, no more hum when I touch the volume knob. I must say it sounds absolutely wonderful. Listening to Bob Berg's Silverado now, Mike Stern's guitar never sounded so good.
  11. vixr
    Beftus...that is a very nice build...love the penny idea. Mind if I steal it?
  12. Beftus
    Be my guest! I read that removing the solder pins from these heat sinks is pretty difficult so I had to come up with a solution. And a cheap one too, in true Starving Student spirit. Never had so much fun drilling holes in pennies. 
    Don't tell her but I raided my daughters piggy bank for those pennies... [​IMG]
  13. the_equalizer

    Nice build !  Great to hear you're enjoying it. I also like it very much for anything guitar: Stern, Burrell, Metheny, Green, Montgomery; not to mention Gilmour, Hacket, Beck, Page, Clapton, Hendrix...  they all sound great through it!
  14. ArtemF
    Hi everybody and many thanks for this thread.
    Here’s my build. I modified the circuit a bit to use 6J6 tubes that are still abundant and available at ~$2 a piece. The modification is straightforward: one will need two 39 Ohm 10W resistors (mouser part# 71-CP10-K-39) and two 150 Ohm resistors (286-150-RC). The latter replace the heaters while the former connected  in series with two "real" heaters make them work.
    An obvious drawback of this scheme is extra heat produced by the ohmic voltage divider. But one can live with that taken into account the tubes availability.
    I also added diode protection to the output (2 x 2 x 2 = 8 diodes = forward/reverse 2.4V threshold protection for two channels). I used blue LEDs so they flash nicely when the power is on.
    Now about the sound: it's very nice. I made a test using the same source and different outputs: Harman Kardon AVR75 amplifier, new tube amp and internal headphones amp of the player. The new amp definitely outperforms Harman Kardon though this amplifier works very well with the speakers.  The internal amp, though, is very competitive. If one compares apples to apples (same volume level) then it’s difficult to tell what is better. Perhaps, the tube amp is softer (in a good sense) in the mid-frequencies. An obvious advantage of the tube amp is higher volume level. The sound is distortion-free and rich. Overall, I'm very pleased :wink:
  15. wiisus
    I'm going to be starting this project soon.  I'm building the 12AU7 version.  I wanted to order almost everything from one place to save on shipping.  Mouser has everything I need except .22uF 250v and .22uF 63v capacitors.  They only have 50v 100v and 200v.  Will any of those work as replacements? Otherwise, where I else should I order from? 
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