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Millett "Starving Student" hybrid amp

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  1. UKToecutter
    Tom,

    Always better to be busy than idle...........
     
  2. m11a1
    Hey Tom,

    I purchased the SSMH about 3 weeks ago and recently I have finished the kit. I would like to just thank you to putting together such an awesome sounding kit. Since it is my first DIY project ever, you have made my introduction to DIY very exciting and educational.

    Also, I'm super happy that I was able to grab one of the last remaining kits. Well, after this one, I'll be looking forward to the MiniMax. [​IMG]

    [​IMG]

    [​IMG]

    Thanks again.

    Cheers!
     
  3. the_equalizer
    Quote:

    Originally Posted by m11a1 /img/forum/go_quote.gif
    Hey Tom,

    I purchased the SSMH about 3 weeks ago and recently I have finished the kit. I would like to just thank you to putting together such an awesome sounding kit. Since it is my first DIY project ever, you have made my introduction to DIY very exciting and educational.

    Also, I'm super happy that I was able to grab one of the last remaining kits. Well, after this one, I'll be looking forward to the MiniMax. [​IMG]

    <snip>

    Thanks again.

    Cheers!




    Very nice pics! Congratulations!

    Quote:

    Originally Posted by tomb /img/forum/go_quote.gif
    If someone can provide me with a writeup, parts list/BOM, schematic, etc., on the variants (would want to include logistics' 12SR7 variant, too) - I can try to post it on the SSMH website. No guarantees as to when, though, it seems I'm staying pretty busy these days.[​IMG]



    I'll try my hand at drawing the schematic for the 12A_7 version. Is "Eagle" a good program to do it?

    cheers !
     
  4. Juaquin
    I'm a big fan of Eagle, mostly 'cus it's free, it works, and there are a lot of part libraries for it. I've designed a couple schematics / PCBs with it, feel free to ask if you have questions.
     
  5. the_equalizer
    Quote:

    Originally Posted by Juaquin /img/forum/go_quote.gif
    I'm a big fan of Eagle, mostly 'cus it's free, it works, and there are a lot of part libraries for it. I've designed a couple schematics / PCBs with it, feel free to ask if you have questions.



    Thanks Juaquin! I certainly will [​IMG]

    cheers!
     
  6. tomb
    Quote:

    Originally Posted by the_equalizer /img/forum/go_quote.gif
    <snip>
    I'll try my hand at drawing the schematic for the 12A_7 version. Is "Eagle" a good program to do it?

    cheers !




    Actually, Eagle may not be the best thing to use. What may be more useful is to Photoshop the existing Pete Millett schematic for the necessary changes, just as was done for the PCB differences over the original.[​IMG]
     
  7. the_equalizer
    Quote:

    Originally Posted by tomb /img/forum/go_quote.gif
    Actually, Eagle may not be the best thing to use. What may be more useful is to Photoshop the existing Pete Millett schematic for the necessary changes, just as was done for the PCB differences over the original.[​IMG]



    Note taken. I don't have Photoshop, but I'll try doing it with GIMP.

    cheers!
     
  8. ezzieyguywuf
    GIMP ftw. Could anyone with the knowledge simply let me know what the necessary changes are? I have the feeling that it's as simple as changing some resistor values. I'm trying to get together a BOM because I want to build this bad boy over spring break, in two weeks. I may even try my hand at an Alien DAC, but I've read that it has issues with the SSMH? Any comments on that? Any alternatives?
     
  9. Juaquin
    Search the thread, the_equalizer has posted the required changes a few times.
     
  10. tomb
    Quote:

    Originally Posted by ezzieyguywuf /img/forum/go_quote.gif
    GIMP ftw. Could anyone with the knowledge simply let me know what the necessary changes are? I have the feeling that it's as simple as changing some resistor values. I'm trying to get together a BOM because I want to build this bad boy over spring break, in two weeks. I may even try my hand at an Alien DAC, but I've read that it has issues with the SSMH? Any comments on that? Any alternatives?



    There is a charge issue that sporadically seems to develop on the RCA input jacks of the SSMH. This is enough under the right conditions to blow out the DAC chip on the Alien or BantamDAC. This seems to occur if there's ever an occasion of connecting/disconnecting the DAC from the SSMH while it's on. I've actually seen the static charge jump from the RCA jack (ground connection) to the RCA plug from the DAC (signal connection). The DAC was fried on that channel from then on.

    You can test this yourself while listening to the SSMH - try disconnecting the RCA cables from the SSMH while it's on and playing. Sometimes you'll get a huge hum that won't go away until you touch the RCA jacks and ground them to your body.

    We don't know what causes it, but it seems peculiar only to the SSMH. As for DACs, the ones that are in danger because of this are the type of DACs that have only a filter capacitor separating the DAC chip from the connection on the amp. I don't know if this exists for the GrubDAC, but I would be reluctant to test it out on the SSMH.

    OTOH, I've had an SSMH connected to a PC's sound card for over a year with no ill effect - connect, disconnect, whatever - no issue at all.
     
  11. ezzieyguywuf
    Hm. I'd like to know if maybe theres a way to mod the Alien DAC to prevent this from happening? I don't know what a "filter capacitor separating the DAC chip from the connection on the amp" is, but I hope my Compass has it! I know it's got separate boards for the amp, dac, a power supply but I don't know how they're connected.

    Juaquin: thanks for that, at least now I know which posts to look for.

    Also, I saw on this thread somewhere that someone said something along the lines of "it sounded great even though I had it on my proto board". I'm planning on building this thing on a bread board, mainly cuz I'm still newb at this and I want it to be neat and easy to enclosure. Are there sound benefits to doing it point-to-point, or rather, are there sound detriments to doing it on a board?
     
  12. tomb
    Quote:

    Originally Posted by ezzieyguywuf /img/forum/go_quote.gif
    Hm. I'd like to know if maybe theres a way to mod the Alien DAC to prevent this from happening? I don't know what a "filter capacitor separating the DAC chip from the connection on the amp" is, but I hope my Compass has it! I know it's got separate boards for the amp, dac, a power supply but I don't know how they're connected.



    What's meant by a filter capacitor is that the DAC's output is offset at about 2.5VDC (same as the output in the SSMH - it's at 19VDC.). In order to prevent this DC from damaging your equipment or headphones, blocking or "filter" capacitors are used to block the DC. AC (the music signal) passes through unaffected, assuming the caps are sized correctly.[​IMG]

    In the case of the Alien and BantamDACs, the only thing separating the output directly off of the PCM (DAC) chip from anything it's connected to are those capacitors. Meaning, there's nothing to absorb spikes if/when they occur in the SSMH. Many other DACs use filter/output capacitors too, but there's often a small amplifier circuit, opamp, etc. inbetween. The protective circuitry in those, while coloring the signal even more, tends to protect the sensitive DAC chip from extraneous charges.

    It's been suggested before that some output resistors - probably 100R - on the output of the DAC may protect it from these issues. I'm not aware of anyone who's tried it, though. However, there are users out there who are using the SSMH with the BantamDAC without issue. On the other hand, I've blown two AlienDACs and one BantamDAC myself with the SSMH - but I was prototyping and switching a lot of things around, so who knows? It's safest to give the warning, though.
    Quote:

    Juaquin: thanks for that, at least now I know which posts to look for.

    Also, I saw on this thread somewhere that someone said something along the lines of "it sounded great even though I had it on my proto board". I'm planning on building this thing on a bread board, mainly cuz I'm still newb at this and I want it to be neat and easy to enclosure. Are there sound benefits to doing it point-to-point, or rather, are there sound detriments to doing it on a board?



    Either one is fine, as long as you have sufficient material for grounding. You should note that Pete Millett's original contained a hefty copper plate that had everything that was grounded soldered to it. The copper plate was in his original BOM, too.[​IMG]
     
  13. hss3
    Quote:

    Originally Posted by tomb /img/forum/go_quote.gif
    Actually, Eagle may not be the best thing to use. What may be more useful is to Photoshop the existing Pete Millett schematic for the necessary changes, just as was done for the PCB differences over the original.[​IMG]



    Here is a "flipped" image of the PCB ready for laser printing and toner transfer etching in .pdf form for 12AU7 tubes. It follows the same schematic as the Beezar circuit boards minus the modifications for the 9pin sockets.

    Someone check the circuitry also...

    SSMH 12AU7.pdf

    I screwed up my first PCB etch.. hoping to try again soon.
     
  14. ezzieyguywuf
    Some more questions. I've heard of "boutique" parts, but I don't know exactly what is being referenced to here. I know that they are more expensive, and that they're supposed to be better, but what kind of difference are we really looking at here? I'm not exactly the most audiophiliphic audiophile, and my ears aren't super sensitive or anything, but I do appreciate some good noise :)-P) coming out of my D2000's. Also, I'm looking to invest in another set of cans in the (not so near) future. Maybe some Senns or something. Something different from the Denon's. Something that mates good with tubes. Anyways the point I'm getting at is, how much of a price difference will these "boutique" parts make, and will there me a notable audible difference on a range of headphones? Including IEMs actually.
     
  15. the_equalizer
    Quote:

    Originally Posted by hss3 /img/forum/go_quote.gif
    Here is a "flipped" image of the PCB ready for laser printing and toner transfer etching in .pdf form for 12AU7 tubes. It follows the same schematic as the Beezar circuit boards minus the modifications for the 9pin sockets.

    Someone check the circuitry also...

    SSMH 12AU7.pdf

    I screwed up my first PCB etch.. hoping to try again soon.




    Am I correct in assuming it's a double sided board?

    cheers!
     
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