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Millett "Starving Student" hybrid amp

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  1. Dunceiam
    Well, finished mine today, however, doesn't work as I had hoped, wishful thinking?

    Plugged everything in, a $10 Sansa MP3 player as source, and stock earbuds. Soon as I turn on the amp, the Sansa makes a loud cracking noise, the screen flickers black, the entire device turns off, and refuses to turn on, and one of the amp's tubes lights up. Despite the bricked Sansa, I left the amp on for a few minutes to make sure nothing's overheating, and noticed how the tube's got too hot to touch for longer than one second, within 2-3 minutes, normal? The tube was also much brighter than I was expecting, I could see the light being emitted from it as a circle on the ceiling.

    Any idea's towards the now-dead Sansa? I'm afraid to plug in any other source before I have the problem figured out.
     
  2. tomb
    Quote:

    Originally Posted by Dunceiam /img/forum/go_quote.gif
    Well, finished mine today, however, doesn't work as I had hoped, wishful thinking?

    Plugged everything in, a $10 Sansa MP3 player as source, and stock earbuds. Soon as I turn on the amp, the Sansa makes a loud cracking noise, the screen flickers black, the entire device turns off, and refuses to turn on, and one of the amp's tubes lights up. Despite the bricked Sansa, I left the amp on for a few minutes to make sure nothing's overheating, and noticed how the tube's got too hot to touch for longer than one second, within 2-3 minutes, normal? The tube was also much brighter than I was expecting, I could see the light being emitted from it as a circle on the ceiling.

    Any idea's towards the now-dead Sansa? I'm afraid to plug in any other source before I have the problem figured out.




    Sorry that this advice is too late, but you should always check the inputs/outputs on a DIY-build for voltage offset before you go plugging in your equipment. Obviously, you have something crossed and/or shorted. It sounds like you've over-voltaged one of the tube heaters, too - so that tube may be fried if you left it on too long. Sorry to have such bad news. If we can see your wiring, maybe someone can spot the errors.

    Pics ...
     
  3. tomb
    OK - as promised, the weekend has let me catch up with shipping.[​IMG]

    All purchased kits have now been shipped.[​IMG] There are still 8 kits left, plus some odds and ends. I've also got several extra power supplies and tubes, too, but will wait until I hear that everyone is OK with their kits before putting those up for sale.

    ** Remember that this is it for the Starving Student Millett Hybrid PCB, unless more tubes show up in volume. **

    Thanks for your patience everyone![​IMG]
     
  4. MoxMonkey
    i'd likely be interested in an extra psu or two if and when all the kits are gone and the extras remain to be sorted
     
  5. tomb
    Quote:

    Originally Posted by MoxMonkey /img/forum/go_quote.gif
    i'd likely be interested in an extra psu or two if and when all the kits are gone and the extras remain to be sorted



    The way things worked out, I'll almost have more PSU's than anything else, probably - at least a dozen, I think.

    Tubes are probably 2 dozen. I've got about 10 top-halo's that I saved, quite frankly, because they seem to be the most rare. Plus, top-halo's have always been my favorite, regardless of the tube type - always liked them best in the MAX/MiniMAX, too. Most important - I have 6 special 19J6's that have thickly-plated gold pins. I've never seen any others like them anywhere. Branded "International", it appears that company applied the coating post-production.

    There will be some other stuff, too - some of which is available now, including 8 kits still remaining.
     
  6. Dunceiam
    Alright, here are some photos. Good luck deciphering the maze of wires [​IMG].

    Oh, and the switch in between the heatsinks is a DPDT. I'm going to have a second 3.5mm jack at the back, for my speakers to plug into. If the switch is on, the audio will bypass the amp and just go straight to the speakers, if the switch is off, the audio will go into the amp, and out the 1/4" to my headphones. Also, should the pot be wired, G-I-O with the shaft pointing away from you? And finally, the tube that lit up was the right (looking down from the top)

    (Large Images)
    http://img41.imageshack.us/img41/2061/28932598.jpg
    http://img403.imageshack.us/img403/6595/92538694.jpg
    http://img341.imageshack.us/img341/6568/12497374.jpg
    http://img197.imageshack.us/img197/4425/43789515.jpg
    http://img25.imageshack.us/img25/7897/84860904.jpg
    http://img15.imageshack.us/img15/5489/17413807.jpg
    http://img683.imageshack.us/img683/5882/57829775.jpg
    http://img25.imageshack.us/img25/1938/12631784.jpg

    Thanks for all the help!
     
  7. Entropy1
    I just received and build my SSMH. First off, compliments to tomb for putting everything together so nicely and shipping everything in good time. Unfortunately I am having a couple problems. First is that I have audio only through the left. I have swapped tubes with no effect. Next off is a bit of static with is rather bothersome. Any suggestions before I start probing around comparing the two channels? If not, what would be the best way to do this? Thanks for any help

    edit: Also, both tubes are heating up like they are suppose to and the leds are both working properly.
    edit2: while messing around with stuff, i just picked up my low impedance iems and am actually getting audio of both channels. the right is significantly louder than the other but i'd even say the left side sounds better. it must be some powering issue as i can only get a faint clicking with my hd580's. any ideas?
    edit3: Somehow my x-fi card was broken while testing the amp. I now have no audio except crackling and a vague outline of the music with volume maxed. I am at a loss as to what I should do. Any help is appreciated, thanks.
     
  8. tomb
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    I just received and build my SSMH. First off, compliments to tomb for putting everything together so nicely and shipping everything in good time. Unfortunately I am having a couple problems. First is that I have audio only through the left. I have swapped tubes with no effect. Next off is a bit of static with is rather bothersome. Any suggestions before I start probing around comparing the two channels? If not, what would be the best way to do this? Thanks for any help

    edit: Also, both tubes are heating up like they are suppose to and the leds are both working properly.
    edit2: while messing around with stuff, i just picked up my low impedance iems and am actually getting audio of both channels. the right is significantly louder than the other but i'd even say the left side sounds better. it must be some powering issue as i can only get a faint clicking with my hd580's. any ideas?
    edit3: Somehow my x-fi card was broken while testing the amp. I now have no audio except crackling and a vague outline of the music with volume maxed. I am at a loss as to what I should do. Any help is appreciated, thanks.




    The PCB has been thoroughly tested and vetted. There are no mistakes or bugs with it. Unfortunately, that leaves the likely prospect that you have some parts in the wrong position, or some other building error has ocurred (MOSFETs not insulated?). Can you get us some pics?

    Meanwhile, check to see if your resistors are in the correct positions. Hopefully, you installed them with the ratings up so that you can read the values - as pointed out in the build instructions in the Head-Fi thread and on the SSMH website.

    Also, check to see if your MOSFETs are insulated and that you didn't torque them down so much that the Bergquist pads were cut. You can check this by measuring the resistance between the MOSFET tabs and an un-anodized place on the case lid.

    Check the LED resistor and whether one of the leads is shorting out with the center standoff.

    Finally, check to see that you didn't mix up the input wiring. Switching a ground wire with one of the signal wires is a common mistake and can cause some of the symptoms you describe.
     
  9. Entropy1
    Sorry, I did not mean to imply that I thought there was an issue with the PCB. I'll try to get some pictures but as I don't have a camera, that may take a while. The input cables are correct from what i see but I am kind of puzzled as to how the MOSFETs can be grounded. Mine are not insulated like you say as there is a metal screw causing contact between the case and MOSFET. How do I get this grounded? Thanks again.
     
  10. tomb
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    Sorry, I did not mean to imply that I thought there was an issue with the PCB. I'll try to get some pictures but as I don't have a camera, that may take a while. The input cables are correct from what i see but I am kind of puzzled as to how the MOSFETs can be grounded. Mine are not insulated like you say as there is a metal screw causing contact between the case and MOSFET. How do I get this grounded? Thanks again.



    No implication was taken about the PCB. That was just laying out the facts that the only way you can mess one up is by installing the parts in the wrong place or installing some things incorrectly (as in MOSFETs and heatsinks below).[​IMG]

    I'm concerned about your description of the MOSFETs, however. Did you study this page on the SSMH website: SSMH Heat Sink ? The proper heat sink mounting was also described and pictured in detail in the build thread and in the construction instructions on the website.[​IMG]

    If you didn't use the shoulder washer and the Bergquist pads, it will cause a whole heck of a lot of trouble.
     
  11. Juaquin
    The MOSFET tab and the Case should NEVER come in electrical contact. This will cause a short because the case is at Ground and the MOSFET tabs have quite a bit of voltage on them.

    The fact that you're getting very low audio in the left channel with loud audio in the right suggests that your right channel is working correctly and that what you're probably hearing in the left channel is crosstalk from the shared ground.

    Check that there is very high or infinite resistance between the metal MOSFET tab and the case. If there is very little resistance, you have a short and this is a problem. You do not want them grounded, you want them isolated. If you're building the kit, it came with Berquist pads for this purpose. Check that they are placed between the MOSFET and the case as the build guide says to do, and that they have not been cut/torn. Also, do not forget the isolation washer bit that is part of the heatsink mounting kit (it's a little, brown, oddly-shaped washer that is not conductive). This is what allows the screw to clamp down on the MOSFET and case without electrically connecting the two.

    Your dead soundcard is probably a result of this short coming back from the SSMH to your soundcard. Live and learn. In the future try to use a cheap source (handheld radio, walkman, cheap MP3 player, etc) when testing.

    [EDIT] TomB beats me to the punch again.
     
  12. Entropy1
    Yeah, I must have missed that page on the MOSFETS. That is fixed now but unfortunately there is still the static and the major volume difference present. I suppose the most likely explanation for the volume discrepancy is a swapped resistor so I will double check all of them again. Thanks for the help and hopefully I can at least get the amp working.
     
  13. Dunceiam
    I've troubleshooted a little, and I found quite a few errors. Firstly, the MOSFETS were indeed shorting to the case. My first measurements didn't show it at first because the chassis' black outer coating is insulating, so no continuity was being shown. But when I tried a spot of bare metal, continuity existed. Also, the ground for the MOSFET (for the tube that was not lighting up) was not soldered properly and became loose.

    I've ordered new mosfets, along with the insulating pads. Let's do this properly this time [​IMG].
     
  14. Juaquin
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    Yeah, I must have missed that page on the MOSFETS. That is fixed now but unfortunately there is still the static and the major volume difference present. I suppose the most likely explanation for the volume discrepancy is a swapped resistor so I will double check all of them again. Thanks for the help and hopefully I can at least get the amp working.



    At this point I'd say that it probably isn't a resistor issue (that could still exist, of course). Most likely you've blown the MOSFET in the quiet channel, and what you're hearing is crosstalk from the good channel. This is all theory, of course. Check the resistors and if they are correct, time to order a new MOSFET.
     
  15. simwells
    I'm still waiting for my tubes to arrive but before I wire this up to a source and phones when they arrive what other checks do I need to do on my wiring, the earths are all checked and fine anything else to make sure I won't damage anything?
     
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