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Millett "Starving Student" hybrid amp

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  1. Entropy1
  2. tomb
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    Here are the pictures. I apologize about the poor picture quality but they're all I can get hold of. Not all of the soldering points are pretty, but I'm pretty sure all are okay. I have no idea what else could be wrong.

    Imageshack - img00018201002171926.jpg
    Imageshack - img00017201002171926.jpg
    Imageshack - img00014201002171925.jpg
    Imageshack - img00008201002171921.jpg




    Well, I can't tell anything from the pics - they're too out of focus. Besides, this doesn't tell us anything if you've got an issue when casing it up - momentary short, exposed wire, uninsulated MOSFET touching the case, etc.

    I'm also wondering about the LED resistor - I saw someone else snake that resistor lead around like that - curious. What was wrong with the open pad right there at the end of the resistor?[​IMG]
     
  3. Entropy1
    Yeah, I guess I didn't see that extra hole for the led resistor. Also, I get the same readings with the case on or off so I'm pretty sure I don't have a short. Any other suggestions?
     
  4. iPoodz
    I'm going to sidetrack for a second, while I'm waiting for a part to come from Mouser, and ask you all:

    Where do you go, online, to get real basic parts, like wires, RCA cables, solder, flux, etc?

    I'm trying to support my local mom+pop electronics shop, but the parts there suck [really flimsy 1/4" and 1/8" plugs, crappy switches for $8 a pop, and such], are overpriced, and they don't have a lot of variety. I've spent maybe maybe 80$ there over the last few weeks for various projects, and maybe 40$ at RadioShack, and never seem to walk away with the feeling that I got my money's worth.

    Do you have any favorite online vendors for parts/basic supplies?

    I know Harbor Freight is pretty good for helping hands, thanks to TomB's BantamDAC website.
     
  5. Lil' Knight
    Redco has a great variety of the parts you mentioned. Markertek has larger collection but price is not as good as that of Redco.
     
  6. tomb
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    Yeah, I guess I didn't see that extra hole for the led resistor. Also, I get the same readings with the case on or off so I'm pretty sure I don't have a short. Any other suggestions?



    Unless you can get us some pics that are in better focus:
    • Concentrate on those MOSFETs - make absolutely certain that they are isolated from the case.
    • Check all of your resistors - look at the rating designations and make certain that they're in the right positions. Refer to the Layout and/or PCB pages on the SSMH website. Reference those pics with the part #'s and ratings on the BOM. Make certain that you haven't switched up a resistor somewhere.
    • Go over your terminal block connections. Make certain you have the correct polarity coming in from the power supply and that you have proper grounding from the RCA jacks to the signal input terminal block at the volume pot.
    • If you've got any dodgy soldering, go over that again with more heat, more solder, and more flux. Be certain that you get wicking on the part side of the board. If you're unsure about what this is, refer to the Build Thread (link below) or the Construction pages on the SSMH website.
    • Check for any leads, standoff, etc. that may be touching a pad it shouldn't - especially around the LED resistor. Are the LED's lighting or is there any possibility of a short in the LED leads? Check for solder joints that may intrude into other areas. In one of your pics, it may have been the out-of-focus issue, but it looked like some significant solder blobs around the MOSFET pins. Is it possible those pins are shorting?
    I hate to mention this again, but please remember that the PCB was/is thoroughly vetted. Every build has been successful - at least from every one of the kits - so far. So, you either have a part in the wrong place, wires/leads touching somewhere they shouldn't, or the MOSFETs are not properly isolated. That's pretty much all it can be.
     
  7. Meliphcient
    Quote:

    Originally Posted by UKToecutter /img/forum/go_quote.gif
    I can't see the cable being the culprit (although it's possible).
    Have you checked that you have the correct value resistors in all positions?

    The volume pot is a possibility. Do you have another you can test?




    No, but I do have an old dmm! I opened up my ssmh and took some readings - the volume pot is out on the rear set. I'll have to get another and swap them. If that solves my problem I'll be ecstatic [​IMG]
     
  8. iPoodz
    Quote:

    Originally Posted by Lil' Knight /img/forum/go_quote.gif
    Redco has a great variety of the parts you mentioned. Markertek has larger collection but price is not as good as that of Redco.



    Thanks, Lil' Knight!

    Btw, I really like your build. Very neat, on the inside.
     
  9. amc
    Quote:

    Originally Posted by tomb /img/forum/go_quote.gif
    Unless you can get us some pics that are in better focus:
    • Concentrate on those MOSFETs - make absolutely certain that they are isolated from the case.
    • Check all of your resistors - look at the rating designations and make certain that they're in the right positions. Refer to the Layout and/or PCB pages on the SSMH website. Reference those pics with the part #'s and ratings on the BOM. Make certain that you haven't switched up a resistor somewhere.
    • Go over your terminal block connections. Make certain you have the correct polarity coming in from the power supply and that you have proper grounding from the RCA jacks to the signal input terminal block at the volume pot.
    • If you've got any dodgy soldering, go over that again with more heat, more solder, and more flux. Be certain that you get wicking on the part side of the board. If you're unsure about what this is, refer to the Build Thread (link below) or the Construction pages on the SSMH website.
    • Check for any leads, standoff, etc. that may be touching a pad it shouldn't - especially around the LED resistor. Are the LED's lighting or is there any possibility of a short in the LED leads? Check for solder joints that may intrude into other areas. In one of your pics, it may have been the out-of-focus issue, but it looked like some significant solder blobs around the MOSFET pins. Is it possible those pins are shorting?
    I hate to mention this again, but please remember that the PCB was/is thoroughly vetted. Every build has been successful - at least from every one of the kits - so far. So, you either have a part in the wrong place, wires/leads touching somewhere they shouldn't, or the MOSFETs are not properly isolated. That's pretty much all it can be.





    Awesome summary Tomb - I too have a PCB build that has been giving me trouble but has been gathering dust for the last month out of frustration and lack of time for hobbies. This is new inspiration to dust it off again when things calm down around the house (pregnant wife seems more demanding these days of my time - go figure)...
     
  10. Entropy1
    I'll do my best to get hold of a better camera but in the meantime here are some of the results of what you suggested.

    1. I'm assuming both MOSFETs are isolated as I get the same reading on both MOSFETs with or without the case. Whether or not these readings make sense I don't know. Between ground and pin 1, I get the odd ~120k and between ground and 2 and 3 I get a reading approaching 0 continuity. This goes for both MOSFETs

    2. I've looked through all the resistors several times and haven't noticed anything incorrect.

    3. I've redone terminal connections several times and get the same readings regardless of whether or not they are connected.

    4. I've tried to do what I with the soldering but I have no solder wick or solder sucker to redo anything. I will attempt to get hold of something and redo some connections though.

    5. The LEDs glow fairly brightly as I believe they should. The MOSFETs are rather messy but each time I've resoldered them, I've gotten the same readings. Pins 1 and 2 give the 120k, 1 and 3 give infinite, and 2 and 3 give infinite.

    Thanks for the suggestions. I'll keep working with and and do not mean to sound like I am blaming the kit at all. I too am almost certain it is my own fault although I would like to verify that the volume pot is good. What bothers me most is that I get a continuity between left signal and the output. With that, the only thing I can think of is that the left signal must be touching ground somewhere. I honestly don't mind troubleshooting as it has kind of caused me to learn a bit more and somewhat understand the schematic. [​IMG]
     
  11. Entropy1
    So I just found the source for the difference in readings although I'm not sure which is correct. I just found that one of the two pins circled was grounded while the other was not. Now each channel is the same so that is a good thing. Should both of these be grounded or should both not be grounded? (I assume they should be the same) I can't quite tell by the pictures of the PCB which is correct.

    http://img193.imageshack.us/img193/2...cb2800x650.jpg
     
  12. Jrome
    So I spoke a bit too soon when i said everything was going well....There's a problem!
    The weird thing is, the amp sounds fine, BUT there's only one channel going through both left and right.
    I only noticed this after listening to a song that i know pans from left to right. Through the amp, the left channel was loud and clear through both sides, but the right was through both as well but ultra quiet.

    Do any of you know what could be causing this?

    thanks
     
  13. tomb
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    So I just found the source for the difference in readings although I'm not sure which is correct. I just found that one of the two pins circled was grounded while the other was not. Now each channel is the same so that is a good thing. Should both of these be grounded or should both not be grounded? (I assume they should be the same) I can't quite tell by the pictures of the PCB which is correct.

    http://img193.imageshack.us/img193/2...cb2800x650.jpg




    Those are both grounded pads (connected to the ground plane). If you don't have good solder contact on those pads, it can cause all sorts of problems.
     
  14. tomb
    Quote:

    Originally Posted by Jrome /img/forum/go_quote.gif
    So I spoke a bit too soon when i said everything was going well....There's a problem!
    The weird thing is, the amp sounds fine, BUT there's only one channel going through both left and right.
    I only noticed this after listening to a song that i know pans from left to right. Through the amp, the left channel was loud and clear through both sides, but the right was through both as well but ultra quiet.

    Do any of you know what could be causing this?

    thanks




    1. You've mis-wired the RCA jacks, or
    2. You've mis-wired the terminal block connections at the volume pot, or
    3. The soldering is messed up on the headphone jack, volume pot, or input terminal block, (worst culprit is bad connection to ground) or
    4. You don't have the headphone plug plugged in all the way in the jack.[​IMG]
     
  15. UKToecutter
    Another SSMH was born @ 15:30 UK time today.......

    :)
     
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