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Millett "Starving Student" hybrid amp

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  1. Entropy1
    Yes, I know that it's the first thing the signal hits. It has to be a problem between the terminal cables and the volume pot. I think I will try remounting the terminal block to see if anything is changed.
     
  2. dsavitsk
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    How often are volume pots bad?



    Not very, but too much heat while soldering could certainly short it.
     
  3. the_equalizer
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    When testing for the channel bleed, I noticed that in one channel, I get the same volume regardless of where the volume pot is. To me, this would suggest that there is a problem before even hitting the volume pot, yet I can't seem to find any bad connections. Are there any other inferences I'm missing? How often are volume pots bad? I'm sure it's more likely that I messed something up rather than a component being bad, but I've gone over it so much. Anyways, thanks again and I'll keep looking.



    It would be quite the opposite: the problem should be AFTER the volume pot, since it's not affected by it.

    The only part of the circuit where the two channels come together is the 48 V line, and indeed bad supply decoupling causes channel crosstalk. Make sure R13 has the correct value but specially that C1 and C6 are the correct value, are properly installed (check the polarity) and soldered (no cold solder joints).

    I'll test my 12AU7 P2P build for crosstalk when I get home and let you know how it behaves.

    cheers!
     
  4. ezzieyguywuf
    Quote:

    Originally Posted by tomb /img/forum/go_quote.gif
    Last time I looked, SND Tube Sales (vacuumtubes.com) had them for $10.



    Just sent them an email, thanks.
     
  5. Entropy1
    Thanks, that'd be really nice. I assume that the signal must be the same intensity regardless of where the pot is turned to, and assuming the pot is good, it should make a difference but I'm not sure. C1 and C6 are both soldered in well and are oriented properly. R13 reads 2k and measure to around 2.1k which seems within reason. Oddly, the issue of getting ~150k between left signal and ground has come back (I thought I had it fixed at least.) Hope this helps, and thanks for the help.
     
  6. sam_cat
    Another one lives [​IMG]
    All in, probably about 6 hrs from start to finish including some testing time and hunting for the right sized allan key.

    Left channel sound slightly different to the right, not as much presence. It moves if I swap the tubes over too... Any ideas?

    Should have my shiny new scope tomorrow, so will be able to map out any differences/problems.

    Sam
     
  7. Juaquin
    If it moves with the tube, it's the tube. Replacing the tubes will fix it (if you can carefully match them), although that's not really an option nowadays with the scarcity of the 19J6. If it's a matter of volume, you can fine-tune the input resistors for one channel or the other to get it louder or softer.
     
  8. tomb
    Quote:

    Originally Posted by Juaquin /img/forum/go_quote.gif
    If it moves with the tube, it's the tube. Replacing the tubes will fix it (if you can carefully match them), although that's not really an option nowadays with the scarcity of the 19J6. If it's a matter of volume, you can fine-tune the input resistors for one channel or the other to get it louder or softer.



    Yeah, I hate to be a downer, but I warned everyone up front about this last round of kits. Each customer got the best matched tubes that were available according to his/her time of purchase and the availability at that time. So iow, the tube matching is as good as it's going to get. I still have enough left to replace a few outright failures, but that's all.[​IMG]
     
  9. the_equalizer
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    Thanks, that'd be really nice. I assume that the signal must be the same intensity regardless of where the pot is turned to, and assuming the pot is good, it should make a difference but I'm not sure. C1 and C6 are both soldered in well and are oriented properly. R13 reads 2k and measure to around 2.1k which seems within reason. Oddly, the issue of getting ~150k between left signal and ground has come back (I thought I had it fixed at least.) Hope this helps, and thanks for the help.



    So I tested my P2P build and there is indeed audible crosstalk; thought it's only really noticeable with IEMs. I tested by plugging in only the right channel and inserting only the left IEM; then I reversed the setup

    You can start hearing the crosstalk with the volume knob at around 8 o'clock and it's clearly audible with the volume knob at 9 o'clock (a volume level that would melt your eardrums in normal use with IEM's). Now if I understand your previous posts correctly, this is clearly a difference since in my case the crosstalk level is affected by the volume knob; as would be normally expected.

    cheers!
     
  10. Narwhalius
    Is there a list of voltage that I should be getting at certain points on my board? I'm still having the issue of no sound out of the left channel. Picked up a multimeter and I tested the RCA jacks to the terminal blocks. Both moved the meter, though only a little ways so I'm guessing that I have continuity there?
     
  11. tomb
    Quote:

    Originally Posted by Narwhalius /img/forum/go_quote.gif
    Is there a list of voltage that I should be getting at certain points on my board? I'm still having the issue of no sound out of the left channel. Picked up a multimeter and I tested the RCA jacks to the terminal blocks. Both moved the meter, though only a little ways so I'm guessing that I have continuity there?



    From what I read on your last post, I'm not sure you were testing anything. No, there isn't a list of voltages for certain points on the PCB. Quite frankly, the PCB doesn't rise to the level of complication where that might be required.

    Your best bet is to provide us with some pics. Unless you've blown the tube out on that side, you've got a wire loose somewhere - bad terminal block connection, mixed up ground/signal connection, etc. Since you fail to recognize it yourself (not unusual for most folk, else they wouldn't ask for help[​IMG] ), the best bet is to provide a pic or two and see if someone else can spot the issue.[​IMG][​IMG]
     
  12. Entropy1
    Thanks equilizer. I did only notice this with my small IEMs. ( <12 ohms impedance I would suspect ) The amp will only be used with my 300 ohm HD580's and I don't notice the crosstalk when using them. I guess this means my only problem is the volume difference which is most likely due to a bad solder joint somewhere. Thanks for the help and I'll do my best to get some pics once I'm up and running.
     
  13. the_equalizer
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    Thanks equilizer. I did only notice this with my small IEMs. ( <12 ohms impedance I would suspect ) The amp will only be used with my 300 ohm HD580's and I don't notice the crosstalk when using them. I guess this means my only problem is the volume difference which is most likely due to a bad solder joint somewhere. Thanks for the help and I'll do my best to get some pics once I'm up and running.



    Ah yes, then the channel bleed you're hearing is really normal. All multi channel headphone amplifiers exhibit it in varying degrees. IEM's pose a bigger problem because of their high sensitivity and (usually) low impedance (crosstalk levels tend to increase as load impedance goes down).

    So hunt down that volume difference bug and you'll be done ! [​IMG]

    cheers!
     
  14. Lil' Knight
    Quote:

    Originally Posted by sam_cat /img/forum/go_quote.gif
    Another one lives [​IMG]
    All in, probably about 6 hrs from start to finish including some testing time and hunting for the right sized allan key.




    Did you find out the correct size of the allen?
     
  15. the_equalizer
    Quote:

    Originally Posted by Lil' Knight /img/forum/go_quote.gif
    Did you find out the correct size of the allen?



    I'm pretty sure it's the one labeled 3''/32 in my set.

    cheers!
     
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