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Millett "Starving Student" hybrid amp

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  1. Meliphcient
    Ok I thought it was in my head....but the left channel is slightly weaker than the right. I pulled my headphones (Senn HD215) off and swapped them around, the difference is very noticeable when you A/B it like that.
    Any suggestions where to look for the fault? I was very careful and inspected every solder along the way - could it be the wires connecting the RCA inputs to the board?
     
  2. UKToecutter
    I guess you could swap the tubes around and see if the weaker channel appears on the other ear.
     
  3. tomb
    Quote:

    Originally Posted by Meliphcient /img/forum/go_quote.gif
    Ok I thought it was in my head....but the left channel is slightly weaker than the right. I pulled my headphones (Senn HD215) off and swapped them around, the difference is very noticeable when you A/B it like that.
    Any suggestions where to look for the fault? I was very careful and inspected every solder along the way - could it be the wires connecting the RCA inputs to the board?




    UKToecutter's advice is good. However, keep in mind that there are no tubes left to provide matching.[​IMG] You may be able to adjust the input resistors to a higher rating (I provided two choices in the kit - 50K and 100K). Using higher value resistors would move the typical volume setting to a point higher in the volume pot's travel - where it may be better matched.

    Hopefully, you're experiencing the imbalance in the pot. CD players tend to have fairly high outputs and earphones are pretty efficient. The combination may mean that you're in the very low end of pot travel and the little Alpha is not matched very well between channels at that point.

    P.S. Just a word to the wise - don't ever have your headphones plugged in when you power it up. Power it up first, make sure the tubes are warmed up, then plug in your headphones.

    Strictly speaking, there is 19V on the headphone output until the output coupling caps charge up. The SSMH is a bit forgiving in this regard because the power supply takes a while for the voltage to develop. If you had done that with another OTL tube amp or hybrid without a relay-delay, you might've blown out your headphones.[​IMG]
     
  4. the_equalizer
    Quote:

    Originally Posted by Meliphcient /img/forum/go_quote.gif
    Just started to test mine after building thisevening. Took a bit more than I expected, maybe 10 hours all told. I'm new to DIY audio stuff and literally had to wipe the dust off my soldering iron from highschool.

    This is my first experience with tubes so I wasn't sure if i'd seated them hard enough or not. Turned on the amp - LEDs lit up nice and green - turned on my old discman (ready to be sacrificed if I'd wired something up wrong) and plugged in some el-cheapo headphones (again incase something went wrong). At first...silence....then a gentle glow from the tubes! ALL WAS NOT LOST! faintly at first, then slowly louder it came - the music!

    I popped the earphones in for a moment to see what sort of volume this beast was going to give me...and I was almost in tears. I have never heard a soundstage like it. My post count and join date are probably very good indicators that I am damn new to this, but what an eye opener. If this is what's on offer from a relatively cheap amp, cheap source and cheap headphones...I know where all my money will be going soon [​IMG]

    Thanks Tom for making the kit available and getting it all the way out to Australia for me [​IMG]




    Ah, yes! That sweet moment when you turn the amp on and the tubes soft glow starts coming up.... Congratulations on your build!

    As to the channel-imbalance issue and related to TomB's comment on the output of your portable CD player. Try lowering the volume in your CD player, and turning it up in the amp. Sure, this will worsen the signal-noise ratio a bit, but hopefully not much, and it will allow you to turn up the pot to a point where the channels are better matched.

    If this doesn't work, well then you can try the input resistors or get a better volume pot. Try reading this post and the ensuing discussion.

    cheers!
     
  5. tomb
  6. Yaka
    that was quick, your hard work deserves such popularity
     
  7. Lil' Knight
    Quote:

    Originally Posted by Meliphcient /img/forum/go_quote.gif
    Ok I thought it was in my head....but the left channel is slightly weaker than the right. I pulled my headphones (Senn HD215) off and swapped them around, the difference is very noticeable when you A/B it like that.
    Any suggestions where to look for the fault? I was very careful and inspected every solder along the way - could it be the wires connecting the RCA inputs to the board?




    I also noticed this with my SSMH. As mentioned, try swapping the tubes and waiting for the tubes warming-up. The channel would be much more balanced.
     
  8. oxymoron08
    Hi guys,

    I have been reading up on the cmoy build, a few guys on recommended on another forum. I don't really wanna build a cmoy as I will have no use for it.

    I have never even held a soldering gun before, is this easy enough for someone who's most electrical experience is building his own pc's, and thats just mechano [​IMG]

    Am I going to be biting of more than i can chew?
     
  9. simwells
    Quote:

    Originally Posted by oxymoron08 /img/forum/go_quote.gif
    Hi guys,

    I have been reading up on the cmoy build, a few guys on recommended on another forum. I don't really wanna build a cmoy as I will have no use for it.

    I have never even held a soldering gun before, is this easy enough for someone who's most electrical experience is building his own pc's, and thats just mechano [​IMG]

    Am I going to be biting of more than i can chew?




    I wouldn't say so no, I'd just practise soldering random wires together and things first, there's nothing at all complex with the soldering needed to do one of these P2P.
     
  10. oxymoron08
    Quote:

    Originally Posted by simwells /img/forum/go_quote.gif
    I wouldn't say so no, I'd just practise soldering random wires together and things first, there's nothing at all complex with the soldering needed to do one of these P2P.



    ok, my Dad is pretty handy and I need to learn these things anyway. My uncle is a sparky so should be able to help out too.

    Where can I source parts in England?
     
  11. simwells
    Quote:

    Originally Posted by oxymoron08 /img/forum/go_quote.gif
    ok, my Dad is pretty handy and I need to learn these things anyway. My uncle is a sparky so should be able to help out too.

    Where can I source parts in England?




    Farnell, maplin, RS etc.

    Tubes and PSU will have to come from elsewhere though, PSU's are available through eBay. Tubes may not be so easy to find anymore.
     
  12. oxymoron08
    Quote:

    Originally Posted by simwells /img/forum/go_quote.gif
    Farnell, maplin, RS etc.

    Tubes and PSU will have to come from elsewhere though, PSU's are available through eBay. Tubes may not be so easy to find anymore.




    ah thanks man!

    been on the bay and found this psu:
    Quote:

    Original Cisco Systems AC Adapter
    Model: EADP-18FB B
    P/N: 34-1977-05

    INPUT: 100V-240V~ 0.5A, 50-60Hz
    OUTPUT: 48V 0.38A
    Connecter size: Int. Diameter: 2.50mm
    Ext. Diameter: 5.50mm

    Dimensions: 100 x 54 x 28 mm



    It's a tenner, buy it now. Is it the right one?
     
  13. UKToecutter
    yep, that's the one
     
  14. quarzo
    Hi people, I've read most of the thread but not all since its imposible. My build is complete and it's working as it should. But the tubes are not lightening too much, the mosfets are ok, the sound it's great but the I can barely see any light coming from them. They are a pair of Hungary made Tungsram. Should I worry about that?
     
  15. UKToecutter
    Quote:

    Originally Posted by quarzo /img/forum/go_quote.gif
    Hi people, I've read most of the thread but not all since its imposible. My build is complete and it's working as it should. But the tubes are not lightening too much, the mosfets are ok, the sound it's great but the I can barely see any light coming from them. They are a pair of Hungary made Tungsram. Should I worry about that?



    And you're sure they are 19J6?
     
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