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Millett "Starving Student" hybrid amp

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  1. tomb
    Quote:

    Originally Posted by Narwhalius /img/forum/go_quote.gif
    Which other ones do you think could be cold? And could this possibly be my volume pot?



    I'm not so sure those solder joints look bad, IMHO. However, the pics are great - but it's tough to get a perspective on your amp when we're only seeing postage-stamp views here and there.

    That said, I'm concerned with the wiring going to the right LED. That wiring is an accident waiting to happen. I'd wrap some black electrical tape around those joints.

    At this point, you may need to test the pot. The channels are the rows of three pins - three pins for left, three pins for right. The signal input are the two pins closet to the terminal block. See if you can measure resistance between that pin and one of the other pins in the same row of three (same channel). Rotate the pot shaft and see if the resistance changes. It's very easy to verify the pot condition this way, because any differences between the two rows of three are the differences between the right and left channels.

    Tell us what you get. Again, perfect values are not necessarily important, but differences in the measurements between pins on on row of three versus the other row of three - before and after rotating the pot shaft.
     
  2. timmyGCSE
    Quote:

    Originally Posted by getllamasfast /img/forum/go_quote.gif
    Are you following the vanilla ssmh schematic or are you following the one with Dsavitsk's modifications?

    The_equalizer's build is based on the modified schematic which can be found here




    ha this is exactly what I've done!! doh! what a wally. Clever chap you are and thankyou for pointing that out

    Now..presumably (or I'm hoping) I can still build it using the original schematic and translate in the different pin mappings? or are the pin mappings specific to the modified design?

    Its just that..I've bought all my components from teh original bill of materials, and sure there aren't that many extras and it would cost me a couple of quid more but I would have to get them from maplins and not rapid where I got my original stuff (otherwise I will be charged another £4.95 delivery) so the caps will be different..does that matter? or as long as I get the correct caps of a decent brand it should be cool?

    what does the modded schematic give extra?

    Quote:

    Originally Posted by the_equalizer /img/forum/go_quote.gif
    Hello timmyGCSE

    Ok, I'll try to address your questions one by one. What we need to do when substituting the tubes is wire the connections to the equivalent pins, that is, if a wire connected to the 19J6's grid, we now need to find the 12AU7 grid pin and run the wire to that instead.

    So here's the pinout mapping again with a description added

    ______________19J6 12AU7
    ------------------------------
    Plate 1 -------- pin 1 = pin 6
    Plate 2 -------- pin 2 = pin 1
    Heater --------- pin 3 = pin 4
    Heater --------- pin 4 = pin 5
    Grid 2 --------- pin 5 = pin 2
    Grid 1 --------- pin 6 = pin 7
    Cathode ------- pin 7 = pin 3, pin 8

    About pins 3 and 8, even though both the 19J6 and the 12AU7 contain two triodes in a single bulb, the 19J6 has only one cathode for both triodes, whereas the 12AU7 has an individual cathode for each triode.

    Finally, remember that we want to wire the triodes in each 12AU7 in parallel.



    These are the tube plates. I see the confusion, the pic does look unclear on that point. Indeed, pin 1 in the picture connects to pin 6 through the orange wire.




    Pins 2 and 7 in the 12AU7 are the grids. Again this must be wired together. That's what the white wire does.




    The cap IS soldered to pin 3. Pins 3 and 8 in the 12AU7 are the cathodes. You need to wire them together, that is done by a gray wire, barely visible in the picture at pin 8. Since the two pins are wired together, the cap and resistor (which is also barely visible behind the cap) can go to ground from either one of them; I chose to do it at pin 3.




    Pins 4 and 5 are the tube heater; now the heater has no polarity, so you can wire either pin 4 to ground and pin 5 to the MOSFET or viceversa. I chose the former, indeed.

    I hope this helps with the confusion. Feel free to post or PM me if you have more questions.

    cheers!




    massive help, really I appreciate the explanation so much. As above..do I need to use the modified schematic? or as long as I stick to the modified pin mappings I will be ok?

    edit: I sound very n00bish asking about this I know..I just want to be sure [​IMG]
     
  3. the_equalizer
    Quote:

    Originally Posted by timmyGCSE /img/forum/go_quote.gif
    ha this is exactly what I've done!! doh! what a wally. Clever chap you are and thankyou for pointing that out

    Now..presumably (or I'm hoping) I can still build it using the original schematic and translate in the different pin mappings? or are the pin mappings specific to the modified design?

    Its just that..I've bought all my components from teh original bill of materials, and sure there aren't that many extras and it would cost me a couple of quid more but I would have to get them from maplins and not rapid where I got my original stuff (otherwise I will be charged another £4.95 delivery) so the caps will be different..does that matter? or as long as I get the correct caps of a decent brand it should be cool?

    what does the modded schematic give extra?

    massive help, really I appreciate the explanation so much. As above..do I need to use the modified schematic? or as long as I stick to the modified pin mappings I will be ok?




    No problem, I'm glad it helped! [​IMG]

    No, you do not need to follow the modified schematic. You can follow whichever you choose [​IMG] as both are essentially the same circuit. But please let's not forget that for the 12AU7 build to work, aside from remapping the tube's pins, you need to make R4, R10 = 390 Kohms

    The modified schematic basically adds bypass capacitors to tube cathode resistors (labeled C7 and C8 in the modified schematic) and film bypass capacitors for the output electrolytics (labeled C3a and C5a in the modified schematic). The effect of bypass cathode caps is a slight (but very noticeable) increase in gain, whereas the film output bypass help improve the amplifier's response to high frequency transients.

    Other modifications are the input and grid stopper resistors (R16, R17 and R15, R16 respectively in the modified schematic). These help you control gain and compensate for some of the volume pot's tracking deficiencies and would be very useful if you plan to use your amp with sensitive IEMs.

    But don't think that if you build a 'vanilla' SSMH you're stuck there, as a matter of fact, my amp started life as a vanilla flavor, and later on I added some features from the modified schematic (the cathode bypass and output bypass caps) while ignoring others (the input and grid stopper resistors).

    Whichever you choose, good luck with your build! Let us know how it goes [​IMG]

    cheers!
     
  4. timmyGCSE
    ah great [​IMG] you've outdone yourself in helpfulness! ok I will go vanilla for now, its my first DIY amp ever and I'm not expecting miracles..even if it just works I will be dead chuffed and will spur me on to build bigger and better lol.

    thanks again so much

    edit: oh I forgot to say..I've picked my case now..I'm not going to say what it is yet but provided I can pull it off, its going to be rather unique [​IMG]
     
  5. Entropy1
    I was wondering if adding some RCA pass through jacks would be okay. This way, I could have speakers attached and turn them on if I want them on, and turn off the amp to stop music from playing in my headphones. Would this degrade the signal at all? I know it shouldn't theoretically, but I don't know in application.
     
  6. Entropy1
    I was also wondering, is it normal to notice a faint hiss while music is playing? I can pause music and it is completely silent. I don't notice this without the amp. I'm not sure if my bad onboard sound card produces this but I can't hear it as it doesn't have enough power to produce it on my headphones or what could cause this. It may even be in the recordings but I've never heard it before due to my headphones not being powered correctly.
     
  7. UKToecutter
    Short both inputs to ground and crank it up.
    That'll tell you if the noise is from your source.
     
  8. audiophile8706
    My internet decided to hang and it never said that the post went through... so this post can be deleted...[​IMG]
     
  9. audiophile8706
    Hey everyone.. I'm new here so forgive me if this question has been posed. (325 pages is a lot to go through :p)

    I was searching google for an inexpensive and easy tube amp build and came across the pmillet.com ssmh, and thus followed the links to here and diyforum. I'm just curious where this build stands at the moment. Both pmillet and diyforum seem to have a different list of parts and schematics. Which build is better when it comes to audio quality?

    Also.. I'm rather new to the whole tube thing.. what is the difference between 19J6 and 12AU7 in terms of schematic and tonal qualities?

    Thanks!
     
  10. UKToecutter
    Quote:

    Originally Posted by audiophile8706 /img/forum/go_quote.gif
    Hey everyone.. I'm new here so forgive me if this question has been posed. (325 pages is a lot to go through :p)

    I was searching google for an inexpensive and easy tube amp build and came across the pmillet.com ssmh, and thus followed the links to here and diyforum. I'm just curious where this build stands at the moment. Both pmillet and diyforum seem to have a different list of parts and schematics. Which build is better when it comes to audio quality?

    Also.. I'm rather new to the whole tube thing.. what is the difference between 19J6 and 12AU7 in terms of schematic and tonal qualities?

    Thanks!




    Hi and welcome.
    Yes, there has been a fair amount of modification done since the thread started.

    Have a look at SSMH Overview

    That'll give a good idea of where we are at the moment.

    The bad news is that the 19J6 tubes are in short supply and therefore have become rather expensive. As a result, there are no more kits available.

    So....
    You could do a Point 2 Point build (as described on the earlier posts on this thread).

    As far as the difference in sound between the 12au7 and the 19J6, I personally cannot comment as I have only built the 19J6 version.
     
  11. audiophile8706
    Quote:

    Originally Posted by UKToecutter /img/forum/go_quote.gif
    Hi and welcome.
    Yes, there has been a fair amount of modification done since the thread started.

    Have a look at SSMH Overview

    That'll give a good idea of where we are at the moment.

    The bad news is that the 19J6 tubes are in short supply and therefore have become rather expensive. As a result, there are no more kits available.

    So....
    You could do a Point 2 Point build (as described on the earlier posts on this thread).

    As far as the difference in sound between the 12au7 and the 19J6, I personally cannot comment as I have only built the 19J6 version.




    So the schematic and parts list that's on diyforums is the most up to date version?

    Thanks for the info!
     
  12. UKToecutter
    Yes,

    Use the schematic with the yellow highlights on it
     
  13. Narwhalius
    Quote:

    Originally Posted by tomb /img/forum/go_quote.gif
    I'm not so sure those solder joints look bad, IMHO. However, the pics are great - but it's tough to get a perspective on your amp when we're only seeing postage-stamp views here and there.

    That said, I'm concerned with the wiring going to the right LED. That wiring is an accident waiting to happen. I'd wrap some black electrical tape around those joints.

    At this point, you may need to test the pot. The channels are the rows of three pins - three pins for left, three pins for right. The signal input are the two pins closet to the terminal block. See if you can measure resistance between that pin and one of the other pins in the same row of three (same channel). Rotate the pot shaft and see if the resistance changes. It's very easy to verify the pot condition this way, because any differences between the two rows of three are the differences between the right and left channels.

    Tell us what you get. Again, perfect values are not necessarily important, but differences in the measurements between pins on on row of three versus the other row of three - before and after rotating the pot shaft.




    Following what you said the row of pins closest to the knob only seem to have continuity when its turned up to about 95% of the way. The other row moves the multimeter no matter where the knob is turned. That would explain why I'm hearing a click and the left speaker comes on at about the same spot? Would you still like some pictures of the whole amp?
     
  14. UKToecutter
    I think you should change that pot.......
     
  15. tomb
    Quote:

    Originally Posted by UKToecutter /img/forum/go_quote.gif
    I think you should change that pot.......



    Unfortunately - agreed.
     
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