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Millett "Starving Student" hybrid amp

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  1. -=Germania=-
    OK,

    I am thinking of making one of these and I want to enable two modes.
    -Pre-amp
    -Headphone amp

    Does anyone know of a switch that will do two channels from Mouser? (I am not very familiar with the site).

    Thanks ahead of time!
     
  2. thrice Contributor
    Any DPDT (double pole, double throw) toggle switch will do the job. NKK makes some nice ones.

    EDIT; sometimes you see 2P2T or 2PDT or DP2T...etc. Same thing.
     
  3. n_maher Contributor
    I'd just use a switched 1/4" jack, that way you ensure that you can never get confused about which mode the amp is in. It's also one less thing to wire, which I'm always a fan of.
     
  4. -=Germania=-
    what is part number for said jack? [​IMG]

    Seriously, I think that this woud make a great pre-amp and add a bit o tube to analytical equipment.
     
  5. n_maher Contributor
    Quote:

    Originally Posted by -=Germania=- /img/forum/go_quote.gif
    what is part number for said jack? [​IMG]



    There are too many to list. Just have a look around Neutrik's site and find something you like the look of.
     
  6. Gross
    just need to solder up my input and output jacks and mine will be done...
     
  7. Gross
    Finished! Only been listening for 5 mins or so, but so far I like. I is kinda the CMOY of tubes, as far as being simple to build. The longer it is on, the lower my DC offset gets on the output. When I first fired it up it was around 60-70mv per channel, and right now I am around 20mv. I will get some pictures up ( actually, it will be my first build pics I have posted, I havent shown you all my pint, soha, millet-max, aliens, blah blah blah).

    I pretty much stuck with the original BOM, just upped the 150uf caps to 270uf since they were out of stock.

    I mounted my tube sockets backwards too, which is purely cosmetic, but I suppose with just the few hours I have invested, I can rebuild this one with the sockets the right way. Who needs LED indicators when you have tubes to light the way. Oh yeah, this is quite the little space heater. I have 1.5" heatsinks, but bigger surely wouldnt hurt.
     
  8. J.D.N
    Excellent! Really looking forward to hearing what you think.

    Pic's would also be excellent...
     
  9. n_maher Contributor
    Gross, you should be getting 0 DC offset with the coupling capacitors, not quite sure how you'd be reading anything unless you're using a crappy meter that just isn't accurate at that level of DC.
     
  10. Gross
    It must have just been the initial charge up of the caps or something, cuz I read practically nothing now. I thought the caps should charge up faster than that. I am using a Fluke 8050A Bench meter, which hasn't failed me yet.

    On another note, I flipped and resoldered my sockets, so that the silver coating of the tubes is facing backwards, and letting the 'user' look into the tube better. That makes the wiring look a bit messier, since I did not want to rewire everything, but I did have to extend a few wires.

    Since I will primarily be using these with my Grados, and the fact that these tubes have a gain of 38, I am going to throw some resistors on the output, otherwise I sit so low on the pot, the tracking is off a bit.
     
  11. n_maher Contributor
    It shouldn't take very long for the output caps to charge, but it's certainly something that can be measured. I'd be shocked if it took more than a minute or so to fully charge though, even with your 220uF cap (assuming that's what you used). I'm sure your meter is more than up to the task. [​IMG]

    As far as tracking error goes, yeah, my amp does that as well if I'm right in the bottom of the range. But for me it's not a big deal since the amp is in my work rig (computer as source) and I just attenuate the source material a bit so that I've got more usable range.

    And please, post up some pictures, messy wiring and all. The wiring in my amp is nothing to write home about.
     
  12. Gross
    Ok, here we go. I stuck with the starving student theme and used a lot of parts I already had, and tried not to spend much money on the rest. The case was about $8 from mouser.
    [​IMG]

    [​IMG]

    [​IMG]
     
  13. -=Germania=-
    Tehe, I just realized that I can just take a lot of this stuff from the lab (cylindrical caps and resistors) + I have the wire.

    looks like I would just need the sockets for everything and a power supply.....I have an entire drawer of power supplies and none that would work [​IMG]


    Question:

    I am wondering if using different, higher quality parts will make much of a difference?
    Namely, which parts will make the most.
    I am assuming POT and Caps.
    Also, what tubes would be a good choice?
     
  14. n_maher Contributor
    Quote:

    Originally Posted by -=Germania=- /img/forum/go_quote.gif
    I am wondering if using different, higher quality parts will make much of a difference?



    I'd try near stock to start and see what you think of it's sound. Modifications are pretty easy to a ptp amp, especially this one. For now only three or so of these exist so there's not much of a knowledge pool to pull from.

    Quote:

    I am assuming POT and Caps.



    You could use a different pot and perhaps use different output coupling capacitors, but again the aim of this project was to see how cheaply good sound could be found. Rather than fret over parts selections with this amp I decided that I'd just build it and see how it sounded. But there's nothing stopping you from experimenting with it.
    Quote:

    Also, what tubes would be a good choice?



    I don't know how many producers of the 19J6 there were so just get what you can, I just asked for brand-matched pairs when I got mine and ended up with a bunch of RCA tubes.

    And nice work Gross. There's one tweak that you might want to make. The resistor that attaches to MOSFETs (pin 1 IIRC) really should be directly attached to the mosfet. If not you may experience some instability (this is what Pete tells me, maybe he can explain it more).
     
  15. Gross
    I will see about moving that resistor when I add my output resistors.

    Ok, this is what people are waiting for, how it sounds. It has a clean sound to it, and almost no background noise to it. My first thoughts were actually that it is almost kinda bright sounding, nice clean highs to it(I am using RS-1s though, so take that with a grain of salt). I thought the bass was 'O.K.' and didn't put a whole lot more thought into it until I went back to my uncased SOHA with a JRC 4556AD on the output (I bought a bunch of them while working on my RA-1 Clone, and Grados do like that OpAmp) and there was tons more bass. When I get home tonight from visiting my Mother for Mother's Day I am going to put in larger caps for C1 anc C6, cuz if I am reading this right, they are the power reserve caps. Also on the output with 150uf caps and 32 Ohm drivers, isn't that essentially a 33hz hi-pass x-over? I have 270uf in there which brings it down to 18hz, but I am thinking by adding 100 ohm resistors after the cap, in series with the headphones that should bring the x-over point to 4hz, as well as drop the output so I can use more of the pot.

    Hopefully that all made sense, and I wasn't reading something wrong.

    And don't take any of this as thinking this is a bad amp design, it is deliciously simple for some nice sounds. Besides, who here can actually leave something alone? [​IMG]
     
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