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Some of my amps and preamps

Discussion in 'Shock Brother's DIY Amps' started by bancika, Mar 6, 2015.

  1. bancika

    bancika TDPRI Member

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    Wanted to introduce myself and show some of the things I've done in the past. I don't do this commercially, and lately I don't have time to do it at all, as I'm playing through VST plugins most of the time anyways. But I still have most of the amps I built. Here it goes:

    • Mesa IIc+ inspired preamps with quite a few modifications. The two-channel version I built last ended up being my main preamp. No electrolytic caps anywhere in the amp (other than switching relay supply).

      [​IMG]

      More info here http://diy-fever.com/amps/mesa-mark-iic-pcb/

    • 3w 6ak6 push pull poweramp. My own design, completely over the top, crazy. Again, no electrolytics, all poly-film caps. LC filtered power supply for the whole amp. LED cathode bias (effectively making it operate close to fixed bias amp), overspec'd output transformer. Switchable solid stage boost stage...

      [​IMG]

      More info here http://diy-fever.com/amps/3w-tube-power-amp/

    • 2W version of trainwreck express amp. I was into heavier music when I built this, so I couldn't find much use for its tone...eventually I sold it. Still feel bad about it, it's an awesome little amp.
      [​IMG]

      Mode info here http://diy-fever.com/amps/ax84-4-4-0/

    • 5W version Soldano SLO. This is a killer amp. I had to make dual power supply, one for the preamp and one for EL91-based power amp. 3 channels, lots of volume for home.
      [​IMG]
      [​IMG]

      More info here http://diy-fever.com/amps/5-watt-slo/

    There are a few more on the website...

    Cheers
     
  2. telex76

    telex76 Doctor of Teleocity Ad Free Member

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    Nice looking work.
     
  3. Vostre Roy

    Vostre Roy TDPRI Member

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    Nice job man!
     
  4. andyfromdenver

    andyfromdenver Friend of Leo's

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    wow bancika.
    very cool.
    thanks for sharing!

    you just hate elytics!?!? :) just kidding of course.
     
  5. bancika

    bancika TDPRI Member

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    Thanks for the comments, appreciate them!

    I really do hate electrolytic caps, they are terrible, no joking :)

    And the fact that I'm building low power amps for my bedroom leaves me room to use the huge poly caps. Doing that for a 100w amp would be costly and impractical. But polyester caps are sooo much better, I use them whenever I can for amps and pedals. They will not dry out and have very low ESR.
     
  6. flyswatter

    flyswatter Friend of Leo's

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    Some real artistry here in your builds. Thanks for sharing. I'm just embarking on the process of building (after lots of modding), so it's inspiring to see your long-term experience at work.
     
  7. robrob

    robrob Poster Extraordinaire Ad Free Member

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    That is a very cool batch of amps there. Very nice indeed.
     
  8. jonrpick

    jonrpick Friend of Leo's

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    Awesome work... It never dawned on my to use non-electrolytic caps in the power supply. For kicks, I priced some 22uf 600v caps through Mouser.

    :eek: :eek: :eek:

    $93.25 EACH! And I'd need 3 of them for something as simple as a Champ.

    If you'd never have to change them, I definitely see the benefit... still, that's a lot of cap jobs for the money.

    But now I want film caps in my power supplies... :D
     
  9. celeste

    celeste Friend of Leo's

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    Nice work, an I hear you about the electro's, Thank goodness for polypro motor run caps, I am also not adversed to using smaller caps and getting the filtering with a cap multiplier.
     
  10. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Did a google search on celeste's polypro motor run caps and found:

    CBB60 AC 450V 80uF Polypropylene Film Motor Run Start Capacitor for $18 on Amazon.

    Hmmmmm.
     
  11. jonrpick

    jonrpick Friend of Leo's

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    Bancika, could you give a little more info on the LED cathode biasing a bit? I'm not familiar with that.
     
  12. celeste

    celeste Friend of Leo's

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    An LED acts like a resistor bypassed by near perfect capacitor. They have constant voltage drops across them regardless of current across them. In the past they were most useful of preamp tubes because of their low current ratings, but with the advent of LED lighting there are now big units available. How they will work to bias power tubes I don't know yet, no plans any time soon to find out afaor my self, but they are in the back of my mind. Out on the great Web there is a page about someone who built an EL34 amp and biased them with LED's. series connected strings to get the needed voltage, and parallel strings to get the current needed. So many LED's it looked like a sigh board in LV

    One other thing they do is they can be a power indicator light as well, they glow when the tube conducts. One uses them by deciding on the bias voltage you want, find an led that has that forward drop across it and replacing the cathode resistor and bypass cap with it
     
  13. bancika

    bancika TDPRI Member

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    yes, another way to achieve similar results is a conventional cathode bypass resistor in parallel with a really large (compared to traditional values) capacitor. Like 2200uF or 47000uF. The idea is to have a fixed bias that will not sag under higher currents like resistor bias does. I wanted the amp to have fast response and no sag and compression. As clean as possible.

    Like with poly power supply caps, LED bias is only practical on small, low power tubes like 6ak6 or el91 or small signal triodes/pentodes that are used for even less power. Even for a 3W amp, you need 4 diodes in the array to get the bias voltage of 10.5V. I put two arrays in parallel just to be safe they can take the current. Maybe I could get away with one array. EL34 class AB push pull amp that needs -38V to bias the grid. It would take a lot more diodes to bias it. At that point, it's easier to make a traditional bias supply circuit.

    [​IMG]

    And yes, poly caps I used on IIc+ build and few others are motor run. They are really cheap (they cost less than electrolytics would cost me to order them from abroad), they are readily available as they are not intended for a niche industry like guitar amps, they have high voltage ratings and they work well...

    On the 3w power amp I used some NOS vishay poly caps that are only rated 250v, but it was just perfect for the job. I saved a lot of room using them.
     
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