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Millett "Starving Student" hybrid amp

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  1. rds
    Pete - Thanks for the detailed information. That's just what I needed to know before placing my order.
     
  2. J.D.N
    x3 Thats excellent info.

    Due to living in England it's hard to get access to the range of capacitors that you guys do in the US. Could someone please run their eye over my choices bellow and OK them? They are partly chosen by what i can get hold of, and partly due to price (what i could get cheap-ish). Surprisingly they dont seem that expensive at all, but then ive never bought that many caps so i cant really compare.

    C1: 150uF 63v: MUNDORF TYPE - br63 - Bipolar electrolytic

    C2/C4: 0.1uF 63v [630v]: Clarity Cap - metallized polypropylene

    C3/C5/C6: 470uF 63v: MUNDORF TYPE - br63 - Bipolar electrolytic

    Also, is it possible to use 2W resistors instead of 1/4W?
     
  3. Ferrari
    Quote:

    Originally Posted by J.D.N /img/forum/go_quote.gif
    x3 Thats excellent info.

    Due to living in England it's hard to get access to the range of capacitors that you guys do in the US. Could someone please run their eye over my choices bellow and OK them? They are partly chosen by what i can get hold of, and partly due to price (what i could get cheap-ish). Surprisingly they dont seem that expensive at all, but then ive never bought that many caps so i cant really compare.

    C1: 150uF 63v: MUNDORF TYPE - br63 - Bipolar electrolytic

    C2/C4: 0.1uF 63v [630v]: Clarity Cap - metallized polypropylene

    C3/C5/C6: 470uF 63v: MUNDORF TYPE - br63 - Bipolar electrolytic

    Also, is it possible to use 2W resistors instead of 1/4W?




    The Mundorf BR63 bipolar electrolytic are developed for speakers manufacturing/industry.
    It's generally larger than generic (polar) electrolitics of the same value and can be considered as a step up from generic (polar) electrolitics. So, you can use these BR63 bipolar electrolytics in this build, the size should not be an issue here.

    Regarding the resistors, 2W power resistors can be used, however power resistors are very often 5% tolerance resistors (check this for sure)! It's better to use 1% tolerance resistors instead of 5%, so try to buy 1/4W 1% tolerance resitors if the 2W type is indeed 5%. Resistors are not so expensive, though. The MKP for C2/C4 is OK !
     
  4. J.D.N
    Quote:

    Originally Posted by Ferrari /img/forum/go_quote.gif
    The Mundorf BR63 bipolar electrolytic are developed for speakers manufacturing/industry.
    It's generally larger than generic (polar) electrolitics of the same value and can be considered as a step up from generic (polar) electrolitics. So, you can use these BR63 bipolar electrolytics in this build, the size should not be an issue here.

    Regarding the resistors, 2W power resistors can be used, however power resistors are very often 5% tolerance resistors (check this for sure)! It's better to use 1% tolerance resistors instead of 5%, so try to buy 1/4W 1% tolerance resitors if the 2W type is indeed 5%. Resistors are not so expensive, though. The MKP for C2/C4 is OK !




    Cheers Ferrari, the 2w resistors are indeed 5%. Found a few places selling 1/4W but they are all 5%. The BOM says 5%, am i missing something?
     
  5. Ferrari
    Quote:

    Originally Posted by J.D.N /img/forum/go_quote.gif
    Cheers Ferrari, the 2w resistors are indeed 5%. Found a few places selling 1/4W but they are all 5%. The BOM says 5%, am i missing something?



    Have no time to look at the BOM yet, but 5% resistors can be used and it will work as I posted earlier.
    Metal film resistors 1/4W are usually 1%, it's hard to find wider tolerance (> 1%) metal film resistors 1/4W nowadays, at least in the Nethelands.

    Generally, 1% metal film resistors are prefered in audio applications and ... personally I have never used resistors with 5% tolerance in my amps, unless there are no other choices for small values (< 1Ω) power resistors.

    Edit: Just looked at the BOM, Pete listed carbon film resistors in the BOM (these are cheaper), that explains 5% resistors!
    The good man tried to keep the bill as low as possible for starving students, probably.
     
  6. rds
    How close you want the resistors to be depends on how obsessive you want to be. In my opinion 1% is generally plenty good. Although you'll be ordering 5%, since they'll be from the same batch they'll probably be less than 1% (that's my experience). Remember the rating is the absolute max deviation over all batches.
    With these large values you can hand match resistors with a multimeter easily.
     
  7. HypnoLobster
    How did you more successful people mount the heatsinks? The ones I have (the right part number, I swear!) only have little metal lugs protruding from the bottom. Nothing to screw or bolt to.
     
  8. Gross
    Quote:

    Originally Posted by HypnoLobster /img/forum/go_quote.gif
    How did you more successful people mount the heatsinks? The ones I have (the right part number, I swear!) only have little metal lugs protruding from the bottom. Nothing to screw or bolt to.




    I ordered those too... I pulled the pins out with a pair of pliers and then tapped the holes with a 4-40 tap, and used screws to mount them. It would have been easier to buy heatsinks without pins, but oh well.
     
  9. HypnoLobster
    Quote:

    Originally Posted by Gross /img/forum/go_quote.gif
    I ordered those too... I pulled the pins out with a pair of pliers and then tapped the holes with a 4-40 tap, and used screws to mount them. It would have been easier to buy heatsinks without pins, but oh well.



    That was my plan as well.
    What are the pins intended for? All I can think of is soldering the heatsink to a board or something as such.
     
  10. Ech0
    Quote:

    Originally Posted by HypnoLobster /img/forum/go_quote.gif
    What are the pins intended for? All I can think of is soldering the heatsink to a board or something as such.



    Yep, that's it. Which makes it a little hard to remove if you need to.
     
  11. tomb
    If you look closely, Pete soldered his to the copper board that's in his BOM. This sandwiches the tin between the bottom of the heat sink and the copper board. This is probably a convenient and easy way to do it.

    On the other hand - if you look at Nate's pics, he used screws. Unfortunately, I think we're stuck with pulling the pins out if you go that route. I didn't see any "no pin" options for the size heat sinks we need at Mouser or DigiKey.

    BTW, heat sinks are soldered to PCB's on a regular basis (almost all of the MAX's are built that way). The only reason you might want to remove them is if you decide to use a different size.
     
  12. bhjazz Contributor
    I found a few old-school smoke shops in Seattle, and was considering using a cigar box. If the heatsinks are screwed to the box, though, how much heat would get transferred? Would the whole thing go up in flames on a particularly loud passage?








    Edit: okay, maybe that's a bit extreme....but still....
     
  13. Gross
    Quote:

    Originally Posted by bhjazz /img/forum/go_quote.gif
    I found a few old-school smoke shops in Seattle, and was considering using a cigar box. If the heatsinks are screwed to the box, though, how much heat would get transferred? Would the whole thing go up in flames on a particularly loud passage?



    I used a plastic enclosure for mine, and while the sinks get toasty, and I have had it on for several hours at a time, It hasn't done anything to the plastic.

    So, I think you'll be ok [​IMG]
     
  14. bhjazz Contributor
    Thanks, Gross.

    BTW: I got a good chuckle out of your post yesterday about dropping the .022uf cap into the build. Glad you figured it out!
     
  15. trains are bad
    I used an aluminum box, with holes drilled for the pins. I just dabbed a bit of JB weld on the pins and stuck it on top till it cured.
     
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