newb question - cap voltage rating?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Normster, Jul 23, 2005.

  1. Normster

    Normster Member

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    I'm about to order parts for my first amp project and have a few questions about coupling cap and tone cap voltage ratings.

    1. Does a "too high" voltage rating effect the tone or circuit?

    2. Are there any ball-park guidelines to use when choosing cap voltage ratings.

    From what I can see, it looks like the PI coupling caps are typically 600-630VAC while the pre-amp coupling caps seem to be 400+VAC. Not sure about tone caps.

    The amp in question a Pignose G60VR (60 watt) that I'm building a dumble clone board for. I've done lots of tweaking to the tone circuit and had some luck messing with Ck values, but I thought I'd take the plunge and try a d-clone.

    Any help would be greatly appreciated.

    Thanks,
    Norm
     
  2. TheAmpNerd

    TheAmpNerd Member

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    Generally no, but don't go overboard, i.e., using
    1600V caps when only 600V rating is required.

    You should be fine sticking with those ratings.
    Many even use 600 - 630 in the pre amp section
    just because they don't carry the inventory.

    Most pre amp stages are between 150-350V so
    it is fine to use caps with a 400V rating.

    EDIT: Don't ASSUME, alway check voltages
    and compare them to the scematic.


    There is not a lot of room in there if I recall. The key
    is to have fun and be safe. That is what it is all
    about. Make some good tone out of it too.
     
  3. scottl

    scottl Member

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    Norm, just order the Xicon MPP series from Mouser. 630v, although 400v is fine for preamp. Nice size, good tone. Do NOT use Mallory 150 caps in your Dclone. They will deaden the tone.

    Call me if you want advice.

    Scott
     
  4. Normster

    Normster Member

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    Thanks for the responses! Scott, I ordered orange drops before I read your response, but I'm glad the Xicons are good caps since I used a couple in the tone stack. :)

    BTW, thanks for offering advice. I'm sure I'll need it before I get this thing sounding decent. Here's what I have so far:

    [​IMG]
    Before

    [​IMG]
    After (Note the PS board and reverb tube locations)
     
  5. TheAmpNerd

    TheAmpNerd Member

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    You've got plenty of room in there.

    I must have been thinking of the 30 or 40 watter,
    the tall thin square one.
     
  6. mark norwine

    mark norwine Member

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    I always use 600 - 630 v caps.....here's why:

    The preamp has lower voltages because of the current being pulled through the ladder resistors in the power supply.

    But when you're working on your amp and have the tubes removed {or any other times when you might have the tubes out}, there's no current being drawn, ergo little-or-no Vdrop. The result being full B+ all along the rail, and that can be considerablly more than 400V in many amps.

    Measure for yourself & see.

    Also: don't get sucked into the "Orange drop trap". "Orange drops" is a brand name of SBE {formerly sprague} and the caps come in polyester, polypropylene, polystyrene, etc. For example:

    "Orange Drop" type 225 = polyester
    "Orange Drop" type 715P = polypropylene

    If you want to say "this amp works best with polypropylene", that's fine. But to say "you gotta use orange drops" means nothing.

    The comment was made that Mallory 150's would sound bad. I have no opinion, but here's my observation:

    Mallory 150's are polyester, so what's being said, in reality, is "don't use polyester".

    But if you bought "Orange Drops" {series 225} then you bought polyester, and I contend that they'll sound almost exactly like the Mallorys that ought not be used!

    See the trap? This one needs to be learned & understood, or you'll spend a lot of money on the wrong stuff & you'll chase down tone issues with no idea why things sound the way they do!

    Good luck,

    mn
     
  7. scottl

    scottl Member

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    Thanks Mark. Just to clarify, Norm is my friend. We have spoken on the phone a few times about the project. Mallory 150 caps DO sound bad in Dumble style circuits to MY ear and the ears of my friends. I do not use 225 series caps so I can't comment on them. I can say unequivocally that the amp sounds dead with the Mallory caps. The polyprop caps sound much better to me. Xicon MPP caps are metallized polyprops.

    Norm, you should use ceramic as your treble cap. Mica is a fine but is not the traditional Dumble sound you seek.

    Also, DO NOT use any shielded cable. Use coax. The capacitance of the shielded cable is a tone sucker and very noticeable.

    Your primary filter caps should have a minimum of 50uf and the screen filter cap should be at least 20uf.

    Scott
     
  8. mark norwine

    mark norwine Member

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    I think we're saying the same thing......judge by "construction", not by "tradename"

    I didn't mean to sound as if I was in disagreement with your opinion of 150's in that amp.....I stake no opinion at all.

    My contention wast this: if you don't like 150's, I doubt you'd like *any kind* of polyester cap....225P's, etc.

    Conversely, if you like the Xicon MPP's {which stands for metalized polypropylene, BTW}, I contend you'd like other metalized polypropylene caps as well....again, regardless of brand name.
     
  9. Normster

    Normster Member

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    You guys can't imagine how much I appreciate the discussion wrapped around this project. I've learned a lot and so far, haven't wasted a whole lot of money...yet. ;)

    I ordered the 715Ps primarily based on reputation, but it's good to know that it's the construction (and not the brand) that matters.

    For me, this is a lot like building hot rods back in the '70s. You start out bolting on a bigger carb, and end up reworking the whole car before it's fast enough. :D

    Since I still have a working amp (Fender Blues Deluxe) I'm not afraid to experiment with all suggestions. In fact, for this first effort I'll be pleased if it makes noise! I've already discovered a few things that I'll probably have to change later, such as using 1/2 watt carbon film resistors. I've decided to leave these in but replace them with metal film later just so I can hear the difference.

    Scott, I assume you're talking about RG174/U cable. It's on my list, but I haven't found anyone who sells less than 100 ft. rolls. Does brand matter or is RG174 a spec that all manufacturers must meet?

    BTW, acplink.com has some pretty good pics of a real dumble without goo.
    Amp Chassis Pics - '77 Dumble
     
  10. TheAmpNerd

    TheAmpNerd Member

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    Well next time just the the 1 watt xicon carbon films. You can't go wrong with them and tons of builders use them.

    Metal films can be funny, dependidng on which brand where you put them. They can also be sterile sounding.

    I've got some of that mini coax if that is it. It is silver
    teflon with a silver shield, pretty hi dollar stuff.

    Pop me a PM of stuff you need and qty and we'll fgo from there.
     

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