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Adding a bright cap...what size?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mike80, Feb 14, 2009.

  1. mike80

    mike80 Member

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    It was pointed out to me in another thread about the Tremoverb's additional cap across the gain control on the clean channel as opposed to a standard Dual Rectifier. I looked at the schematic for both amps. The DR has a .001uF cap, and the Tverb has a .001 and a 680pF.

    So, if I want the cleans to be even brighter, what value cap would be a good one to install?
     
  2. phsyconoodler

    phsyconoodler Member

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    A .001uf cap adds tons of gain across a volume control.The typical value to get more brightness ranges from 47pf to 120pf.That's what a Fender amp uses.As the values get larger,the brightmess gives way to increased gain and the brightness tapers off as the values approach 500pf and larger.You need to experiment with your amp and see what floats your boat.I like 120pf for cleans.
     
  3. hasserl

    hasserl Member

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    You'll also find lot's of threads of folks removing the bright cap from their amp. This is a case where if a little bit is good, a lot is not better. physchonoodler's 120pf value is good, I like to use 100pf, if you're especially sensitive to hf's but want a little brightness added try using a 47pf.
     
  4. schmidlin

    schmidlin Member

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    The bright cap is a high-pass filter. IE, it picks a frequency and and lets ALL those above it through (with roll-off of course) and the larger the cap, the further you go down in frequency cut-off (what you let thru). I find this limiting, and have found that by adding a resitor in series you can also pad it down nicely. Why all or nothing? Throw a 500K-L pot in series and 'tune' in to your tastes (swap around caps too), then lock it in with a resistor.
     
  5. mike80

    mike80 Member

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    Thanks guys. I guess I'll buy a few values and see what I like best.

    I don't think that's a problem on a Dual Rectifier...lol. The cleans are rather dull to me. I like a shimmery, sparkley clean, and that's the only thing keeping me from being 100% happy with my DR.
     
  6. mike80

    mike80 Member

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    Well, I bought an assortment of caps ranging from 47pf to 680pf. I tried them, and I didn't notice much of a difference, even with the 680pf. :confused:

    I ended up leaving the 680pf in there.
     
  7. phsyconoodler

    phsyconoodler Member

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    Well,you have to notice a difference if the caps are installed correctly.Do you have a schematic?Where is the bright cap in there now?
    But honestly,a dual rectifier will never sound sparkly clean like a Fender without lots of other mods.Too many R/C couplings going on in that amp to make the cleans nice.
     
  8. mike80

    mike80 Member

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    Here's the original schematic with the cap circled. I piggybacked the cap the same way the other one is installed.

    [​IMG]
     
  9. schmidlin

    schmidlin Member

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    I would try the same excercise on C10 of orange's master volume. And you may want to dink with C7: it's pulling out some highs: maybe unhook it and test.
     
  10. mike80

    mike80 Member

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    Thanks. I'll give that a try.

    I did notice the channel is much brighter when set on high gain. I usually keep the orange channel cloned to modern on the clean setting with the gain around 9 o clock. It didn't seem to make much of a difference with that setting. When I set it to high gain and turn the gain up to around 1 o clock, it's noticeably brighter. The highs are nearly identical on the orange and red channels with the same settings.
     
  11. phsyconoodler

    phsyconoodler Member

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    With that .001uf cap in there,it's like a boost rather than adding brightness.Did you try the amp with the .001 cap out of the circuit?
     
  12. mike80

    mike80 Member

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    No, I didn't try taking it out. I just added to it.
     
  13. schmidlin

    schmidlin Member

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    Ah! That's why you didn't get any real results. You need to subtitute the caps, not add to them.
     
  14. mike80

    mike80 Member

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    I see. I was going off the schematic for a Tremoverb. I can't get it to upload to photobucket, but it has a 680pf cap in parallel with the .001uf cap. I read where that is why the T-verb's cleans are better than the Dual Rec's. I don't know much about amp circuits, so I was going off that.
     
  15. schmidlin

    schmidlin Member

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    You mean this guy:
    http://schematicheaven.com/boogieamps/boogie_tremoverb.pdf

    .001uf (1000pf) + 680pf = 1680pf, in parallel.

    That guy has a couple dozen LDR/switchers for the channels, and about half alter the high end. Some bumping-in bypass caps, cathode caps, feedback loop, etc., and you can't tell which LDR is for which channel. That's why I don't mess with Boogies: they got way too complex over the years.

    Enjoy :)
     
  16. mike80

    mike80 Member

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    That would be the one.

    At any rate, I've figured out a way to get a pretty good clean with my effects unit, so I'm probably done tinkering for now.

    Thanks much for the help ;)
     

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