EQD Crimson Drive Noise

Discussion in 'Burnt Fingers DIY Effects' started by Rock_Glenn, Feb 1, 2016.

  1. Rock_Glenn

    Rock_Glenn TDPRI Member

    Posts:
    75
    Joined:
    Aug 10, 2014
    Location:
    Western NY
    I've been on a pedal building tear, and recently built a Crimson Drive. It has a great sound with the exception of some high pitch (~3kHZ) background noise. It sounds like a static-like buzz that gets quieter, not completely though, when I touch the strings. Sometimes it pops it's head in between notes, and that's the most annoying part, I could deal with it otherwise.

    I know the original version had noise issues, but how can at the very least "tame" this noise. Should I add an electrolytic between 9V and ground? Is there any solution, or is this a germanium tranny issue that can't be fixed?
     
  2. luckett

    luckett Banned

    Posts:
    3,614
    Joined:
    Jun 14, 2011
    Location:
    .
    You almost always want to add noise filtering on the power supply. If you don't have them, try adding a ~100uf and ~0.1uf in parallel from 9V to ground.
     
  3. Rock_Glenn

    Rock_Glenn TDPRI Member

    Posts:
    75
    Joined:
    Aug 10, 2014
    Location:
    Western NY
    The circuit has two 100uF caps already filtering. Would adding third do anything? Or adding a large one like a 470uF help at all? It seems like it's a power filtering issue that's exasperated by humbuckers and wall-warts. I've never had this problem with any other pedal, at least not nearly this bad.

    Would adding a small ~1nf capacitor at the output to ground "mask" the problem.

    EQD added a tone pot to the pedal on the current production, I imagine that helps with this problem, if it's a circuit design flaw.

    I just want to be able to use the pedal, because it sounds great, with the exception of the background noise.
     
  4. luckett

    luckett Banned

    Posts:
    3,614
    Joined:
    Jun 14, 2011
    Location:
    .
    Add a 0.1uf in parallel to the 100s. Or just replace one of the 100s with a 0.1uf.
     
  5. Rock_Glenn

    Rock_Glenn TDPRI Member

    Posts:
    75
    Joined:
    Aug 10, 2014
    Location:
    Western NY
    Adding the 100n in there definitely made the noise more tolerable. Thank you.

    There's still a buzzing between 2Khz and 5Khz and a little bit around 60hz, but the extra cap cut the noise floor down enough for my tastes.
     
  6. luckett

    luckett Banned

    Posts:
    3,614
    Joined:
    Jun 14, 2011
    Location:
    .
    You might want to try going smaller than the 0.1uf to see if that helps with the higher frequencies.
     
  7. ICTRock

    ICTRock Tele-Afflicted

    Posts:
    1,474
    Joined:
    Jul 31, 2014
    Location:
    Tampa,FL
    time to audition some different germie transistors then
     
  8. NotAnotherHobby

    NotAnotherHobby Tele-Afflicted

    Posts:
    1,594
    Joined:
    Oct 27, 2015
    Location:
    Da' Magic Mittin'
    There is a 100pf cap that goes from the junction of the transistor's bias resistors to ground, correct? I suspect this is there to bleed off any stray high-end input before the transistor amplifies it, and before the clipping takes effect. I'd check there first to see if you have a bad joint. If not, try adding another 100pf cap in parallel to see if this helps the noise by extending the range of the filtering.
     
  9. NotAnotherHobby

    NotAnotherHobby Tele-Afflicted

    Posts:
    1,594
    Joined:
    Oct 27, 2015
    Location:
    Da' Magic Mittin'
    Also - if I remember correctly - germanium components tend to be more heat-sensitive than silicon. You may have damaged the junctions during soldering, or maybe even have a bad joint in there somewhere.
     
  10. Rock_Glenn

    Rock_Glenn TDPRI Member

    Posts:
    75
    Joined:
    Aug 10, 2014
    Location:
    Western NY
    I added a 51pf silver mica I had lying around in parallel to the 100pf because it has nice long leads. It had little effect. I also reflowed all solder around the germanium transistor, and no effect.

    Poking around in there I notice the noise doubles in volume whenever I put my finger on the input electrolytic capacitor... Changing to a film capacitor could have any effect? or is that wasting my time?

    Also this circuit has a 100uF electrolytic spanning the 9V rail and the emitter on the AC128, but the negative lead is at the 9V rail, this just seems odd to me.
     
  11. NotAnotherHobby

    NotAnotherHobby Tele-Afflicted

    Posts:
    1,594
    Joined:
    Oct 27, 2015
    Location:
    Da' Magic Mittin'
    I think you may have found the problem. If you did – good call. I missed it for sure.

    If you and I are looking at the same circuit, then yeah – the polarity on that specific electrolytic doesn’t look right. I looked at the schematic and a veroboard layout, and they both place it with the negative going to the positive Vcc. I think that’s actually wrong. I looked at a bunch of PNP fuzz face schematics, and in most of them, the cap has the negative side attached to the emitter of the PNP transistor in some form or another. The Rangemaster clones do the same thing.

    Usually, having an electrolytic in reverse isn’t that big of a deal unless you are nearing its rated voltage (in which case it tends to go BOOM!). You’re probably running 9v on a 16v electrolytic, so that wasn’t enough to pop the cap. But if you’re going to reverse the polarity, I’d replace the cap in the event that the current one is damaged internally.

    Reversing the polarity on an electrolytic tends to be bad. I had a guy wire one up wrong in a power supply circuit once. I happened to get up and get something off a shelf across the room when it finally blew up. It sounded like a stick of dynamite when it did. Of course…the cap’s voltage rating was lower than the voltage that it was handling, so that didn’t help things either…
     
  12. Iago

    Iago Friend of Leo's

    Posts:
    2,051
    Joined:
    Sep 18, 2006
    Location:
    Brazil
    I'd just keep trying more germ transistors. Some are much more prone to be noisy than others. Other than that, I wouldn't bother much about a circuit others have assumed to be noisy. Sometimes it's just the nature of the thing.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.