DSL Pop/Crackle... Help!

Discussion in 'The Workbench' started by Moose Lewis, Jul 24, 2011.

  1. Moose Lewis

    Moose Lewis Well-Known Member

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    I just picked up a '98 DSL 100 in a swap today. Has all new tubes, but the bias has not been set yet.

    Has a slight hum, even with nothing plugged in. The real issue is as I play I hear an intermittent crackle/popping noise - reminds me a bit of a blown speaker, but my speaks are fine and the guitar is too. When it crackle/pops it is also louder than the perceived playing volume. It also sounds a bit fizzy, but I'm hoping that's just the need to set the bias.

    Does this sound like anything anyone is familiar with? Very worried - don't have the bucks for any major repairs to this thing.

    Thanks guys :cheers:
     
  2. chuckharmonjr

    chuckharmonjr Well-Known Member

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    Could just be a tube going bad Moose.
     
  3. jcmjmp

    jcmjmp Well-Known Member

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    1) Could be tubes
    2) If you're using the 4/8Ω speaker outputs, it could be a bad ground.
     
  4. Buggs.Crosby

    Buggs.Crosby New Member

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    1st i would do the 4/8 ohm mod regardless if i was you and have some pre's handy
     
  5. chadjwil

    chadjwil Active Member

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    Sounds tube related to me, but could also be filter caps. If I were you, the very next thing I would do is check the bias. There's some bad info going around about Marshall recomending the bias be set to 90mV...bad idea in my experience. I did that and heard some crackling as well...about an hour before one of my output tubes blew. :(
     
  6. Moose Lewis

    Moose Lewis Well-Known Member

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    4/8 ohm mod? Is there a link here for that?

    Thanks guys. Any suggestions are helpful.
     
  7. chuckharmonjr

    chuckharmonjr Well-Known Member

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    Its in the joey mods Moose...the ground for the speaker outs goes thru the switch in the 16 ohm jack. That switch goes bad, then you have no ground for the 4/8 ohm jacks. Solder a jumper from the 16 ohm jack ground to the 4/8 ohm jack ground to bypass the switch. Quick and easy to do.
     
  8. Buggs.Crosby

    Buggs.Crosby New Member

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    on the rear board it is the link for the grounds on the speaker jacks
    you only nee to do the part in yellow
    [​IMG]
     
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  9. Moose Lewis

    Moose Lewis Well-Known Member

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    Cool. Hey, I might even be able to do that myself. I assume all speaker jacks will still be functional?

    You ARE talking about soldering a jumper wire just above where the yellow line is, right?

    Yes, treat me like an idiot. I can't believe that when I was young I would boldly go in my amps, and now I'm afraid of screwing something up. A mind is a terrible thing to waste. With my finances being what they are this year, I need to start learning this stuff for real (probably starting with discharging capacitors). I've even got a really nice meter... just been so long I don't remember how to use it. Doh. But here we go. I'm gonna start reading the Joey Mod Thread that Twin organized, and see what I can glean from it. Got to get this sucker rockin'.

    ... aaaand the more I read, the more I think I'm not one of the people who should be working on their own amps - just gather intel to share with a real tech. :(
     
    Last edited: Jul 24, 2011
  10. Ken

    Ken Well-Known Member

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    Yes, all 3 jacks work; the only difference is there is no failsafe if some idiot uses all 3 at once.

    I did mine myself and it was even easier than I thought it would be. Anyone who ever soldered once or twice can do it. Just don't touch anything other than what you're working on. I just added a wire to the ground on the 16 ohm jack itself and connected it to the ground on the nearest 8 ohm jack; the pictured version is neater but more difficult.

    As for your problem, if it's not the speaker jack, I would retube the amp; in fact I'd do that anyway. Once biased with new tubes, it won't be as "fizzy". DSL's are easy and fun to bias with the pins; if you're more ambitious you can measure the tube voltages too. Mine (50 watt) is about 42 per side; people bias these between 35-45 so let your ear be your guide. Double these values for the 100 watt.

    Ken
     
  11. chadjwil

    chadjwil Active Member

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    Do you know how to check your bias? It's extremely easy on a DSL. I'm asking because I haven't heard you mention anything about it yet. You say you have a DMM, so set that thing to DC Volts, turn your amp on and not in standby (always connected to the speakers) and find the three little pins sticking out of the back of your amp. The middle one is ground, so the black lead goes to that, and the outside two are the bias for each pair of tubes. Measure between one of the outside pins and the center and use the little phillips head pot on the opposite side of the pin that you are measuring to adjust it to around 78mV (.078V) or so. Do that for both outside pins keeping in mind that you may have to go back and forth a couple times, as adjusting one side can and probably will affect the other.

    I have a little apparatus with pin sockets on the end that allows me to connect the meter to the test pins while keeping my hands free to adjust the pots. If you don't have the time or resources to do something like that then keep in mind that you do NOT want to create a short between those pins by letting the meter leads touch each other and the pins at the same time. Sorry if that sounds insulting, but I'd rather be safe than assume someone knows something that they may not.

    Check the bias please, I bet it's too high, besides if you don't know how to do that yourself now is a great time to learn...as a tube amp owner, that's the one thing that you should know how to do yourself for a number of reasons.

    By the way, this is the sort of down and dirty method of biasing. Once you get comfy with the process it will behoove you to get a little more involved and figure out how to actually do it properly. I just gave you 78mV as a sort of safe region. And you should really be able to check and set the bias in about 5 minutes once you warm the amp up for about 15 minutes or so and locate the bias pins.

    By the way, even if this fixes your problem you should still check it again after about a half hour(ish) of playing through it. These amps can drift a good bit from heat. Just something that you should be aware of for future issues.

    Good luck Moose
     
  12. jcmjmp

    jcmjmp Well-Known Member

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    Checking the bias, although not a bad thing to do, will not fix the OP's problem.
     
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  13. chadjwil

    chadjwil Active Member

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    And FYI, if you only use the 16ohm output then the ground mod won't do anything for you...still not a bad idea to install it when it's convenient, but it won't fix what ails you if you only use the 16ohmer.
     
  14. chadjwil

    chadjwil Active Member

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    Fair enough J, but neither will stickin fresh tubes into it if he's gonna cook em off in 3 days. Agree?
     
  15. jcmjmp

    jcmjmp Well-Known Member

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    Right, but if he's changing power tubes, I'd have to assume that he would bias them.

    To the OP, try this: Plug into the effects loop return and play. If the problem dissapears, you've isolated the issue to V1, V2 & V3.
     
  16. chadjwil

    chadjwil Active Member

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    I was just trying not to assume anything, and that was based on the comment he made about not knowing how to use his meter anymore in an earlier post. I know it can sound condescending to write up a huge post about biasing when it wasn't directly asked for, but considering the circumstances I thought it wise to do so.

    I'm not trying to get into a disagreement with you J, just wanted to clarify myself a little.

    And yes, I think it's very unlikely it will fix his issue. If it is running too hot then the damage is surely done by now, but it's easy to check and it would be helpful to know.
     
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  17. LBKENNEDY

    LBKENNEDY New Member

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    probably sling a cat to the city limits of knoxvil
    dude, i just did a dsl 100 of the same age as yours recently, i too had those static pops and
    whizzes, when i opened the hhed and safed it, i turned
    over no i think it was the card with sockets had a white granular deposition such
    as sea salt in between some of the hv traces, could even see corona ar c markings frim sam2.
    used oencil eraser and cleaned boards and cable connextionsand thinngs started sounding
    mo better lbk
     
  18. jcmjmp

    jcmjmp Well-Known Member

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    I didn't understand a thing in this post. Is this how the kids today write?
     
  19. Moose Lewis

    Moose Lewis Well-Known Member

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    Thanks for the info guys. It's going to American Viking to get the work done - he's done some excellent fixes for me in the past. At this point, I'm just gathering intel to shorten the shop time.

    I didn't sleep last night. Just sat up reading any threads I could find on the DSL 100. Frankly, most of it goes right over my head. I think when I learned to build and wrangle computers along with coding for web sites, it was all the tech my old brain could handle, lol.

    It does have brand new tubes all 'round... doesn't mean one hasn't gone feet up ~ and it does need the bias set. The guy it came from told me it was fine, and was perplexed about the noise since he had sat and played it all day after re-tubing. That might be the source of the problem. I'm givin' AV extra 12AX7s, just in case.

    I will give this a try jcmjmp - thanks.
     
  20. chadjwil

    chadjwil Active Member

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    Well it's in good hands Moose. Let us know what the problem is/was when AV gets ya fixed up.
     

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