DIY 5E3 humm hiss?

Discussion in 'Shock Brother's DIY Amps' started by Preacher, Feb 11, 2019.

  1. Preacher

    Preacher Friend of Leo's

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    OK all,
    some of you know of my 5E3 Trepidation Amp build.

    So I have been enjoying the tar our of it lately and have noticed something.

    When I have the volume of Volume 1 past 5 I get a pretty good hummmm, hiss out of the speaker. But when I roll back the tone it pretty much goes away.

    So I have been playing through channel 1 and rolling the tone back to eliminate the humm/hiss.

    So yesterday I am messing around and decided to try to play with channel 2s volume while I was playing through channel 1 as everyone says it affects the tone. So channel 2 was set at 8 on the dial. I played a chord, had hiss and humm and then rolled the volume back on channel 2 and it decreased the humm/hiss to nothing.

    With the volume up on channel 1, volume all the way down on channel 2 I get a just a touch of humm, but when I run volume 2 up the hum increases although I am playing in channel 1.

    Do I have a faulty pot or a bad ground on pot channel 2?

    I have checked all the other grounds and I should be good but this hum persist.
     
  2. flyswatter

    flyswatter Friend of Leo's

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    It would be helpful to see some gut shots, particularly some of your grounding scheme to determine whether there is a grounding issue at large. If you notice hum, it is helpful to know whether it is at 60Hz or 120Hz. One way to check if it is either (or both) of those is to download WAV files of sine tones and play them on your computer or phone against the hum from the amp. Google around; they are plentiful.

    One thing you might check, too, is whether your input jacks have grounding pins (aka: tip shunt) on the jacks that close properly when no cable is plugged in. "Live" jacks on the unused channel can be a source of noise when you turn up the volume, because you end up amplifying noise in the channel circuitry that would otherwise be eliminated if the jack shorts to ground.

    It sounds like when you turn the tone down, you are simply filtering out the noise frequencies, not actually curing the problem.
     
  3. Lynxtrap

    Lynxtrap Tele-Holic

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    Hum and hiss are two completely different things. "Mmmmm" and "ssssss". Do you have both?
     
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  4. clintj

    clintj Friend of Leo's

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    Hiss is inherent in tube amps, and circuits using carbon comp resistors and no negative feedback (most vintage style 5E3s, IOW) are especially prone to it.

    +1 on some pics

    Sent from my Pixel 2 using Tapatalk
     
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  5. D'tar

    D'tar Tele-Afflicted

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    You may get lucky and have reduced noise by changing v1 to a different tube. Engage nfb and reduce further. My sylvania 12ay seems noisy at volume but once the music starts it is irrelevant.
     
  6. Preacher

    Preacher Friend of Leo's

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    Last edited: Feb 14, 2019
  7. jtcnj

    jtcnj Tele-Holic

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    I too have wondered how much noise is considered "normal".
    I think some low hum is typical (higher in SE circuits), and increases a little with volume, while hiss may increase more with volume.


    mmmm mmm mmmm is definitely diferrent than hisssssssssssssssssssss

    Things can get pretty noisy high volume, single coils, and gain pedals.
    Especially when you stop playing and take you hands off the strings.

    So I just keep playing.
     
  8. Preacher

    Preacher Friend of Leo's

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    Just to clarify, once the music starts you don't hear anything but the guitar. It is when the amp is setting with nothing plugged in.
    I will say that I compared it to a vintage '56 Deluxe and the hmmm was comparable.
     
  9. Preacher

    Preacher Friend of Leo's

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    I need to check this as well as I had one jack that had an issue when I started that was shorting out the jack even with it plugged in.
    thanks for the suggestions.
     
  10. flyswatter

    flyswatter Friend of Leo's

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    Good luck and please report back. If you are using the Switchcraft-type tip shunt jacks, I find they often have issues with the grounding tab either not closing when nothing is plugged in, or closing back up against the sleeve of the plug. Usually a little careful bending will fix it.

    One little test I always do is to plug a short cable into the jacks with the DMM set to continuity test, then to ohms. Clip one lead to the cable (tip then sleeve), the other to the points where you should have a signal path or short to ground and the beeps on the DMM will tell you what's what. The resistance test will show whether you have the proper 68K ohms on the high-impedence input and 33 or 34k on the low impedence input (caused by either one 68K grid resistor or both 68Ks in parallel). I fixed a mistake on my last build when I discovered only 33ohms on what should have been the high imp. input -- because the grounding tab on one of the other jacks was bent open.

    Good luck
     
    Last edited: Feb 15, 2019
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  11. Uncle Daddy

    Uncle Daddy Tele-Holic

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    I used metal film grid stop and load resistors, and it's almost hiss free apart from when I dime the tone pot.
     
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