Squealing in 5e3 with channels bridged and all knobs turned way up

Discussion in 'Shock Brother's DIY Amps' started by doof, May 14, 2021.

  1. JamesAM

    JamesAM Tele-Meister

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    This might be a long shot, but what guitar are you using and how close are you sitting to your amp when you check? I actually have a similar problem if I’m too close to the amp or in the wrong position with my es-335 because my PAFs aren’t wax potted and I’m in kind of a small room. Do you have another guitar to test out, and does turning guitar volume down fix it? Your hand could be shielding a slightly microphonic pickup.

    The amp looks awesome, you should be proud! Another long shot: the runs on v2 might be maybe a teeny bit long and could be causing some oscillation with the heaters, so it might help to poke around there a bit.

    I am probably missing it in your pics, but I don’t see a CT from the PT or an artificial CT with 2x 100R coming off the pilot lamp- not sure if that would cause the noise, but it’s definitely good praxis to include for safety I think.

    Good luck!
     
  2. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    This is what sometimes happen when you build an amp with a bunch of mods rather than following the tried-and-true circuit/layout first. Did you use the "Trainwreck Type-3 Post Phase Inverter Master Volume"? Looks like a great way to add an antenna to your power tube grids if you're not careful -- I would try ripping that out before any other band-aid fixes.

    Your wiring looks decent overall, though! :)
     
  3. doof

    doof Tele-Holic

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    Well, after a miserable week at work I was finally feeling motivated to work on my 5E3 some more last night.

    • I had originally grounded the Tone Cap and Bright Volume Lug 1 to the backs of the pots. I removed those connections and wired the tone cap to lug 1 of the Bright volume, and then connected that directly to the preamp ground buss.
    • I moved the HV Centre Tap from the ground lug by the transformer to the turret of the first filter capacitor.
    • I tried to add shielded wiring to the other two lugs of the Master Volume, and the thin wire kept breaking off. Two wires, twice in a row as I was putting everything together. At that point I decided to just remove the Master Volume all together and just wire it up with the stock 4 inputs.
    • To reverse the MV mod, I installed the 1M PI Grid Leak resistor and connected Pin 7 of V2 to this resistor, and then added the jumper wire between the 0.022 coupling cap and the junction of V2 Pin 7 and the 1M Grid Leak resistor.
    After getting everything together, I fired it up and now there's a bigger problem. The signal is very weak and anemic, very little volume even when cranked. I'm feeling pretty dejected at this point, but I'm trying to stay positive since it must be just something simple I'm missing.

    I'll try to look at it more over the long weekend coming up, but as of right now I think I need a little time away from this amp haha.

    Thanks again to everyone offering up ideas and suggestions, sorry I'm not replying to individual comments! When I have better news I'll update again.
     
    Last edited: May 21, 2021
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  4. Commodore 64

    Commodore 64 Friend of Leo's

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    Don't get dejected! We've all been there. I'm there with every damned amp I build, for at least a day or 2! They never work on the first try.

    Now for some tough love:

    You've made a big mistake that we've all done. You changed a bunch of **** at once and now you don't know WTH is the culprit.

    If you would have taken my advice. CHANGED NOTHING, except split your 100k plate resistor into 2,56k, and tapped the center, you'd have a perfectly functional amp. And it would have taken you 90 seconds. I'm almost willing to bet you a UPCB and jr. Chassis on it. But it's too late for that now. :p

    • Every cathodyne amp I've ever built has that MV mod on it. That ain't it.
    • Your input wire is shielded coax. That was fine.
    • 8 million amps in the world have their pots grounded to the case. It ain't that.
    • Every amp I've every built or seen has the HV center tap to ground at the chassis or on a transformer lug. It wasn't that.
     
    Last edited: May 21, 2021
  5. monkeybanana

    monkeybanana Tele-Holic

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    Keep at it man! These simple schematic are very deceiving little devils! You’ll get there.
     
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  6. doof

    doof Tele-Holic

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    You're right, man. You're completely right. I appreciate the tough love, I really do. I've been building pedals long enough I know not to make a bunch of changes at once, but I thought I'd save myself the hassle of prying that board out of the amp more than once, but here I am anyways! I only tested it on the one input last night when I got the weak signal, before calmly, and without cussing, turning off the amplifier and deciding to deal with it later. I'll try the other inputs tonight. I'm wondering if the shielded cable on that input might be at the point of breaking off now after all that handling. Silver lining is that this is a learning opportunity!
     
  7. doof

    doof Tele-Holic

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    I've played this with a tele, a strat, and an SG and it reacts the same for all of them. If I move to a different position, it changes the amount of hiss I hear, but it didn't help the squealing. Thanks for the kind words, I tried to do a good job but neat wiring has never been one of my strengths. I had the HV CT tucked away below the standby switch, but have since moved it to connect directly to the cathode of the first filter cap, and I used an artificial centre tap on one of the power tubes connected to an elevated voltage.
     
  8. Commodore 64

    Commodore 64 Friend of Leo's

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    I tried to show you my street cred. I showed you the table I made chasing squealing and whistling at the top end of the dial(s). Hahahahah. Always learning. That's what we do.
     
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  9. doof

    doof Tele-Holic

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    Well everyone, I have a beautifully playing 5E3. There was a bad solder joint where the jumper from the 0.022uf cap connects to the 1M resistor, no continuity. I replaced that wire and triple checked continuity, threw everything back together and she sprang right to life, without a master volume control though. Standard 4 inputs now. I can dime all the knobs now and there's no oscillation whatsoever. Feels good to finally consider it done. Thanks again to everyone for their comments and suggestions, especially to Commodore! Sorry I didn't just listen to you in the first place! :)

    I took a few pictures in the driveway last night, I hope you like it!
     

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  10. Commodore 64

    Commodore 64 Friend of Leo's

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    Well if you had listened to me, it wouldn't have fixed your problem. So no apology necessary, and I shall eat a slice of humble pie :oops::oops::oops:. Glad you are up and running.


    Now, put the MV back in. :p
     
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  11. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Good for you. Well done. I admire your patience and good attitude.
     
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