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Thread: Another reverb down, unbelievable

  1. #21
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    Quote Originally Posted by hinekadon View Post
    audio loop ,something has lost its ground or the center tap of the 15vdc rails
    Center tap is connected to ground.
    Looks like the ground needs an antenna ... If I place one of my meter probes on the chassis, with the other probe not touching anything, the noise disappears. That's weird !



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    Default old fart

    you have an open circuit input not connected to the ground uhummm is that the way to describe it ? I know what i mean but do you?mite be getting old eh hahaha
    ok a lot of these have three contacts per input plugs one tip next ring then body the tip is normally connected to ground via the last connection this opens when the plug is put into an input and the tip carries the signal so check the input sockets regards don
    Last edited by hinekadon; 31-08-18 at 07:52 PM. Reason: more

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  • #23
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    Quote Originally Posted by hinekadon View Post
    you have an open circuit input not connected to the ground uhummm is that the way to describe it ? I know what i mean but do you?mite be getting old eh hahaha
    ok a lot of these have three contacts per input plugs one tip next ring then body the tip is normally connected to ground via the last connection this opens when the plug is put into an input and the tip carries the signal so check the input sockets regards don
    Yep I get where you're coming from ( although I had to read it 5 times )
    Ok so I checked all plug switchings and run emery through them.
    If I remove plug A (send/receive) the noise ceases.
    Both instrument inputs & headphones have gnd on the tip.
    All sockets have gnd on their shield except headphones.
    Pedal, send and receive do not have gnd on their tip. Don't think gnd is meant to be there because the solder joints are good and the ground wire connects all the way back to the chassis.

    Do you think maybe that resistor I replaced (1k) might be too high ? That runs from the headphones tip through the resistor,then through a green cap to gnd.



    Last edited by loopyloo; 31-08-18 at 10:57 PM.

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    The Spring is an aerial for 100Hz from the power supply.
    Have you still got the cover off ?

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    loopyloo (01-09-18)

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    Default dumbguy

    yep could be but as i said im an old fart and the memory is not that great ,had a bit of a look at a jansen from the old circuits and it was 120 ohms so you cant do any harm playing there have a play you will learn more that way rather than my brain ill send you a pm regards don

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    Quote Originally Posted by Reschs View Post
    The Spring is an aerial for 100Hz from the power supply.
    Have you still got the cover off ?
    Are you referring to the reverb spring ?
    I thought about that early on. It's mounted in a sheet steel box like any usual reverb tank but it doesn't have a metal cover like some do. It just sits in the bottom of the amp face down. Anyway, when I first noticed the noise it was facing up towards the amp and then the thought hit me so I moved it back to its secured position but that didn't help the noise.
    I even tried turning off the room fluro.
    Last edited by loopyloo; 01-09-18 at 01:03 AM.

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    Quote Originally Posted by hinekadon View Post
    yep could be but as i said im an old fart and the memory is not that great ,had a bit of a look at a jansen from the old circuits and it was 120 ohms so you cant do any harm playing there have a play you will learn more that way rather than my brain ill send you a pm regards don
    Guess I'll try a lower value one tomorrow then.
    Last edited by loopyloo; 01-09-18 at 01:01 AM.

  • #28
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    Ok so here's what I found.
    Placing a 220ohm resistor in parallel with that other resistor to create 180ohms made no difference, but to clip a lead from the chassis to the body of the reverb tank removes the noise.
    The ground side of the input to the tank does not connect to the chassis. Don't know if it's supposed to but then the output does. I tested this by checking at the board with the tank disconnected.
    I guess I'll pull the board again and see if something's amiss there otherwise it might be just as easy to run a wire chassis to tank body.
    Thoughts ?

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    wire to ground thats a good idea glad to see your thinking ,
    thinking???? i dont think i have seen a reverb tank without a top ??I have seen them sitting in the bottom of the case or stuck on the back of the speaker magnet
    the reverb unit will have an audio effect from the speaker without the top but likely to create some weird effects
    are you familiar as to the theory of the reverb unit and the principles it works on ??? educate available if you want it ?? regards don

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    Spring reverberation units are very simple in principle and have been around for 50 years or more. In simple terms they are a delay line.

    There is an extremely good in-depth article at .

    The article is rather lengthy but don't let that fool you into thinking such units are complicated at their heart. They aren't.

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    a good article tristren but it dont tell you that the springs are a magnetic coil and the winding interact with each other to form the delay thus causing the delay to be out of phase to the input its actually the out of phase that is picked up by the output therefore forming the delay , if you want to create sounds that are re reverberated this can also be done by placing magnetics to alter the delay magnetics in the springs thats a lot of fun regards don

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    Got it ! It's in the reverb tank.
    See when I first tested why the reverb wasn't working, one of the first things I did was to disconnect the tank coils for testing. It was when I reconnected them that the noise was set to happen.
    Look at the following photos you'll see how the ground line (black wire) on each coil is joined to the connector shield by solder bridging. I did not notice one of them was not joined after resoldering, so yes, it's my fault. But then again......maybe not.
    Bridging the connector didn't work either, hmmm !

    It now has a wire from the tank case to the chassis and works perfectly ? ... nope, I put the whole thing back together and the noise is back.
    Stuff it.... it can stay that way.





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    Default whoa back

    ? the springs havent by any chance been stretched ? cos if they are sitting on the magnetic shield the reverb will be yukky

    hey looking at the casing its covered in rust therefore the socket mount is rusty and forming diodes hence the noise mite have to remove the sockets and sand rust off for hey presto don
    Last edited by hinekadon; 01-09-18 at 06:44 PM. Reason: more

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    Quote Originally Posted by hinekadon View Post
    ? the springs havent by any chance been stretched ? cos if they are sitting on the magnetic shield the reverb will be yukky

    hey looking at the casing its covered in rust therefore the socket mount is rusty and forming diodes hence the noise mite have to remove the sockets and sand rust off for hey presto don
    Nah the springs are good and both sockets are well grounded, I made sure of that.

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    ok the short out the output noise /no noise
    noise = from the reverb unit grounding
    no noise from cabling to input
    put scope on various ground points get the highest acv its closer to the source then should be able to find it ???

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