Yamaha G50-112 II

Discussion in 'Amp Central Station' started by Telecastoff1, Apr 11, 2019.

  1. Telecastoff1

    Telecastoff1 Tele-Holic Silver Supporter

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    I have a Solid State Yamaha G50-112 II guitar amp that started making a "Whooshing" noise that gets louder as the volume goes up. It does this on both channels. I pulled the chassis out of the cab. Cleaned the pots and jacks. Looked for obvious burnt components, but everything appeared normal. Cleaned all the jacks. Looked for loose wires and connections, they seem fine. Searched for broken, cracked and cold solder joints, to no avail. Did the wooden chopstick "poke-around" and nothing changed.
    Has anyone experienced this and possibly know where/what the culprit might be, without me throwing parts at it indiscriminately? Thanks.
     
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  2. Lynxtrap

    Lynxtrap Tele-Holic

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    Can you describe the problem in more detail? Is it a constant hiss or does it come and go? Is it affected by the EQ? Reverb? Does it appear with nothing plugged into the amp? Does the guitar sound normal through it besides the noise?
     
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  3. mexicanyella

    mexicanyella Tele-Holic

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    Adding to this...if the amp has effects send/return jacks, or preamp out/power amp in jacks, you could see if the whoosh was present in the preamp signal by sending it to another amp’s effects return. Sending a known “whooshless” preamp signal from some other preamp into the Yamaha’s effects return or power amp in jack could let you know if the Yamaha’s power amp is involved in the whoosh noise, also.
     
  4. Telecastoff1

    Telecastoff1 Tele-Holic Silver Supporter

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    The noise starts when the volume or gain controls start coming up. No noise when the volumes or gain are turned all the way down. The guitar sounds normal, but the whooshing is riding right along with it. The tone of the whooshing is affected by turning the Frequency control either way.
     
  5. Telecastoff1

    Telecastoff1 Tele-Holic Silver Supporter

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    There aren't any effects send or return jacks on this amp. Just two speaker jacks, two remote footswitch jacks and a direct out jack. None of them, or the reverb control have any effect on the whooshing noise.
     
  6. galaxiex

    galaxiex Tele-Holic Silver Supporter

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    How old is the amp?

    Solid State amps have electrolytic caps that need replacing, just like tube amps.
     
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  7. Chiogtr4x

    Chiogtr4x Poster Extraordinaire

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  8. mexicanyella

    mexicanyella Tele-Holic

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    The direct out jack is functionally the same as an effects send jack, or a preamp out jack. If you plug this into some other amp’s effects return or power amp in jack, or a mixer channel’s line input, or a rack power amp driving a guitar cab, you will be tapping into the Yamaha’s signal path between the preamp and power amp stages of its circuitry. If you do that and still hear the whoosh, you know the problem occurs before the Yamaha’s power amp stage. If you do that and don’t hear the whoosh, you’ll know the problem occurs downstream of the preamp stage. If nothing else, doing this will give you a little more info to get a repair guy started if you choose to fix it.
     
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  9. W.L.Weller

    W.L.Weller Tele-Holic

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    20190411_194904.jpg

    It is the 50w combo version of this amp, right? I know you said the frequency control changes the pitch of the whoosh, do the level and Q controls also affect it?
     
  10. Telecastoff1

    Telecastoff1 Tele-Holic Silver Supporter

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    Yup, the Level and Q controls definitely have an effect on it. They change the over-all tone of the "whooshing". In fact the Q control tends to make it even more profound...louder and erratic.
     
  11. Lynxtrap

    Lynxtrap Tele-Holic

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    It should be safe to say the problem is between the input jack and the volume control in the preamp. Can't say what it might be, but that's where I would look.
     
  12. W.L.Weller

    W.L.Weller Tele-Holic

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    When @Telecastoff1 says that the level, frequency and Q controls affect the unwanted noise, he's talking about the parametric EQ section of this amp, which is after the preamp.

    Does the 50 watt version have the switchable A and B channels? Is the same whooshing present in both channels? Because that would make me think the problem is with the parametric EQ.
     
  13. Telecastoff1

    Telecastoff1 Tele-Holic Silver Supporter

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    Yes, it is switchable between both channels. And yes, it is present in both channels.
     
  14. W.L.Weller

    W.L.Weller Tele-Holic

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    The issue you may run into is that the Level pot, with the center detent, isn't easily available. If your amp still has the ca. 40 year old electrolytic caps it left the factory with, those are overdue for replacement, but I'm not positive that they're the source of the problem you're having. The other issue is going to be finding someone willing to work on the amp. If you're comfortable doing the work yourself, I'm pretty sure you can find the service manual and schematics online. If you can't, I can at least send you the G100 version, I assume stuff like the EQ board would be identical.
     
  15. Lynxtrap

    Lynxtrap Tele-Holic

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    Yes, that indicates that the noise comes from the preamp. So does the fact that it follows the volume and gain controls.
     
  16. W.L.Weller

    W.L.Weller Tele-Holic

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    No, the parametric EQ is after the preamp in this amplifier, which has 2 channels. And he just said that the noise is present in both channels. To me, that sounds like an issue arising after the preamp.
     
  17. Lynxtrap

    Lynxtrap Tele-Holic

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    I could be, but if noise is present at one stage, it is likely to have gotten there from a preceding stage. In this case where the noise is following the volume control, it seems to stem from somewhere very early in the chain.
     
  18. Telecastoff1

    Telecastoff1 Tele-Holic Silver Supporter

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    Would an opamp in the preamp stage do this? Any idea anyone?
     
  19. Tele-phone man

    Tele-phone man Tele-Afflicted

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    Not on this amp. The line out jack is fed directly from the power amp output to the speaker. They reduce it with a voltage divider to line level. It is NOT a preamp output.

    I have the schematic and service manual for this amp, but not in pdf format, just in print. When I get a chance later I will look and see if I can tell where the most likely trouble spot is that symptom set. As others have noted, you are most likely looking at a dried-up electrolytic cap in the preamp circuitry.
     
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  20. Lynxtrap

    Lynxtrap Tele-Holic

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