Smoke from guitar amp during recording

Discussion in 'Guitars' started by Unregistered, Mar 26, 2012.

  • AT5047

    The New AT5047 Premier Studio Microphone Purity Transformed

  1. Unregistered

    Unregistered Guest


    my band and I have decided that we're going to record a few of our own songs to have something to put up on youtube, myspace etc. Since we don't have the hardware or cash for a proper studio, we decided to create a poor-mans studio using my digital bass-pedal (which acts as a soundcard when connected to a computer). The idea was to hook it up like this:

    Instrument -> Amp -> (Headphones Out) -> Pedal (Bypass mode) -> Split to the PA we use for voice (and feed the guitar through monitors since amp is mute), and to the computer.

    I hooked it up like this at home with no issue, and recorded some tracks with good quality. I then took this down to our rehearsal room, and plugged it in. However, when we started playing (20 minutes after plugging it in) the sound very quickly became distorted, and after ~1 minute smoke started coming out of the PSU in his amp, so we unplugged everything. However, no accessible part of the amp, cables or such was warm to the touch, and when we plugged it back in after 20 minutes (minus recording stuff) it worked fine. Our guess is that the bad electrics in the room caused a ground loop, though we're not sure. If it's valuable info, the PA and pedal went onto a split socket, which was connected to the same wall socket as the computer. Another monitor went into its own wall socket, and the amplifier went into a third wall socket. All sockets are supposed to be on the same fuse, and everything has grounded security plugs. The amp is a HiWatt G50 112R, 50-watt combo. The pedal is a Zoom B2.1u, and no idea on the PA.

    Anyone got any ideas why this happened? As said, we think it's a ground loop but that's a very uneducated guess, at best. A few ideas we dismissed were that the phones out would be high-powered (compared to a lineout), as well as an impedance mismatch as those would've caused a distorted sound later in the chain, or caused the pedal to error. However, no other equipment showed any signs of damage, and this worked when recording at home.

  2. dvdhawk

    dvdhawk Well-Known Member

    Dec 18, 2008
    Western Pennsylvania, USA
    First, let me say, I admire your creative use of what you've got to work with, that shows some degree of ingenuity.

    As far as your smoking amplifier, I'm much more inclined to go back to an impedance mismatch overheating the headphone amp circuitry. Or a bad/incorrect cable can cause the amp to overheat. Have you plugged in a pair of headphones to confirm that still works?

    An impedance mis-match could take some time to overheat.

    From what I see, the Hiwatt has a "Line Out", why not use it instead?

    Ground loops cause constant humming, which by itself wouldn't cause something to overheat and smoke. It can kill speakers over a very long period of time, but not in 20 minutes.

    If however, the electrician got sloppy wiring the receptacles and wires got reversed all manner of welding and pyrotechnics can occur. - most of those result in an instantaneous shower of sparks when you complete the short - not 20 minutes later.
  3. Unregistered

    Unregistered Guest

    While I'm not entirely home on the impedance concept, I cannot properly understand how an impedance mismatch could cause a PSU to overheat. I'm guessing that my soundcard sort of acts as a pump, and the impedance difference made the PSU struggle to deliver enough current (Garden hose -> fire fighting nozzle) causing the garden hose to overheat when trying to match the fire fighting nozzle throughput. Correct?

    If so, what sort of damage could've been done to the amplifier? Is it safe to continue to use it? Obviously, a repairman would be wise but we're kinda strapped on cash, else we'd have done it the proper way... So I guess we've dug deeper now. :p¨

    As for not using the line out - I had used the phones socket on my 15 watts bass amp without issues at home so I told my guitarist to stick it in the phones socket. I guess I've either been lucky with my amp, or it's modern enough to handle the impedance mismatch (or another million reasons). In the end, it has no line-output nor does any of my other amps as far as I know (Got a Laney 15w and a Fender 110w top/box). How would we go about recording those? We do have microphones, but they're live-use primarily, and give us lousy recording quality (we tried that after our 'mishap'). You literally can't hear the difference between say E-Em chords, and so on. Since we have a lot of such transitions it waters down our music a lot.

  4. Unregistered

    Unregistered Guest

    I am inclined to agree with DVDhawk about it being an impedance problem. I am also surprised that it was your amp that gacked an not the things down the chain. By using the headphone output you were sending a signal that is significantly more powerful than the microvoltage that the receiving devices were expecting to see. Also I imagine that you used a "mono" guitar cable to come out of the amp, and possibly shorting to chassis either the left or right signal from the headphone output. Chances are all you did was burn out a capacitor in the headphone circuits amplifier stage, but it should be looked at. As a general rule it is not a good idea to use headphone outputs as signal sources, there are so many potential things to go wrong.

    As to how to record it, the answers are endless (such as using a DI box that accepts signals from an amplified source like a Countryman type 85 - But I am not a fan of that), using a microphone usually works well, because after all the sound of the speaker is often what you desire to capture and not a direct out from a guitar or amp. It really depends on what your trying to accomplish.

    And lastly the problem in all likelyhood was not a ground related issue, but one thing to remember is grounding problems in musical setups can be potentially lethal so never use a ground lift plug or break off the ground pin on your AC cords.

    Cannonball (not yet signed up)
  5. RemyRAD

    RemyRAD Member

    Sep 26, 2005
    If you took any guitar cable out of the output of your amplifier to the input of your next device, that cord/cable may have caused that issue? That's because a lot of amplifiers do not want to see a shielded cable on the speaker output. It's capacitive and amplifiers don't like to be loaded with capacitance. They only want to see a low impedance, resistive load. So it's not unusual for an amplifier that is not properly loaded down to exhibit the problem you described. Had you placed an 8 ohm resistor across the output of the amplifier and then fed that to your input source, your amplifier would like it better. So it's not necessarily a ground loop. But plugging in all of your AC into numerous outlets around your room doesn't mean you won't have a ground loop even though it's on the same fuse/circuit breaker. If it's all on the same circuit, there is no reason to plug it into the other outlets. You'd be better served by pulling everything from the same 20 amp outlet utilizing a couple of those 1 by 6 AC strips. Ground loops, everybody knows, causes hum. Ground loops can also cause ultrasonic oscillations that you can't hear. The transistors hear it just fine and they go super thermal. The input on your equipment may not even pass that frequency? Meanwhile, the amplifier is trying its damnedest to pump that out and without a load. OMG! Noooo. Poof.

    Sorry about that chief...
    Mx. Remy Ann David

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