Record Amp High Level out to Computer

Discussion in 'The Projects Forum' started by chetgnegy91, Jan 21, 2012.

  1. chetgnegy91

    Thread Starter New Member

    Sep 17, 2010

    I have a Mesa Dual Rectifier Guitar amp (100W) head that I would like to record from. I live in a house with others and would like it to be relatively silent when doing so. I bought a 16 Ohm, 100W resistor online to dissipate the power of the head, and I was hoping that I could use the signal across the 100Ohm resistor to record into my computer. See the picture below. The 32K and 100 Ohm resistors have a power rating of 1/4 or 1/2 W. I would just hook this up and find out if it works, but amps and computers are are expensive. Is there any reason why this would not work?

    I am using the 16 Ohm output on my amp and using an audio jack and 14 AWG wire to connect the jack to the resistors. My other idea was to use a transformer, but this seems easier (I already have all the parts).

    Thank you,

    The peak power is shown for the 16, 100, and 32K resistors are shown in the picture below. (In that order)
  2. MrChips


    Oct 2, 2009
    Good heavens, why do you need 100W?
    Turn your volume control down and a 1/4 or 1/2W resistor will work.
    Also many amps have a headphone out, Line out, or Monitor out. You can use these also.
  3. mik3

    Senior Member

    Feb 4, 2008
    100W is the maximum output power of the amplifier. If you use high value resistors above 10k, their power dissipation will be less than 1/4W. The amplifier will not deliver its maximum power but the voltage across the resistor will be the same.

    I do not suggest you to do it because you might destroy your computer if the input voltage to the mic line is big enough.
  4. chetgnegy91

    Thread Starter New Member

    Sep 17, 2010
    The amp sounds far better at high volumes. I use the 100W resistor because it is taking nearly all the power of the amp (because I have detached the speakers). I chose the resistances so that the voltage across the 100 Ohm never exceeds 1V. The math works out fine on all of this, but I don't have a lot of experience doing this in practice, so I was mostly wondering if there is something I am overlooking in that aspect. I want the amp to deliver as much power as possible to the resistor, otherwise the power stays in the amp. Ka-boom!
  5. Georacer


    Nov 25, 2009
    Doesn't your amp have a headphone output? You could use that output in that case.
  6. Adjuster

    Well-Known Member

    Dec 26, 2010
    Another approach might be to get a low-level distortion effects unit for this, and / or a small practice amp.

    Running an amplifier at high power in a way where its sound level would not be noticed might tempt you to thrash it too hard, possibly shortening its life.
  7. rollinstoney

    New Member

    Feb 14, 2012
    The reason your amp sounds better at high power levels has nothing to do with the output power rating of the amp, it is the relationship of the output to the speaker(s). The sound you get from the amp input is the same as the as the output less the amplification. there is no sound output from a resistor, and I'm sure that the frequency response of the resistor will be pretty bad.
  8. Audioguru

    New Member

    Dec 20, 2007
    I think you like the sound of the "100W" amplifier clipping like mad and producing severe distortion when it is turned up to maximum output. A 0.5W amplifier can also be turned up so that it is clipping like mad and is producing severe distortion.
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Come on guys..There is NO need for an amplifier at all for this problem.

    To record an electric guitar on your computer you just need the right cable (standard to mini audio cable) to plug directly into your sound card (line input). And jam away.
    You can get a "better" sound card for really cheap if your stock one isn't "good" enough.

    They even have USB devices for recording guitars for like $30 or less. Or stuff like a tascam USB audio interface for under $100. There are TONS of solutions.. Not a single one requires the amp.
  10. Audioguru

    New Member

    Dec 20, 2007
    The pickup of an electric guitar needs a very high impedance preamp for it to deliver high frequency "twang" sounds. Its inductance resonates with the capacitance of the connecting cable at about 5kHz to make a peak of the "twang" sound. A load lower than about 3M ohms damps the resonance and makes the sound muffled. The poor quality of guitar speakers also makes the sound muffled.

    Here is a high input impedance preamp for an electric guitar pickup that explains it: