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Does a capacitor hide the load?

  1. Oct 18, 2009 #1
    Here's a question no one at present seems to know the answer to.
    In "Talk Boxes" from the 70s they used a light bulb as a limiter to prevent overload to the compression driver that then sent the sound into the plastic tube you have in your mouth.
    I put a 33uf cap in series with the + lead to the compression driver and this seems even better giving a cleaner less distorted sound from the driver by reducing the lower frequencies.
    But! when trying to measure the ohms to my valve amplifier the cap stops any ohms/load that can be read on my ohm meter.
    Does this mean my amp is not getting a safe 8 ohms load on the valve output stage and could be damaged? or is this safe?

  2. jcsd
  3. Oct 18, 2009 #2


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    As long as the impedance of the thing is of the order of 8 ohm you amp will be fine.
    Ohmmeters measure resistance, not impedance. It is useless for this type of measurement.
    Resistance is essentially the "impedance at DC", but there is no direct relation between the resistance at DC and the impedance of the circuit at the frequencies that an amp is made to operate at.
  4. Oct 19, 2009 #3
    It's OK to put a higher resistance than the specified 8 ohms on any normal amplifier - the problems start when the resistance is too low. If resistance is too low the output transistor (or other device) may try to deliver more current than it can safely handle into the load, resulting in a blown-up amplifier.

    Please note that this is a 'usually true' answer but more details are needed about both amplifier (circuit diagram would be nice!) and load for me to be completely confident about my reply.
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