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How much power should a Thunderfunk TFB550 pull in repose?

Discussion in 'Amps and Cabs [BG]' started by westland, Nov 27, 2005.


  1. westland

    westland

    Oct 8, 2004
    Hong Kong
    I put an ammeter in line with the plugs on my electronics, and was surprised to find that at 220 volts, the TFB550 pulls a bit over 1 amp. This changes only slightly whether there is no signal being amplified, or if it is cranked up. I am not sure about the circuit design, but I had heard that power consumption at rests was a characteristic of Class A amps. Is the TFB550 a Class A amp, and is this level of power draw to be expected?
     
  2. Well for starters 1A at 220V is 220W...:D

    I'm sure Dave will chime in here, but I would guess that the TFB550 is a class AB amp. The preamp circuitry is probably pure class A, though it's possible he uses opamps which wouldn't be class A. A class AB power amp does operate in class A at low levels. You need some class A operation to prevent distortion around the 0 crossing of the output signal. How much the amp operates in class A varies from amp to amp depending on design.

    Class AB amps are only about 50% efficient as well, so if the amp can produce 550W output power, it can draw around twice that. So when you look at 220W at idle, it's really only 1/4 maximum draw. Crank it up with a pure sine wave at the input and you'll see current draw rise..

    Unless the amp is getting inordinantly hot, I'd say that current draw is normal.
     
  3. +1. The preamp is usually class A, constant current draw regardless of output level. TF is tube pre also, right? Need power to produce heat in the tubes. And correct, 1A @ 220V = 220W, not 550.... Add an AB power amp, I wouldn't be surprised at an amp while idling. That'd be equivalent to about 2 A at 110V, still not so high. That's not much more than a big light bulb.

    Randy
     
  4. Fuzzhead

    Fuzzhead

    Sep 26, 2005
    Australia
    The Thunderfunk is solid state with a tube emulation switch. I think the previous "550 Watts" figure was relating to the rated output, not an actual calculation based on the amps his was drawing. :)
     
  5. K Dubbs

    K Dubbs Just graduated from OSU, Go Bucks!

    Mar 16, 2002
    Toledo, Ohio
    its 100% solid state

     
  6. westland

    westland

    Oct 8, 2004
    Hong Kong
    ...Duuuuhhhh (head knocking on wall) ... no, this resulted from a minor brain fart on my part ... rather than multiplying I unconsciously put a TFB550's draw at 550 watts
     
  7. westland

    westland

    Oct 8, 2004
    Hong Kong
    Thanks for the quick response ... OK, this all makes sense. Just curious about what would be 'normal' operation. I notice none of my other electronics come close to 1 amp; but then they don't have a power section.