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 Supporting Member

    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.

  4. Fuzzhead


    Sep 26, 2005
    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 Supporting Member

    ...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 Supporting Member

    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.