SK47

The SK47 is a discrete Current Feedback Amp that is pin compatible with the API* 2520. It is a low noise, high performance CFA that will perform extremely well in every audio applications.

Highlights

• Pin compatible with 2520 and “99” DOA's
• 100% Class A with RL ≥ 600 Ω
• Low noise, high speed
• Very musical distortion, mostly second harmonic and decreasing level with the harmonic rank
• Large supply voltage range
• Output short circuit protected
• Rich 20mA quiescent current

More details...

The SK47 is a current feedback amplifier. The output offset voltage is around -0.5 to -1V and the minus input is a low impedance current input. It make the use of an output coupling capacitor necessary. This is the price to pay to get an extremely stable and fast amplifier, with a constant bandwidth at all gains. The circuit needs no external compensation to stay stable down to unity gain.

Because of this topology and a relatively low open loop gain, this circuit exhibits a very musical distortion characteristic. The distortion is mainly second harmonic, and the level decreases quickly with the harmonic rank. This make this circuit a very good candidate to many audio application.

The SK47 is available in 2 versions corresponding to different current in the input transistor.

• SK47A : 135uA. It will give its best noise performance with high impedance source, like high ratio input transformers (1:4 and above).
• SK47B : 2mA. It will give its best noise performance with low impedance source, like low ratio input transformers (1:1 to 1:5) or transformerless input. It also has a wider bandwidth than the A type.

Measurements

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