Single-ended amplifier without magnetic gap output transformer

The circuit is shown in the figure. LED×3 provides bias for the power tube (only for field effect power tubes with higher on-voltage VGS, such as MLE20, R413, etc. Power tubes with smaller VG3 are slightly modified according to the actual situation).

The quiescent current of the power tube is between 500mA and 2A (pay attention to heat dissipation). The current of the constant current tube is the same as the quiescent current of the power tube. Since the current directions of the two tubes (in the two sets of coils) are opposite, the magnetic fields generated cancel each other out, thus eliminating the DC magnetization phenomenon.

Another modified circuit is shown in the figure below: the amplifier tube and the constant current tube share a set of biases (the two power tubes need to be strictly matched at this time), making circuit debugging simpler. You can try to disconnect point A from the power supply and connect it to point B. See if the sound quality changes.

The two circuits do not use the filter inductor necessary for a single-ended amplifier circuit. The actual listening signal-to-noise ratio is very high.

It has been one month since the production was completed, and the circuit works very stably.

Sound sweet. The highs and lows are well balanced. This machine has the high sound quality of a single-ended machine and the high signal-to-noise ratio of a push-pull machine, but the output does not require a magnetic gap. Reduce the difficulty of production. The constant current source plays an important role (short-circuit the input terminal or connect it to the signal source. Put your ear close to the speaker to hear a little noise). The price paid is twice the static power consumption of a single-ended machine.