When developing this preamp, I wanted to preserve most of the functions of the original ENGL-E530 as much as possible. As a result, my preamp lost only the bypass, but acquired the best speakersimulators. In general, this preamp is quite versatile and has wide range of settings. For example, the manufacturer consider it as a four-channel preamp. Yes, that's fair. Four channels are absolutely different in sound. There is "clean", there is crunch, and there are two leads. Moreover, "lo" and "hi" leads are quite different. It is possible to increase the mid frequencies - Contour (at the leads). Also preamp has a 4-band equalizer with low and high middles so it is possible to determine this range more precisely. On a clean channel (the same as Fender Twin clean), everything is traditional - gain, volume and tone stack with "bright". 

When looking at the back panel, there is a stereo sound path - left and right. Yes, preamp has a stereo "return" with a serial "loop" with a pair of line and speakersim outputs. And there are two mini power amps (2 x 1.5 watts) that allow you to play guitar with hi-fi or guitar cabinets. Output type switch (missing at the photo) is placed on the back. By the way, it is possible to use the headphones. There is an additional level control +15dB for driving the power amp or for other purposes. There is also an alternative guitar input at the back. In general, the functionality of this device is quite high.

The sound path consists of four tube stages. 

1 - 4 = clean 

1 - 3 - 4 = crunch

1 - 2 - 4 = lead

1 - 2 - 3 - 4 = super lead

SOUND SAMPLES - https://disk.yandex.ru/d/k8h8uUBcKNxqdw