I'm back with a new Exar circuit traced
, unfortunately, I was a bit busy all the time. I traced Exar HV-03 Hoover, and it appeared to be quite interesting inside. Here is what it looks like with a box.
- Exar HV-03 Hoover top
The translation of a pedal description from the user manual:
"HV-03 is a device operating on the principle of overloading the input stage of the amplifier. The signal is subjected to the process of compression and extension of the sound. In addition to the harmonic-rich output signal, it has the unique ability to add a double-frequency signal, which gives the impression of higher sustain. The applied regulations give unique overall ral character of the sound of collaborating of the instrument."
- Exar HV-03 manual side 1
- Exar HV-03 manual side 2
The PCB is a standard single-sided one with many BJT/FET transistors, three ICs, and a trimmer.
- Exar HV-03 PCB top
- Exar HV-03 PCB bottom
So what is the circuit inside? It is a slightly modified Boss PW-2 Power Driver with a simplified power supply and Lows EQ frequency a bit different, but the biggest difference is the Vacuum potentiometer. The signal is split as a boost stage before the discrete op-amp part; then it has an additional gain stage, full-wave rectifier circuit, 2nd order Sallen-Key highpass filter, and gain recovery stage. The octave and distortion signal are mixed together at the EQ stage, and the Vacuum pot controls the octave up a level. The full-wave rectifier used seems to use that topology
https://www.electronics-tutorial.net/an ... rectifier/ . The octave is not very pronounced, especially with high gain settings - best results at gain at 0, neck pickup, and higher frets. How cool is that design, considering it was the early 00s when nobody cared about PW-2 circuit at all? Attached is the schematic without buffered bypass switching.
