The HPDI is a discrete class A JFET, transformer balanced direct box that can run on either phantom power, or from the optional 24VDC wallwart included.  It provides a high impedance input (inst), and parallel (inst), buffered (inst), and balanced (mic level) outputs.  The buffered and balanced outputs have internal calibration pots, that can be adjusted to either increase or decrease the signal relative to unity, factory set to 0.0dB (See internal calibration below).  The HPDI is built with the same amplifier philosophy and build quality as our HJFP2 micpre, except that it has cool handmade wood sides (100% reclaimed Oak in Oregon).


1                     IN: High impedance instrument input, 2.2Mohm with pad off, 150K with pad on.  When no cord is plugged in, all outputs are muted.

2                     PARALLEL OUT:  Direct connection to input.  Typically used to connect the instrument to a stage amplifier.

3                     AMP (BUFFERED) OUT:  Signal is buffered through a HIz JFET amplifier, which lowers the impedance making it far less susceptible to noise.  This output is useful if you want to plug a piezo pickup into a stage amplifier, the HIz buffering maintains the signal bandwidth and integrity.

4                     BALANCED OUT:  Transformer balanced mic level output, typically sent to PA or studio micpre.  Phantom power can be applied to the output to power the unit.

5                     INPUT PAD:  Inserts a -14dB pad before the first JFET gain stage.

6                     PHASE:  Inverts the phase of the balanced output, parallel and amp outs remain unchanged.

7                     POWER LED:  Illuminates when phantom power is turned on, or the wallwart is plugged in

8                     LIFT GND:  Lifts pin 3 of the balanced output.  Cannot be used when using phantom power (because it’s the ground connection for the power).

9                     OPT WW INPUT:  Optional 24vdc wallwart input.  Use only with wallwart provided or equivalent.  The WW connection is reverse voltage protected, in the event an improper WW is accidently plugged in, it will not work, or pass signal poorly.  The 24vdc WW when very little current is pulled from it actually generates over 32vdc, and this added headroom is used in the design.  When the WW is plugged in, it activates an internal relay to switch the source of the internal regulation, eliminating the possibility of phantom power being mixed with the WW power.


The AMP (buffered) OUT and BALANCED OUT connections have internal calibration pots, figure 2 shows their locations and range of adjustment.