Double Bass Phil Jones (PJB) BG-400 / BG-300 input impedance

[bilias]

Maybe this info is usefull to others too.

I've send an email to PJB to find the input impedance for BG-400. This is what I got back.

I'm also attaching that BG-400 schematic for archives.

The input impedance of the BG-400 is 1.5M & 22pf & actually the published input impedance of the BG-300 is a misprint.
Actual input impedance of the BG-300 is 1.5M & 22pf.
The early 1st production run BG-400's (before serial #580) had an input impedance of 100K & 470pf.

The input impedance of the BG-400 is the same for active & passive. The active/passive switching merely lowers the gain for active. Schematic is attached but is for 1st production run with lower input impedance.
There is no updated schematic showing subsequent production changes which include change of R106 & R206 to 2M & change of C102 & C202 to 22pf.

Mine is #350 so 100K impedance...
Although reading the schematic I see R101/R201 to be 4.7M

Earl,
If memory serves me the Super Flight Case, Flight Case, Brief Case, and Suit Case are all set at 4.7 Meg Ohms. The Double Four is a bit later in the PJB amp production runs.

 

[bilias]

And an update for this.

The series networks of C101,R102,R106/C201,R202,R106 are in parallel with those input resistors, which lowers the input impedance to that of the parallel combination, which in the case of that schematic is a bit under 100K ohm.

C102/202 are there to block DC & undesirable low frequency. C102/C202 basically set input capacitance to filter out RF.

 

[bilias]

And about the Briefcase:

That is also a misprint result of the person who drew up the manuals making the same error in reading the schematic as you did, by only looking at the ground referencing resistor at the input & not taking into account the resistance network in parallel with it. The Briefcase input impedance is 1.5M.

The Briefcase & BG-300 have separate input stages for Active/Passive with an active input impedance for each as published 100K. Only the passive input impedance is misstated, which corrected is 1.5M for each. Of the amps mentioned only the BG-400 has the same input impedance of 1.4M for Active & Passive.

 

[Paul tillery]

I wouldn't want to just assume. But I'm guessing the bg-100 would be 1.5 megaohms as well. Which leads me to wondering what the bg-120 is rated at. Kinda disgruntling news to me. Maybe I'm alone in this. ‍

 

[Ric Vice]

Regardless of the input impedance, the EQ section that works in additional tone shaping can also improve timbre (tone color) Walter Woods amplifiers were set a 1Meg Ohm as early as 1975. I've plugged every pickup you could imagine into my Woods and they always sound great with a touch of EQ. The input impedance is only one of several things that can improve the sound of a Piezoelectric pickup.