Question about the Pathogen Schematic

[jimilee]

I am slowly learning about pedal design and reading schematics, so that's where this question is coming from. On the Pathogen power section schematic, there is vref a through f. They appear to all be the same voltage divider. Why are there so many on the schematic, would one not do the same thing?

Thanks
Jimilee

 

[bowanderror]

The Pathogen's array of voltage dividers is not something I've really seen before:


The only reason I can think of for generating separate 1/2Vcc bias voltages is due to the huge differences in impedance for the various bias points. You can see that VREF_A & E needs to bias a high impedance input (through 470k resistor), whereas the input impedance seen by VREF_B is almost 2 orders of magnitude lower (through 6.8k resistor). The other VREFs are biased directly to the non-inverting inputs. If they were all using the same voltage divider, you might see the bias voltage drop for the high impedance stages.



Overall, it's probably a bit over engineered, and a buffered Vref or rail splitter would probably avoid many of those issues. At the least, sharing one voltage divider between C, D, & F and another for A & E should be sufficient, and would cut out a lot of extra circuitry.

That said, I'd be interested to hear if there are any advantages in terms of noise or interference to this approach. Maybe the ability to place each voltage divider closer to the bias point could improve stability to a (very) small degree?

 

[jimilee]

Thank you sir. Makes sense.