[sdiy] Negative-going triggers in the Boss DR-110 drum machine - Why?

Gordonjcp gordonjcp at gjcp.net
Fri Sep 29 19:43:20 CEST 2023

On Fri, Sep 29, 2023 at 11:43:24AM +0100, rburnett at richieburnett.co.uk wrote:
> I'm guessing it's so that they can use those PNP Common Emitter stages to
> boost the current for charging the envelope capacitors.  If they used
> active-high pulses coming out of the micro instead they would have to have
> an NPN at the bottom and a PNP at the top to get sufficient current to
> charge the envelope capacitors.  So using active-low pulses out of the micro
> means they can do away with the common-emitter NPN at the bottom and drive
> the C-E PNP at the top directly, saving a few NPN transistors.

It's also very likely that the outputs can sink far more current than they can source, so they can drive a PNP trannie on a lot harder than they can an NPN, which means you need a lower gain part, which is cheaper, and so on.


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