Mixiing Actives with passives - circuit related question

[David Schwab]

And when is a buffered passive pickup not active? Come on now, folks... It's not gain that defines active, it's a transistor of some sort...or a tube if you're really freaky...in the guitar. And the transistor can be part of the front end of an IC.

You once said that all electric instruments are active, it just depends on where the first gain state is! That's it in a nut shell.

Until we invent passive amplifiers, they are all active.

[Steve Conner]

Passive amplifiers? You mean like a Dobro or a gramophone horn?

To me "passive amplifier" is the same sort of oxymoron as "corporate responsibility" or "self-effacing frontman". Active and amplifier pretty much have the same definition: boosting a signal by using it to modulate an external power source.

[peskywinnets]

boosting a signal by using it to modulate an external power source.

Gotta say...that's the first time I've seen it described in that way, but that sums up succintly what's going on - nice one. (though having enjoyed your definition, I would go a little further & said 'using a signal to modulate DC'!)

[Steve Conner]

Well, on Douglas Self's amp museum site, there is the Auxetophone, an early 20th century PA amp powered by compressed air. The US Army made similar devices on a much larger scale to experiment with military uses of infrasound.

So I think it's too narrow to assume the power source is even electrical, let alone DC. (I will build that oxy-propane sub whoomfer one day.)

[David Schwab]

Passive amplifiers? You mean like a Dobro or a gramophone horn?

Right, so all pickups are part of an active system. Some just have active stages closer to the pickup.

Active and amplifier pretty much have the same definition: boosting a signal by using it to modulate an external power source.

Yep, that's the way an amp works.

[Stealth]

You can tailor the input of the preamp for the passive to simulate a passive signal chain, so it doesn't brighten the tone of the passive pickup

Pardon the late comment on this (it's almost two weeks, I know), but to see if I got this right, this'd mean a standard passive volume control, passive tone control and a parallel 30 pF or similar capacitor to emulate the cable capacitance prior to feeding the signal into the preamp, right?

[Mike Sulzer]

Pardon the late comment on this (it's almost two weeks, I know), but to see if I got this right, this'd mean a standard passive volume control, passive tone control and a parallel 30 pF or similar capacitor to emulate the cable capacitance prior to feeding the signal into the preamp, right?

You will need a lot more than 30 pf. 500 pf, typically.