Effects Loops: Passive vs. Active

[keithv]

I want to add an FX loop to my Plexi.  The passive fx loops looks appealing because it's simple, and I'm assuming, it's not going to add any extra noise.  So why do some people go to the trouble of adding an active effects loop.  What are the pros and cons of each?

[HotBluePlates]

So why do some people go to the trouble of adding an active effects loop.

You're probably using pedals in your loop. Most pedals are designed for guitar-level input signals, and output to an amp input jack which is also guitar-level (though some can provide significant boost).

Your loop is probably after some portion of preamp boosting and signal shaping; then you knock the signal level back down to near-guitar-level to keep from overdriving your pedals. The output is probably relatively-high impedance, which can result in treble loss if your cables are long. When the signal returns to the amp, you may have guitar-level signal again late in a preamp when more preamp boosting is needed.

A passive loop can't provide make-up signal boosting, if needed. An active loop can provide the signal boosting. It might also use a feedback stage for mixing various signals (maybe dry & effect). It almost certainly will have a cathode/emitter/source follower to drive the send to the effects with a low output impedance, preventing treble loss.