Active and Passive Inputs
Moderators: pompeiisneaks, Colossal
-
Metalhead9
- Posts: 1
- Joined: Wed Aug 11, 2021 7:31 pm
Active and Passive Inputs
I just purchased a Randall head and it has an "Active Input" and a "Passive Input" to plug my guitar into. What is the difference between "active" and "passive" inputs?
-
CraigGa
- Posts: 228
- Joined: Sun Mar 08, 2020 12:02 am
- Location: Up in't north of England
1 others liked this
Re: Active and Passive Inputs
I'd suspect that they have different gains to suit active or passive guitar pickups.
Craig
Craig
Thinking about my second build.
Re: Active and Passive Inputs
yes and no
the inputs have no gain, they attenuate differently. The questions is, what happens to the subsequent gain stages. An input circuit designed for passive PUs will be overdriven already in stage 1 with unpleasant sound in many cases when too much voltage is fed into it, as the designed gain structure in the entire amp is normally designed for passive PUs.
Usually the active input has a voltage divider to tame the hot output of active pickups to suit the rest of the preamp circuit. While a passive PU puts out something between 20 and 100 mV, some active PUs/Preams put out up to 2V (depending on playing style and the actual circuit).
another consideration is impedance matching. Usually the input impedance of active inputs is very low (below 100k) in the active input, so a passive PU (high source impedance), which needs some 1 Meg input impedance, will lose signal level (only a fraction of the source signal reaches the amp) and highs due to the low pass formed by the guitar circuit, cable and input circuit.
An active guitar circuit usually has an output buffer (decouples the guitar circuit from the rest) with low source impedance and will not lose highs, even with low impedance inputs but signal level.
Sound is always a matter of taste, you won't destroy your amp when plugging into the "wrong" input, but sound/control wise it can be unpleasant. I own an active bass with the same low output as a passive one (50mV when plucked normally). Due to the output buffer I don't lose sound but signal level when plugging into the active input. I could make up for it using the Gain pot, but the signal to noise ratio is worse when using the wrong input.
the inputs have no gain, they attenuate differently. The questions is, what happens to the subsequent gain stages. An input circuit designed for passive PUs will be overdriven already in stage 1 with unpleasant sound in many cases when too much voltage is fed into it, as the designed gain structure in the entire amp is normally designed for passive PUs.
Usually the active input has a voltage divider to tame the hot output of active pickups to suit the rest of the preamp circuit. While a passive PU puts out something between 20 and 100 mV, some active PUs/Preams put out up to 2V (depending on playing style and the actual circuit).
another consideration is impedance matching. Usually the input impedance of active inputs is very low (below 100k) in the active input, so a passive PU (high source impedance), which needs some 1 Meg input impedance, will lose signal level (only a fraction of the source signal reaches the amp) and highs due to the low pass formed by the guitar circuit, cable and input circuit.
An active guitar circuit usually has an output buffer (decouples the guitar circuit from the rest) with low source impedance and will not lose highs, even with low impedance inputs but signal level.
Sound is always a matter of taste, you won't destroy your amp when plugging into the "wrong" input, but sound/control wise it can be unpleasant. I own an active bass with the same low output as a passive one (50mV when plucked normally). Due to the output buffer I don't lose sound but signal level when plugging into the active input. I could make up for it using the Gain pot, but the signal to noise ratio is worse when using the wrong input.
-
Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Active and Passive Inputs
It's real simple!
If your guitar ( other then a acoustic) has a battery in it, then use the active input.
If your guitar ( other then a acoustic) has a battery in it, then use the active input.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!