Here are three common, simplified, impedance values: If you use a wireless system, and it's plugged into the pickup output, the WIRELESS system's input impedance is the one to be concerned with, as even if you then plug into a preamp, the impedance buffering has already been done by the wireless transmitter.If you put a preamp into the "effects loop" of an amp, it won't correct an impedance mismatch caused by the amp, because the pickup is still plugged into the amp, and that's the buffer point.If you choose to use a preamp, the preamp buffers the input and the amp's impedance is of no major consequence.If you plug directly into an amp input, it's the amp's impedance that matters.The only device that matters is the FIRST device that the pickup is plugged into. So, the idea is to "match" your amp to your pickup - to ensure that the load presented by the amplifier's input is optimal for the pickup you're plugging into it, which eliminates this unwanted filtering effect, allowing the true, unmodified sound from the pickup to get through to the amp and speaker. And now, although the stereo system still makes music, now it sounds rather out-of-whack. Sound-wise, it's kind of like having fancy tone controls on your car stereo but you turn it on only to realize that your 3-year-old has completely skewed the knobs to crazy new settings. But when it's unintentional and uncontrollable, it can make for rather odd sound - that brittle, raspy, all highs and no lows sound that makes you think you have a bad pickup. Now, a controllable filter can be useful (see our FAQ on amp features for details on notch filters and low-pass filters). The reason that this happens - without getting too technical - is because a "non-optimal" resistance load creates a sort of unintentional (and usually undesired) filtering effect which may decrease the level of certain orders of frequencies. If the loading (amount of resistance) is not optimal for the type of pickup, problems result. Why? Put simply, when you plug your pickup into an amplifier, it becomes part of one big cooperative circuit. essentially, completely out of whack, and sounding like you need to do a lot of EQ correction to even make it sound passably good. That same pickup and amp, with the "wrong" level of buffering, can sound "quacky" or thin. The level of resistance (called input impedance) can radically change how a pickup sounds when a pickup is well-paired to its preamp or amp, the result can sound full-bodied, natural, and open. The "buffer" I speak of is related to electrical resistance, which is (in layman's terms) the degree in which the amplifier's circuit "resists" the pickup signal. But this buffer could already be built into the amp, if you choose that amp wisely, which may negate the need for an "extra" preamplifier or effects unit. It can do this by boosting their gain levels, allowing for changes to the sound (using equalizers, etc.) - and, in the case of the specific type of pickup (piezo-electric) in the bass, creating an ideal " buffer" (a sort of electronic "liaison") between the instrument and amplifier. The amp reverses that process, turning those impulses back into vibrations on the speaker of the amp, which makes sound waves and projects them into the room.Ī preamp can further "improve" those electrical signals from the pickup. That means you have a small ceramic-encased "sensor" that captures the vibrations created by the strings, turns those vibrations into electrical impulses, and sends them through the cable to an amp. If you are like most of us, you are using a piezo-electronic transducer for a pickup. It depends on several factors.īefore you decide, though, do you already have an amp that you intend to use with your bass? If you are in the market for an amp, you can make some choices while shopping that can have an impact on whether you will need a preamp.
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