Joey -
When you add an active EQ circuit to an instrument with passive pickups you gain all the well-known benefits of active electronics. This includes the ability to drive long cables without any loss of treble and usually the ability to turn the level down at the guitar without loss of treble or tone.
The sort of hybrid configuration that you mention is very common and isn't just hype. Those Carvin, EMG-HZ+ active EQ systems are all set up this way. Most Bartolini setups on high-end basses are high-Z pickups with active EQ. In fact, this appears to be the way that all the Alembics are made with the exception of the Series basses. It's a real improvement with real benefits.
The only pure active systems would be EMG-equipped instruments or the Series bass. In these cases, the raw output from the coils is too low to be amplified directly by normal equipment. They require the inline, onboard preamps to get to a regular output level. Each active EMG pickup has a powered preamp built right into the pickup housing. In the Series bass, there are three preamps that amplify the output from the two pickups and the dummy coil so they can be blended without loss. Active systems with preamps for each pickup can do some things that the hybrid systems can't - you can smoothly blend the pickup outputs for instance. They also have the potential for a different kind of tone. Because they know that there will be an active preamp and raw output can be low, they designers can wind much less wire on the coils or use different and much weaker magnets. This will give extended high end with less coloration. This is why EMGs claim greater sustain on guitars - it's not just higher output from the preamp, they also have less magnetic drag on the strings which really does increase sustain.
What's really going on here?
You make a pickup by winding a lot of wire into a coil which surrounds a magnet. Your bass' strings pass through the magnetic field from the pickup. When the strings vibrate, they interfere with the magnetic field that that interference (literally) generates an output voltage which is the signal from the pickups.
You have to use quite a lot of wire for this to work. This wire has resistance if you measure it from a DC perspective. The signal from the bass is AC which means that we really care about the impedance, which is sort of the AC analog to DC resistance. They're similar - more wire means higher impedance - but not exactly. Because electromagnetic fields are involved, the impedance varies with frequency, for instance.
By adding in the active preamp between the pickup and output jack, the onboard electronics are completely isolated from the cable and amp. The onboard preamp is set up to get the output level you want but has super-low output impedance so the effects of the cable become negligible.
It's pretty cool stuff. Alembic was the first implementation of active guitar electronics and it's quite a testament that 30 years later I don't think anybody has even come close to the design that Ron put together. There are many really novel aspects - purpose-made pickups, the hum canceller, powered amps on all channels, stereo out, external power, etc.
David Fung
