Preamp with crossovers on pickups? (Acustic guitar) ...Novice looking for help

[Natman]

Hey guys,

I'm still pretty new to this stuff and I don't really know where to stick this thread so I opted for general. My only background in acoustic pickups was with a small manufacturer. I only did assembly; no design! I've built a few pedals and amps however...

Try to follow me on this:

A certain gutar company from Australia has a darn good-sounding pickup/preamp going on. When I spoke to their rep, he explained that they isolated the frequencies at which each pickup sounds best by using crossovers (I even wrote the Hz down after our conversation).
There are 3 pickups in this guitar: 1 internal mic, 1 bridge piezo and 1 soundboard piezo. There is a pot to blend the 2 piezos, then volume and bass/mid/treble. I know they use op-amps -I saw the Texas Instruments chips, but the SMT construction hurt my eyes. There were 2 quad chips and one dual (I wrote down which models but don't have them in front of me right now).

I want to try my hand at building something similar but the material I've read online about crossovers has me confused because they are mostly used for speakers (obviously). Does anyone here know how they might have done it?

[Leo_Gnardo]

I want to try my hand at building something similar but the material I've read online about crossovers has me confused because they are mostly used for speakers (obviously). Does anyone here know how they might have done it?

Just a WAG, they may have used a crossover as a filter to find what bandwidth they need to support the sound from each pickup, then design their preamp/mixer to similarly filter out and eliminate out-of-band frequencies. Let's say you plug your guitar into a 3 way crossover and monitor only the midrange. By selecting the hi and lo crossover points that don't remove what we want to hear, you find the band-stop frequencies which leave out unnecessary hi and lo frequencies. Old sound engineer maxim: the wider you open the window, the more s#!t flies in. It would be wise to do without useless low end thump and annoying hi end sizzle, right out of the guitar, and not leave it up to sound engineers who have a zillion other problems to solve. If the guitar actually sounds terrific after that, amplified I mean, then they're on to something good.

[Mick Bailey]

The crossovers used in speakers are usually passive and essentially direct the output from an amp to the most appropriate driver to reproduce that part of the signal.

Another way of doing it is to have separate amplifiers that are optimized for individual frequency bands and power handling, and to use an active crossover in the preamp stage to route the input signal to each amp. This is very common in powered speakers where you typically have an LF and HF power amp each driving its own load. Typically opamps are used to create the crossover bands.

Similarly, compressors sometimes use active crossovers to allow different compressor functions to act on different frequency bands.

Take a look at the 3-way crossover here: 3-Way Electronic Crossover Network. I think maybe the mid-band filter could be used to give an optimized band for each pickup - one filter per pickup - and set the component values to suit.

I'd maybe begin looking at this by drawing a block diagram of signal flow and then designing the electronics for each block.

Another point is maybe the salesman's presentation of how it works could be different to how the pickup system actually works. I could see the need to trim the HF from piezos and boosting bass, and maybe the opposite for a mic. So really a band-pass filter for each pickup maybe, rather than a crossover.

So after writing this up I've pretty much repeated what Leo_Gnardo has already said........