Augusto - > I have questions though... As I understand, my maker will probably use three piezo pickups and I will have to use an offboard mixer (That yamaha mg 10/2 looks really interesting! Does that only mix the signal or does it amplify it as well? I really do not understand this well).
A mixer typically does a couple of things. It brings low level signals from microphones up to a working level, called line level. The part of the mixer that does this is called the preamplifier, usually called the preamp. It also takes two or more signals and mixes them together. After the mixer the signal goes to some kind of amplifier. In a sound reinforcement situation, such as a large concert, this would be a power amplifier and speakers. For a smaller situation you can use a keyboard amplifier. You can use a guitar amp, but the output and input impedances don't match up right, so this is not a good combination. A mixer can also have an amplifier built into it, in which case it's called a powered mixer. The Yamaha 102C is not powered. I haven't used the Yamaha 102. The currently available Yahama 102C looks like a reasonable mixer for this. A Mackie 1202 is a good option. Behringer makes a knockoff of the Mackie, the Xenyx 1202. > I don't know how exactly the signal will get outside the instrument, I have to ask him that, but what he emphasized is that each group of strings will be on a different, independent channel and that he will provide me with a 3-channel canon (XLR) cable. He said that I will have to mix the signals externally myself. Is there a XLR cable that can carry 3-channels in one cable or is that just one of those "medusa" cables? A typical XLR cable carries just one signal. If three separate signals are being carried by the 3-pin XLR, it will need to have breakout cables and connectors at the other end to bring the individual signals into separate channels on the mixer. > > What do you mean exactly by this active electronic device that buffers the signal? This has to do with impedance and level matching between the output of the transducer and the input of the mixer. A microphone has a typical output impedance of 600 ohms. The mixer has a typical input impedance of 2500-5000 ohms. This is the usual relationship between input and output impedances. A piezo pickup has a typical output impedance of 100,000 ohms or even higher. Plugging a pickup directly into a mixer will result in a pretty poor sound - the mismatch between the input and the output will require that the preamp be turned up very high, resulting in noise from the preamp. Also, if the signal is run through a long wire (a meter or more) to the mixer, the capacitive load will reduce the high end (treble) response. The way to solve this is with one or two pieces of equipment. A built-in preamp with a very high impedance designed for the piezo will bring the level up and the impedance down to microphone or line level. A built-in low-gain "buffer" preamp designed for the piezo will strengthen the signal strength without changing the impedance very much. If a buffer is used, a Direct Injection box (usually called a DI box) is used to match the impedance, allowing a high-impedance signal from a pickup to be run into a lower-impedance microphone input. For both of these, I have said "built-in" because the cable run from the piezo to the preamp should be kept as short as possible. Both of these solutions require some kind of active circuit in the instrument - by "active" I mean something that needs a battery to power it. This is as opposed to "passive" circuitry, where there may be volume and tone controls (as on an electric guitar), but nothing that requires power to function. > He may have that in mind already, I did not get all technical > details on how he does his amplification system besides what I mentioned above, but I would like what you mean exactly by that and how should I ask the maker about this specific device... What you need to ask him is whether it uses a battery, and whether you need mic level or line level inputs on your mixer, and what kind of connectors are used at each end of the cable. I hope this helps, Alden
