I wonder if a common base stage is appropriate for a phono cartridge, wouldn't it also be appropriate for a guitar pickup?
I'm not convinced CB is appropriate for phono. Maybe moving coil, 5 to 50 Ohms. It seems a very poor fit for moving magnet (47k load).
On conventional ~~5Henry e-guitar pickup it seems a very poor load.
On conventional ~~5Henry e-guitar pickup it seems a very poor load.
I would call it the worst approach I can imagine. A classic magnetic guitar pickup works best loaded with 220k-1meg.
Common base has very low input impedance (tens of ohms) and could only be used with an MC cartridge (which are a few ohms), not an MM cartridge. (many kohms and about 1 henry) I suspect its very hard to linearize such a stage too.
Guitar impedances are more like MM cartridges and require very high input impedances (1M or so to avoid HF roll-off) as they are strongly inductive too (many henries is common, so they have a source impedance up at 100's of kohms at frequencies of interest. The amplifier input impedance needs to be much larger than the source impedance to avoid colouring the frequency response.
This means the emitter-follower topology (common collector) is usually the one used with a guitar input, or even better a FET. Either can be part of an opamp of course, and a JFET opamp is a pretty sensible choice for a guitar amp front end, especially as they are much less susceptible to RF injection from the guitar lead acting as an antenna.
A common base input is about 4 or 5 orders of magnitude wrong for a guitar input.
They vary over a very wide range, but agreed only a few select grados are low enough for any MC type topologies. My own limited MM collection goes from 80mH to 700mH
Thanks Mark for your clear explanation.
Ok, then we must go for a FET, so we'll get high input impedance and low output impedance.
My target is to put a little preamp powered with a battery, so we could plug this preamp into output jack guitar directly with a male jack with a very short cable for lowering cable capacitance and get whole highs freqs in my guitar amplifier, being the long cable (3 metters) out of this preamp (low output impedance ) and so we'll get cable capacitance out of equation.
A good choice for a guitar input is bootstrapped bias (bjt). Besides a very high impedance, it also has a hint of 2nd order distortion.
High input impedance is an important reason musician prefer tube amps. The inductance of typical guitar pick-ups is so high that the guitar cord/cable has a real effect on the sound. Less Paul's famous guitars used (relatively) low impedance pick-ups. The problem is similar to passive scope probes that use special wire with a tiny steel center conductor in order to achieve a higher cable impedance, typically 500 Ohms vs 50 Ohms. The actual impedance of analog phone lines is about 100 Ohms, but analog phones were about 600 Ohms because audio electrical wavelengths are so long that wire losses are a bigger concern.
High input impedance is an important reason musician prefer tube amps. The inductance of typical guitar pick-ups is so high that the guitar cord/cable has a real effect on the sound. Less Paul's famous guitars used (relatively) low impedance pick-ups. The problem is similar to passive scope probes that use special wire with a tiny steel center conductor in order to achieve a higher cable impedance, typically 500 Ohms vs 50 Ohms. The actual impedance of analog phone lines is about 100 Ohms, but analog phones were about 600 Ohms because audio electrical wavelengths are so long that wire losses are a bigger concern.
Due to current noise BJTs are outperformed by discrete JFETs or OpAmps with FET-input in this application.
This is 20 years old. And there is prior art. (Including the box underneath some of Hitler's microphones.)
http://www.till.com/articles/PreampCable/
Be careful what you wish for. String overtones are inharmonic and we usually WANT a top-cut in the 3kHz to 7kHz range. But go ahead and try.
A similar plan which may be more convenient:
https://www.tdpri.com/threads/phantom-powered-fet-preamp-cable-with-output-buffer.279401/
https://www.tdpri.com/threads/phantom-powered-fet-preamp-cable-with-output-buffer.279401/