On Sun, 9 Jun 2002, Olin Lathrop wrote:

>It would help to look at the pickup output on a scope before designing the
>circuit to receive it.  I'm not familiar with guitar pickups so I have no
>idea what level this signal is.  I always assumed it was a low level signal
>like a microphone, but that wouldn't get thru the circuit you described.
>Apparently a full signal is a volt or two peak to peak, probably from an
>amplifier built into the guitar somewhere.

No, from a steel string vibrating with up to 1cm peak amplitude across the
gap of a strong electrodynamic transducer with 5000+ turns of wire and a
strong magnet ;-) Normally the coil is hardly damped and plays a big role
in the produced sound.

There is no amplifier in normal electric guitars, unless it's an effect
amp. Some have a transformer to make 600 Ohms output suitable for stage
use and some tone controls.

Looking at a scope will not help much, you need a DSO to make sense of
what is going on. A PC sound card based one will do for start. The string
has a ADSR behavior when plucked. The R part is what you need when
measuring frequency, up to a point. The spectrum changes with amplitude as
Jinx has said. This is due to the higher Q of higher resonance modes.
Also spiraled bass strings induce deliberate harmonics when plucked hard
(adjacent spiral coils touch at high amplitudes). The guitar signal is
very complex and very hard to imitate right. The 'fundamental' to be tuned
is the strongest amplitude signal in the beginning of the R phase, but
after the initial plucking sound has died down.

Dale, maybe you should look into using a PLL to lock onto the highest
available amplitude. A CMOS4047 comes to mind. It will lock onto signals
of 100mV or more without trouble and spans the frequency range you need.
This and a 3-6dB low pass (your current transistor stage modified and a
3dB RC lowpass) should do it imho.

Peter

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