Questions about op-amp of guitar tuner

[dennis86]

hi everyone, I'm newbie. i have few questions wanna ask about this guitar tuner.

The guitar tuner website is: **broken link removed**

The incoming signal is passed through an operational amplifier (U2A), which amplifies it by 800 times. The amplifier is a rail-to-rail National Semiconductor LMC6462 or equivalent. It presents a "zero" at about 133 Hz in its Bode diagram to emphasize the harmonic components of the strings. The output of the amplifier is directly connected to the input of the Schmitt trigger (U2B) that present an hysteresis window centered at ½ VDD with a 1% of power supply voltage width.

1) what is this 800 times input and what is means of rail to rail?
2) why it present a 'zero' at about 133 Hz in its bode diagram? what is the types of harmonics?
3) what U2B is using schmitt trigger? what is the means of hysteresis window?

anyone can answer my question or can tell me more details about this guitar
tuner? im newbie here. im interested to know how to build a guitar tuner. hope anyone can help me. thanks alot : )

 

[laktronics]

Hi,
1. 800 times represents the voltage gain of the amplifier.
2. Rail to Rail means that the signal peaks can swing to the full range of the power supply. That is, for a single supply operaton, the signal on the -ve side can reach to ground level and on the +ve side up to the supply value.
3. A zero at 133 Hz means that the amplifier gain increases at this frequency onwards,proprtional to the signal frequency. It will stop increasing within around 10 times the frequency.
4.Many instrument signals like that of Guitar are rich in harmonics, meaning they produce complex signals different from pure sine/cosine waves. Such signals will be represented as sum of a basic sine wave with a frequency called fundamental frequency and other sinewaves with frequencies which are multiples of the fundamental frequency. These additional sinewaves are called harmonics., but their amplitudes will be small compared to the fundamental. Inorder to accenuate these harmonics and to give a better listening pleasure the amplifier gives an increased gain at the frequencies of the harmonics.
5. Outputs of single supply amplifiers will be biased at Supply/2 point to allow symmetric swinging of signals. Inorder to ensure that the noise does not affect the output when there is no signal, a hysterisis of 1% of the supply is provided in the amplifier. This will means a hysterisis of 100mV if the amplifier supply is 10V. The amplifier output will not change unless the signal is strong enough to make the output exeed beyond this limit.
Regards,
Laktronics