frequency doubler - raise your guitar one octave

1-22 — elektor january 1980 frequency doubler raise your guitar one octave This frequency doubler circuit for guitars produces an output that is one octave higher than the original input signal. An uncommon, but particularly useful, feature is that the original signal and the frequency- doubled version can be mixed in any desired proportion. As can be seen in the block diagram given in figure 1, the signal from the guitar is amplified and then fed along two separate paths. The lower path carries the basic signal; in the upper path, full-wave rectification is used to obtain frequency doubling. After a "balance" control, the two signals are summed; the output is at the correct level to drive a suitable "guitar" amplifier. The complete circuit is given in figure 2. In practice, it is rather more compact than it looks: the four opamps are all contained in a single IC. The first stage, Al, is an input preamplifier/buffer. The gain can be varied between x 50 and x 1, by means of P1. T...