The original wow-prefix. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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The original wow-prefix. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Musician

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In the "wow" prefix described below, instead of pedal control, a touch, electronic one is used. The effect is realized when playing stringed instruments with a metal or metallized pick. The strings must be connected to the common wire of the console. At the moment the mediator touches the string, the base circuit (see diagram) of transistor V2 closes. The resistance of the transistor quickly decreases from tens of kiloohms to several ohms, due to which the frequency of the quasi-resonance of the controlled filter of the prefix is tuned.

After opening the mediator and the string, the capacitor C3 will begin to discharge through the resistor R4 and the emitter junction of the transistor V3, which will lead to a reverse tuning of the quasi-resonance frequency of the prefix filter and, at the same time, to a change in the attack of the sound. This creates an interesting sound, slightly different from the usual "wow" effect. Resistor R4 can smoothly change the filter frequency tuning time and sound attack at the request of the performer. In addition, the R4СЗ chain serves to weaken the click at the moment the pick touches the string.

Original wow prefix

When working with a signal source having an output impedance of several kilohms, the attachment provides a filter frequency tuning interval of approximately 200 ... 2500 Hz (it is determined mainly by the values of the capacitors C2, C5 and the resistance of the transistor V2) and an increase in the characteristic at a quasi-resonance frequency of about 15 dB. With an input voltage of 5 mV, the maximum output voltage is about 30 mV. The prefix can work both from the signal from the output of the guitar tone lock, and from the output of any other electronic prefix. In order for the operation of the described device to be less dependent on the difference in the output impedance of various signal sources, a resistor R1 is connected at its input. Applying a signal with a level of more than 10 mV to the input of the set-top box can lead to the appearance of non-linear distortions that are noticeable to the ear.

In order to reduce the level of intrinsic noise, the transistors in the set-top box operate in low current mode. The current drawn from the main power supply is only 0,3 mA. Any element (or battery) with a voltage of 1 ... 1,5 V can be the power source G4,5 of the pick circuit. The current consumed from it at the moment the pick touches the string. - only 10 ... 20 μA.

KT312B transistors in the attachment can be replaced with KT315 with any letter index. Transistor V2 - any low power pnp structure.

A metallized pick can be made from thin formed fiberglass or copper foil can be glued onto a regular pick. The foil is connected to the prefix with a thin shielded wire. The sound will be harder if the player who plays the instrument does not touch the metallized part of the mediator with his fingers, that is, he does not close the G1 source circuit through himself.

To realize the "wow" effect, it is not necessary to touch the string. You can stick a metal plate connected to the common wire of the set-top box on the guitar deck and touch it with a plectrum - this will expand the capabilities of the instrument. The prefix can be successfully used together not only with string EMP.

Establishing the set-top box is reduced to setting the mode of transistors V1, V3. The resistor R2 is selected so that the emitter current of the transistor V1 is approximately 40 ... 50 μA, and V3 is 250 ... 300 μA. In the event of self-excitation in the attachment, resistor R5 should be shunted with a capacitor with a capacity of 10 ... 150 pF.

Author: A. Murzin, Kharkov; Publication: N. Bolshakov, rf.atnn.ru

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