Karaoke with integrated echo circuit

The circuit

The circuit has two parts, which are different. One part is audio, which ensures the mixing of the signals, which come from the microphone, those of a high-level source and a digital section that implements the echo effect. Let's first look at the part of the sound. The signal coming from the microphone is adjusted by the potentiometer P1 before being amplified by the integrated IC1a, which fits it into the digital section via the resistor R4 and capacitor C4 and the audio mixer via the resistance R5 and capacitor C6. This mixer has been built around the integrated IC1b. Accepts inputs of high-level signal through the line input and mixes it with the direct signal, coming from the microphone, as well as the echo signal provided by the integrated IC2 via the P3 potentiometer, which allows you to set the level and consequently the effect. 

The output of the integrated IC1b is at a high level in a way so that it can be connected to each input of the same type of amplifier. An attenuator has obviously been provided, thanks to the resistors R9 and R10, in order for the circuit to be adapted in all cases. Digital section has been left to the integrated IC2, which is a specialized circuit of HOLTEK, which works with a dynamic RAM, the integrated IC3. 

Without going into the details, let's say this circuit digitizes the signal coming from the microphone and then stores it in memory before reading it again after a while space, to turn it back into analog. This time period is the one that implements the effect of echo and whose loneliness is regulated by P4. P2 allows to adjust the re-input of the echo signal into this circuit and therefore it can adjust its depth. The supply of the circuit is left in a power supply block, providing a voltage of about 12V. This trend is filtered via R18 and C11 to power the analogue section. It is stabilized at 5V thanks to integrated IC4 to power the purely digital segment.

CONSTRUCTION

To simplify this construction, there is a printed circuit that supports all components, including power potentiometers, which minimizes the wiring. The parts required are not difficult to find in the market. The circuit can be built on the classic series on side PCB. You start from the bases of the ICs, then the passive components and then the active components. Pay careful attention to the direction of electrolytic capacitors and the orientation of the integrated circuits, which will be last installed in their respective bases. In the first phase, replace the R9 resistor with a bridging. After a final test, connect the circuit to the sound or your installation in the following way.

- The microphone at the 'micro' input (caution, use a true full microphone, potential or thickener, But not just a thickening capsule without power feed Provided.)

- The amplifier's CD or recorder output to the line input (EL) This input accepts 100mV to 4V active and has not danger to saturate.

- Line output of the circuit (SL) to a high-level input of the high-fidelity amplifier.

Connect the circuit to a 12V power supply. The consumption is very low (in the order of 25mA) and therefore the circuit is suitable to work with any power supply. Reversing polarity of the feed can happen without risk for the circuit thanks to the D1 diode. Adjust the potentiometers P2 and P3 to their minimum setting and slightly increase P1. The sound, which received by the microphone should be heard. So increase P3 and you should observe the appearance of an echo, too fast and prolonged. Turn the potentiometer P4 to adjust the speed of this echo and P2 to adjust the depth. If you think the signal coming from the microphone is too low compared to the musical signal, even if P1 is at maximum setting, reduce resistance R2. You can reduce it to 10kΩ if necessary. If output "fills" the high-level input of your 
amplifier, something that is quite likely to happen, replace the bridging you have been placed in place with resistance R9.

Components

IC1: 4558, 1458
IC1: HT 8955A (HOLTEC see text)
IC3: 41256 or the like
IC4: 7805 in shell TC92
D1: 1N4004
R1, R10: 10KΩ
R2: 47KΩ
R3: 470KΩ
R4-R8, R11, R13: 100K
R9: bridging, see text
R12: 560KΩ
R14, R16: 150KΩ
R.15: 5,6KΩ
R17: 12KΩ
R18: 100Ω
R19: 4.7 Ohm
C1, C2, C8, C9: 1μF / 25V electrolytic suture
C3: 68 pF ketamate
C4-C7, C13, C16: 1 μF mylar
C10: 10μF / 25V electrolytic suture
C11, C4, C21: 100μF / 25V electrolytic suture
C12: 470μf / 25V electrolytic suture
C15: 3.3nF ceramic or mylar
C17: 680pf ceramic
C18, C19: 10nF ceramic
C20: 0.22 μF mytar
P1: 10kΩ potentiometer logarithm for PCB
P2, P3: 100kΩ linear potentiometer for PCB
P4: Potentiometer 470kΩ linear for PBC
1 base DIL8
1 base DIL16
1 base DIL24