ADDING YOUR VOCALS TO MUSIC
V.Vidyalal, V. Sivanand and K. Rajasree,
Floyds Inc., "KAILAS"
EDAKKAD P.O, CALICUT,
INDIA - 673005
Or
V.Vidyalal
Uni-Tel. Inc, 8111 LBJ Freeway, Suite 1100
Dallas, Texas-75251,
USA
Introduction
This is a project for budding musicians who want to sing along with their favourite tunes. This is accomplished by eliminating the vocals from the songs and substituting ones own voice. Recently there has been an upsurge in such type of equipment and popularly it is known as "Karoke" system. The working principle of the unit is given by the following block diagram:-
Output from a microphone is amplified by a mic. preamp. and fed to one of the inputs of a mixer. On the other hand, music with the vocal contents are send through a filter circuit where the vocals are attenuated to a good extent. The output of this section is fed to the 2nd input of the mixer. The output of the mixer is the signal output (without the vocals) which is to be fed to a power amplifier for reproduction.
Circuit Description
The complete circuit diagram
IS TO BE REQUESTED FROM THE AUTHOR:-lal@uni-tel.com . It can be divided into the following sections:-1) Mic Preamplifier :- The microphone output is amplified by a non-inverting amplifier based on a low noise Op-Amp. OP 27 ( a slightly inferior and cheap substitute is the TL071). The input impedance is to be selected for proper matching with the microphone used. For high impedance dynamic microphones (eg - Shure, A K G etc) a standard value of 47K for R1 will suffice. For low impedance types a value of 680 W to 1KW will be sufficient. A condenser microphone with proper voltage biasing can also be used successfully by sacrificing sound quality. The gain of this stage is determined by the preset P1. If the gain is insufficient it maybe increased to 100K. The output of this stage goes to the mixer based around A6.
(2) Buffer :- Configured around Op-Amp. A 2, is an inverting amplifier with an input impedance of 47KW . This stage is followed by the voice attenuator stage.
(3) Filter section :-This is based on gyrators centered around A3, A4, A5 and A7. The attenuation depends on the settings of potentiometers P2, P3, and P4 which is maximum when the wipers are near the non-inverting input of the amplifier A4. The maximum attenuation level obtained in this case is 15db. The output of this section goes to the level control P 5.
In other words, each RC network along with Op-Amps. A3, A5 and A7 attenuates certain discrete frequencies and therefore a band of frequencies can be attenuated. The theoretical relations to calculate for other frequencies are given in our earlier article "A simple design of a high quality bandstop filter" (which can be requested from the author:- lal@uni-tel.com).
(4) Mixer :- The microphone output level control P6 as well as the music signal level control P5 are connected to inverting input of A6. This stage functions as an inverting amplifier with unity gain and mixes the two signals.
Setting-up
After populating the PCB's, it is better to check the unit section by section. Make sure the IC's are inserted correctly with their pin numbers corresponding to the power lines as 7 and 4 for OP27/TLO71 and 8 and 4 for the NE 5532's. First the P S U is to be checked for correct voltages at its output and should not exceed 15V (and ground) and - 15V (-ve and ground) when powered. The power supply leads should then only be connected to the mains PCB. Before energising the circuit, remove IC1 ie op-amp A1 . The input to the Opamp A2 circuitry should be connected to a line out socket of a deck or other music systems. Connect the output of the board to an amplifier. Switch on the PSU. Keep P5 at the mid position. Adjust P2, P3 and P4 to the desired mid frequency level. Increase level control P5 to the maximum position. The amplifier should still deliver undistorted audio and when P2, P3 and P4 are varied, the mid frequencies should be attenuated. If everything is okay, the mic. preamp is to be checked by connecting a microphone at the input. Insert IC1. Keep P5 and P6 at minimum positions. Switch on the power supply. Sing into the mic and slowly increase P6 by keeping P1 at the mid position. Trim preset P1 for required mic gain if necessary. Too much gain will result in acoustic feed back (howling), noise pickup and distortion. The amplifier should then deliver undistorted sound. Connect the music systems to the input and trim P2 , P3 and P4 to eliminate the vocals. Substitute your vocals by adjusting P6.
COMPONENTS REQUIRED
Resistors (all 1/4 W 5% )
R1, R2, R4 = 47KW Metal film resistors (M.F.R), R2 = 2K2 , R5, R15 = 5K6W (M.F.R), R6, R7, R8 = 470W, R9, R10, R11 = 10KW (M.F.R) , R12, R13, R14 = 100KW (M.F.R) , R16, R17, R19 = 47K W ,R18 = 220 W , R20 = 1K5 KW .
Capacitors
C 1= 1m F, C2 = 2m F, C3 , C4 = 4.7m F, C5 = 220pF ( Ceramic disc), C6 = 0.22m F, C7 = 4K7pf, C8 = 220pF (Ceramic disc) , C9 = 4m 7, C10 = 0.1 m F, C11 = 2K2 pF, C12, C13 = 2m 2F, C14 = 47Kpf, C15= 1Kpf, C16 = 4m F. C17, C18, C19, C20, C21, C22 = 0.1 m F (6 Nos.), C23, C24,C25,C26 = 22Kpf, (4Nos.) C27, C28 = 1000m f / 35V, C29, C30 = 10m f / 35V.
Presets and Pots.
P1 = 47K preset , P2, P3, P4 = 10K lin Pot., P5, P6 = 22K log.Pot.
Semiconductors
IC1 = OP27 or TLO71, IC2 = NE5532, IC3 = NE5532, IC4 = NE5532 , IC5 = 7815 (Positive voltage regulator), IC6 = 7915 (Negative voltage regulator)
Miscellaneous
TR1 = 2 X 18V @ 500mA transformer, S1 = Switch., Connecting wires , suitable enclousure etc.
NOTES
WARNING AND DISCLAIMER
(!!!!!!!)Mains-powered electronic equipment contains high AC voltages. These can be potentially lethal. If you do not know how to safely handle the inside of equipment containing high voltages, please do not attempt to open the equipment. Before carrying out any work inside equipment containing high Voltages, ensure that you disconnect the Unit from the Mains. Opening any kind of electronic equipment and modifying it will almost always invalidate your warranty. There is also a likelihood that workshops will refuse to repair custom modified equipment or that they will charge significantly more. (2) The information included herin is provided as-is, with no warranties express or implied. No resposibility on the part of the author is assumed for the technical accuracy of the information given herein or the use or mis-use of said information.
The equipment described in this article was designed, fabricated, and tested spending my own personal time and using my own personal resources.
The information on this site is Copyright © 1998 of Dr.LAL. You may link to these pages or print them out for your own personal use, but no parts of these pages can be reproduced, sold, or transmitted in any form without my explicit written permission. By copying or paraphrasing the intellectual property on this page, you're automatically signing a binding contract and agreeing to be billed $10,000 payable immediately. © Dr LAL's Homepage (CKT.DESIGN) 1998.
MY e-mail
:- lal@uni-tel.comHOME ` FOR THE INDEX AGAIN !.....
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