2Channel + Microphone Stereo Mixer

2ch_mixer_1.gif (41431 bytes)

A lot of friends me asked to draw a more shrunk circuit 2-ch mixer, which will contain also, operation CROSSFADER. The circuits can be modified and added also other channels, repeating basic that I give. It can are added channels stereo PHONO/line or even channels microphone with proportional modification of next stages. In the Fig.1 exist the input circuits of two channels and input of microphone channel. The two basic channels she is same between them. Thus that it’s go for a channel, the he is also go for the other. In each stereo channel exist two inputs, classic stereo input PHONO that is practical a correction filter RIAA and concerns the signal amplification of sound that emanates from the classic reproduction heads of classic disks LP. Exist also a stereo input of LINE ‘’high level’’ for signals that emanate from CD players, Tuners, DVD, etc. The exits of this two stages are selected with switch S1 or S2 and they are applied in the next stage which is constituted from adder IC3. Here is regulated the BALANCE with the RV5 and GAIN with the RV1. In the next stage round the IC4 exist a classic 3-band regulation of tone circuit, the regulation of which becomes with the RV2-3-4. The exit of IC4 drive the RV6 that is at preference pontesometer [FADER]. By points 1-2-5-6 the signals connected to next stage [Fig.2]. In the Fig.1 exist also the microphone input, which is in electronic Balance connection, round the IC9A. Here exist the regulation of GAIN with the RV13. It follows a stage of tone two-band regulation, round the IC9B and a stage of parametric regulation of mid band with RV16 [Gain] and RV17 [Frequency Band]. With the RV19 we regulate VOLUME [FADER] and with the RV18 we regulate the BALANCE. By points 9-10-11 the signal is connected to the corresponding points that are found in the Fig. 2.

Part List [Fig.1]

R1-7-15-16-41-48-55-56=47 Kohms C1-13-37-45=150pF mylar-ceramic IC1-5-9-10=NE5532-LM833
R2-8-42-49=150 ohms C2-3-15-16-20-21-27-28-38-39=47nF IC2-3-4-67-8=TL072
R3-5-9-11-43-45-50-52=180 Kohms C4-5-9-11-42-44-47-48=18nF RV1-7=  22 Kohms Log. pot.*
R4-6-10-12-44-46-51-53=15 Kohms C6-10-41-46=3.9nF RV2-3-8-9=2X100 Kohms Lin. pot.*
R13-14-17-18-47-54-57-58-95=100 Kohms C7-12-43-49-82-83=5.6nF RV4-10=2X470 Kohms Lin. pot.*
R19-22-59-62-98-100=4.7 Kohms C8-14-17-18-40-50-53-54-88=10uF 16V RV5-11-18=10 Kohms Lin. pot.*
R20-23-60-63-21-24-61-64=10 Kohms C19-30-55-66-89=22pF RV6-12=2X22 Kohms Log. pot. 45mm Slider [FADER]
R25-26-33-34-65-66-70-71=10 Kohms C22-31-58-67=47nF RV13=10 Kohms Log. pot.*
R27-35-67-73-74-75-78-79-96=10 Kohms C23-32-59-68-25-34-61-70-85=4.7nF RV14-15-16=47 Kohms Lin. pot.*
R28-29-36-37-68-69-76-77=3.3 Kohms C24-33-60-69=22nF RV17=2X100 Kohms Log.pot.*
R30-31-38-39-70-71-78-79=1.8 Kohms C26-35-62-71=1.2nF RV19=10 Kohms Log. pot. 45mm Slider [FADER]
R32-40-72-80=330 ohms C29-36-65-72-80-90=10uF 16V J1-2-5-6=4pin conn. 2.54mm pin step
R81-83=2.2 Kohms C56-57-63-64=47nF J3-4-7-8-9-10=3pin conn. 2.54mm pin step
R82-97=6.8 Kohms C73-74=1uF 100V MKT Jf1....8=RCA female Jack
R84-88-93-94=22 Kohms C75-76=68pF ceramic or mylar JF9=3pin XLR male
R85=100 ohms C77-78-86-87=47nF
R86-87=2.7 Kohms C79=47uF 16V
R89-90=5.6 Kohms C81=2.2nF *ALPS or PIHER type Potentiometer
R91-92=3.9 Kohms C84=10nF All the Resistors is 1/4W 1% metal film
R99-101=10 Kohms S1-2=2X2 0N/ON SW All the [nF] capacitors is 63-100v 5% MKT

2ch_mixer_2.gif (31020 bytes)

In the Fig.2 abut the various signals that emanate from the Fig.1. Switches S3-4-5 execute the operation of pre-Fader-listen [PFL] of proportional channels. If some switch functions then turns on corresponding diode led D4-5-6. Simultaneous turn-on the relay RL1 disconnect the program in the headphone and supply with the PFL signal. Round the IC14 exist the amplifier circuits of headphone drive. Round the IC12 exist the addition circuit of the signals from the two channels and the mic channel, as well the RV20 which function as CROSSFADER between the two stereo channels. The RV21 is final MASTER VOLUME [FADER] and adjust the final percentage of signal to the output. This role undertake the IC13 that has the leading possibility via the outputs Jf13-14 a power amplifier, simultaneously from the exits Jf11-12 we can take signal for recording.

Part List [Fig.2]

R102-103-106-107-113-114=10 Kohms RV20=2X22 Kohms Log. pot. 45mm Slider [FADER] Q2-4=BD140
R104-108-117-122-125-126=22 Kohms RV21=2X10 Kohms Log. pot. 45mm Slider [FADER] S3-4=3X2 PDT 0N/ON SW
R105-109=1 Mohms RV22=2X10 Kohms Log. pot.* S5=2X2 PDT ON/ON SW
R110-111-112=1 Kohms C91-95-97-101-103-106-111-114=22pF RL1=12V Relay 2X2 SW
R115-118-120-123-127=10 Kohms C92-93-98-99-104-105-109-110=47nF JF10=Jack female stereo 6.3mm
R116-119-121-124-130=10 Kohms C94-96-100-102=10uF 16V JF11....14=RCA female Jack
R128-131=27 Kohms C107-108-113-116=470uF 25V J11....14-17=3pin conn. 2.54mm pin ste
R129-132-137-138-140-146=100 ohms C112-115=47uF 16V J16-17=4pin conn. 2.54mm pin step
R133-135-139-145=100 Kohms IC11-12=TL072 RV20=2X47 Kohms Lin. Slider [FADER]*
R134-136=47 ohms IC13-14=NE5532 - LM833 RV21=2X10 Kohms Log. Slider [FADER]*
R141-147=10 ohms D1-2-3=1N4002
R142-148=4.7 Kohms D4-5-6=LED 3 or 5mm RED *ALPS or PIHER type Potentiometer
R143-149=820 ohms D7=1N4148 All the Resistors is 1/4W 1% metal film
R144-150=47 Kohms Q1-3=BD139 All the [nF] capacitors is 63-100v 5% MKT

2ch_mixer_3.gif (22467 bytes)

In the Fig.3 exist a classic supply circuit and stabilization of various voltages that needs the various circuits of mixer as +/-15V for the Audio department and + 12V for the RL1 and VU meter supplying. The regulators IC18-19-20 good it’s they are placed on small heatsinks. Transformer T1 it’s placed in a separate box, far from the remainder circuit, so that is not created problem of influence of rests circuits, from noise, unless it’s toroidal. In the Fig.4 is found the indication circuit of level. This becomes with two classic circuits round the IC16-17 that drive the diodes Led D12…..D31, that portrays the level in steps of 3dB. The IC15 functions as precision rectifier.

Part List [Fig.3-4]

R151-152-156-157=10 Kohms BR1= 80V/3A BRIDGE RECTIFIER IC20=7915  on Heatsink
R153-154-155-158-159=1 Kohms D8-9-10-11=1N4148 T1=230V//2X15Vac >30VA
R160=2.7 Kohms D12.......31-32=RED LED F1=500mA SLOW BLOW FUSE
C117-118-124-125-127-128-130-131=100nF D33=12V 0.5W ZENER S6=2X2 ON-OFF SWITCH
C119-121=1uF 25V IC15=TL072 J18=3pin conn. 3.96mm pin step
C120=10uF 25V IC16-17=LM3516
C122-123=4700uF 40V IC18=7812  on Heatsink All the Resistors is 1/4W 1% metal film
C126-129-132=19uF 25V IC19=7815  on Heatsink All the [nF] capacitors is 63-100v 5% MKT



Sensitivity 2.5mV rms
Impedance 47K//150pF

LINE INPUT [Unbalaced RCA]

Sensitivity 1V rms
Impedance 47K
Gain X1 until X3
3-band EQ  

50HZ, 1KHZ, 10KHZ [±18dB/oct]

MIC INPUT [Balanced XLR]

Sensitivity -56dB
Impedance 2K
Gain 36dB
EQ. Section
High ±18db at 20KHZ
Mid. Freq. 200HZ - 6KHZ
Mid. Gain ±15db
Low ±18db at 20HZ
impedance 100 ohms min.

Block Diagram

2ch_mixer_block.gif (19431 bytes)

In the Fig.5 appears the block diagram of circuit, which it will help in the comprehension of logic of circuit.


Sam Electronic Circuits 10/02

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