2Channel + Microphone Stereo Mixer

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.

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.

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.

Block Diagram

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