便携式混频器电路 Portable Mixer

Design description:

The target of this project was the design of a small portable mixer supplied by a 9V PP3 battery, keeping high quality performance.
The mixer is formed assembling three main modules that can be varied in number and/or disposition to suit everyone needs.
The three main modules are:

Input Amplifier Module: a low noise circuit equipped with a variable voltage-gain (10 - 100) pre-set, primarily intended as high quality microphone input, also suitable for low-level line input.

Tone Control Module: a three-band (Bass, Middle, Treble) tone control circuit providing unity-gain when its controls are set to flat frequency response. It can be inserted after height=449 src="/data/attachment/portal/201007/ET30794201007221016341.jpg" width=593 border=0>

Input Amplifier Module

Parts:

R1,R2,R7_______22K   1/4W Resistors
R3,R4,R5_______47K   1/4W Resistors
R6______________4K7  1/4W Resistor
R8,R13________220R   1/4W Resistors
R9______________2K   1/2W Trimmer Cermet (See Notes)
R10___________470K   1/4W Resistor
R11___________560R   1/4W Resistor
R12___________100K   1/4W Resistor

C1____________470nF   63V Polyester Capacitor
C2,C8_________100΅F   25V Electrolytic Capacitors
C3,C4,C5________2΅2   63V Electrolytic Capacitors
C6_____________47pF   63V Ceramic Capacitor
C7______________4΅7   63V Electrolytic Capacitor

Q1____________BC560C  45V 100mA Low noise High gain PNP Transistor
Q2____________BC550C  45V 100mA Low noise High gain NPN Transistor

IC1___________TL061   Low current BIFET Op-Amp

Circuit description:

The basic arrangement of this circuit is derived from the old Quad magnetic pick-up cartridge module.
The circuit was rearranged to cope with microphone input and a single-rail low voltage supply.
This low-noise, fully symmetrical, two-transistor head amplifier layout, allows the use of a normal FET input Op-Amp as the second gain stage, even for very sensitive microphone inputs.
The voltage-gain of this amplifier can be varied by means of R9 from 10 to 100, i.e. 20 to 40dB.

Notes:

R9 can be a trimmer, a linear potentiometer or a fixed-value resistor at will.

When voltage-gain is set to 10, the amplifier can cope with 800mV peak-to-peak maximum Line levels.

Current drawing for border=0>

Parts:

P1,P2_________100K   Linear Potentiometers
P3____________470K   Linear Potentiometer

R1,R2,R3_______12K   1/4W Resistors
R4,R5___________3K9  1/4W Resistors
R6,R7___________1K8  1/4W Resistors
R8,R9__________22K   1/4W Resistors
R10___________560R   1/4W Resistor
R11___________100K   1/4W Resistor
R12___________220R   1/4W Resistor

C1______________1΅F   63V Polyester Capacitor
C2_____________47nF   63V Polyester Capacitor
C3,C5___________4n7   63V Polyester Capacitors
C4_____________22nF   63V Polyester Capacitor
C6,C8_________100΅F   25V Electrolytic Capacitors
C7______________4΅7   63V Electrolytic Capacitor

IC1___________TL061   Low current BIFET Op-Amp

Circuit description:

This is a straightforward design using the Baxandall-type active circuitry slightly modified to obtain a three-band control. Total voltage gain of this module is 1 when controls are set in their center position.

Notes:

Current drawing for border=0>

Parts:

P1,___________100K   Linear Potentiometer
P2_____________10K   Linear Potentiometer

R1,R2,_________15K   1/4W Resistors
R3,R4,R11,R12_100K   1/4W Resistors
R5,R6__________22K   1/4W Resistors
R7,R8_________390K   1/4W Resistors
R9,R10________560R   1/4W Resistors
R13___________220R   1/4W Resistor

C1,C2_________330nF   63V Polyester Capacitors
C3,C8_________100΅F   25V Electrolytic Capacitors
C4,C5__________10pF   63V Ceramic Capacitors
C6,C7___________4΅7   63V Electrolytic Capacitors

IC1___________TL062   Low current BIFET Dual Op-Amp

Circuit description:

The schematic of this circuit is drawn as a stereo unit to better show the input Main Fader and Pan-Pot connections. The TL062 chip contains two TL061 in the same 8 pin case and is wired as two virtual-earth mixer amplifiers having a voltage gain of about 4, to compensate for losses introduced in the passive Pan-Pot circuitry. Therefore, total voltage-gain is 1.
Each channel added to the mixer must include the following additional parts:
P1, P2, R1, R2, R3, R4, C1 and C2.
These parts must be wired as shown in the above circuit diagram, connecting R3 and R4 to pin #2 and pin #6 of IC1 for Right and Left channel respectively. These IC1 pins are the "virtual-earth mixing points" and can sum together a great number of channels.

Notes:

Current drawing for one stereo Main Mixer Amplifier Module is 800΅A.

Frequency response is 20Hz to 20KHz - 0.5dB.

Total Harmonic Distortion measured @ 2V RMS output = < 0.008% @ 1KHz; < 0.017% @ 10KHz.

THD is 0.005% @ 1V RMS output.

Maximum undistorted output voltage: 2.8V RMS.

Further Parts:

To parts listed above should be added: one Main on-off SPST switch, a LED used as pilot-light with its dropping 2K2 1/4W series-resistor, DPDT switches to enable or omit Tone Control Modules as shown in the Block diagram, input and output connectors of the type preferred, one stereo dual-gang 100K potentiometer to fade the Stereo Line Input as shown in the Block diagram, battery clip, PP3 9V battery, knobs etc.