Circuit examples

Mixer with optional offset function and inverted/non-inverted outputs

Inputs J1 ... J3 are standard inputs.
Input J4 has offset function provided that no plug is inserted into J4 as the switching contact of J4 is connected to the positive supply voltage in this case (via the protection resistor R8).

At J5 the inverting sum of all inputs is available. J6 outputs the non-inverting sum. P5 allows an additional attenuation of the complete signal (affects only J6).

Typical values for the parts used:
O1, O2 = LM1458, TL082, NE5532
P1...P4 = 47k linear (CV) or log (audio)
R1...R7 = 100k (for overall amplification 1)
To obtain a higher overall amplification R5 has to be increased (e.g. to 220k for overall amplification ~ 2 or to 1M for overall amplification ~ 10).

The value of R8 defines the offset range (about 0...+6V for R8=33k, a lower value of R8 will increase the offset range and vice versa).

Matrix Mixer

The CV mixer described above can be expanded to a so-called matrix mixer. This circuit has several inputs available (three in the example circuit) that can be mixed to different outputs (three in the example circuit) with adjustable levels. At each point of the matrix a potentiometer is available that defines the level for the matrix junction in question.

The circuit can be used for CV or audio applications. The number of inputs and outputs can be increased to the desired value of columns and rows. For each of the outputs the two OpAmp circuit with the corresponding output socket is required. For each input another socket and the corresponding quantity of potentiometers and resistors is required.

Typical values for the parts used:
All operational amplifiers: LM1458, TL082, NE5532
All potentiometers: 47k linear (CV) or log (audio)
All resistors: 100k

To obtain a higher or smaller overall amplification the feedback resistor of the first (left) OpAmp of each output circuits has to be adjusted (as described above).

It is recommended to use a separate pcb for the output circuits. The input sockets and matrix potentiometers/ resistors can be wired by hand very easily.

Manual Gate

The left picture shows the basic circuit of a manual gate. The 470 Ohm resistor serves as a short circuit protector. Without this resistor the +12V supply would be shorted to GND if a patch cable is inserted to the socket while the button is pressed.

The right picture is expanded by a LED display that lights up while the button is pressed.

Or-wired sockets

The left picture shows the circuit of "or-wired" sockets. This circuit is useful to combine gate or trigger signals. The incoming signals are or-wired, i.e. if any of the inputs is "high" the output turns "high" too ("high" means a positive voltage in the range of typical +5...+12V). If none of the inputs is high the 10k pull-down resistor pulls the output to GND, i.e. "low". For most applications this resistor is not required as the input load of the following module acts as pull-down resistor. But it should be added to be on the safe side.

As a modification of this circuit even "and-wired" sockets can be realized. But this type of combination is not used very often: all inputs have to be "high" to turn the output to "high". For all other conditions the output remains "low". On this the diodes have to be flipped (i.e. the cathodes at connected to the input sockets) and the resistor has to be connected between the output and +12V (so-called pull-up resistor). In addition the switching contacts of the input sockets have to be connected to GND (normalled to GND). This measure is necessary in order that unused sockets read "low". Otherwise unused sockets would read "high" because of the pull-up resistor.

For example a multiple A-180 can be modified with 7 additional diodes and one resistor to obtain seven or-wired sockets and one output socket. For this the pcb tracks between the eight multiple sockets have to be interrupted (not the GND connections, only the "hot" connections) and re-wired with the diodes and the resistor.

Non-inverting power amplifier

This is a simple non-inverting power amplifier that can be used to drive loads like light bulbs, LED bars, fairy lights, motors, magnets, relays or other loads. Pay attention that the connected load is suitable for 12V supply voltage. Otherwise the supply voltages of the operational amplifier and the power transistors have to be adapted. If only positive output voltages are required Q2 can be omitted. If an operational amplifier is available in the preceding module (e.g. a mixer A-138) this operational amplifier can be used and only Q1, Q2 and R3 have to be added. The maximum output current depends upon the specifications of the power transistors. Pay attention that the power supply has to be able to deliver the additional load current ! For higher currents (~ beyond 100mA) the transistors have to be mounted on suitable heat sinks.

Attention: The output is not short circuit protected. If a standard A-100 jack socket is used the output connection has to be established before power is turned on ! During the insertion of a plug into the jack socket a short circuit is made for a short time. Therefore another type of socket is recommended for the output (not the jack socket shown in the picture).