YuSynth Dual Auto-Bend

Introduction

A bare double sided PCB (no need for the wire jumper links shown on the PCB layout) for the Yusynth Dual Auto-Bend synth module. These PCBs are manufactured by Soundtronics with a percentage of the sale going to the creator of the YuSynth - Yves Usson. These are early days for the YuSynth Modular Synth at Soundtronics, our plan is to stock PCBs for all of the projects as well as components, kits and front panels. This is going to take time but will eventually be as comprehensive as our MFOS range.

No components are included with the PCB but check out our Synth Components section where you should find what you need. We do suggest visiting the YuSynth Auto-Bend project page for detailed information including Yves panel layouts but a summary is shown below.

Erratum

Sorry but there is two small errors on the PCB. Cut the track between the MOTM +15V pad and the 0V ground track.

A track is missing but is easily resolved by putting a wire link as shown below

Description

This module is very useful utility module to simulate the transient frequency bend that can be heard at the onset of a note played by some instruments such as trumpets and oboes. The same effect could be achieved using an ADSR module connected to the FM input of a VCO. However, having such a dedicated autobend module makes it possible to reserve ADSR modules for a "posher" use.

Yves designed a single PCB that can be used either to build a single 1U module or a dual 2U module.

The TIME knob let choose the bend time within a range from 1ms to 0.5s (this can be extended by changing some part values). Two outputs are provided than can be set independently within a range of +/- one octave. Switches are also provided to enable/disable the autobend function.

The PCB can accept a choice of three types of power connector, it can be either a Synthesizers.com 6 pins MTA connector, a MOTM 4 pins MTA96 connector or a 10-pin Eurorack connector.

Circuit

Click on the schematic thumbnail above for the circuit diagram.

When no GATE signal is applied to the GATE IN jack, the R3 resistor pulls down the base of Q1(NPN) to ground level. Thus, Q1 is forced to the non-conductive state and in turn forces Q2(PNP) to the non-conductive state. When a GATE signal (>3V) is applied to the GATE IN jack, the rising edge of the GATE signal is differentiated by the capacitor C3 and converted to a positive pulse (few ms). The diode D1 filters out the negative pulse that arises on the falling edge of the GATE signal. The positive pulse turns Q1 to a brief conductive state. When Q1 is conductive, Q2 is turned to the conductive as well. During this brief conductive state, the capacitor C5 is quickly charged. When Q1 and Q2 return to non-conductive state, the capacitor starts discharging through R7 and P1. The discharge time depends on the value of P1 and can be set from 1ms to 0.5s . The variation of voltage at the level of C5 is measured by the voltage follower U1b. This voltage is inverted by U1a and the direct and inverted voltage are sent through R10 and R11 to the clockwise lug and counter clockwise lug of two the potentiometers P3 and P4. Each pot has its wiper connected to a voltage follower (U1c,U1d) through a toggle switch. This switch makes it possible to disconnect the autobend effect.
With the resistor values selected for R10, R11 and P2, the output range can be set between -1V (-12 semitones) and +1V (+12 semitones). By changing the value of R10 and R11, one can adjust the maximum range to what one see fit.

PCB Assembly

The same PCB is used for both the single channel and the dual channel versions. The parts list below indicated the component count for both th single and dual versions

Wiring

The wiring schematic image in the above thumbnails show the panel wiring to the pots and sockets etc.

Setting and Trimming

No trimming is required

Parts List

The parts list below is direct from the YuSynth website.

The parts list excludes knobs although we have standardised on the Cliff KM20B but it does include 1/4" jack sockets. All parts are available individually (use the part number in the search box above) or as a components kit that excludes sockets and knobs.

* only required for the dual module.
** if using a tantalum capacitor, make sure that it is mounted on the PCB such that the - pin is connected to the ground rail.
*** with 120K for R10,R11 the range of the output is +/-1V that is +/-1 octave, you may change the value of these resistors to achieve a greater or smaller range
**** with a 500K potentiometer the TIME range is 1 ms to 0.5s, if you wish a longer range (say 1s) use a bigger value (1M or 2M)