YuSynth Quad VC Panner & Mixer

Introduction

A bare double sided PCB for the Output Stage & Monitor synth module. Being double sided, there is no need for the wire jumper links shown on the PCB layout or the MOTM Eurorack wire link shown in the YuSynth build instructions. 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.

Erratum

The PCB shows R439, this is actually R429, value is 10K

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 Mixout VC Panner project page for detailed information on both this PCB and the accompanying VC-Panner including Yves panel layouts but a summary is shown below.

Description

The Mixout VC Panner module is the combination of two utility modules :

• the first utility is a quadruple VC-PANNER (and mixer, though not VC ) using this PCB 7220-041.
• the second utility is an output module using PCB 7220-044 available separately providing master volume control, tonality control and old-school vu-meters as well as a monitoring output for headphones.

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. See above images for wiring details for MOTM and Eurorack connections.

Circuit

The Mixout-VC Panner This sub module is based on very classical circuits that can be found in many electronics textbooks.
For one channel and from left to right :

• a classical baxandall tonality filter, with both cut & boost for treble and bass, it is build around two OPA (U1a,d)
• a line output buffer based on a classical buffer inverter (U3b)
• a level display, based on a single OPA amplifier and a rectifier bridge (D5,D6,R28,R29) and an oldschool analogue panel vu-meter connected betwen the diodes,
• and a headphone amplifier stage (based on the Yamaha CS15 circuit) using a single OPA combined with a complementary pair of transistors providing enough current to drive a HiFi stereo headset.

Click on the schematic thumbnail above for the circuit diagram.

Wiring

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

Setting and Trimming

VC-Panner
The trimmers T101 to T104 are used to adjust the midrange for the paning for each channel.
Basically, for each channel :

• use a voltmeter and adjust the trimmer in order to measure -4V on the wiper pad of the trimmer (normally you are very close from the optimal setting)
• Then send a TRIANGLE WAVE(1kHz) with an amplitude of 10Vpp (-5V/+5V) on the input of the channel.
• Set the PAN LEVEL pot to 0, and the PAN pot to 12 o'clock.
• Connect a dual channel oscilloscope at the outputs. You should obtain the triangle with equal amplitude on both channels, then turn the PAN pot from Clockwise to Counter-clockwise position : you should observe the disappearing of the triangle on one side and the increase in amplitude on the other side.
• Now, adjust the trimmers such that when the PAN pot is at 12 o'clock, the amplitude of the two triangle waves is roughly half of that can be measured for one wave when the PAN pot is set to clock-wise or anti-clockwise positions. (If you don't have an oscilloscope by ear using hadphones, check for an even balance at 12 o'clock, then verify that the panning effect acts as expected when rotating the PAN pot).

Parts List

The parts list below is direct from the YuSynth website. The value in the parts list is the default value and may differ to that quoted in the schematic / PCB silk image.

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.

All resistors are 1% (1/4W to 0.6W) unless specified otherwise
Trannies are to be matched by pairs (Q101/Q102),(Q201/Q202)...
Color black is used for components belonging to the common part of the circuit, colors red, blue, green, brown are used to discriminate the components as a function of the channel they belong.