YuSynth Noise + S&H Module Bare PCB

YuSynth Noise + S&H Module Bare PCB

(£16.06 exc. tax)
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YuSynth Combined Sample & Hold with Noise generator


A bare double sided PCB (no need for the wire jumper links shown on the PCB layout) for the Yusynth S&H with Noise generator 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 Noise + S&H project page for detailed information on both this PCB and the accompanying VC-Panner including Yves panel layouts but a summary is shown below.


Sorry but there are a couple of small errors on the PCB.

A track from the junction of R3 & R4 on the S&H side of the PCB should go to pin 3 of U1, not pin 2. This is easily corrected by cutting the track connection with pin 2 and solder a link from R4 to pin 3. The photo below shows this although you should carry this out after soldering in the components.

The second error requires the track between R13 & R14 cutting then R14 linked to the anode of D3. The photo below has these corrections shown in blue.


This single modules integrates two sub-modules : a noise voltage generator and a sample and hold (S&H) processor.

The noise generator generates three different signals : white noise (evenly distributed frequency spectrum), pink noise (1/f frequency spectrum, that is with a 3dB/octave slope), and a slow varying random voltage (frequency smaller than 6Hz).

The Sample and Hold processor has an internal clock but can be driven from an external clock. The clock rate ranges from 0.1Hz to 100Hz. The clock I/O acts either as an clock input or as a clock output depending on the position of the EXT/INT switch. A yellow LED shows the clock rate. A slew rate is also provided (its behaviour either linear or exponential can be selected with a jumper on the PCB).

As a default, the input of the S&H processor is connected to the white noise source.

Yves designed three different PCBs : a PCB that integrates both the noise generator and the S&H processor (this board 7220-046), a PCB for the noise generator on its own (7220-045) and a PCB for the S&H processor on its own (7220-030). Thus one can build the module of one's choice, either combined or separate.

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.


Separate supply rails are used for the two sub-modules. This was made necessary to solve an issue on the first prototype, the clock and trigger stages of the S&H were interfering with the noise amplifier stage of the noise generator!

Noise submodule : Q2 is connected as a reverse polarised diode in order to generate as much noise as possible. This noisy signal is first amplified by Q3 and routed both to U3b which amplifies the white noise signal and to Q4. A network or resistor-capacitors (R2-R24,C9-C11) shapes the spectrum. The result is a low-pass filtering with a 3dB/octave slope giving rise to the so-called pink noise.  Then the pink noise is amplified by U3d which is followed by two low-pass filters to provide slow varying random voltages. The first filtering stage is second order low-pass with a cut-off frequency close to 5Hz the second stage provides a 6dB/octave lowpass with a cut-off frequency of 4.7Hz with some amplification in order to level up the random voltage.

Sample and Hold : U1 is an OPA in a classical astable multivibrator configuration, with the values of R3, R4, R5, C3 and P1 the slowest rate is 0.1Hz and fastest 10Hz. The positive part of the pulse is selected by D1 and routed to a switch that is used to toggle the S&H trigger between the internal clock and an external clock. Q1 drives a LED which flashes as a function of the clock rate. C4 differentiates the clock signal in order to convert the rising edge of the clock into a brief positive pulse (10ms). U2d is connected as a comparator. D2 selects the negative part of the pulse to drive the gate of the Q2 FET.

Click on the schematic thumbnail above for the circuit diagram.


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

Setting and Trimming

The trimming is quite simple, it consists of taking a batch of BC547 transistors and selecting among these which one gives the highest white noise level while being symetrically balanced around 0V level, with the flatest spectrum. In order to do so, it is a good idea to use a transistor socket for Q2, this way one can swap easily the transistors to find the best one. It is a good practice to wait about 1min before checking the noise level and quality of white spectrum in order that Q2 has reached a steady temperature.
Below are the spectra Yves measured on the two boards he built. Some resistor values may also be adjusted to obtain the desired output levels.

Measured audio spectrum - white noise output (0dB position set arbitrarily)

Measured audio spectrum - pink noise output (0dB position set arbitrarily)

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.

S&H sub-module

Reference Value Part No. Qty
U1 LM741/TL071 7212-580 1
U2 TL074 7212-544 1
Q1 BC547 7212-401 1
Q5 BF245B 7212-407 1
D1,D2,D3 1N4148 7212-480 3
R1sh,R2sh 10 7163-007 2
R10 100 7163-027 1
R5,R6,R8,R15 1K 7163-051 4
R7,R12 10K 7163-075 2
R37 22K 7163-083 1
R3,R9,R11,R13 100K 7163-099 4
R4 120K 7163-101 1
R14 2.2M 7163-138 1
C4 1n (any value between 1n and 10n will do) 7212-740 1
C5 100n Polyester Film 7212-718 1
C19,C20,C22 100n 7212-749 3
C6 680n polyester film 7212-723 1
C3 10µF/35V electrolytic 7213-119 1
C1sh,C2sh 22µF/35V electrolytic 7213-113 2
P1 500K reverse audio potentiometer (ALPHA) 7300-150 1
P2 1M log potentiometer 7300-070 1
SW SPDT switch 7212-250 1
LED1 Panel Mount 7213-900 1
LED1 Yellow LED 7213-903 1
Jk1,Jk5,k6 female jack socket 7212-203 3


Noise Generator sub-module

Reference Value Part No. Qty
U3 TL074 7212-544 1
Q2* BC547, *selected for maximum noise level and whitest spectrum 7212-490 1
Q3,Q4 BC547 7212-401 2
R1n,R2n 10 7163-007 2
R19 22 7163-013 1
R32,R35,R36 1K 7163-051 3
R25 3.9K 7163-065 1
R26 8.2K 7163-073 1
R18,R30 10K 7163-075 2
R24 18K 7163-081 1
R28,R29,R33 33K 7163-087 3
R16 47K 7163-091 1
R20 82K 7163-097 1
R23 100K 7163-099 1
R17 150K 7163-103 1
R31 220K 7163-107 1
R22 390K 7163-113 1
R27,R34 470K 7163-114 2
R21 1M 7163-122 1
C13,C18 10p ceramic 7212-730 2
C11 1n yellow LCC 7212-708 1
C10 3.3n yellow LCC 7212-711 1
C9 47n yellow LCC 7212-717 1
C21 100n ceramic 7212-749 1
C16 150n yellow LCC 7212-719 1
C14,C15 1µF yellow LCC unpolarized 7212-724 2
C12,C17 10µF/25V electrolytic 7213-106 2
C7,C8 47µF/25V electrolytic 7213-109 2
Jk2,Jk3,Jk4 female jack socket 7212-203 3




There is a bad trace on this board. See: http://electro-music.com/forum/topic-68333.html This should be added to the FAQ.

Asked by Dale | 02/03/2017, 14:56 | 1 answer(s)

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