This is a modified version of Yves Usson's Yusynth ADSR envelope generator, which is in turn based on an 1980 article by Jonathan Jacky and similar to the design published by René Schmitz. The design is based around a 7555 timer (a CMOS version of the classic 555) to provide the logic, and three diodes to guide the charging (attack) and discharging (decay, release) currents of the timing capacitor through different potentiometers. Design modifications (Getting technical now, read ahead first if you want to see how the circuit works). I first built up Yusynths version on a breadboard, and while it worked in general I had some issues with the diode forward voltages. For example during the release phase, the output voltage decays quickly (as set by the Release potentiometer) to roughly 0.7V, the diode forward voltage ('diode drop'). Taking a simple diode model, the diode would now stop conducting and the output would stay at 0.7V, which is not ideal but would be manageable. In reality, however, the diode still conducts albeit with much lower current. The result is that the output very slowly decays, reaching 0V only after 10s of seconds. The samey issue occurs during the decay phase. All this can be quite annoying, for example when modulating the pitch of an oscillator with the ADSR. Surprisingly, I have not read about this problem elsewhere, even though it is an obvious and understandable issue with such diode based envelope circuits. Even more surprising, my Microbrute does not show this issue, although it almost certainly has the same envelope circuit (the Minibrute, at least, has the exact same ADSR). Well, anyway, I decided to fix it and my final solution was to use a type of precision rectifier in place of the decay and release diodes (hence the title). It's a bit of a special one, because it rectifies current in stead of voltage. The basic schematic is as follows: The opamp's negative input is a virtual ground point. For a positive input voltage, a current flows through the resistor as defined by Ohm's law. This current flows through the diode into the opamp output. The output therefore is at a negative voltage, which compensates the diode's forward voltage drop. For a negative input voltage, however, the diode cannot conduct any current (the opamp will saturate at the positive rail). So, this circuit can sink a current, but not source any. Complete circuit Here is the complete circuit of my implementation: All transistors are BC547C (but can probably be almost any NPN), all diodes are 1N4148 (apart from L1, which is a red LED). U1 is an Intersil ICM7555, and U2 is a TL074 quad opamp (powered from +12 V and -12 V). The maximum current draw is about 10 mA from both the positive and the negative rail. C6 should be close to U2 on the board. Gate input The first part of the circuit converts an incoming gate signal or button press into a well-defined gate signal (GATE) and a short trigger pulse (TRIG). Q1 and Q2 form a discrete Schmitt trigger, turning any input signal into a gate with sharp edges between 0V and 12V. C1 and R6 turn the sharp edge into a short pulse of a few 10s of microseconds, which is then buffered and inverted by Q3. So the TRIG signal is normally at 12V and makes a short pulse to 0V at the start of each GATE. 7555 timer core These signals are used to start the 7555 timer via the trigger and reset pins (these are both inverting inputs - e.g. a high input on pin 4 means not reset). The Out pin will go high (to 12V), and the Discharge pin will be floating. The timing capacitor C3 will start charging from Out thourgh D2 and the Attack potentiometer. The voltage over C3 is buffered by U2c, giving the envelope output. The buffered output is also fed back to the 7555s Threshold pin. When this pin reaches 2/3 VDD (about 8V), the timer will switch off. Out will go low, so the charging will stop. At the same time the Discharge pin is connected to ground. R14 now defines a sustain voltage between 0 and 8V, and the precision rectifier of U2b/D4 allows C3 to discharge through the Decay pot to the sustain level. The output will remain at the sustain level until the gate signal ends. When GATE goes to 0V, the U2a/D3 rectifier allows discharge through the Release pot until finally reaching 0V output. Inverted output and LED driver Yusynth uses one additional opamp to invert the output, and one as a LED current driver, but I had only one opamp left. While the inverted output is not essential, I found these functions can be combined, which is done in U2d. This is again similar to a precision rectifier. R17 converts the envelope voltage to a current, which is then (for positive input) forced to go through the LED. Again, the opamp compensates for the LED forward voltage drop. The current also goes through R19, which gives the inverting amplifier function. This voltage is tapped of as second output. D6 is there such that the opamp never goes to the positive rail, which would be too much reverse voltage for a typical LED. Built circuit Breadboard version: Version built on prototype board: I used a piece of board designed for DIP packages, which turns out to work quite well for the discrete transistor stages as well. Most resistors and diodes are on their side to make it fit, and a bunch of jumper wires and solder bridges complete the connections. This is probably not the style for everybody, as the result is always chaotic, but it gives quite compact results for a prototype board (much more than the typical veroboard layout). The board is held in place only by the connecting wires. The front panel is a prototype cut out of cardboard (4HP eurorack size). Finally a picture of the back. Note the generous use of solder. The three small wire bridges were needed because I accidentally inverted all the power lines when planning the board... Performance I'm quite satisfied with the result. The decay and release phases go nicely to their final level (sustain or 0 V, respectively) without any slowing down. A nice side effect is that the reverse leakage through the decay diode (which is now bigger because the opamp can create a large reverse voltage) compensates leakage of the timing capacitor and through other diodes, so the sustain phase stays accurate indefinitely. After the final release there is an output offset on the order of 10 mV (presumably the low voltage of the gate and discharge signals), but this is quite acceptable and it seems stable. ADSR envelope Shortest AD envelope With the component values show, the shortest envelope is a bit under 1 ms (attack + decay), and the longest has about 1 second attack and decay/release with the same time constant. For longer envelopes a larger capacitor could be used for C3, or higher value A,D,R potentiometers. The shortest time is mostly limited by the (dis)charging current the 7555 and opamps are able to supply, and somewhat limited by the 100 Ohm resistors R8/R10/R12 (these can be omitted, but the difference is small). Further modifications Analog Output has further evolved this design by adding retrigger and loop functions. See his blog post and this youtube video with detailed explanations. He also shares the PCB design in Kosmo format.
Gristleizer famous audio effects unit Throbbing Gristle DIY stripboard layout and explanation build your own.
How to start a synth DIY adventure? A list of possibilities depending on your skills, example sound synthesizer projects for beginners and advanced music enthusiasts.
Here's a dump of layouts, pics and info about my EPFM modular build. I didn't include any of the schematics in this post. They are eas...
The "WP-20 Mini-Synth Sound Effects Synthesizer" is probably the best project out there for getting started in Synth-DIY proper. It packs all the basic
Moog Style Synth: First and foremost, I have to give a massive shout out to Pete McBennett who designed this awesome circuit. When I came across it on YouTube I couldn't believe the sound that he managed to get out of a handful of components. The synth has a MASSIV…
This module calculates simple boolean arithmetic between two GATE inputs. Any GATE signals may be connected to A and B inputs. 0V = logical 0 or FALSE, 5V = logical 1 or TRUE. A AND B The output wi…
The Tiny TS is a credit card sized (100x65mm) fully open-sourced synthesizer with a 1-octave capacitive touch keyboard.
Cigar Box Synth : Here’s my latest synth made from a 555 and 556 timer along with a 4017 ic. A few months ago a build like this would have been way out of my skill level. Over the last few months however I’ve been putting together some simple synths to get a better…
Collection of vero (stripboard) & tagboard layouts for 100s of popular guitar effects, with over 500 verified designs. DIY your own boutique effects!
How to start a synth DIY adventure? A list of possibilities depending on your skills, example sound synthesizer projects for beginners and advanced music enthusiasts.
SABER ELETRÔNICA Vol.74 RITMO BOX - gerador de ritmo 11-1978 SÍNTESE SONORA & ELETRÔNICA ARTESANAL
Build a 1V octave voltage-controlled oscillator (VCO) module and create your own analogue synth sounds.
RADIO ELECTRONICS 1980-05 - Percussion Synthesizer-PAIA - SÍNTESE SONORA & ELETRÔNICA ARTESANAL
I was reading discussions about various vintage effects on freestompboxes.org when I stumbled upon a thread about the Systech Harmonic Energizer. I knew I had
HANDMADE ELECTRONIC by EDYNEL (VISITE!) :Este blog é uma janela do meu trabalho (Hobby), ao qual chamo “ ELETRÔNICA ARTESANAL”
Build a multifunction sound synthesizer using a surprisingly fun audio chip.
Selezione Radio 1976_10/11 - GERADOR ELETRÔNICO DE RITMO SÍNTESE SONORA & ELETRÔNICA ARTESANAL
Complete Synth Build Guide For Beginners This guide is for complete beginners in electronics & synth making. We'll be building the 'Helios ...
Korg Mini-Pops DIY Drum Machine This is a really cool build; It a recreation of the Korg Mini-Pops drum machine, an instrument which has been on a ton of records the most famous of which might be Jean Michelle Jarre’s ‘Oxegen’ album, hence this clone being called the ’O2’. The brilliant Jan Ostman built this using only an Arduino nano and a few barebone parts. Jan is giving away the full details on his website and is only asking for a $3 donation in return. Bargain! https://janostman.wordpress.com/the-o2-source-code/ ***Update*** If the linked website is no longer working, use the Internet Archive to visit a cached version of the site (copy and paste the address and choose a date from around when this pages was posted: around Dec 2016). ***MIDI update*** From the forums of Look Mum No Computer, somebody has posted the code but with the MIDI update; https://www.mediafire.com/file/5hwyuvykzn8kszg/O2minipops2midiout.ino/file (Read the forum for more info and schematic). ***More Advanced Model Update*** If you'd like to build a more advanced version, head over to the NoiseyMaker website for more info and a nice detailed guide. This version builds on the original & adds some advanced features like a display and even pitch control of the samples. Also the drum patterns have been updated to be a bit more 4/4 time 'electronic-style', rather than than some of the 3/4 time waltz in the original code (you could always copy & paste these over to the old code if you wished). .... I started by building my first version using a cheap Maplin plastic enclosure, but I thought it was worth spending a little more time on it so I got the table saw out. Because the table saw has a maximum cutting width of 7cm, I based the case around this limitation. The switches mute the individual drum hits. The pots select the pattern and its tempo. V3. ***UPDATE Arduino Drum Machine**** Simplified Schematic Ok, so this 'simplified' schematic might not actually make things any simpler! But some people have asked for it, so maybe it'll help clear somethings up a little bit - especially how to wire up the audio output and pots/switches. This was drawn from memory so I hope it's correct - give me a shout if not and I'll update (the pots might work in reverse, but they'll still work). I'd also urge you to look at the schematic on Jan Ostman's website for more help; https://janostman.wordpress.com/the-o2-source-code/ Thanks!