I’m very excited to start writing about this delay processor. A piece, I believe, that deserves some more words, as I couldn’t find too much written on it. The reason for not being popular, not to be found on its low digital resolution or for being very noisy, but for the reason that it has never been produced in series. The Powertran DDL came out in 1982 as a DIY project, published on the popular electronics magazine Electronics & Music Maker, so just a small number of units were built. The project was developed by the electronic designer Tim Orr, famous for the EMS synthesizers. The idea was giving access to the new digital technology, before extremely expensive and present only in big studios, to a wider public.
I’ve been lucky enough, to having fun with three different units of the Powertran Delay in the past, all a bit different from each other. Being the DDL a DIY project, all these processors had some modifications like the optional CV/Gate or additional knobs/switches.
The first unit I had was borrowed, a friend kindly left his Powertran in the studio and it remained in my hands for several years. Being his music more focused on acoustic instruments, he wasn’t using it anymore. Those were times when a dirty digital sound wasn’t appreciated too much and just a few bit-reduction plugins like the Digidesign Lo-Fi, existed. My friend’s Powertran had voltage control too, samples could be played from the keyboard, through a MIDI/CV interface and its dirty 8-bit sound reminded me a bit, the Emulator Paul Hardcastle had used in “19”, a song I’ve been loving so much. The Powertran delay became the crazy spice for almost anything experimental I’ve been doing, until before moving the studio to an other country, when I wanted to give it back. My actual Digital Delay was bought on eBay in a lucky bid, as very few units were still around, a few years ago. Unfortunately, my second unit, bought in the UK in 1999, had died after a few years of use and I couldn’t stay without a DDL!
The Powertran Digital Delay Line front panel is pretty simple and there’s nothing surprising, apart the time selector switches same as the MXR, we have already seen in a previous post.
The Time Delay buttons always select multiples of the original tempo. If the delay is in sync with the track tempo, pushing different switches, gives a today very fashionable Beat Repeater effect, where, for example, a loop is faster or slower, but always remaining in sync with the song. Some machines like the Powertran, had a freeze button so that the sample could be repeated without decaying, same as a sampler.
“Digital encoding for studio quality results. Time delays from 0.625ms to 1.6 seconds. Produces all popular time delay effects: Phasing, Flanging, ADT and chorus, Echo (including “freeze” for infinite repeats), Time domain vibrato, etc.”
The Powertran Delay has a delay time of 0.625ms to 0.64 at 10KHz Bandwidth, while it has 1.6ms up to 1.6 seconds at 4KHz, these times can be halved through the delay knob.
The modulation LFO has a range from 0.025Hz, up to 17Hz and a triangular shaped waveform.
The input signal, once amplified, is passed through two switchable HPF at 4KHz and 10KHz, working as anti-aliasing filters. The ADC analog to digital converter is an 8-bit one. The dynamic range of the Digital Delay is 72dB. The RAM memory is 16K bytes.
Included are some examples of the crazy effects obtainable with this processor:
The MXR M-113 Digital Delay has been one of the most popular first generation audio delays, as it had a good quality but was more affordable than the previous processors. Introduced in ’76 at around 1000 USD, it was still expensive, but a lot less than the other digital delays available in the market.
MXR was specialized in guitar pedals, this delay was instead offered in a 19″ rack unit and, same as the other effects of the professional rack series, (Flanger/Doubler, Graphic EQ, Pitch Transposer) became very popular and used by famous artists such as David Gilmour, Frank Zappa, Roger Waters, Brian May and Mike Rutherford.
To contain costs, a modular architecture was chosen. Optional memory boards were inserted in slots, to increase the delay time, but these were pretty expensive, costing almost like a complete unit.
Digital noise..well not only that! :D
Unfortunately the M-113 Digital Delay, same as its collegues of the same period, is pretty noisy and not only referring to the actual standards. Apart digital noises always present, these processors have a marcated tendency to generate audio hum.
The Model 113, Digital Delay has a maximum bandwidth of 20KHz, but this decreases with longer delays, down to 2.5KHz. The longer the time between repetitions, the tighter the passing frequency band, being reduced through antialiasing filters (HPF and LPF) the more the delay time is increased.
MXR Digital Delay Test Drive
As there are several video examples already of this delay tested on guitar, I thought it could have been a good idea to try it, using some unusual but hopefully interesting sounds.
To record, I used a dbxDI box and the signal sent to a Universal Audio610 tube preamp, even taking all possible counter-measures, still a bit of hum is audible.
On the examples below, I feeded as sound source, a sweep from the filters in feedback of an old Korg MS-50 synthesizer, some piano chords I had recorded from a real piano and a couple of seconds of an oldschool reggae classic.
MXR Digital Delay, Test-01, (MS-50 Filter Sweep)
01) Dry sound, straight from the MS-50.
02) Delay Range 160ms, Delay Time x2, 50% mix and maximum regen (feedback)
03) Delay Range 160ms, Delay Time 0, 50% mix and maximum regen (feedback)
04) Delay Range 160ms, Delay Time 1/2, 50% mix and maximum regen (feedback)
05) Delay Range 160ms, Delay Time Sweep 01 (moving the Delay Time knob)
06) Delay Range 160ms, Delay Time Sweep 02 (moving the Delay Time knob)
MXR Digital Delay, Test-02 (Piano)
I chose these piano chords I recorded as, having long decays, are ideal to test the effect of short repetitions, when modulated. The effects space from phasing to complete madness. The last one is a strong modulation at the higher band of frequency of the sweep, reminding the effect of a ring modulation.
1) Dry Piano
2) Delay Range 1.3ms, 50% mix 3) Delay Range 10ms, 50% mix
4) Delay Range160ms, 50% + Mod
5) Max Frequency Mod
MXR Digital Delay, Test-03 (Rhythmic Loop)
On the following examples, let’s try something that really impressed me first time I played with a Powertran (An article on it, is coming soon). On the MXR the feedback has a faster decay and there’s not the “freeze” function, but the effect it is interesting, too. Once the delay is at tempo with a rhythmic pattern, having adjusted the decay time knob, all Delay Range buttons create a different version of the pattern, but on different speeds. Being the buttons based on a double time sequence, all these are compatible in tempo. Let’s experiment with a small classic reggae riddim loop:
1) Dry loop
2) Loop effected as sort of Beat Repeater
MXR Digital Delay, Test-04 (MS-50 patch)
Last example, this time using a more complex sound from the MS-50.
1) Dry MS-50 sound
2) MXR MS – 50%MIX, 75% Feedback
3) MXR MS – 50%MIX, 75% Feedback + Mod
4) MXR MS – 50%MIX, 75% Feedback + Fast Mod
Since ancient times, places destinated to public speech or shows, were chosen in base of their acoustical characteristics. A powerful voice listened near a sharp rock wall, could impress the public and add a magic ingredient, like if forces of nature were happy to help the venue, amplifying the wanted message.
The Echo was so important, to have a dedicated character in Greek/Roman mythology:
Echo, a mountain nymph, was helping Jupiter in distracting his wife Hera, with interminable discussions, while the god was cheating on her with the other nymphs. Realizing the trick, Hera cursed Echo, removing her ability to speak. The only sounds she could emit, were the endings of words she could hear. As usual in ancient myths, the story ends in a tragedy, with Echo dead but not her beautiful repetitive voice, forced to live forever, but only in the most remote and inaccessible places.
Natural echo or reverb of special rock formations, or the reflecting shape of caverns, were used to create a dramatic effect on human speech, chants (and minds) for ritualistic or entertainment purposes.
The Art of Procrastination
Builders with time could, through architecture, recreate nature’s big spaces and the possibility to impress public with special effects, could slowly move from remote areas to the cities. Acoustically shaped amphitheaters and later, closed spaces like theatres and religious buildings were built for this function. Music started being played in dedicated “chambers” or “halls“, with reflecting walls and high ceilings, to obtain long reverberation times and decays.
At the beginning, recording studios used to record the space where musicians were playing, with microphones pointed to ceilings or walls, to capture the returning delayed sound and the signal was mixed to the original.
Later, rooms were dedicated exclusively to reverberation. A sound from the control room was sent to an amplifier in an empty room or chamber, completely empty and with reflective materials. One or more microphones were used to capture the effect, that was mixed to the rest of the sounds in the mixer. To add colour or to obtain special effects, metallic thin plates or springs, were recorded while resonating in the room, too.
At the end of the 50s, technology arrived to a point where the process of reverberation could be standardized and every major studio had a plate reverb like the EMT 140, or a DIY simpler version of it. The effect was obtained through the use of a big reflecting surface, in this case a metal foil put in tension through springs. A speaker inside the unit, puts the plate in resonation and a pickup captures the signal then amplified, through a tube preamp. There was a mechanical damper, to reduce the decay and later two pickups, placed in different places of the box, to obtain a stereo signal.
The effect is warm and beautiful, but unfortunately the technology needed big spaces as the plates were more than 1 meters long and these reverbs were very heavy and expensive.
A low quality delayed signal, could be obtained with the same process, implementing springs in tension, instead of plates. The idea, commercially developed by Laurens Hammond, the organ pioneer, was much less bulky then plates and even portable, to the point to become a standard on electric guitar amplifiers.
Spring reverbs give a particular vintage flavour to guitars, drums and percussive instruments, really great for old Funk or Reggae.
With the advance of technology, magnetic surfaces in the form of tapes (Echoplex) or disks/drums (Binson/Meazzi), were used to record and reproduce the delayed signal, on dedicated processors.
The tape loop has been the first form of reproducing a sound with a delay. Two tape recorders where used before dedicated machine were born, one to record and the other for the playback. Delay time increased, the furthest the second recorder was placed from the repro machine.
One of the most popular tape echo units, has been the Roland RE-201 Space Echo, still searched by Dub producers has pretty high values, today. Its tape was left unrolled in a transparent compartment inside the box. Rising the top and watch the tape moving in an apparently chaotic way, listening to the smooth noise of it, while smelling the characteristic chemicals odour, remains a very unique experience.
Some special effects, obtained using tape echoes, were pretty popular in the 60s and 70s, especially for Sci-Fi and Dub. I recorded a few examples with my RE-201 with the “Intensity” (Feedback) at maximum, conditions under where the Space Echo starts auto-oscillating feeding its own noise. The effects obtained are warm and immediately bring back to the past. The first track, called RE-201 Slam, is obtained instead slapping the unit with force. The shock is captured by the internal spring reverb. The third track is dry at the beginning, while has some additional effects from the second part. Track 2 and 4 are sweeps, moving the “Repeat Rate” knob.
Many virtual tape delay plugins of today, are based on the RE-201Space Echo, the most popular of the RE series
In the wiki we can read that a bucket brigade or bucket-brigade device (BBD) is a discrete-time analogue delay line and that an analog delay line is a network of electrical components connected in cascade, where each individual element creates a time difference. A series of capacitors created the delay. Summing a big number of those, could create the desired long echo. Analog delays, cannot reproduce the same sound for long, each repetition has a dirtier sound and this, with the eyes of those times, was seen as something to improve. They are very popular and still produced for guitarists.
Digital Delay Lines
Digital delays, can repeat the same sound, maintaining intact the quality of the original same as a sampler, only when sample rate and bit resolution are high enough.
The first commercial machines had a very low resolution, so samples were noisy and with a limited bandwidth. This is the characteristic that, in my point of view make them attractive and useful still today, when clean sound is no more a priority.
At the beginning, these machines, were only at the range of professional studios or rich producers. Until Electronic & Music Maker Magazine published a series of articles with schematic and instructions for a DIY delay, making affordable and available to a wider public this new technology.
Being a lover of Dub and vintage equipment, I’ve been lucky to own a few of the classic delay devices, bought when prices were extremely affordable, as nobody on those times needed a bulky and noisy delay only, machine.
Vintage delay lines have an other interesting aspect.
Their buttons select always multiples of the original tempo. If the delay is in sync with track tempo, pushing different switches, gives a today, very fashionable Beat Repeater effect, where for a example a loop is faster or slower, but always remaining in sync with the song. Some machines like the Powertran, had a freeze button, so that the sample was repeated without decaying, same as a sampler.
Effects obtained apart the Echo
A Delay Line, is able to create a series of effects, not stricktly limited to repetitions of samples. Through the modulation of the processed signal and blend it to the original, a series of interesting effects are obtained, too.
When the same signal is combined with its delayed copy, it’s like having passed it through a filter. The Comb Filter resulting from counter phasing if modulated, changing the delay time through a Low frequency oscillator (LFO), becomes the pleasant effect called Phasing.
Same as Phasing, but with longer delay (10ms). Similar to chorus, but a more dramatic effect and with a marked SciFi like, character.
Even more delay and slow modulation, possibly with dry and wet signals on the opposite sides of the stereo field, gives the classic chorus effect that doesn’t need too many words more.
Automatic Double Tracking, was pretty popular in the 80s. Time delay is kept just below the perception of the single repetitions and is used especially on vocals, to give the illusion of doubling, without the need of recording two different voices.
On the next posts, we will test drive, three of the oldschool digital delays still in my hands: MXR Digital Delay, Powertran Digital Delay Line and the Roland SDE-3000
maxpro comes from maxprofessor, a nickname that was given to me while I was a fan of the Dub master Madprofessor, trying Dub techniques in the studio and giving classes of music technology, in a music school.
As I grew up under my mother’s piano, I’ve been lucky to learn playing pretty early in age. My first teacher, is still an excellent classic piano performer.
I was still a boy, when my father arrived home with a stereo radio and a good pair of headphones, this fact can have helped me in developing my musical tastes, for sure. As we are talking about the beginning of the 70s, the only local radio station transmitting stereo, was an American one, with lots of fresh Funk, Soul and Jazz on air all the time, music I’ve been loving (and played) for the rest of my life.
At the age of 14, discovering progressive rock and in particular Emerson Lake and Palmer and the Yes, I started playing rock organ and later keyboards with local bands, turning slowly from Rock to Jazz Fusion and Acid Jazz.
In the years, I had the opportunity to study Jazz with three excellent teachers: Still in Italy, Jazz piano with Danilo Memoli, while in Spain, Jazz guitar with Marcelo Saenz and harmony with Leonardo La Peruta.
Regarding the technical side, I started composing and arranging as soon as MIDI was introduced. My preferred machine for sequencing on those times, was a Yamaha QX-3, but was the arrival of a small Macintosh SE and MOTU Performer, that consolidated a long marriage with digital music creation and production.
In the 90s I built a production/recording studio in the north of Italy, based on Digidesign Pro Tools III on a Macintosh 9600 and ADAT.
I soon became specialized in Dance music and Reggae.
I’ve been lucky on those times, to be working with the best Dance DJs, producers and singers in my area, releasing a few records with majors such as EMI and WEA.
At the end of the 90s, I moved to the south of Spain where I opened a production/recording studio, updated including analog tape, in 2007.
It was based on a 1980 Trident 80b mixing console, a 2″ tape 24 tracks Otari ATR90II and an 1/2″ Ampex ATR102 for the master. On the digital side, it had a Pro Tools HD rig, with Apogee X Series converters.
I’ve been lucky to have an excellent technician helping me, there. Brian had worked as engineer at Trident Audio in London and was very kind in sharing lots of his precious knowledge, to me.
I’m now producing mainly on Propellerhead Reason, but using external gear, as well.
I have a post that explains a bit how I do work, here:
The Theremin can easily be consider the grandfather of the analog monophonic synthesizer. Looking very much as a vintage laboratory tool, its two antennas tend to make it look more as an experimental valve radio than a musical instrument, with some obvious Cyberpunk flavor!
Invented by Lev Termen almost 100 years ago, its name Theremin is the Americanized version of the inventor’s name. The ghosty like and very natural sounding voice it has, could have become much more popular if it wasn’t for the Theremin’s ridiculously difficult interface, that make playing it in tune a really hard task without a proper preparation. The two antennas capture the movement of any object around. Arms and hands are used for the two possible variables that can be changed: Pitch and volume. What sounds pretty easy is in reality very tricky, the movements must be very precise, millimetrical. I suppose this is the main reason Theremin has been popular to violinists. Violins are notoriously difficult to play in pitch with precision, to do it you have to dedicate a hard work of learning.
Just a few manufacturers build theremins today, the most popular one, being Moog Music still producing one of the classic designs:
To be honest a Theremin with a USB port only, can look extremely suspicious to the more traditionalists of us.
Especially considering that from a Theremin, we should expect one of the purest analog sounds possible,
having to do with a soft synth sound generator, can look not too interesting.
What we will consider here, is the opportunity to have a valid and easy to setup interface, to be used to drive our trusted analog synths. The scope of this experiment will be to play through the Theremino Theremin interface a 1977 Minimoog. Using one oscillator only and its triangular waveform, we should arrive to a pretty good Theremin sound!
As the cards can be bought already assembled, mounting a Theremino Theremin is an easy and fast operation.
What we need for a complete Theremin is a Master and two CapSensor cards. All is connected through simple multi connectors ribbons and the USB is connected to the PC.
What happens is that the two antenna capture the movement of the body and generate SLOT values, that are converted from the Theremino Theremin software in notes. Usually the left hand is used for volume and the right for pitch information.
Originally the Theremino Theremin was able only to play its soft synth, but recent developments permit do a lot more. Installing the LoopMIDI shareware application, Theremino Theremin slot data can be converter in MIDI values through the Theremino SlotsToMidi, avoiding the use of the Theremin soft synth, but using the MIDI to play a real synth instead. To be closer in sound to the original, we will use a vintage Minimoog, converting MIDI to Voltage control, through a Kenton Interface.
The Theremino engineers designed a special card to be used as PWM to MIDI converter, but only the DIY design project and schematics exist.
OK, a failure can happen even to the most modern synths, most commonly caused by a failing component, but finding a tiny polystyrene pellet right inside the contacts of my Elektron Analog Keys keyboard, has been really surprising. The small fluffy ball, found the way through, still in the production phase I guess, as when I opened the keyboard assembling all looked clean and the rubber tops were well sealed. As the warranty had expired already, I had the perfect excuse to check what was inside the only of my “unexplored” synths.
There are plenty of tiny screws to have access to the “insides”, better using a powered screwdriver.
Under the contact pads is where I found the small pellet
Simply removing it and assemble all parts back, the synth’s keyboard returned to working smoothly.
For “The Dark Side”, I mean the real nightmare always lurking, while playing with vintage machines: Their tendency to break apart, often in the middle of an important session.
Always the best option, if possible, is to be able to do some small fixes in “DIY mode”, to save money and have the repair done promptly. The older the machine, the easier the repair is, usually. This is valid, if some rare parts availability, doesn’t interfere in the logic.
Doing some tests recently, I found that the auxiliary VCA section of my Korg MS-50, had one of its jacks broken inside. The plug was not kept in its place, like if there was nothing inside to retain it. I suspected the positive pole plate got broken.
Good occasion to open up the synth and look what’s inside ;)
As soon as I unscrewed and removed the later panels, I remained impressed by the fact that in the interior of its panels the Korg MS-50,..ehm…IT’S EMPTY! :D It’s pretty impressive how Japanese technology was advanced, considering that this synth was in production, since 1979.
In the interior of the Korg MS-50, there are just a couple of thin PCBs, plus the PSU board.
What occupy much place, are the plastic slots for the jacks metal connectors plates.
The only thing really modular to me, is the placement of the jacks in the front panel, simulating the modules of a real modular synth. Modules can be connected through external connections only , same as a modular and not as the rest of the MS series, where some internal patching is placed already.
This not complete modularity, can look a bit suspicious by the most purists, but the sounds that this machine is capable to create are fantastic, even with it’s limited single oscillator configuration.
The Korg MS-50 have been pictured in Aphex Twin studio and should have been used by The Chemical Brothers.
Inspecting the interior, (with major relieve) I discovered wasn’t necessary to disassemble the whole synth, as removing the main PCB from the front plate, must be a really tedious process, considering all the jack bolts, to unscrew.
The cause of the fail for the broken jack, resulted in being the connector plate of the + polarity, that I found off its slot.
Just some glue solved the problem, a much easier solution than what I thought was necessary, at the beginning.
To test the VCA repair, I decided to make a demo, squeezing from the Korg MS-50 single oscillator, all its waveforms. I triggered them from its two Envelope Generators and a Korg SQ-10 Analog Sequencer that plays the sequence.
Are you sure analog recording is reserved to just to a few lucky audio nerds, with big budgets at their disposal?
Even if this, considering the price and maintenance requirements for top end professional analog equipment, is pretty true today, recording in analog isn’t expensive when we take in consideration the amount of cheap consumer grade, analog recording devices we can find used for almost free, still around us. They have been lying down somewhere in our homes unused for decades, it’s time to give them a new life, tranforming them in “effect” processors!
With the abilities in time stretching and audio quantize, present on most of present day’s DAWs, time shifting problems of cheap devices, can be corrected in seconds.
Why, as plugins can do that?
Tape simulation software, can do a good job, at maybe 1/10th of the time needed for a real analog recording.
If your objective is to produce one hit after the other, time is money. Better to recur to plugins and stay tight to them, in this case.
But who loves producing music as a form of creativity expression, have fun in the process of making it, too.
Joy comes not only from the results obtained, but from the memories of the experience, by the process itself.
Creative and experimental techniques are many times the key to activate and stimulate creativity.
The collateral effect, is that the musical results are unique and very personal. The infinite number of variations obtainable while experimenting, is not possible by any plugin.
PC synchronization to tape
In the professional analog recording realm, to synchronize tape and a computer, the only way has always consisted in using a track of the multitrack recorder as guide for the computer, recording on it a special audio tracking signal. The sequencer is then adjusting continuously track tempo, taking this time code as reference, to remain synchronized. Tape recorders have always had small fluctuations in time and pitch (Wow & Flutter), impossible to correct, even on the most expensive machines, due to their mechanical nature. The problem was resolved through the standardization of a synchronization signal code, called SMPTE. https://en.wikipedia.org/wiki/SMPTE_timecode SMPTE audio track, can be read from an interface (for example a MOTU MIDI Time Piece) and transformed into MIDI clock, signal which keeps the DAW in tight synchro.
The perfect tool
Let’s go back to the main subject of this post and let’s start having fun, too!
Do you want to experiment with analog, without having to spend a fortune on rare equipment and with no hassle?
First we have to identify the perfect tool, maybe easy to find in a parents old technology drawer: a microcassette dictaphone or a walkman type cassette tape recorder, are perfect. Usually the narrower the tape, the less quality you would expect. Same with tape speed: Lowest speeds, less highs and more noise. Microcassettes have the most distorted and noisy sound around and can be useful for “sampling” speech and single instruments. Standard cassettes can be used to record drum loops too, their quality is a bit better.
What I’m suggesting on this post, is to record straight to one of these old analog devices, bounce the result in an audio track and time stretch the audio results, until correcting the differences induced by the “cheap analog” manipulation.
These devices have often an internal speaker, recording from it through a microphone, can add some variation to the recording sound.
We gonna make an experiment using my old GE Microcassette tape player/recorder:
Some audio manipulation will be needed after processing. When we deal with short vocals or effects, there’s nothing really needed apart normalizing the file, that will then sound super loud, due to analog narrow tape heavy compression. It will be also “enriched” with low frequency noise (hum) and its high counterpart (hiss). To make the file usable, we need to reduce its audible band through a band pass filter or a HPF/LPF combi. In the following example we will use a 250Hz High Pass Filter, combined to a 2kHz LPF, add some room effect, some phasing modulation and some delay.
I’m gonna record a drums loop, to make things a bit more difficult. To be usable, instead of only filtering, it will need some time stretching to correct analog recording tempo fluctuations. We then will see how it can work added to the original track.
As the effect we gonna expect is of a low quality, distorted oldschool sound, we gonna work on a classic Roots Reggae “standard”,
Studio 1, Sound Dimension “Real Rock”. This is the original:
On the first example I playback the track to be recorded on the dictaphone. On the second you’ll listen to the result in the analog microcassette, but already filtered and effected, while on the third, you’ll find a mix including our analog dirty loop. The result should sound nice (at least it does this effect on me) and give the necessary dirtiness, to a loop otherwise too “cold”
Once bounced the audio from our tape recorder, we need to identify which is the first beat of what we consider the first bar and move the file to the beginning of one bar, in our sequencer. Having the sequencer grid as reference we then time stretch the audio, to make it correspond to the DAW tempo grid.
Due to the typical tape behavior, there will be some time shift from the original loop, even if time stretched correctly. Once in the right position, we can give an audio quantize (of more or less % depending on the variation required) and mix the result to taste.
Vintage gear have a special appeal, but need continuous cures and repairs to remain operative during the years. Older machines are usually easier to maintain, due to their simpler “discrete” design. Most of the components are easily available and rare parts are usually not too many.
The Minimoog is one of these machines, potentially “eternal”, if periodically maintained.
One of the most recurrent fails is its keyboard mechanism. The switches are small springs moved by the keys up to touching a contacts rail. Oxidation tends to form, making the contact erratic.
I took some pictures while cleaning the small springs of the keyboard contacts of my 1977 Minimoog:
Removing the bottom panel, gives access to the keyboard contacts
Keyboard mechanism and the rear of the control panel.
Keyboard contacts. Below the transparent plastic supports there are the tiny contact springs.
Cleaning the small springs with cotton swabs and alcohol. Notice the dirtiness left on the cotton.