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This module is a synthesizer voice in one module. It has one VCO with two waveforms and built in modulation options. It has a built in low pass voltage controlled filter, voltage controlled amplifier, and envelope generator. It can also use either S-Triggers (switch triggers as used in Moog, Steiner-Parker, and some other vintage modular synthesizers) or voltage triggers. From what I’ve been able to gather, the intended use was for the wind controller that Nyle developed or as a very portable synthesizer. The original came with a jack designed to interface with Nyle’s wind controller as well as 1/8″ jacks to interface to other systems and controllers, like a Steiner-Parker keyboard controller.
There are effectively 3 inputs:
- VC In. This is a traditional 1 volt/octave control voltage.
- VCF Frequency. This is a voltage input to control the cutoff frequency of the filter. It also has an effect on the input to the VCA, see more below.
- -Trig and +Trig. These are the trigger or gate inputs. The -Trig is an S-Trigger and will trigger when this input is grounded. The +Trig is a traditional voltage trigger input and will trigger when a positive voltage is applied.
There is one output, the signal.
There are a few added knobs to this implementation. Nyle did not bring controls like the square wave duty, the “Q” setting, or the sustain level to the front panel. These were “factory set” and were trimmers on the PCB. I decided in the spirit of SDIY, I would give the builder the option to leave these as set trimmers or to bring them to the front panel. Because they were not meant to be a front panel, user control they don’t necessarily respond over the full range of the pot. See below for some suggestions for modifications to make some of the controls better behaved. It isn’t a knob, but I also added an option for the user to add an input for a voltage control input for the square wavy duty. You will need to select the summing resistor to your liking and add a jack to the front panel.
I also added the option to remotely mount the high frequency trim and the volt/octave “VC Trim” on the front panel. The high frequency trimmer is not one that I think will be used too often, but the VC Trim is nice to have to keep the oscillator in tune.
There are 11 total knobs.
- Attack. The rise time for the envelope
- Decay. The decay time for the envelope
- Sustain. The sustain level for the envelope
- Squ Duty. The square/pulse wave duty cycle.
- LFO Rate. The frequency for the LFO
- LFO Level. The magnitude of the LFO wave.
- Q Set. The feedback, or resonance control.
- VCF Freq. A fixed cutoff frequency for the low pass filter
- VCO Coarse. The coarse adjustment for the VCO frequency.
- VCO Fine. The fine adjustment for the VCO frequency.
- Output. The output level attenuator.
There are 4 switches:
- Damp. This switch when enabled will cause the envelope generator to immediately decay to zero on a key lift. When disabled, the decay is controlled by the decay knob setting on key release.
- Beat/Vibrato. This switch selects whether the modulation is a beat or vibrato type modulation.
- Plse/Sq. This switch selects whether the Beat/Vibrato wave is a square wave or a pulse with a width set by the square duty control.
- Ramp/Square wave. This selects whether the output signal starts as a square wave or ramp. This initial signal is then modified by the VCF.
Connect a voltage to the VC In, typically from a keyboard, ribbon controller, sequencer, or other source of varying voltage. VC1 (see schematic) is meant to the the 1 volt/octave control voltage. It also feeds the filter cutoff circuit so that the cutoff frequency will track this voltage control. VC2 is meant more for modulation and can’t be tuned (except by choice of the summing resistor). The VC Trim control tunes VC1 to get a one volt/octave response on the VC1 input.
If you want, connect another voltage control source to the VCF Frequency jack. You can set an initial cutoff frequency with the VCF Frequency control. The cutoff frequency voltage feed a vactrol that is also inline with the signal path. This means, that when the voltage drops below a certain level, the signal is blocked. If you are not using an external voltage control of the filter cutoff, you will need to manually turn up the VCF Freq control to hear an output. You will simply need to play with the VCF Freq control, the VCF Freq VC input jack, and the VC1 input to get a feel for the interaction between these controls and the vactrol’s response.
Last, you will need a trigger or gate on one of the trigger inputs. These inputs are isolated and so you can have both connected to appropriate triggers or gates at the same time. When the Damp switch is disabled, a short trigger will cause the envelope generator to rise to its maximum over a time defined by the Attack setting. It will then immediately start to decay according to the Decay setting. When a longer trigger (called a gate by many) is present and the length of the gate is longer than the time set by the Attack control, the envelope will rise to its peak and then decay to the level set by the Sustain knob (or pre-set by the trimmer if you don’t bring it out to the panel) and will remain there until the trigger/gate ends. The envelope will then decay according to the Decay control setting.
When the Damp switch is enabled, the envelope will immediately decay to zero as soon as the trigger/gate ends. If the trigger is very short, you may only hear a “pop” or may not hear anything.
Select the type of waveform for your primary signal, either a ramp or a square/pulse waveform. Input a voltage control into VC1 and adjust the VCO Coarse and VCO Fine to tune the module.
If you want a little more complex sound than a simply ramp or square/pulse, you can add vibrato or a beat to the signal. Turn up the LFO level and play with the Beat/Vibrato and Beat/Pulse-Square switch and LFO rate and levels to achieve a more complex harmonic rich waveform. The Square Duty control will also affect the overall interaction.
See the Component Notes page for more information.
This module was originally built with carbon core, 5% resistors with one or two 1% metal film resistors. So, you have a wide range of options here. I recommend using 1% tolerance, metal film resistors everywhere, but the critical resistors are R37 and R38, input summing resistors. These should ideally be hand matched or purchased to 0.1% tolerance to insure consistent response between the inputs.
You will need a 1k ohm temperature compensating resistor. It should span the discrete transistors or the monolithic pair used for Q4. Use a little heat sink grease and make sure the resistor is in good mechanical and thermal contact with Q4. It should have a positive temperature coefficient of about 3300 ppm to 3500 ppm. I get mine from Precision Resistor, but there are many other sources now. If you need more help, check out the Links pages on my website.
There are probably a billion different ceramic capacitors at a place like Mouser. Pick a capacitor that can fit the hole easily, typically 0.1 inch on centers.
Pick good quality electrolytics where designated.
There is a Schmidt Trigger IC in the design, 74C14. Make sure you buy the the type that can take high supply voltages, 15 volts or more. Do not get the low voltage ones, they will blow up and emit large quantities of magic smoke. I think the CD40106 is a suitable cross reference, but I have not tried them. make sure for yourself first.
There are also 4 MC1458 Dual OpAmps in the design. Easy to find.
The FET used is a 2N5246. They were easy to find up to a couple of years ago. Cricklewood has some at the time I’m writing this.You can check a cross reference, too. NTE probably has several choices that should work fine.
The 2N5172s are found at many normal sources like Mouser. The PN5138 or 2N5138 is becoming harder to find. Mouser has a few. However, These can be any normal small signal transistor. Nothing to special about them.
The matched pair can either be a pair of 2N5172s or a monolithic IC like an SSM2210. You can also use a Linear System matched NPN pair, or an Analog Devices matched pair. The monolithic pairs will be more expensive and only really get you some convenience. The pin layout is compatible with any of the common monolithic packages. If you use the 2N5172s, you will have to twist the leads because the 2N5172 uses a BCE pin sequence rather than a CBE.
1N4148s or some other smiall signal diode. Use a 1N4001 or other diode for the power supply protection.
Use some decent pots. I use the Alpha mostly. They have served me well but you can always use higher quality like a Bourns. Just make sure the holes in the panel are suitable for your pot choice.
The trimmers are set up for a “Y” series like a Bourns or Vishay type. I like this pad layout as I think it lends a bit more stability to the trimmer as it uses three non- co-linear solder pads and so defines a plane and will resist getting bent over better.
I use the Switchcraft “true” 1/8″ jacks, their “tini=jax” series. Enclosed and switched 142AX, open frame switched 42A, open frame no switch 41. You can use any suitable jack. Note that some jacks are switched with a normally closed SPST switch.
Use a good quality switch.
Several users have made suggestions on the electro-music and Muff Wiggler forums. I’m just going to link to the discussion groups and you can read through. Search for “modif” and I find it finds most if not all the suggestions.
I assume you know the basics of soldering. I like to insert the low lying parts first, like resistors, diodes, etc. After these, I install the IC sockets. Next capacitors, transistors, connectors. Use a good solder, either an organic flux, which you should wash regularly, or a no-wash flux.
Take a break every so often, wash off the flux if you are using a flux which required cleaning. Double and triple check orientations, pins, and solder joints.
Nothing unusual really. Just make sure you don’t mount trimmers on the PCB if you use the option to bring that control to the front panel.
Please pay close attention to wiring the switches. Nyle always mounted the switches so the typical position is down. Pay particular attention to the DPDT switches and make sure you wire each side appropriately. If the switch seems to be operating opposite to how you think it should, rotate it.
Note also that Nyle wired the LFO Frequency control backwards on purpose. Turning it counterclockwise increases the rate. That’s because he couldn’t find a 2M reverse audio pot.
Nothing really unusual here.
You need a control voltage source which will give you a selectable voltage output and a range comparable to that which you use to play the synthesizer. The high frequency correction in the Microcon is implemented in a different way than in the Synthasystem VCOs. This is because the original VCOs did not have high frequency correction and Nyle and I added it as a “modification” for those who wanted potentially better tracking at the high end.
- Turn the HF correction trimmer to ground, CCW.
- Connect this voltage source to a VC1 input.
- Input a known voltage like 0 or 1 volt.
- Select the square wave (easier to use with a frequency counter).
- Set the pulse width to something like a 50% duty cycle.
- Connect a frequency counter to the output, or if you have a good ear, connect the output to headphones or a speaker.
Second Step: THE V/Oct TUNING
- Press a “low” key, a control voltage around 0 to 1 volt, and tune the Frequency and Fine Frequency knobs to a desired pitch. A good start is around 100 Hz.
- Input a voltage twice or four times as great (following a 1 volt per octave scale). I suggest one or two octaves higher.
- Adjust R4 (on the PCB if used) or R2 (on the panel if used) to get the proper tracking.
- Re-input the first voltage. Now, you can either
- Reset the Frequency / Fine Frequency to get your original pitch and repeat, or
- Just note the new low frequency and multiply it by 2 for one octave, 4 for two octaves, 8 for three octaves, etc. to get the new target pitch for the high end.
- It should only take 4 or 5 repetitions or so to get pretty good tracking.
Third Step: HIGH FREQUENCY TRACKING
- Now, hit the highest note on your voltage source and see how close you are to the proper frequency (4 or 5 octaves higher is pretty good). You will almost certainly be low.
- Turn the HF correction trimmer to overshoot your desired high frequency a little, probably around the middle.
- Go back to step 1 in the “Second Step”, then repeat steps 1 through 5 for the V/Oct trimming because adjusting the HF Correction trimmer will affect the V/Oct. When you get good low frequency tracking, 1 or 2 octaves at about 100 to 200 Hz, then re-do the “Third Step” section until you get the desired HF tracking.
Repeat the “Second Step” and the “Third Step” until you get good low and high end tracking.
Make sure the hole size and spacing work with the pots, switches, and jacks you choose.