I’ve heard that VCOs have to use temperature compensating resistors. Do yours use tempcos?
No, they do not. Instead they use a diode that is part of the CV summation IC. In practice this compensation is as good as the best of the circuits that use tempcos. On paper, it’s better because it provides exact compensation at a wide range of temperatures. Circuits that use a temperature compensating resistor have a small error because the tempco’s resistance is a function of temperature T, rather than 1/T as is theoretically perfect. The fact that tempco circuits are de-riguer attests that this remaining error is not significant to most people, but still … it is not present in the 9720.
The illustration shows a working example that pumps from 1uA to 1.024mA in response to a 0V. to 10V. CV change. Full schematic and other details on the 9720 page.
Are the modules V/Hz. or V/octave?
V/octave. The response of frequency to Control Voltage is scaled so that a 1.0V. increase in Control Voltage produces a 1 octave change in frequency. This is commonly called V/oct scaling or less commonly “exponential response”. While 1.0V./octave is the most common exponential scale factor there are also classic synths that work to 0.8V./oct and 1.2V/oct and all modules can be calibrated to these scale factors as well.
Then I can use them with gear from Moog and ARP or an EMS synth?
Yes, you can.
Since your FatMan Synth is scaled V/Hz and the modules are V/oct it means that the two are not compatible, right?
In the most limited sense, that’s true; but it’s a very narrow view of the situation. It’s better to think of our FatMan as a single super-module with all the elements needed to produce a complete instrument voice . The FatMan audio output is compatible the audio ins/outs of the modules and the MIDI Thru of the midi2cv8 can chain directly to FatMan’s MIDI In, so on this higher level they’re very compatible and very complementary.
I have a really hefty bi-polar 15V regulated power supply. Can I use it with 97xx modules?
You sure can. You may need to change connectors to ones compatible with the supply you’re using. For example, if using a Blacet Research PS-CONN distribution board you will probably want to get some .156 connector housings and pins from Blacet. When using +/-15V regulated supplies always short out isolating resistors R1 and R2 on the 97xx board. Be very careful not to interchange (G) and (sg) on any 97xx modules as this corruption of the module’s Star Ground system will guarantee “noise”. If the power supply has only a single ground, run separate wires from the (G) and (sg) of each 97xx module back to this single ground
Several places it says “DC Coupled”; what does this mean — is it important?
DC Coupled means that the modules have no lower frequency cut-off point. The VCAs in the 9710 Module, for example, can pass a signal with 0.0 Hz. frequency — in other words a DC Control Voltage. It’s important because it allows the VCAs to serve as voltage controlled attenuators for CVs, a typical example might be ramping the amplitude of an LFO modulating a pitch source for a trill to the leading or trailing edges of notes. The amplitude of one LFO being modulated by a second LFO can produce a wide range of interesting effects. As a somewhat more esoteric example, the 9730 VCF can process very slowly varying bio-frequency voltages such as those that come from an EEG, EMG or similar bio-feedback apparatus.
Do I need that V/Hz adapter to make the midi2cv8 work with the 9700 series modules?
No, you do not.
What’s the deal with the ring terminal of the midi2cv8’s output jacks. I try to measure a voltage there and don’t see any change.
See next question …
I’d like to control (relays, motors, light bulbs, etc.) using a cool freeware MIDI sequencer I found on the ‘net. Can I use a midi2cv8 for that?
Yes you can, it’s what the ever mysterious Ring terminal is for. The Ring terminal of a MIDI2CV8 is connected to the collector of a transistor that is turned on when the CV output is greater than a volt or so. This transistor can be used to control a variety of electrical loads such as relays and small motors. Think of it as a switch that closes to complete a circuit to ground.
The illustration shows some examples. Notice that one side of the lamp or other load connects to the Ring terminal of the jack while the other connects to the power supply for the load. This power supply may be the 9700’s power or for heavier loads it may be some other voltage source up to about 35V. The transistor can handle up to 100mA of collector current.
The midi2cv8 Mode 4, “Continuous Controller” mode is the most useful for these applications. CC data can be treated as switch opening and closing by having 0 represent switch open and 127 represent switch closed — or vice-versa if you prefer.
9700 MIDI2CV8 product page.
What’s taken so long on these modules? What issues kept them from coming out sooner?
In a small company there are many issues that have nothing to do with the performance of a product but rather arise from one or two folks wearing many hats. I wrote about this a while ago and if you change the names of the characters and tweak a few of the circumstance you can apply the same narrative to any of the time gaps between module introductions.
Sometimes very late in the development process it would become apparent that a change in normalization, for example, would interact with other modules for increased flexibility or ease of use. These often required changes to circuit boards, panels, illustrations, documentation and the like. A classic case of the last 10% of the work taking 90% of the time — the grinding detail that makes the difference between a good product and a great one. I hope you will agree that the final results live up to the hundreds of hours spend on design and development.
— John Simonton