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Kits : Voice of Saturn ~Modulator - Curious Inventor

Kits: Voice of Saturn ~Modulator

by recompas (electronic musician / composer) [profile] and mckay (audiovisual artist / electrical engineer) [profile]
Short Description:
This unit has a VCA (voltage controlled amplifier), triangle and square wave generator and AR (Attack / Release) envelope shaper. Together, they can be used to add tremolo or AM (amplitude modulation) effects to audio signals, and also add attack and release ramps to control signals. There are two summing CV inputs, as well as an "Instant On" button that maxes out the control voltage. The triangle output can be adjusted into a quasi square wave with adjustable duty-cycle (% on or off in each cycle). This gives you a chopper effect that can be used to fade out a sound by chopping larger and larger chunks each cycle.

Skill level: Intermediate... maybe beginner

Post mods / hacks, pics, videos and support questions here. We'll be giving away a limited number of toys to anyone that posts a video or hack.

Features / Specs / Video:

VOICE OF SATURN ~MODULATOR
  • Voltage Controlled Amplifier (VCA): Two summing inputs allow for control from multiple sources, including audio frequencies for AM effects. An "Instant On" button sets the control to full-on somewhat independent of the input control voltages. The first input (CV1) has gain sensitivity and offset, but the 2nd does not.
  • Function Generator: Based on the XR2206, both a triangle and square wave output are available from 1Hz to 100Hz. Changing the timing cap on the 2206 circuit will allow for different ranges. The Triangle wave has a Wiggle and Wobble knob that affect it's magnitude and offset. These adjustments let you push the wave up against its limits to produce a triangle with flattened tops and bottoms. The shape approahces that of a square wave with an adjustable duty cycle. The signal can be used to go from a subtle tremolo effect to an abrupt chopping one.
  • Attack / Release Envelope Shaper: This lets you add a ramp to the onset and release of a square gate signal. The circuit is ultra simple, and consists of two caps, two potentiometers and two diodes.
  • Effects that can be applied to audio: Tremelo, chopping, note shaping with AR gen, AM (amplitude modulation).
Buy:
Full-kit_thumb
A Kit that includes all the components, case and knobs.
out of stock, products typically restock in less than a week - $124.99
Barebones_thumb
Just the essential parts (see parts list below) for putting one in your own case. No knobs or case are included.
in stock - $59.99
Vos_mod_angle_thumb
Fully Assembled and Tested, ready to go out of the box.
out of stock, products typically restock in less than a week - $214.99
Just the PCB. RoHS Compliant (lead free).
in stock - $21.99

We highly recommend you get some colored ribbon cable if you're getting the everything kit. It's not included in the kit since we thought some people would already have enough wire. There's nothing particularly hard about building the kit except the large amount of wiring, we estimate 3-7 hours to get everything running.

Operating Instructions:
Parts List and Spec Sheets:
All versions:
  • U1 - U5: OPA2134 High quality audio op-amp (spec) (get yourself some free samples)
  • U6: NTE996 Transconductance Op-Amp, current is the output instead of voltage, like a typical op-amp. It also has an additional input that scales the gain according to how much current goes into it. This is NTE's replacement for the CA3080 (spec), which is sadly gone. (spec)
  • U7: XR2206 Function Generator - makes voltage controlled sine, triangle and square waves up to MHz (spec)
  • Capacitors:
    • 10uF (6): C1, C13, C14, C15, C16, C18 (buy)
    • .1uF (4): C5, C6, C7, C8 (buy)
    • 100uF (2): C3, C4
    • 100pF (2): C2 (make bigger to add more low-pass filtering on CV1), C17
  • Resistors:
    • in total: 1k (5), 10k (10), 510k (2), 3.3k, 4.7k, 5.1k, 330k (2), 1.8k, 100k (2), 100 (2) --> 27
    • R1: 1k (buy)
    • R2: 510k
    • R3: 100k
    • R4: 510k
    • R5: 1k
    • R6: 4.7k (pull-up)
    • R7: 10k (buy)
    • R8: 10k
    • R9: 10k
    • R10: 3.3k
    • R11: 10k
    • R12: 10k
    • R13: 5.1k
    • R14: 10k
    • R15: 1.8k
    • R16: 330k
    • R17: 330k
    • R18: 1k
    • R19: 100
    • R20: 100
    • R21: 10k
    • R22: 10k
    • R23: 10k
    • R24: 1k
    • R25: 10k
    • R47: 1k
    • R48: 1k
    • R49: 100k
  • Potentiometers:
    • total: 100k (3), 10k, 50k, 500k (2) --> 7
    • R40: 100k linear pot
    • R41: 100k linear
    • R42: 100k
    • R43: 50k linear (wobble / gain)
    • R44: 10k linear (wiggle / offset)
    • R45: 500k linear (release)
    • R46: 500k linear (attack)
  • Transistors: Q1,Q2 BC560 PNP transistor (spec)
  • (2) Diodes: D1, D2 (buy)
  • (3) Red LEDS: D3-D5 (on panel) (buy)
  • (3) Panel Mount LED holders (buy)
  • (1) Custom PCB (buy)
  • (1) DPDT Switch that connects the power from both batteries
  • (1) push button momentary switch
Also included in the Everything-Kit and Fully Assembled Versions:
  • (2) 9V Battery and holder (buy)
  • (7) black knobs (buy)
  • A silk-screened and pre-drilled case, with hardware and rubber feet (buy unfinished case)
  • (8) 4-40 nuts (buy)
  • (8) 4-40 screws (buy)
  • (4) standoffs for the PCB (buy)
Building Instructions:
Back-of-the-case connection diagram:

Click for larger version.
How it Works:

Function Generator:

There's not much to say here, this is a simple implementation straigh from the spec sheet (see above) for the XR2206. You can mod the circuit to allow for lower or higher frequencies by changing the 100k pot or the capacitor C14. It can also be configured to output a sine wave instead of a triangle wave.

Attack Release Generator:

The capacitor charges through R46 if the input voltage steps up, and discharges through R45. The diodes, D1 and D2, keep charge from flowing the wrong direction. The op-amp is just a buffer. We might add another op-amp buffer on the input for the next rev, what do you think?

VCA (Voltage Controlled Amplifier):

This is the meat of the circuit, and we'll explain more later. But for now, here's the path:
  • Input gets scaled and offset by R40 and R41. The scaled CV1 input, offset voltage and CV2 voltage are all summed through the simple op-amp summing circuit.
  • The level then gets scaled down before going into an exponentiator.
  • The exponentiator (the two PNP transistors and the U3A op amp) turns the input voltage into a current that's proportional to e^input_voltage. We want an exponential voltage because we hear volume according to the log of the pressure. In other words, the pressure has to increase by more than double for the sound to sound twice as loud.
  • The NTE996 does most of the work, and simply amplifies the audio input according to the current input from the exponentiator.
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