Summary of Modular Synthesizer Project

Project Overview

This modular synthesizer project involved designing and building multiple waveform generation and blending circuits, aimed at creating a versatile and adjustable synthesizer module. The primary goals were to implement various waveforms, include a noise source, and blend all the generated signals into a single output. The project also included specific modifications, such as fine-tuning, power supply design, and signal buffering to ensure stability and reliability.

Key Components and Stages

1. Oscillator Core (Ramp Core)

   • A ramp core oscillator was designed using a TL072 operational amplifier as the integrator, along with a 2N3904 transistor and CA3086 transistor array for current mirroring.
   • The integrator frequency is controlled by RV1, with an additional fine-tuning trimmer (R36), allowing precise frequency adjustment.
   • CD40106 Schmitt Trigger inverters were used for signal buffering, ensuring the stability of the output signal.

2. Waveform Generation and Blending

   • The circuit generates several basic waveforms: sawtooth, triangle, sine, and pulse.
   • Each waveform output is blended with an adjustable amount of noise using JFETs (2N5457) as voltage-controlled amplifiers (VCAs).
   • The blend output of each waveform was further processed through a buffering stage using TL072 operational amplifiers.

3. Noise Source and Filtering

   • A white noise generator was implemented using a BC547 transistor, with the noise amplified by a TL072 operational amplifier.
   • Adjustable filtering was added to shape the noise characteristics, providing both high-pass and low-pass controls, implemented with RV7 and RV6.
   • The filtered noise was further buffered to ensure clean blending with the other waveforms.

4. Signal Mixing

   • The blended outputs of the sawtooth, triangle, sine, and pulse waveforms were mixed into a final output using a TL072 operational amplifier configured as a summing amplifier.
   • Mix Out provides a composite audio signal with all waveforms mixed with noise, with individual blending for each waveform.

5. Power Supply Design

   • A Eurorack power connector (J9) was used for powering the module, providing ±12V, +5V, CV, and Gate signals.
   • Protection diodes (1N5819) were added to each power line, followed by capacitors for decoupling and stability (±12V and +5V).
   • A single power-on LED indicator was added to the +5V line, indicating when the module is powered.

Challenges and Improvements

• Thermal Coupling: The CA3086/3046 transistor array was used for better thermal coupling of the transistors, which helped reduce frequency drift and improved pitch stability.
• Signal Buffering: The use of CD40106 Schmitt Trigger inverters for buffering was initially a concern due to their threshold nature. This was addressed by careful selection of the threshold voltage levels, ensuring proper signal integrity.
• Component Selection: The decision to use TL072 for all operational amplifier needs was made due to its wide availability, cost-effectiveness, and adequate performance characteristics for audio signal processing.

Outcome

• A fully functional modular synthesizer module was designed, capable of generating sawtooth, triangle, sine, and pulse waveforms, each of which can be blended with an adjustable amount of noise.
• The project successfully addressed all the initial design goals, providing flexibility in waveform generation and blending, along with a stable power supply and efficient signal buffering.

This modular synthesizer is now ready for integration into a Eurorack system, providing unique sonic possibilities through its noise blending and waveform generation features.

Comprehensive Review of Synthesizer Schematics

Project Overview

The goal of our project was to create a versatile analog synthesizer module capable of generating multiple waveform outputs, including sawtooth, triangle, sine, pulse, and noise. We also aimed for flexibility in signal blending, along with a reliable power section for consistent operation. The design uses commonly available components, ensuring it can be built with minimal specialized parts while providing a high level of functionality.

Below is a detailed review of the individual sections of the schematics, and how they align with our goals:

1. Ramp Core Oscillator

• Schematic (01_ramp_core.png): The ramp core oscillator is at the heart of this synthesizer. It utilizes a TL072 op-amp to generate a stable ramp waveform, which serves as the basis for shaping other waveforms.
• Components & Design Considerations:
  • CA3086/3046 transistor array forms a current mirror, which is key for controlling the ramp's linearity and stability.
  • RV1 (100kΩ) is used for frequency control, with R36 (10kΩ) added to ensure finer tuning.
  • The use of Q2 (2N3904) as a current sink and the Schmitt trigger (CD40106) for buffering ensures a sharp and well-defined ramp reset.
• Conclusion: This section effectively creates the ramp waveform with control over its frequency and reset characteristics. The fine-tuning and thermal coupling of transistors enhance pitch stability, meeting our goal of producing a precise core waveform.

2. Triangle Wave Shaper

• Schematic (02_triangle_wave.png): The ramp waveform is shaped into a triangle wave using a TL072 op-amp and a pair of diodes (1N4148).
• Symmetry Control:
  • RV4 (10kΩ) allows for symmetry adjustments, ensuring a balanced triangle wave. Proper alignment of diodes helps achieve a linear slope on both halves of the triangle.
• Conclusion: The triangle wave is a fundamental waveform in many synthesis processes, and the use of a symmetry adjustment meets our goal of ensuring waveform accuracy.

3. Sine Wave Shaper

• Schematic (03_sine_wave.png): The triangle waveform is converted into a sine wave through a feedback network using capacitor C4 and TL072.
• Shaping and Adjustment:
  • The trimmer RV2 (10kΩ) is critical for reducing harmonic distortion and shaping the sine wave properly.
• Conclusion: The sine wave shaping circuit effectively smooths the triangle waveform, creating a sine with adjustable harmonic content. This fulfills our goal of generating a clean, adjustable sine output.

4. Pulse Wave Shaper

• Schematic (04_pulse_wave.png): The TL072 (U4B) op-amp shapes the input from the triangle waveform and LFO into a pulse waveform.
• Pulse Width Control:
  • RV5 (10kΩ) allows manual control of the pulse width, while the LFO input modulates the pulse width, adding versatility for different modulation scenarios.
• Conclusion: The pulse width modulation capability, along with manual control, provides the desired flexibility in sound design, meeting our project objectives for waveform variety.

5. Noise Generator

• Schematic (05_noise_generator_v2.png): Noise is generated using a CA3086/3046 transistor and amplified with a TL072 (U5A).
• Filtering:
  • RV7 and RV8 are used to control the high-pass filter characteristics, allowing adjustments in the coloration of the noise output.
• Conclusion: Noise generation with adjustable filtering is useful for creating diverse sound textures, aligning well with our goal of a versatile noise section.

6. Waveform Blending and Summing

• Schematic (06_mixed_out.png): Each waveform output is blended using a summing amplifier (TL072, U10B).
• Mixing Control:
  • Equal resistances (100kΩ) for each input ensure that all waveforms are summed evenly, providing a balanced mixed output.
• Conclusion: This blending stage achieves the goal of providing a single output that contains a mix of all generated waveforms, offering a comprehensive signal suitable for various applications.

7. Power Supply and Distribution

• Schematic (07_power_connector.png): The power section delivers +12V, -12V, and +5V to the different parts of the circuit.
• Power Integrity:
  • Diodes (1N5819) protect against reverse polarity, and capacitors ensure proper decoupling.
  • The addition of an LED indicator for the +5V line serves as a power-on visual indicator.
• Conclusion: The power section is robust, ensuring stable operation across the synthesizer. Proper decoupling and visual status indication align with the goal of reliability.

8. Output Connections

• Schematic (08_outputs.png): Each generated waveform, including the mixed output, is connected to individual output jacks.
• Labelling and Accessibility:
  • Proper labeling of outputs ensures that each waveform can be accessed easily, making the synthesizer user-friendly.
• Conclusion: The output interface meets our objective of making all waveforms accessible for external use, fulfilling the goal of usability.

Overall Assessment

The project successfully meets the outlined objectives:

• Versatility: The synthesizer offers a wide range of waveforms—sawtooth, triangle, sine, pulse, and noise—each with adjustable parameters, providing a rich palette for sound design.
• Stability and Control: The use of thermal coupling, fine-tuning trimmers, and proper filtering ensures the oscillator remains stable, while the power section guarantees reliable operation.
• User-Friendly Design: The interface, including labeled outputs and the power-on indicator, makes the synthesizer easy to operate.

Overall, the design is well-executed, with each section effectively contributing to the synthesizer's versatility and reliability. The schematics illustrate a thoughtful and methodical approach to achieving a high-quality analog synthesizer module.

Complete Bill of Materials (BOM)

No	Reference	Value	Qty
1	C1	22nF	1
2	C2, C3, C5, C6, C10, C11, C12, C17, C18, C19, C20, C21, C22, C23, C24, C25, C26, C27, C28, C29, C32	100nF	21
3	C4, C7	10pF ~ 33pF	2
4	C8, C13, C14, C15, C16	10uF	5
5	C9	10nF	1
6	C30, C31, C33	47uF	3
7	D1, D2	1N4148	2
8	D3, D4, D5, D6	1N4148	4
9	D7, D8, D9	1N5819	3
10	D10	POWER ON	1
11	J1	SAWTOOTH	1
12	J2	TRIANGLE	1
13	J3	SINE	1
14	J4	PULSE	1
15	J5	MIX OUT	1
16	J6	NOISE	1
17	J7	HP NOISE	1
18	J9	POWER	1
19	J10	CV IN	1
20	Q2	2N3904	1
21	Q3, Q4, Q5, Q6	2N5457	4
22	R1, R15, R20, R21, R22, R23, R24, R25, R26, R27, R28, R29, R30, R31, R32, R33, R34, RV1	100K	18
23	R2, R6, R9, R10, R11, R12, R18, R19, R36, RV2, RV4, RV5	10K	12
24	R3, R4, R5, R7, R8, R13, R35	1K	7
25	R14, R16	1M	2
26	R17	470K	1
27	RV3, RV6, RV7, RV8	50K	4
28	U1, U4, U5, U6, U7, U8, U9, U10	TL072	8
29	U2	CD40106	1
30	U3	CA3086/3046	1