Summary of "Why & How to Build a Piezo Preamp for your Cigar Box Guitar / Preamp for Contact Mic"
Building a Piezo Preamp for a Cigar Box Guitar
The video, presented by Dr. Liza Seigido from Psyche Electro Acoustic Opera Company, explains why and how to build a piezo preamp specifically for a cigar box guitar (CBG) equipped with a piezo pickup.
Why Use a Piezo Pickup?
Dr. Liza emphasizes that magnetic pickups do not capture the unique resonator sound of a cigar box guitar. Piezo pickups are ideal because they convert vibrations from solid surfaces into electrical signals. However, piezo pickups have:
- High impedance
- Weak, bass-deficient signals
- Noise and level spikes if not paired with a proper preamp
Initial Challenges and DIY Solution
Dr. Liza describes her initial unsuccessful attempt using a cheap preamp, which resulted in poor sound quality. This led her to build a DIY piezo preamp based on circuits found on homemadecircuits.com and Collins Lab.
Circuit Components and Functions
The video breaks down the key components and their roles in the preamp circuit:
- 3.3 megaohm resistor: Preserves frequencies
- mpf102 transistor: Amplifies the signal using a 9V battery
- Capacitors: Block DC and pass AC signals
- Resistors: Lower output impedance for compatibility with modern audio gear
Building Process
Dr. Liza details the steps involved in building the preamp:
- Sourcing components: Resistors, capacitors, transistor, connectors, battery, switch
- Breadboarding challenges: Audio circuits on cheap breadboards were unreliable
- PCB solution: Created a PCB layout using copper tape on a wooden board, housed in a rustic wooden box
- Assembly tips: Checking continuity with a multimeter, careful soldering, and safely wiring the battery with a rocker switch to prevent hazards
Testing and Performance
Once assembled, Dr. Liza tests the preamp by comparing recordings of her CBG plugged directly into an audio interface versus through the preamp. The results show:
- A stronger, bass-rich signal with the preamp
- A slight low-level hum present
She also tests the preamp with guitar effects pedals:
- Good results with a Zoom multi-effects unit
- Poor guitar effects performance through the TC Helicon Play Electric, though vocal effects work well
- Suggests a workaround to use vocal effects from the Play Electric while routing guitar effects through another pedal
Conclusion
Dr. Liza concludes that the DIY piezo preamp is:
- Affordable (about $11 total)
- Effective for live and studio use
- Recommended for other piezo CBG players
She encourages viewers to judge the sound themselves and invites them to explore more audio and music tech tutorials on her channel.
Speaker in the Video
- Dr. Liza Seigido
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