20150503.jpeg.jpeg

 

One of the enchantments for my 50's turntable is an Arduino Light Organ.

The organ uses FFT to calculate the amount of bass, middle and treble in the turntable signal.

I'm building a simple signal adapter to boost the tiny pickup coil signal.

 

Photo 03-05-15 18 37 48.jpg

 

One Transistor Amplifier

 

There are three reasons why I can't feed the pickup coil signal directly into the Arduino.

The amplitude is small, it can't drive the impedance of an analog input pin (it has to drive an audio pre-amp too).

And it's a negative signal half of the time.

 

The quality of the amplifier isn't that important - as long as it doesn't create too much additional harmonics and doesn't feed anything back into the source signal.

The most important thing for this module is that it adds a positive bias to the signal, so that the full signal is within range for the ATMega ADC.

This 5-component amplifier does the job. It has a so-so frequency response due to my choice of capacitor, and it is nowhere near linear.

If necessary, I will make firmware changes to correct for that.

 

drawing.jpeg

I've measured bandwidth and captured the scope output on 4 spots in the audio range. This is measured without the input resistor of 100 K. Input signal is 350 Vrms.

I don't think I have to expect too much on the range of this turntable (Maybe I can test that later. I have a test record).

But you see that it's a poor performer.

 

20 Hz200 Hz2 kHz20 kHz
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It may be bad on the pictures above, but when I use it for what it is intended, it is quite ok.

The signal has its necessary positive dc bias. And although I haven't tried it in practice yet, I bet it'll do the job just fine.

 

signal.jpg

 

I first breadboarded the circuit to do the measurements, but this is a fine candidate for the proto-shield that came with the Enchanted Objects package.

Photo 03-05-15 15 29 23.jpg

 

 

Table of Contents
Chapter 1: Fix the turntable
1: Perpetuum Ebner Musical 1
2: A Time to Kill and a Time to Heal
3: Preparation for Motor Drive
4: Motor control with Infineon Motor Shield and Arduino UNO
5: Turntable speed sample testbed with Arduino UNO
6: Turntable Speed Sensor design
7: Control Theory - End of Chapter 1
Chapter 2: First Enchantments
8: Digital Light Organ Enchantment
9: Autonomous Servo Lift
10: SMD Time - Solder the IR Speed Sensor PCB
11: Yelp - who can Help me to Compile and Run my First SAMA5D4 C Program
12: Son et Lumiere - End of Chapter 2
Chapter 3: Taming the Board
13: Breakthrough - Run my own C++ Program on the SAMA5D4
14: Digital Light Organ Input Buffer
15: SAMA5D4 Blinky
16: Scope Creep
17: Audio Sampling with 16-bit ADC ADS8343
18: Sending Files to SAMA5D4 over USB
19: Port my Light Organ from Arduino to SAMA5D4
20: Fast Fourier Transform on the SAMA5D4 - End of Chapter 3
Epilogue: Reaching for the Clouds
21: Right-Sizing my Plans
22: My Own C++ Buffered Sampler on the SAMA5D4
Interlude
23: Building In the Motorized Light Organ
24: Up to the Clouds with Yún
25: Publish or Perish
26: Turntable Finished
Stretch & Boni
Bonus 1a: Remote Light Organ with WiFI pt. 1
Bonus 1b: Remote Light Organ with WiFI pt. 2
Grande Finale: Paho MQTT Client on the SAMA5D4
Related blog
Vintage Turntable repair: Can I fix a Perpetuum Ebner from 1958
Review 1: Atmel SMART SAMA5D4 Xplained Ultra Unboxing and First Steps
Review 2: Atmel SMART SAMA5D4 Xplained Ultra - Building the Libraries from Source
Review 3: Digital Continuous Rotation (360°) Servo Part 1
Review 4: Digital Continuous Rotation (360°) Servo Part 2
Review 5: Atmel SMART SAMA5D4 Xplained Ultra - TCP/IP running
Review 6: Atmel SMART SAMA5D4 Xplained Ultra - LINUX Distro with SSH support
poem
Enchanted Objects: Let's work together to tame the ATMEL SMART SAMA5D4 Xplained Ultra kit
17 bis: Off South...
Review 7: Atmel SMART SAMA5D4 Xplained Ultra - C++ ADC Example on Linux
Review 8: Atmel SMART SAMA5D4 Xplained Ultra - Product Review
Review 9a: Atmel SMART SAMA5D4 Xplained Ultra - Set up ADC Buffer with Hardware Trigger Part 1
Review 9b: Atmel SMART SAMA5D4 Xplained Ultra - Set up ADC Buffer with Hardware Trigger Part 2
Review 10: Atmel SMART SAMA5D4 Xplained Ultra - New Content on AT91.com
1958 Turntable from the Black Forest - Summary of the Enchanted Player Story