Introduction

When you purchased a vintage Hewlett-Packard 180A Oscilloscope from eBay and want to measure audio trigger and CV signals from your Eurorack system, it's crucial to understand how to configure the oscilloscope to get the most accurate and usable readings. This guide will walk you through the process and provide you with the necessary settings.

Getting Started with Your Oscilloscope

First, familiarize yourself with theasics operating and service manual. The manual is available for free download here.

Setting Up for Audio Signals

For capturing and measuring audio signals, follow these initial settings:

1. Timebase to Auto

Set the oscilloscope's timebase to Auto. This feature automatically adjusts the time scale to match the input signal's frequency, making it easier to capture and analyze transient and periodic signals.

2. Time Scale to 5 ms/Div

Adjust the time scale to 5 milliseconds per division (ms/div). This setting provides a balanced view of the audio signal, allowing you to see both fine details and the overall shape of the waveform without being too zoomed in.

3. Vertical Scale to 0.5 V per Div

Set the vertical scale to 0.5 volts per division. This setting ensures that the oscilloscope can clearly display the amplitude of the audio signals without overloading or underloading the screen.

Adjusting Your Settings for More Accurate Results

To further optimize your measurements, you can adjust the vertical and time scale settings:

1. Increase Vertical Scale for Larger Signals

If the audio signal's amplitude is large, you can reduce the vertical scale (e.g., set it to 0.1 V/div or 0.2 V/div) to see the waveform without clipping. Conversely, if the signal is too small, increase the vertical scale (e.g., to 1 V/div or 2 V/div) to capture more details.

2. Spread the Signal Out in Time with a Slower Setting

To observe the waveform over a longer period, decrease the time scale (e.g., to 1 ms/div or even 2 ms/div). This will slow down the horizontal motion of the signal, allowing you to see smaller time intervals more clearly.

Triggering and Repeatability

While the oscilloscope's settings will help you capture the audio signals, it's important to note that most audio programs (except for test signals) do not repeat reliably. This can make it challenging to achieve a stable, repeatable signal for measurement. However, you can use the following techniques to improve repeatability:

1. Manual Trigger

Use the manual trigger function to capture a specific point in the audio signal. This can help you freeze the waveform at a moment of interest for closer inspection.

2. Edge Trigger with Proper Timing

If you have a known signal edge (e.g., a click or a start of a note), use edge triggering to lock the oscilloscope on this point. Select the appropriate edge (rising or falling) and ensure that the trigger level is set correctly to capture the desired moment.

Conclusion

With the right settings and techniques, you can effectively measure audio trigger and CV signals from your Eurorack system using a vintage oscilloscope. By adjusting the time and vertical scales, and using appropriate triggering modes, you can obtain the most accurate readings and insights into your audio signals.

Remember, the key is to experiment and fine-tune your measurements to suit your specific audio signals. Happy analyzing!