Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Input/Output Impedance

Status
Not open for further replies.

djstumerch

New Member
How can I measure the input and output impedance of a stomp box that I have made. I have built a couple of units for a university project, Wah Wah, Fuzz Unit and a Tremolo Unit. I'm creating a specs sheet and user manual.
So Far I have this:


Tremolo
Features
Merkie Modules Tremolo unit uses a low harmonic waveform to produce an enjoyable stuttering effect. This can be tweaked to the desired effect via two control knobs. A 1980’s Cmos chip has also used to keep the distortion levels low and a heavy duty push down switch as been included so the unit can be foot operated.
Specifications
• Input Impedance………… Ω
• Output Impedance…….... Ω
• Connectors………………….. x2 ¼’’ Jack Sockets
• Power Supply………………. 9V Battery (Alkaline for longer use)
• Current Draw……………….. 4mA (9V Battery)
• Size……………………………….. (L) 120 (W) 95 (H) 34 (mm)
• Weight……………………………
Panel Description:
1. Input Jack
¼’’ Jack socket for connecting a guitar
2. Output Jack
¼’’ Jack socket for connecting an amplifier or audio interface
3. Modulation Frequency Knob
Variable frequency range from 0.5 to 5Hz this enables the user to modulate the amplitude of the guitar signal.
4. Oscillator Operating Frequency Knob
The knob controls the frequency of the output triangular waveform, which can vary between 0.5 to 10Hz. This essentially controls the rate.
5. Push Down Switch (Latching)
A heavy duty push down switch as been included so the unit can be foot operated. This allows the user to bypass the circuit giving a clean or modulated signal.
6. On/Off Toggle Switch
A toggle switch as been included which breaks the circuit when it’s in it’s (off) state, this disconnects the 9V power that is being supplied. Toggle the switch (on) and this allows the current to flow from the battery to the circuit.

Any help or suggestions for this would be greatly appreciated.

Cheers

Stu
 
The input impedance can usually be measured with an ohmmeter or by analysis of the input circuit.

The output impedance is normally not listed, unless it's a power amplifier for a speaker. And even then it's not really the actual output impedance but the recommended load impedance that's given

If your box has an opamp output, then the output "impedance" load is whatever the minimum resistance the opamp can drive.
 
You just need to consider what it is you're trying to measure, and give it a little thought.

Then, with a signal generator, an AC-millivoltmeter (or a scope), and a resistor or two it's simple to measure.

To measure input impedance simply feed the signal generator through a series resistor to the input of the amp. Then measure the signal level at either end of it. It's then a simple matter to calculate the input impedance of the amp (two resistors in series - with the external resistor the first one). If you want to make it dead easy, use a variable resistor instead, and adjust it until the output side of the resistor is exactly half the input - then disconnect the pot and measure it with a meter.

You can do the same at the output, except the resistor goes from output to ground, and you measure the output voltage with and without the resistor - again if you use a pot, adjust it until the output is reduced by half (but don't do this on a low impedance output, such as a power amp).

Remember, it's a simple two resistor potential divider - for input you're trying to find the bottom value, for output you're trying to find the top one.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top