Mini Test Oscillator

        I made this Mini Test Oscillator some time ago but never got around to making a page. This page shows myP86 Miniosc from ESP. I bought the PCB but wasn't able to find a suitable enclosure with the right dimensions so I decided to make one. The board was built as per schematic diagram but with slight modification to increase the range a little bit.



A DC input jack was added for prolonged testing or used when breaking in woofers.

When I originally designed the case, the battery would fit just fine. After sanding it to make the bottom surface flat, it became too thin. Using a thicker bottom cover and milling a pocket solved the problem. It also helped keep the battery in one place.

The additional thickness also allowed to countersink the cover screws.

Here's the bottom cover removed.

Since the piece holding the battery in place was near the BNC connector, a notch was cut to make room for the BNC connector nut.

Top view of the MiniOsc.

Front view; The LED is the bright green variety but driven at only 0.3mA to save battery. Because of the high efficiency, it is still pretty bright as a power indicator.

Here are some measurements using VP7723 Audio Analyzer, No part matching was done. I just used what is at hand.
I changed some values to extend the range (I changed C5-6 to 100nF, R8-9 to 1.5k)
These are what I was able to get:
Lo: 31.32Hz to 1kHz
Hi: 842.89Hz to 22kHz

THD: (was measured before I changed the resistors that's why there's a gap in the ranges)
0.223% @ 31Hz (min at Lo)
0.1544% @ 740Hz (max at Lo)
0.264% @ 842Hz (min at Hi)
0.326% @ 1kHz
1.224% @ 18kHz (max at Hi)

Vout max:
1.287V rms sine wave
1.393Vrms sq wave.

Measurements were taken unloaded. The output of the oscillator connected directly to the input of the analyzer which has 100kohm input impedance

Supply is a 9V battery (charge state unknown, I forgot to test) and op amps are TL062

Page updated and copyright R.Quan © 06 Nov 2011.