Orange Crush Mini 3-watt Micro Amp IN4007 Diode Replacement

ID: 173271

Description: The Orange Crush Mini is a portable guitar...

Start by removing the four wood screws on the rear panel. Gently open the panel. The wires within are long enough for the rear panel to be set down without disconnecting anything.

Test speaker by setting multimeter to resistance. The 4" Voice of the World speaker is rated at 8 ohms. Mine was 7.4 ohms, which is close enough.
Test diode (D1) nearest the barrel jack. A diode can be thought of as a switch: “closed” when forward-biased and “open” when reverse-biased.
Diode circuit voltage measurement figures: (a) Forward biased. (b) Reverse biased.
In forward bias condition, around a 0.7V drop is expected, like a closed switch that drops 0.7V across it. In reverse bias, the multimeter should show 'OL' (over limit) or a very high resistance, like an open switch. Mine showed 1.2V when reverse biased, which indicates a bad diode. It was also visibly cracked.

Diode theory; x-axis is voltage, and y-axis is current. This is where diode test pass/fail ranges come from.

If care is exercised, it is not necessary to unplug any wires or disturb the circuit.
Make sure to remove battery - I touched a ground screw with the soldering iron and an LED on the main board lit up!
Desolder D1 by any method. I used a chisel tip soldering iron with copper wick, but plunger-style desoldering devices are effective as well.

Find a suitable IN4007 replacement diode. IN4007 diodes are available for around $0.37, but I chose to get an assortment kit that contained a variety instead.

Test circuit before reinstalling back cover. I tested the 1/4" jack with a guitar, and the 3.5mm jack with an audio interface.
The amp drew about 0.025A, or 25mA when listening to music through the 3.5mm jack.
With a guitar plugged in, anywhere from 0.025A (no sound) to 0.075A (practice volumes) were witnessed. For those wondering, a timid strum with the knobs set to full resulted in a reading above 0.105A!

Time (hours) = Battery Capacity (mAh) / Current (mA)
Standard 9V battery capacity: 565mAh
Average music listening volume current draw: 25mAh
22.6 Hours = 565mAh/24mA
If using the Crush Mini as an office speaker, it is worth powering with wire and a not battery since it would require a new battery every 22.6 hours.
However, most inexpensive switching-type power supplies are noisy, and that noise is audible through the amplifier. A regulated linear power supply would be ideal. I was able to use a benchtop switching power supply with a lower noise floor. It is tolerable but not a permanent solution.

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