My Notes

Category: Самодельщик

Simple relay and transistor based power-up delay circuit

Here's the most simple (and very old and well known) power-up delay circuit I used for my DIY tube amp and class A solid state (IC) amp. It is very primitive but it may be useful to you if you're more n00b than me ;-)

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Simple LM3886 gainclone audio amplifier for ex-Microlab Solo speakers

Here's a simple LM3886 (LM3886TF) hard-wired amplifier I built during 3 evenings for my wife's ex Microlab Solo computer speakers (modded). I wanted to build it as fast as possible and using only parts I had at hands. Because the speakers aren't super powerful and never used aloud I took a simple $3 polystyrene box for the case and two old heatsinks for Pentium processors for cooling. I also had a power transformer taken from the Solo's dead amp. Originally I wanted to use inverted schematic with op-amp buffers (you can see a card with the buffers on the photo). Then I realized that it makes the box too tight and adds more hum because the transformer is too close to the electronics. So I took the buffer out and converted the amp to normal (non-inverting) gainclone. Without buffer the inverting schematic was oscillating at radio frequencies producing a lot of heat. Later I also removed DC blocking caps as the amp is intended for use with PC sound card which already has output caps. The switch the between volume knob and the headphone socket switches wires from input jacks between amplifier and headphones, i.e. headphones are powered directly from sound card.
Despite the small case I stuffed totally 55800 uF into power supply filters.
Unlike other "super simple gainclone" builders I always leave protective RC and RL circuits. "3 resistor amp" may look attractive and sound a bit better but removing the "extra" components greatly increases chances for a bad end of your speakers.
The amp produces a little static (hum) audible on my testing wide-range speaker but absolutely not audible on Solos because of their low sensitivity.
Working temperature of the amp in is just about 40 degrees so heat dissipation isn't an issue even with such small heatsinks if an amp is not used with continuous power exceeding a few watts. Working at full power for only a few minutes doesn't hurt it as well. BTW most of the heat comes from the transformer, not from the IC's.
The photos and schematics:

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More DIY Audio - LM3886 Mono/LFE Amplifier

Photo
Here's my second complete chipamp. It can be used for driver and speaker testing and warming up or as a subwoofer amp. It was re-soldered about 10 times so it's not very cute inside and got strange knob layout. Two inputs: normal mono input and LFE input with 2 connectors. The LFE board contains channel mixer and two 2-nd order stage low-pass filter, one stage can be tuned to approx. 40..150 Hz cutoff frequency, the other one is fixed at 180 Hz (IIRC ;-)). The power amp has 2 modes, one normal gainclone mode and another one with additional negative current feedback cirquit.

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Active 4rd order Linkwitz-Riley opamp crossover

Наконец-то доделал регулятор напряжения и испытал активный кроссовер (Линквиц-Райли 4 порядка). Много в нём деталей, зараза. Рано или поздно будет что-то биампинговое.

Активный кроссовер

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Разрядник для аккумуляторов (battery discharger)

[Вводное слово] NiCd и NiMH аккумуляторам для нормального функционирования нужно периодически разряжаться полностью, в противном случае они постепенно теряют ёмкость. В этом смысле цифровая техника, которая отказывается работать от батарей, когда они ещё содержат солидный процент заряда, для них настоящее "убийство". К счастью, даже если аккумулятор в результате такой эксплуатации исхудал, то несколько циклов полной разрядки-зарядки могут вернуть его к номинальной ёмкости. Ну и просто после отработки аккумуляторов в камере их следует доразряжать.

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