Audio

The circuit was designed and sold as a card by a purveyor of surplus components but, even using mostly manufacturer's rejected transistors, we managed to get about 0.02% total harmonic distortion at 30 watts with a ±25v power supply into 8 ohms.: no bad figure even in these days of MOSFET and ICs.

The circuit is simple, yet is capable of excellent performance. I designed it specifically for use as an amplifier for the digital sound card in my computer. Audio input can be from any two-channel line level device such as a television, CD player, or VCR. It is of the tube type, using only 5 tubes total with no more than about 45 Watts power consumption from the outlet. It uses 3 types of tube 1 5Y3 GT vacuum rectifier, 2 6SF5 GT high-mu triodes, and 2 6K6 power beam amplifiers. These are all full-size octal type tubes which are commonly available today for between $3-5 each.

This is a four channel amplifier ideally suited for use with quadraphonic equipment such as a Sound Blaster Live card. There is no volume control,audio levels being directly controlled from the sound card itself.

This product comes with quite a story. I remember many years ago, when I install audio system in my own car, I always look for a "black box" that I hope can me my system sounds great. I was hoping that this "black box" can change the whole sound of the system instantly. So I begin to try various IC preamp, like RockfordFosgate PA-1, Precision power PAR225, Zapco SX and PX, Nakamichi PA101, Audio control products, and almost all the signal processor available on the market. They are the best available. It turns out that my dream of such a "black box" is impossible.

This project is a dedicated device. It dials a single phone number when the handset is lifted. There are two different modes of operation.. A slide-switch on the PC board allows the project to operate in automatic or manual mode. If the switch is in "auto dial" mode, a pre-programmed phone number is AUTOMATICALLY dialled when the phone is lifted. If the switch is in "push to dial," the project dials the number when the phone is lifted and "push to dial" button is pressed. This allows the phone to be used as a normal phone.

The preamp circuit is completely conventional, and by necessity is AC coupled throughout. The artificial earth is derived by two resistors (R1 and R2), which will set the "earth" at exactly 1/2 the supply voltage. This is nominally 13.8V in all cars, since this is the proper charging voltage for a 12V battery. To reduce the maximum gain, simply reduce the values of R105 and R205. For example, reducing these to 4k7 will provide a maximum gain of 3 (10dB), which in reality is probably enough.

Whenever I'm in the car listening to my favourite CD, it always happens-my batteries go dead. To solve that problem, I built this extremely simple regulator circuit. It steps down the 12V from the lighter socket to 9V which is used by the CD player. Different CD players (I have a Sony Discman) may require different voltages, so just use the correct regulator. All the 78xx series regulators have the same pin out, so the circuit is universal.

The circuit is simple, yet is capable of excellent performance. I designed it specifically for use as an amplifier for the digital sound card in my computer. Audio input can be from any two-channel line level device such as a television, CD player, or VCR. It is of the tube type, using only 5 tubes total with no more than about 45 Watts power consumption from the outlet.

This power amplifier has a subsonic highpass filter in it, to make sure that too low frequencies will not damage subwoofers. This type of car amplifier must be installed by professional installer. This kind of amplifier needs well prepared car electricity, like good battery, and high-output alternator.

This IC chip was designed specifically for use in power boosting applications in automobiles. It is self protecting against short circuits and thermal problems.

One-farad capacitors require some care. It's a common knowledge that they must be pre-charged with a current-limiting resistor before plugging in. It is less common knowledge that those fifty-dollar 'smart cap controllers' are in fact very simple devices, two dollars for parts and labor. Here's a basic cap switch that will connect capacitor to ground only when it's charged to within 0.4-0.7V from battery voltage (otherwise, it's charging through a 22 Ohm resistor, which can be a low-power 12V lightbulb, too).

If the amp is built on bipolar transistors, and the preamp/crossover on FETs, then they were designed by different guys, right? Not this amp. Here, a strong, experienced designer's hand is evident from schematic to parts layout, PCB routing and general assembly. Which leads to one of the lowest failure rates (don't quote me on this although it's common knowledge in repair industry) and a surprisingly good sound from a $50 per channel device. A unit worth a Web page. LR series - Audison's junior - was formally discontinued in 1999, just to be repackaged under 'Millenium' series name.

An LM556 dual oscillator/timer, U1, configured as a two-tone oscillator drives U2, a dual 4-watt amplifier. One of the oscillators, pins 1 to 6, contained in U1 produces the upper frequency signal of about 200 Hz, while the second oscillator, pins 8 to 13, provides the lower frequency signal of about 140Hz.