audio amplifier

Audio signals are by default oscillations from a common center. One supply designs are therefore limited or impractical. I think the best way to keep the design simple is to add a DC bias to the signal.

I am considering using either a common emitter or a voltage follower BJT amplifier, with a capacitance coupler and two biasing resistors.

The human threshold of hearing is 16 Hz to 20 kHz. This creates a complication for biasing a BJT using two resistors and a coupling capacitor. The equivalent resistance of a capacitor at a given frequency is 1/(2 pi C f) The equivalent resistance of a 0.1 uF capacitor at these frequencies is 100 k and 80 Ohm, respectively. The highest ceramic capacitor is 220 uF. The equivalent resistance for that is 45 and 0.04 Ohm. The higher the capacitance, the less spread the equivalent resistances will be. The problem with going this route is that now the DC voltage will have a low resistance to the signal source, which is something I want to avoid.

To have the widest range of usability, I should use a stand alone analog to digital converter. In Digikey, under the heading Integrated Circuits (ICs), Data Acquisition, Analog to Digital Converters, 8 bits, 100k to 1M Sampling Rate (Per Second), and Dual +- Voltage Supply Source. This ends up being MAX152 to MAX156. More on them later.

http://www.linkedin.com/in/andrewvall
http://www.elance.com/provprofile?userid=184021&rid=3QOZ
Electrical Design Engineer, Minneapolis, Minnesota

speaker amplifier 1

As a start, I think it would be best to start with a midrange speaker set. I am considering Sony SS-F5000 Floor Standing Speakers. They come in pairs.

• Frequency Response : 45 - 50,000 Hz
• Impedance : 8 Ohms
• Mid Range Size(s) : 3 ¼” Midrange Driver
• Power Requirements : 150W
• Quantity (Packaged) : 2
• Quantity of Tweeters : 1
• Quantity of Woofer(s) : 2
• Sensitivity : 88 dB
• Speaker Terminal Type : Binding Post
• Tweeter Size : 1" (2.5 cm)
• Woofer Size(s) : 8" Woofer

A 150 Watts and 8 Ohm impedance results in a peak amplitude of 4.33 Amperes and 34.6 Volts. The frequency response is higher than I would like, but it will do for the price.

My whole goal is to do away with a lot of the necessary components needed for audio amplification. A receiver can be a very complex and pricey piece of equipment. You get what you pay for. Sometimes it is nice to have a lot of bells and whistles, but sometimes you just want high fidelity. I am going for fidelity.

It is simply connected to a computer with a head phone jack. The audio signal is digitized. The 8-bits are sent to the speaker site using a parallel port. Because the signal is digital, the distance possible before high distortion is greatly increased. The speakers are given a pulse width modulated carrier signal, which is filtered.

Keep tuned.

http://www.linkedin.com/in/andrewvall
http://www.elance.com/provprofile?userid=184021&rid=3QOZ
Electrical Design Engineer, Minneapolis, Minnesota