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This circuit could be used for replacing your manual volume control in a stereo amplifier. In this circuit, push-to-on switch S1 controls the forward (volume increase) operation of both channels while a similar switch S2 controls reverse (volume decrease) operation of both channels. A readily available IC from Dallas semiconductor, DS1669 is used here.

For transfer of digital audio between devices is standardized S/PDIF interface (electrical) and TOSLINK (optical) for commercial use, or AES3 for professional use. S/PDIF decoder module is used for converting of this interface to I2S interface, which is usually used on audio DACs. For conversion we can use for example integrated circuit CS8416 or DIR9001. In building of DAC in past I had troubles with resetting circuit CS8416 in hardware mode. Now I select DIR9001 which works perfectly and he has lower jitter than CS8416.

So this time I decided to make pretty simple but powerful enough car audio amplifier. For this I’ve chosen quad bridge car audio amplifier TDA7384 which has four input and four output channels with power capability of 4x35W. As datasheets of TDA7384 says it is low distortion, low output noise, low external component count. Also has Stand-By function and Mute function. It has several protections like from output short circuit to GND or to Vs, capable to handle very inductive loads, thermal limiter, load dump voltage. TDA7384 is an AB power amplifier cased in flexiwatt25 (eagle library is included in project archive) package witch is designed for high end car radio applications. It allows rail to rail output voltage swing with no need of boot-strap capacitors.

Simple Class-A power amp that uses complementary pair of IRFP240 and IRFP9240 MOSFET transistors. The intention of this project was to build simple, but high quality amplifier. The aim was reached by integrating the whole input driver in one IC and adding high power transistor output stage. As you can see on the schematic the amplifier has very simple structure. At the input there is high quality and relative high power TI IC OPA552. It drives a complementary pair od MOSFET transistors IRFP240 and IRFP9240. The gain of the whole circut is set to 40x. The TL431 is to set the operation point of output transistors. The idle current is set to 80mA, so the amplifier works in A class for it's first few watts. The more current the longer it stays in A class, but the more power to be dissipated. With 80mA and these heatsinks it still goes very hot after long playing.

Control audio volume, LCD contrast, frequency, etc. by using two buttons instead of a common potentiometer. This circuit explains how we do it with Maxim's DS1669 IC. This IC is very popular and is widely used because it is a potentiometer that never wears down. By using S1 and S2 pushbuttons you can adjust the resistance. C1 is only a 0.1uF ceramic capacitor. You can use the datasheet of DS1669 to get more detailed information.

DS1802 is a Stereo Digital Volume Control IC. It consists of two 65-position, 45kΩ digital potentiometers with logarithmic resistance properties incrementing 1dB per step. It can be operated under automatic software control via a serial 3-wire interface where wiper settings are written with 8-bit words, or under push button control with simple contact closure. The part can be used in either 3V or 5V environments and anywhere within the industrial temperature range of -40°C to +85°C. The DS1802 supports daisy-chaining with other devices under single-processor control.

I am a big fan of surround sound. Up until the moment I finished this amp, I was using two two-channel amplifiers to power four speakers. This was very annoying, because it meant I had two volume controls. This invariably meant that the balance between front and rear was off. Added to this, was that the amplifier for the rear speakers was not very good. It produced too much noise, and allowed clicks and pops from the power grid through, to be amplified and heard. I decided I was going to build a four channel power amplifier, and later a pre-amplifier to feed it. You might wonder why I didn't choose to make a five channel one instead. This is because I don't see the use of the center channel. I will probably write an article detailing why, but for now, suffice it to say that four channels is enough for 2 dimensional sound, which is what 5.1 is as well.

In this application, we are building a gaincard like amplifier. This application type is named gainclone in the audio world. To take a satisfactory audio response, we are adding a Linkwitz equaliser to the feedback line and adding bass compensation also. We are using LM3886 which is the revised version of its brother LM3875. These are the parameters that we are interested in. Honestly this values are much more better than many of HI-FI amplifiers sold in the market. Especially it is hard to find 110dB signal to noise ratio. And another property is, when there is no input, this amplifier is quite like a dead. It is nearly impossible to hear any noise when you stick your ear to the speakers.

A general purpose audio power amplifier is a must have for the electronics amateur. It's not a good thing to use your HiFi set for an experiment, when there's a risk of blowing it's transistor out. Amplifier for your experiments should be simple in construction, durable, and easy to repair. Also a portable, low power consumption and battery powered. Taking the considerations above, I gave you the PCB design for the TBA820M based amplifier. It is rated for 2Watts of RMS power output (16W PMPO) but gives even two times more if you cool it well by some tricks. I've been using this circuit for over ten years and personally still surprised by it's durability, thinking of how many short circuits and overdrives it is subjected.

This circuit was designed to obtain a valve-like distorted sound from an electric guitar or other musical instrument. For this purpose a very high gain, three-FET amplifier circuit, was used. The output square wave shows marked rounded corners, typical of valve-circuits when driven into saturation. Therefore, the distorted sound obtained from such a device has a peculiar tone, much loved by most leading guitarists.