Based on the classic Baxendall tone control circuit, this provides a maximum cut and boost of around 10dB at 10K and 50Hz. The first [url=http://www.chinaicmart.com/suppliers/174/BC109C.html]BC109C[/url] transistor (left hand side) is acting as a buffer. It provides the circuit with a high input impedance, around 250k has a voltage gain of slightly less than unity. As the Baxendall tone control circuit is a passive design, all audio frequencies are attenuated. The position of the controls and reactance of the capacitors alters the audio response. The last transistor provides a slight boost...

The ISD1000A is a Direct Analog Storage device which allows you to store 20 seconds worth of voice data on an IC chip which can be play backed anytime. The data stored will stay in memory even if the power is removed. To use the circuit below simple apply power to the circuit, press the record button and hold. Speak clearly into the microphone. You have up to 20 seconds of voice message that you can store. If you talk beyond that time the chip will only store the first 20 seconds. After recording, release the record button. To playback the message, press the playback message and the message...

With this circuit you can mix four separate audio inputs. Each input will accept high or low impedance microphones, phonograph, tape or aux signals. You can adjust the gain of each input by adjusting each respective pot. With the Stereo/Mono switch you can combine just inputs 1,2 and 3,4 or in the Mono position combine all four inputs. Signal response is 20 Hz. to 20kHz. with very high input impedance and very low distortion with complete output short circuit protection. This circuit will drive any power amp with an input impedance of 2,000 ohms. Copyright 2000...

I have had many requests to design or provide circuits for graduation projects. Yes, I had to build a graduation project too before receiving my degree. Even though I have always refused to design circuits for this situation, I thought it might be helpful for you to see what I built for my project many years ago when I graduated in 1978. I will also provide a more detailed description of the circuit than I normally do. Hopefully, this may help some of you with your projects. The purpose of this circuit is to automatically turn off any device plugged into its power outlets after a certain...

This circuit is very basic to build and puts out great power for your car or home. Keep all leads as short as possible. Copyright 1999 [url=http://home.maine.rr.com/randylinscott/index.html]Randy Linscott[/url]...

With this circuit you can modify how your voice sounds by changing the pitch of your voice. This circuit can be connected to a phone and with a duplicate circuit on the end of the phone line, you can have a scrambled voice communication. The way the circuit works is as follows: If we cut the circuit in half at the T2 transformer and include the LM324 on the left side, you will see that the LM324 portion of the circuit is a tone oscillator which shifts the frequency of all input signals to a new higher frequency. When the voice and the tone oscillator mix frequencies the voice is not...

I like to see lights move to music. This project will indicate the volume level of the audio going to your speakers by lighting up LEDS. The LEDS can be any color so mix them up and really make it look good. The input of the circuit is connected to the speaker output of your audio amplifier. You want to build two identical units to indicate both right and left channels. The input signal level is adjusted by the 10k ohm VR. If you wish to make a very large scale model of this unit and hang it on your wall there is an optional output transistor that can drive many LEDS at once. The unit I built...

This IC chip was designed specifically for use in power boosting applications in automobiles. It is self protecting against short circuits and thermal problems. In the bridge configuration shown it will deliver 20 watts of power into a 2 ohm speaker operating at 14.4 volts. Copyright 1998 [url=http://home.maine.rr.com/randylinscott/index.html]Randy Linscott[/url]...

This circuit was requested by an school teacher. It is a simple intercom that anyone can put together and get to work. It is based on the LM380 IC chip. This chip is able to put out 2 watts of power if it is heat sink properly. The following pins should be grounded and attached to a foil to dissipate the heat. Pins 3,4,5,10,11,12 should all be grounded. The circuit works as follows. Switch 1 is a double pole double throw switch. In one position is the talk position and in the other is the listen position. In the diagram shown the switch is in the talk position for the speaker on the left....

You'll find that this is a very easy project to build. It will transmit good quality sound in the FM band ( 88 - 108 mhz ). One inportant item is that the IC chip operates on 3 volts DC. The chip will get destroyed if it is operated on any voltage higher than 3.5 volts. The antenna can be a standard telescopic antenna or a 2 foot length of wire. The input is in the millivolt range and you may need to add additional pots for the inputs. I was able to use this circuit for a walkman and a portable CD player in my car. I used the headphone jack on both and varied the signal with the volume...

[img:e6e3b3acc7]http://www.circuitdb.com/download.php?fileID=209[/img:e6e3b3acc7] With the amount of equipment in home entertainment centers today the need to be able to vary the gain of the audio or video signal is needed. I found this particular circuit helpful when used in conjunction with the Universal Descrambler and a Stabilizer circuit I built for making copies of video tapes. It not only allowed me the ability to fine tune the video strength it also helped me increase the recorded audio which typically becomes poor when making tape copies. Circuit operation is straight forward...

This circuit is similar to [url=http://www.circuitdb.com/show.php?cid=176]3 Transistor Audio Amp (50 milliwatt)[/url] but uses positive feedback to get a little more amplitude to the speaker. I copied it from a small 5 transistor radio that uses a 25 ohm speaker. In the circuit above, the load resistor for the driver transistor is tied directly to the + supply. This has a disadvantage in that as the output moves positive, the drop across the 470 ohm resistor decreases which reduces the base current to the top NPN transistor. Thus the output cannot move all the way to the + supply because...

Here is a little audio amplifier similar to what you might find in a small transistor radio. The input stage is biased so that the supply voltage is divided equally across the two complimentary output transistors which are slightly biased in conduction by the diodes between the bases. A 3.3 ohm resistor is used in series with the emitters of the output transistors to stabilize the bias current so it doesn't change much with temperature or with different transistors and diodes. As the bias current increases, the voltage between the emitter and base decreases, thus reducing the conduction....

Both halves of the circuit are identical. Both inputs have a dc path to ground via the input 47k control which should be a dual log type potentiometer. The balance control is a single 47k linear potentiometer, which at center adjustment prevents even attenuation to both left and right input signals. If the balance control is moved towards the left side, the left input track has less resistance than the right track and the left channel is reduced more than the right side and vice versa. The preceding 10k resitors ensure that neither input can be "shorted" to earth. Amplification of the audio...

Using a single op-amp this easy to make equalizer offers three ranges, low frequency,mid frequency,and high. With component values shown there is approximately +/-20dB of boost or cut at frequencies of 50Hz, 1kHz and 10kHz. Supply voltage may be anything from 6 to 30 Volts. Maximum boost 20dB is only realized with maximum supply voltage....

The circuit below uses two quad voltage comparators (LM339) to illuminate a series of 8 LEDs indicating volume level. Each of the 8 comparators is biased at increasing voltages set by the voltage divider so that the lower right LED comes on first when the input is about 400 millivolts or about 22 milliwatts peak in an 8 ohm system. The divider voltages are set so that each LED represents about twice the power level as the one before so the scale extends from 22 milliwatts to about 2.5 watts when all LEDs are lit. The sensitivity can be decreased with the input control to read higher levels. I...

This simple circuit mixes two or more channels into one channel (eg. stereo into mono). The circuit can mix as many or as few channels as you like and consumes very little power. The mixer is shown with two inputs, but you can add as many as you want by just duplicating the "sections" which are clearly visible on the schematic....

This is a basic 555 squarewave oscillator used to produce a 1 Khz tone from an 8 ohm speaker. In the circuit on the left, the speaker is isolated from the oscillator by the NPN medium power transistor which also provides more current than can be obtained directly from the 555 (limit = 200 mA). A small capacitor is used at the transistor base to slow the switching times which reduces the inductive voltage produced by the speaker. Frequency is about 1.44/(R1 + 2*R2)C where R1 (1K) is much smaller than R2 (6.2K) to produce a near squarewave. Lower frequencies can be obtained by increasing the...

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 consumpting, battery operateable one will be suitable. 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...

The circuit below responds to sound pressure levels from about 60 to 70 dB. The sound is picked up by an 8 ohm speaker, amplified by a transistor stage and one LM324 op-amp section. You can also use a dynamic microphone but I found the speaker was more sensitive. The remaining 3 sections of the LM324 quad op-amp are used as voltage comparators and drive 3 indicator LEDs or incandescents which are spaced about 3dB apart. An additional transistor is needed for incandescent lights as shown with the lower lamp. I used 12 volt, 50mA lamps. Each light represents about a 3dB change in sound level so...

As a followup to my VCR Pong project, here is a gadget that is actually useful in the Real World! It superimposes the time of day, in "HH MM SS" format, in the bottom right-hand corner of an existing video signal. My friend Scott uses it with his home security system. In keeping with the tradition of my previous hacks, I use few parts and lots of tricks. All timing signals, including the timebase for the time of day and the clock for the microprocessor, are derived from the incoming video signal. That means if you lose power, or lose video, it loses the time... but in this home security...

Do you want to listen to MP3 on your radio? But yout radio doesn't have a AUX IN or any other Input? Then audioFM can help you. audioFM takes audio signals from a headphone plug and converts it into radio UKW FM signals. The heart of this small FM Modulator is a tuneable voltage controlled oscillator (VCO) from Maxim-IC called MAX2606. This VCO operates from 70MHz to 150MHz and has a up to -8dBm differential output amplifier. [color=red:61ebf9f576]Note: in many countries it's not allowed to broadcast in the UKW (normal Radio) frequency bands!! So use this at your own...

[b:900792506e] * 10W Old-Style ultra-compact Combo * Two inputs - Overdrive - Treble-enhancement [/b:900792506e] [b:900792506e] Circuit description:[/b:900792506e] The aim of this design was to reproduce a Combo amplifier of the type very common in the 'sixties and the 'seventies of the past century. It is well suited as a guitar amplifier but it will do a good job with any kind of electronic musical instrument or microphone. 5W power output was a common feature of these widespread devices due to the general adoption of a class A single-tube output stage (see the Vox AC-4...

[b:acbecb2875]High Quality simple unit No need for a preamplifier[/b:acbecb2875] [b:acbecb2875]Notes:[/b:acbecb2875] * Can be directly connected to CD players, tuners and tape recorders. Simply add a 10K Log potentiometer (dual gang for stereo) and a switch to cope with the various sources you need. * Q6 & Q7 must have a small U-shaped heatsink. * Q8 & Q9 must be mounted on heatsink. * Adjust R11 to set quiescent current at 100mA (best measured with an Avo-meter connected in series to Q8 Drain) with no input signal. * A correct grounding is very important to eliminate hum and...

This design is based on the 18 Watt Audio Amplifier, and was developed mainly to satisfy the requests of correspondents unable to locate the TLE2141C chip. It uses the widespread NE5532 Dual IC but, obviously, its power output will be comprised in the 9.5 - 11.5W range, as the supply rails cannot exceed ±18V. As amplifiers of this kind are frequently used to drive small loudspeaker cabinets, the bass frequency range is rather sacrificed. Therefore a bass-boost control was inserted in the feedback loop of the amplifier, in order to overcome this problem without quality losses. The bass lift...

Here is the schematic for an 8 watt audio amp. This amp can be used as a simple booster, the heart of a more complicated amplifier or used as a guitar amp. Notes: 1. IC1 MUST be installed on a heat sink. 2. C3 is for filtering and to prevent oscillation and should not be omitted. 3. The circuit can be built on a perf board, universal solder board or PC board, the PC board is preferred. I built the circuit on a perf board and had to add extra inductors, capacitors and resistors to prevent oscillation. 4. The circuit draws about 880 ma at 12 V. 5. By swapping the values of R1 and R3,...