An Audio Circuit Collection, Part 1 - TI
Amplifiers: Op AmpsTexas Instruments IncorporatedAn audio circuit collection, Part 1By Bruce CarterAdvanced Analog Products, Op Amp ApplicationsIntroductionThis is the first of two articles on audio circuits. New operational amplifiers from Texas Instruments have excellentaudio performance and can be used in high-performanceapplications.There have been many collections of op amp audio circuitsin the past, but all of them focus on split-supply circuits.Often, the designer who has to operate a circuit from asingle supply does not know how to perform the conversion.Single-supply operation requires a little more care thansplit-supply circuits. The designer should read and understand the introductory material.Split supply vs. single supplyAll op amps have two power pins. In most cases they arelabeled VCC and VCC–. Sometimes, however, they arelabeled VCC and GND. This is an attempt on the part ofthe data sheet author to categorize the part as split-supplyor single-supply, but it does not mean that the op amp hasto be operated with the split or single supply shown by thedata sheet. It may or may not be able to operate from different voltage rails. Consult the data sheet, especially theabsolute maximum ratings and voltage swing specifications,before operating at anything other than the recommendedpower supply voltage(s).Most analog designers know how to use op amps with asplit power supply. In a split-power-supply system, theinput and output are referenced to ground. The powersupply consists of a positive supply and an equal andopposite negative supply. The most common values are 15 V, but 12 V and 5 V are also used. The input andoutput voltages are centered on ground and swing bothpositive and negative to VOM , the maximum peak outputvoltage swing.A single-supply circuit connects the op amp power pinsto a positive voltage and ground. The positive voltage isFigure 1. Half-supply generatorconnected to VCC , and ground is connected to VCC– orGND. A virtual ground, halfway between the positive supply voltage and ground, is the “ground” reference for theinput and output voltages. Voltage swings above and belowthis virtual ground to VOM . Some newer op amps havedifferent high- and low-voltage rails, which are specified indata sheets as VOH and VOL, respectively.5 V is a common value for single supplies, but voltagerails are becoming lower, with 3 V and even lower voltagesbecoming common. Because of this, single-supply op ampsare often “rail-to-rail” devices to avoid losing dynamicrange. “Rail-to-rail” may or may not apply to both theinput and output stages. Be aware that even though adevice may be specified as “rail-to-rail,” some specifications may degrade close to the rails. Be sure to consult thedata sheet for complete specifications on both the inputsand the outputs. It is the designer’s obligation to makesure that the voltage rails of the op amp do not degradesystem performance.Virtual groundSingle-supply operation requires the generation of a “virtualground” at a voltage equal to VCC/2. The external circuitcan be a voltage divider bypassed by a capacitor, a voltagedivider buffered by an op amp, or preferably a power-supplysplitter such as the Texas Instruments TLE2426. Figure 1shows how to generate a half-supply reference if thedesigner insists on using an op amp.R1 and R2 are equal values selected with power consumption vs. allowable noise in mind. C1 forms a low-pass filterto eliminate conducted noise on the voltage rail. R3 is asmall (47-Ω) resistor that forms a low-pass filter with C2,eliminating some of the internally generated op amp noise.The value of C2 is limited by the drive capability of theop amp.In the circuits in the figures that follow, the virtualground is labeled “VCC/2.” This voltage comes from eitherthe TLE2426 rail-splitter or the circuit in Figure 1. If thelatter is used, the overall number of op amps in the designis increased by one.Passive components VCC VCCR1–R3VCC /2 R2C1The majority of the circuits given in this series have beendesigned with standard capacitor values and 5% resistors.Capacitors should be of good quality with 5% tolerancewherever possible. Component variations will affect theoperation of these circuits, usually causing some degree ofripple or increased roll-off as the balance of Chebyshevand Butterworth characteristics is disturbed. These shouldbe slight—almost imperceptible.C2Continued on next page39Analog Applications JournalNovember 2000Analog and Mixed-Signal Products
Amplifiers: Op AmpsTexas Instruments IncorporatedContinued from previous pageSpeech filterHuman speech most frequently occupies an audio spectrumof 300 Hz to 3 kHz. There is a requirement, especially inphones, to limit the frequency response to this range.Frequently, this function is performed with a DSP chip.DSP chips, however, require an anti-aliasing filter to rejecthigh-frequency components. The anti-aliasing filter requiresan op amp. Since there is already an op amp anyway, whynot consider adding a second and doing the entire functionwith analog components? An additional op amp (plus onefor the half-supply reference) can perform the filteringwith no aliasing problems, freeing the DSP for other tasks.Figure 2 shows a single-supply phone speech filter intwo op amps, five capacitors, and four resistors. This circuitis designed to be low-power and compact, and is scalablefor even lower power consumption.Figure 2. Single-supply phone speech filterR2 68 kΩC3 200 pF VCCC1 10 nFC2 10 nFINR1130 kΩ1 3 VCC5R3 220 kΩ4-–2R4 220 kΩ1 35–TLV2221C4100 pFVCC /2C5 1 µF42OUTTLV2221VCC /2Figure 3. Second-order circuitR1 68 kΩR3 27 kΩ VCCC1 10 nFC2 10 nFIN3 2-–R275 kΩ VCC4111C3 10 nFC4 10 nFTLV2464R4180 kΩ11TLV2464C7 3.3 nF VCC10 9 VCC48–C61 nF7VCC /2C5 1.2 nFR6 33 kΩ4–VCC /2R5 43 kΩ5 611R7 39 kΩR8 27 kΩTLV246412 13414–C8470 pFVCC /211C9 1 µFOUTTLV2464VCC /240Analog and Mixed-Signal ProductsNovember 2000Analog Applications Journal
Amplifiers: Op AmpsTexas Instruments IncorporatedFigure 3 shows a second-order circuit.Nearby out-of-band signals, such as 60-Hzhum, are not rejected very well. This maybe acceptable in cellular telephone headsets, but may not be for large switchboardconsoles. A fourth-order speech filter,although more complex, can be implemented in a single quad op amp (with anexternal VCC/2 reference).The response of the second- and fourthorder speech filters is shown in Figure 4.The 60-Hz rejection of the fourth-orderfilter is greater than 40 dB, while that ofthe second-order filter is about 15 dB.Both filters have been designed to have animperceptible 0.5-dB roll-off at 300 Hz and3 kHz.Figure 4. Response of second- and fourth-order speech filters10Output (dB)0-202nd order-4010 Hz4th order100 Hz1.0 kHzFrequency10 kHz100 kHzCrossover filterInside any multiple-speaker cabinet is anarray of inductors and capacitors thatdirects different frequency ranges to each speaker. Theinductors and capacitors, however, have to handle the fulloutput power of the power amplifier. Inductors for low frequencies in particular tend to be large, heavy, and expensive.Another disadvantage of the inductor and capacitorcrossover network is that it is a first-order network. Athigh volume, destructive levels of audio can be transferredto speakers not designed to handle a given frequencyrange. If a speaker is incapable of moving in response tostimulation, the only way the energy can be dissipated isin heat. The heat can build up and burn out the voice coil.A number of audiophiles are beginning to talk about thevirtues of bi-amplification, or even multiple amplification.In this technique, the crossover network is applied to theaudio source before amplification instead of after it. Eachspeaker in the cabinet is then driven by a separate amplifierstage that is optimized for the speaker.The primary reason for bi-amplification or multipleamplification is that human hearing is not equally sensitiveto all frequencies. The human ear is relatively insensitiveto low and high frequencies, but audio amplifiers aredesigned to have flat response (constant power) acrossContinued on next pageFigure 5. Crossover networkR2 200 kΩC3 4 nFC2 2 nF VCCC1 4.7 µFR1 200 kΩIN2–34 VCCU1ATLCO741R3 200 kΩR4 200 kΩ –C41 nFVCC /2 VCC9–104R7 200 kΩU1CTLCO748C7 1 nFC8 1 nFC5 4.7 µFBASS11 VCC12 13 VCC /27VCC /2R6 200 kΩR5 200 kΩU1BTLCO74–11C6 2 nF5 64414–11R8800 kΩU1DTLCO74C9 4.7 µFTREBLE11VCC /241Analog Applications JournalNovember 2000Analog and Mixed-Signal Products
Amplifiers: Op AmpsTexas Instruments IncorporatedContinued from previous page Because there is not much high-frequency spectralcontent but a constant level of white noise throughoutthe spectrum, a lot of amplification in this range willincrease audio perception of noise at high frequencies.The crossover network shown in Figure 5 routes low(bass) frequencies to a woofer, and midrange and highfrequencies (treble) to a tweeter. This is a very commonapplication, because many speaker cabinets contain only awoofer and tweeter.A crossover frequency of 400 Hz has been selected,which should suffice for the majority of applications. Thefilter sections are third-order, which will minimize energyto the wrong speakers.This circuit was designed to be very easy to build. Theop amp sections can be interchanged, of course. There areonly two capacitor values and one resistor value! Three4.7-µF electrolytic capacitors are used for decoupling; theyare sufficiently large to insure that they have no effect onthe frequencies of interest. The 2-nF and 4-nF capacitorscan be formed by connecting 1-nF capacitors in parallel.R8, the 800-kΩ resistor, can be made by connecting four200-kΩ resistors in series.A subwoofer section can be added to the crossovernetwork in Figure 5 to enhance subsonic frequencies (seeFigure 6).Figure 6 shows a true subwoofer circuit. It will not workwith 6- or 8-inch “subwoofers.” It is for 15- to 18-inchwoofers in a good infinite-baffle, bass-reflex, or foldedhorn enclosure, driven by an amplifier with at least 100watts. Most of the gain is below the range of human hearing;and these frequencies, when used in recorded material,are designed to be felt, not heard. The filter is designed togive 20 dB of gain to 13 Hz, rolling off to unity gain atabout 40 Hz. There is no broadcast material in the UnitedStates that extends below 50 Hz; even most audio CDs donot go below 20 Hz. This will prove most useful for hometheater applications, which play material that does havesubsonic audio content. Examples are “Earthquake” andthe dinosaur stomp in “Jurassic Park.”The combined response of the three circuits is shown inFigure 7. One active crossover network will be requiredper channel, with the exception of the subwoofer crossover.the audio band. The result is that the listener uses tonecontrols or graphic equalizers to compensate for the humanhearing curve to make the sound pleasing. This compensatesto some degree for the differential power requirements,but most tone controls are limited to 20 dB—not nearlyenough to make up for human hearing sensitivity at reallylow or really high frequencies. Tone control characteristicsare linear; even if they were devised with more gain, theystill would not follow the human hearing curve. Graphicequalizers are limited to discrete frequency values andproduce an unpleasant degree of ripple when several adjacent controls are turned up.Human hearing is not sensitive to low frequencies, somore power is required to reproduce them at a level thatcan be heard. A high-power class “B” amplifier can drive alarge bass woofer. Crossover notch distortion from theclass “B” topology is inaudible at these frequencies, andthe efficiency of the amplifier allows it to generate a lot ofpower with relatively little heat.Hearing is most sensitive in the midrange frequencies,for which the best amplifier is a relatively low-power, verylow-distortion, class “A” amplifier. As little as 10 watts canproduce deafeningly loud audio in this frequency range.But what about high frequencies? There are purists whowould insist that high frequencies should be amplified thesame way as low, so that the human ear could discernthem as well. While this is technically true, there are somereasons why it is not desirable: The energy required to accelerate a speaker cone to agiven displacement at 20 kHz is 1000 times that requiredto accelerate a speaker cone to that displacement at 20Hz. There are some piezo- and ceramic-type tweetersthat can produce high output levels, but they requirecorrespondingly high amounts of energy to drive. Theseoutput levels are enough to shatter glass and eardrums. The spectral content of almost all music is weightedwith a “pink” characteristic. Simply stated, there ismuch more middle- and low-frequency content thanhigh-frequency content.Figure 6. Subwoofer circuitC2 12 nFR2 750 kΩ VCCC1 4.7 µFR1240 kΩ2–3IN4U1ATLCO741 VCCR3R491 kΩ27 kΩ VCC /2C447 nF6–5R5 22 kΩ11C3820 nFU1BTLCO7447 VCC /2C5 4.7 µFVO11VCC /242Analog and Mixed-Signal ProductsNovember 2000Analog Applications Journal
Amplifiers: Op AmpsTexas Instruments IncorporatedThere is no stereo separation of low bass frequencies, and either channel (or both) can beused to drive the subwoofer circuit (sum intoan inverting input with a second C1 and R1).Figure 7. Combined filter response40Tone controlReferences1. Audio Circuits Using the NE5532/54,Philips Semiconductor, Oct. 1984.2. Audio Radio Handbook, NationalSemiconductor, 1980.3. Op Amp Circuit Collection, NationalSemiconductor AN-031.Output (dB)20SubwooferTrebleBass0-20-401.0 Hz10 Hz100 Hz1.0 kHzFrequency10 kHz100 kHzFigure 8. Tone control circuitC2 .015 µFR1R2 100 kΩR310 kΩ10 kΩIncreaseDecreaseBassC1IN 4.7 µFTrebleIncreaseDecrease VCCVCC /28 U1A3 TLC2272 C5 4.7 µF1 2–OUT4C3.015 µFR5 10 kΩC4.015 µFFigure 9. Circuit response with pots at the extremes2010Output (dB)One rather unusual op amp circuit is the tonecontrol circuit shown in Figure 8. It bearssome superficial resemblance to the twin Tcircuit configuration, but it is not a twin Ttopology. It is actually a hybrid of one-pole,low-pass, and high-pass circuits with gain andattenuation.The midrange frequency for the tone adjustments is 1 kHz. It gives about 20 dB of boostand cut for bass and treble. The circuit is aminimum-component solution that limits cost.This circuit, unlike other similar circuits, useslinear instead of logarithmic pots. Two different potentiometer values are unavoidable, butthe capacitors are the same value except forthe coupling capacitor. The ideal capacitorvalue is 0.016 µF, which is an E-24 value; sothe more common E-12 value of 0.015 µF isused instead. Even that value is a bit odd, butit is easier to find an oddball capacitor valuethan an oddball potentiometer value.The plots in Figure 9 show the response ofthe circuit with the pots at the extremes andat the 1/4 and 3/4 positions. The middle position,although not shown, is flat to within a few millidecibels. The compromises involved in reducingcircuit cost and in using linear potentiometerslead to some slight nonlinearities. The 1/4 and3/4 positions are not exactly 10 and –10 dB,meaning that the pots are most sensitivetowards the end of their travel. This may bepreferable to the listener, giving a fine adjustment near the middle of the potentiometers andmore rapid adjustment near the extreme positions. The center frequency shifts slightly, butthis should be inaudible. The frequenciesnearer the midrange are adjusted more rapidlythan the frequency extremes, which also maybe more desirable to the listener. A tone controlis not a precision audio circuit, and thereforethe listener may prefer these compromises.0-10-2010 HzRelated Web sites100 Hz1.0 kHzFrequency10 kHz100 eplace device with tlc074, tlc2272, tle2426, tlv2221, ortlv2464www.ti.com/audio43Analog Applications JournalNovember 2000Analog and Mixed-Signal Products
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An audio circuit collection, Part 1 Introduction This is the first of two articles on audio circuits. New oper-ational amplifiers from Texas Instruments have excellent audio performance and can be used in high-performance applications. There have been many collections of op amp audio circuits in the past, but all of them focus on split-supply .
765 S MEDIA TECHNOLOGY Designation Properties Page Audio Audio cables with braided shielding 766 Audio Audio cables, multicore with braided shielding 767 Audio Audio cables with foil shielding, single pair 768 Audio Audio cables, multipaired with foil shielding 769 Audio Audio cables, multipaired, spirally screened pairs and overall braided shielding 770 Audio Digital audio cables AES/EBU .
Connect to the audio connector of a camera if the camera supports audio recording. Note: To make a video backup with audio, make sure the camera which supports the audio function is connected to the video-in channel and audio-in channel. For example, the audio data from audio CH1 will be recorded with the video data from video CH1. 3) AUDIO OUT
headphone jack 4 Figure 4: Audio power amplifier circuit. 4 Audio Amp Circuit the circuit used to implement Figure 3 is rather complicated, and we’ll build it up in two pieces. The first piece to build is the audio amplifier. The audio amplifier schematic is shown in Figure
circuit protection component which cars he a fusible link, a fuse, or a circuit breaker. Then the circuit goes to the circuit controller which can be a switch or a relay. From the circuit controller the circuit goes into the circuit load. The circuit load can be one light or many lights in parallel, an electric motor or a solenoid.
Series Circuit A series circuit is a closed circuit in which the current follows one path, as opposed to a parallel circuit where the circuit is divided into two or more paths. In a series circuit, the current through each load is the same and the total voltage across the circuit is the sum of the voltages across each load. NOTE: TinkerCAD has an Autosave system.
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To configure 4/5.1/7.1-channel audio, you have to retask either the Line in or Mic in jack to be Side speaker out through the audio driver. 1-1 Configuring 2/4/5.1/7.1-Channel Audio The motherboard provides five audio jacks on the back panel which support 2/4/5.1/7.1-channel (Note) audio. The picture to the right shows the default audio jack
Abrasive water jet machining (AWJM) process is one of the most recent developed non-traditional machining processes used for machining of composite materials. In AWJM process, machining of work piece material takes place when a high speed water jet mixed with abrasives impinges on it. This process is suitable for heat sensitive materials especially composites because it produces almost no heat .
