Battery-powered Headphone Amplifier

Description:

    

   Some lovers of High Fidelity headphone listening prefer the use of battery powered headphone amplifiers, not only for portable units but also for home "table" applications. This design is intended to fulfil their needs and its topology is derived from the Portable Headphone Amplifier featuring an NPN/PNP compound pair emitter follower output stage. An improved output driving capability is gained by making this a push-pull Class-B arrangement. Output power can reach 100mW RMS into a 16 Ohm load at 6V supply with low standing and mean current consumption, allowing long battery duration. The single voltage gain stage allows the easy implementation of a shunt-feedback circuitry giving excellent frequency stability.

Battery-powered Headphone Amplifier Circuit diagram

     For a Stereo version of this circuit, all parts must be doubled except P1, SW1, J2 and B1.  Before setting quiescent current rotate the volume control P1 to the minimum, Trimmer R6 to maximum resistance and Trimmer R3 to about the middle of its travel.  Connect a suitable headphone set or, better, a 33 Ohm 1/2W resistor to the amplifier output.  Switch on the supply and measure the battery voltage with a Multimeter set to about 10Vdc fsd.  Connect the Multimeter across the positive end of C4 and the negative ground.  Rotate R3 in order to read on the Multimeter display exactly half of the battery voltage previously measured.  Switch off the supply, disconnect the Multimeter and reconnect it, set to measure about 10mA fsd, in series to the positive supply of the amplifier.  Switch on the supply and rotate R6 slowly until a reading of about 3mA is displayed.  Check again the voltage at the positive end of C4 and readjust R3 if necessary.  Wait about 15 minutes, watch if the current is varying and readjust if necessary.  Those lucky enough to reach an oscilloscope and a 1KHz sine wave generator, can drive the amplifier to the maximum output power and adjust R3 in order to obtain a symmetrical clipping of the sine wave displayed. 

Technical data:

Output power (1KHz sinewave):

16 Ohm: 100mW RMS

32 Ohm: 60mW RMS

64 Ohm: 35mW RMS

100 Ohm: 22.5mW RMS

300 Ohm: 8.5mW RMS

Sensitivity: 160mV input for 1V RMS output into 32 Ohm load (31mW)

200mV input for 1.27V RMS output into 32 Ohm load (50mW)

Frequency response @ 1V RMS:

flat from 45Hz to 20KHz, -1dB @ 35Hz, -2dB @ 24Hz

Total harmonic distortion into 16 Ohm load @ 1KHz:

1V RMS (62mW) 0.015% 1.27V RMS (onset of clipping, 100mW) 0.04%

Total harmonic distortion into 16 Ohm load @ 10KHz:

1V RMS (62mW) 0.05% 1.27V RMS (onset of clipping, 100mW) 0.1%

Unconditionally stable on capacitive loads

Class-A Headphone Amplifier

     This circuit is derived from the Portable Headphone Amplifier featuring an NPN/PNP compound pair emitter follower output stage. An improved output driving capability is gained by making this a push-pull Class-A arrangement. Output power can reach 427mW RMS into a 32 Ohm load at a fixed standing current of 100mA. The single voltage gain stage allows the easy implementation of a shunt-feedback circuitry giving excellent frequency stability.

     The above mentioned shunt-feedback configuration also allows the easy addition of frequency dependent networks in order to obtain an useful, unobtrusive, switchable Tilt control (optional). When SW1 is set in the first position a gentle, shelving bass lift and treble cut is obtained. The central position of SW1 allows a flat frequency response, whereas the third position of this switch enables a shelving treble lift and bass cut.

     Before setting quiescent current rotate the volume control P1 to the minimum, Trimmer R6 to zero resistance and Trimmer R3 to about the middle of its travel. 

Connect a suitable headphone set or, better, a 33 Ohm 1/2W resistor to the amplifier output. 

Connect a Multimeter, set to measure about 10Vdc fsd, across the positive end of C5 and the negative ground.  Switch on the supply and rotate R3 in order to read about 7.7-7.8V on the Multimeter display. 

Switch off the supply, disconnect the Multimeter and reconnect it, set to measure at least 200mA fsd, in series to the positive supply of the amplifier.  Switch on the supply and rotate R6 slowly until a reading of about 100mA is displayed.  Check again the voltage at the positive end of C5 and readjust R3 if necessary.  Wait about 15 minutes, watch if the current is varying and readjust if necessary.

P1          : 22K  Dual gang Log Potentiometer 
R1          : 15K 
R2          : 220K
R3          : 100K
R4          : 33K 
R5          : 68K 
R6          : 50K 
R7          : 10K 
R8,R9       : 47K 
R10,R11     : 2R2 
R12         : 4K7
R13         : 4R7
R14         : 1K2
R15,R18     : 330K
R16         : 680K
R17,R19     : 220K
R20,R21     : 22K
C1,C2,C3,C4 : 10µF/25V 
C5,C7       : 220µF/25V
C6,C11      : 100nF
C8          : 2200µF/25V
C9,C12      : 1nF
C10         : 470pF
C13         : 15nF
D1          : LED
D2,D3       : 1N4002 
Q1,Q2       : BC550C 
Q3          : BC560C  
Q4          : BD136   
Q5          : BD135   
IC1         : 7815
T1          : 15CT/5VA Mains transformer
SW1         : 4 poles 3 ways rotary Switch 
SW2         : SPST slide or toggle Switch

Mobile Car Stereo Player TDA1554

     Using a mobile phone while driving is dangerous. It is also against the law. However, you can use your mobile phone as a powerful music player with the help of a stereo power amplifier. This does away with the need of a sophisticated in-dash car music system. Most mobile phones have a music player that offers a number of features including preset/manual sound equalisers. They have standard 3.5mm stereo sockets that allow music to be played through standard stereo headphones/sound amplifiers. Nokia 2700 classic is an example.


Mobile Car Stereo Player Circuit Diagram

     A car audio amplifier with 3.5mm socket can be designed and simply connected to the mobile phone output via a shielded cable with suitable connectors/jacks (readymade 3.5mm male-to-male connector cable is a good alternative). Fig. 1 shows the circuit of car stereo player. It is built around popular single-chip audio power amplifier TDA1554Q (IC1). The TDA1554Q is an integrated class-B power amplifier in a 17-lead single-in-line (SIL) plastic power package.

     IC TDA1554Q contains four 11W identical amplifiers with differential input stages (two inverting and two non-inverting) and can be used for single-ended or bridge applications. The gain of each amplifier is fixed at 20 dB. Here it is configured as two 22W stereo bridge amplifiers. The amplifier is powered from the 12V car battery through RCA socket J2. Diode D1 protects against wrong-polarity connection. LED1 indicates the power status.

Stereo Jack :



(a) 3.5mm stereo socket and (b) 3.5mm Stereo Jack

     Connect stereo sound signal from the 3.5mm headset socket of the mobile phone to audio input socket J1. When you play the music from your mobile, IC1 amplifies the input. The output of IC1 is fed to speakers LS1 and LS2 fitted at a suitable place in your car. Electrolytic capacitor C5 connected between pin 4 of IC1 and GND improves the supply-voltage ripple rejection. Components R2 and C4 connected at mute/standby pin (pin 14) of IC1 eliminate the switch on/off plop. The circuit is quite compact. A good-quality heat-sink assembly is crucial for IC1. Fig. 2 shows the stereo socket and stereo jack.

Proposed enclosure

     Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Small dimensions of the power amplifier make it suitable for being enclosed in a plastic (ABS) case with vent holes. Signal input socket, speaker output terminals, on/off switch, indicator, fuse holder and power supply socket are best located on the front panel of the enclosure as shown in Fig. 3.
Author : T.K. Hareendran - Copyright : EFY

Stereo Amplifier Circuit Diagram with TDA7052

BTL Stereo Amplifier Circuit Diagram with TDA7052

Amplifier Circuit 2W

Amplifier description:

     This amplifier was designed to be self-contained in a small loudspeaker box. It can be feed by Walkman, Mini-Disc, iPod and CD players, computers and similar devices fitted with line or headphone output. Of course, in most cases you will have to make two boxes to obtain stereo. The circuit was deliberately designed using no ICs and in a rather old-fashioned manner in order to obtain good harmonic distortion behavior and to avoid hard to find components. The amplifier(s) can be conveniently supplied by a 12V wall plug-in adapter.Closing SW1 a bass-boost is provided but, at the same time, volume control must be increased to compensate for power loss at higher frequencies. In use, R9 should be carefully adjusted to provide minimal audible signal cross-over distortion consistent with minimal measured quiescent current consumption; a good compromise is to set the quiescent current at about 10-15 mA. To measure this current, wire a DC current meter temporarily in series with the collector of Q3.

Amplifier circuit diagram:

Amplifier circuit partlist:

P1----------10K

R1----------33K

R2----------33K

R3----------33R

R4----------15K

R5----------1K

R6----------1K

R7----------680R

R8----------120R-1/2W

R9----------100R-1/2W Trimmer Cermet

C1 ----------10µF-63V

C2 ----------10µF-63V

C3-----------100µF-25V

C4-----------470µF-25V

C5-----------47pF-63V

C7-----------470µF-25V

C6-----------220nF-63V

C8-----------1000µF-25V

D1-----------1N4148

Q1-----------BC560C

Q2-----------BC337

Q3-----------TIP31A

Q4-----------TIP32A

SW1---------SPST switch

SPKR--------3-5 Watt Loudspeaker

Mini Portable Guitar Amplifier

Guitar Circuit description:

     This small amplifier was intended to be used in conjunction with an electric guitar to do some low power monitoring, mainly for practice, either via an incorporated small loudspeaker or headphones. The complete circuit, loudspeaker, batteries, input and output jacks can be encased in a small box having the dimensions of a packet of cigarettes, or it could be fitted also into a real packet of cigarettes like some ready-made units available on the market. This design can be used in three different ways: Loudspeaker amplifier: when powered by a 9V alkaline battery it can deliver about 1.5W peak output power to the incorporated loudspeaker.  Headphone amplifier or low power loudspeaker amplifier: when powered by a 3V battery (2x1.5V cells) it can drive any headphone set type at a satisfactory output power level or deliver to the incorporated loudspeaker about 60mW of output power. This configuration is useful for saving battery costs. Fuzz-box: when powered by a 3V battery (2x1.5V cells) and having its output connected to a guitar amplifier input the circuit will behave as a good Fuzz-box, showing an output square wave with marked rounded corners, typical of valve-circuits output when driven into saturation. 

Guitar amplifier circuit diagram:

Guitar amplifier partlist:

• R1__________22K 1/4W Resistor
• C1__________10µF 25V Electrolytic Capacitor
• C2__________100nF 63V Polyester or Ceramic Capacitor
• C3__________220µF 25V Electrolytic Capacitor
• IC1_________TDA7052 Audio power amplifier IC
• J1,J2_______6.3mm Stereo Jack sockets (switched)
• SPKR_______8 Ohm Loudspeaker (See Notes)
• B1_________9V PP3 Battery or 3V Battery (2 x 1.5V AA, AAA Cells in series etc.)
• Clip for PP3 Battery or socket for 2 x 1.5V AA or AAA Cells

Technical data:

• Max output power: 1.5W @ 9V supply - 8 Ohm load; 60mW @ 3V supply - 8 Ohm load
• Frequency response: Flat from 20Hz to 20kHz
• Total harmonic distortion @ 100mW output: 0.2%
• Max input voltage @ 3V supply: 8mV RMS
• Minimum input voltage for Fuzz-box operation: 18mV RMS @ 3V supply
• Current consumption @ 400mW and 9V supply: 200mA
• Current consumption @ 250mW and 9V supply: 150mA
• Current consumption @ 60mW and 3V supply: 80mA
• Quiescent current consumption: 6mA @ 9V, 4mA @ 3V supply
• Fuzz-box current consumption: 3mA @ 3V supply

Crowbar Speaker Protection

Description

Crowbar circuits are so-called because their operation is the equivalent of dropping a crowbar (large steel digging implement) across the terminals. It is only ever used as a last resort, and can only be used where the attached circuit is properly fused or incorporates other protective measures.

A crowbar circuit is potentially destructive - if the circuitry only has a minor fault, it will be a major fault by the time a crowbar has done its job. It is not uncommon for the crowbar circuit to be destroyed as well - the purpose is to protect the device(s) attached to the circuit - in this case, a loudspeaker.

There's really nothing to it. A resistor / capacitor circuit isolates the trigger circuit from normal AC signals. Should there be enough DC to activate the DIAC trigger, the cap is discharged into the gate of the TRIAC, which instantly turns on ... hard. A TRIAC has two basic states, on and off. The in-between state exists, but is so fast that it can be ignored for all intents and purposes.

The BR100 DIAC (or the equivalent DB3 from ST Microelectronics) is rated for a breakdown voltage of between 28 and 36V - these are not precision devices. Needless to say, using the circuit with supply voltages less than around 40V is not recommended, as you will have a false sense of security. The supply voltage must be higher than the breakdown voltage of the DIAC, or it cannot conduct. Zeners cannot be used as a substitute for lower voltages - a DIAC has a negative impedance characteristic, so when it conducts, it will dump almost the full charge in C1 into the gate of the TRIAC. This is essential to make sure the TRIAC is switched into conduction.

The TRIAC is a common type, and may be substituted if you know the specifications. It's rated at 12A, but the peak current (non-repetitive) is 95A, and it only needs to sustain that until the fuse (or an output transistor) blows. A heatsink is preferred, but there is a good chance that the TRIAC will blow up if it has to protect your speakers, so it may not matter too much. The 0.47 ohm resistor is simply to ensure that the short circuit isn't absolute. This will limit the current a little, and increases the chance that the TRIAC will survive (albeit marginally). Feel free to use a BT139 if it makes you feel better - these are rated at 16A continuous, and 140A non-repetitive peak current.

The peak short circuit current will typically be about 90A for a ±60V supply, allowing ~0.2 ohms for wiring resistance and the intrinsic internal resistance of the TRIAC, plus the equivalent series resistance of the filter capacitors. That's a seriously high current, and it will do an injury to anything that's part of the discharge path. Such high currents are not advised for filter caps either, but being non-repetitive they will almost certainly survive.

Construction & Use

Apart from the obvious requirement that you don't make any mistakes, construction is not critical. Wiring needs to be of a reasonable gauge, and should be tied down with cable ties or similar. C1 must be polyester. While a non-polarised electrolytic would seem to be acceptable, the circuit will operate if the capacitor should dry out over the years. This means it will lose capacitance, and at some point, the crowbar may operate on normal programme material. This would not be good, as it will blow up your amplifier!

Make sure that all connections are secure and well soldered. Remember that this is the last chance for your speakers, so it needs to be able to remain inactive for years and years - hopefully it will never happen. The circuit doesn't have to be mounted in the amplifier chassis - it can be installed in your speaker cabinet. Nothing gets hot unless it operates, at which point no-one really cares - it just has to save the speakers from destruction once to have been worthwhile.

Remember that the crowbar circuit absolutely must never be allowed to operate with any normal signal. A perfectly good amplifier that triggers the circuit because of a high-level bass signal (for example) will very likely be seriously damaged if the crowbar activates. To verify that no signal can trigger it, you may want to (temporarily) use a small lamp in place of R2, and drive the amp to maximum power with bass-heavy material.

A speaker does not need to be connected. If the lamp flashes, your amp would have been damaged. If this occurs, you may want to increase the value of C1. Note that bipolar electrolytics should never be used for C1, because they can dry out and lose capacitance as they age. This could cause the circuit to false-trigger.

Origianl article sourse learningelectronics.net