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2010-11-13T00:23:00.001-08:00

Amplifier Timer

2009-11-14T03:48:00.000-08:00

Turns-off your amplifier when idle for 15 minutes. Fed by amplifier tape-output

Amplifier Timer schematics

Parts:

R1,R8___________1K 1/4W Resistors
R2,R3___________4K7 1/4W Resistors
R4_____________22K 1/4W Resistor
R5______________4M7 1/4W Resistor
R6,R9__________10K 1/4W Resistors
R7______________1M5 1/4W Resistor
R10___________100K 1/4W Resistor
R11____________15K 1/4W Resistor
R12____________10M 1/4W Resistor
R13_____________1M 1/4W Resistor
R14_____________8K2 1/4W Resistor
R15_____________1K8 1/4W Resistor

C1____________470µF 25V Electrolytic Capacitor
C2,C3,C6______100nF 63V Polyester Capacitors
C4,C5__________10µF 25V Electrolytic Capacitors

D1_____Diode bridge 100V 1A
D2,D7________1N4002 100V 1A Diodes
D3__________Red LED 5mm.
D4_______Yellow LED 5mm.
D5,D6________1N4148 75V 150mA Diodes

IC1___________78L12 12V 100mA Voltage regulator IC
IC2___________LM358 Low Power Dual Op-amp
IC3____________4060 14 stage ripple counter and oscillator IC

Q1____________BC557 45V 100mA PNP Transistor
Q2____________BC337 45V 800mA NPN Transistor

J1______________RCA audio input socket

P1_____________SPST Mains suited Pushbutton
P2_____________SPST Pushbutton

T1_____________220V Primary, 12V Secondary 3VA Mains transformer

RL1___________10.5V 270 Ohm Relay with SPST 5A 220V switch

PL1____________Male Mains plug

SK1__________Female Mains socket

Circuit operation:

This circuit turns-off an amplifier or any other device when a low level audio signal fed to its input is absent for 15 minutes at least.
Pushing P1 the device is switched-on feeding any appliance connected to SK1. Input audio signal is boosted and squared by IC2A & IC2B and monitored by LED D4. When D4 illuminates, albeit for a very short peak, IC3 is reset and restarts its counting. Pin 2 of IC3 remains in the low state, the two transistors are on and the relay operates. When, after a 15 minutes delay, no signal appeared at the input, IC3 ends its counting and pin 2 goes high. Q1 & Q2 stop conducting and the relay switches-off. The device is thus completely off as also are the appliances connected to SK1. C5 & R9 reset IC3 at power-on. P2 allows switch-off at any moment.

Notes:
Simply connect left or right channel tape output of your amplifier to J1.
You can employ two RCA input sockets wired in parallel to allow pick-up audio signals from both stereo channels.
The delay time can be varied changing R13 and/or C6 values.
Needing to operate a device not supplied by power mains, use a double pole relay switch, connecting the second pole switch in series to the device supply.

Amplifier Timer from http://www.redcircuits.com

Amplified Ear

2009-11-14T03:42:00.000-08:00

Useful to listen in faint sounds. 1.5V Battery operation

Parts:

P1_____________22K Log. Potentiometer (see Notes)

R1,R9__________10K 1/4W Resistors
R2______________1M 1/4W Resistor
R3______________4K7 1/4W Resistor
R4,R7_________100K 1/4W Resistor
R5______________3K9 1/4W Resistor
R6______________1K5 1/4W Resistor
R8_____________100R 1/4W Resistor

C1,C2_________100nF 63V Polyester or Ceramic Capacitors
C3,C6___________1µF 63V Polyester or Ceramic Capacitors
C4_____________10µF 25V Electrolytic Capacitor
C5____________470µF 25V Electrolytic Capacitor

D1___________1N4148 75V 150mA Diode

Q1,Q2,Q3,_____BC547 45V 100mA NPN Transistors
Q4____________BC337 45V 800mA NPN Transistor

MIC1__________Miniature electret microphone

SW1____________SPST Switch (Ganged with P1)

J1_____________Stereo 3mm. Jack socket

B1_____________1.5V Battery (AA or AAA cell etc.)

Device purpose:
This circuit, connected to 32 Ohm impedance mini-earphones, can detect very remote sounds. Useful for theatre, cinema and lecture goers: every word will be clearly heard. You can also listen to your television set at a very low volume, avoiding to bother relatives and neighbors. Even if you have a faultless hearing, you may discover unexpected sounds using this device: a remote bird twittering will seem very close to you.

Circuit operation:
The heart of the circuit is a constant-volume control amplifier. All the signals picked-up by the microphone are amplified at a constant level of about 1 Volt peak to peak. In this manner very low amplitude audio signals are highly amplified and high amplitude ones are limited. This operation is accomplished by Q3, modifying the bias of Q1 (hence its AC gain) by means of R2.
A noteworthy feature of this circuit is 1.5V battery operation.
Typical current drawing: 7.5mA.

Notes:
Due to the constant-volume control, some users may consider P1 volume control unnecessary. In most cases it can be omitted, connecting C6 to C3. In this case use a SPST slider or toggle switch as SW1.
Please note the stereo output Jack socket (J1) connections: only the two inner connections are used, leaving open the external one. In this way the two earpieces are wired in series, allowing mono operation and optimum load impedance to Q4 (64 Ohm).
Using suitable miniature components, this circuit can be enclosed in a very small box, provided by a clip and hanged on one's clothes or slipped into a pocket.
Gary Pechon from Canada reported that the Amplified Ear is so sensitive that he can hear a whisper 7 meters across the room.
He hooked a small relay coil to the input and was able to locate power lines in his wall. He was also able to hear the neighbor's stereo perfectly: he could pick up the signals sent to the speaker voice coil through a plaster wall.
Gary suggests that this circuit could make also a good electronic stethoscope.

Amplified Ear from http://www.redcircuits.com

Telephone call Voice Changer

2009-11-14T03:39:00.000-08:00

Voice manipulation device specially intended for props 9V Battery operation

Parts:

P1______________10K Log. Potentiometer

R1,R10__________10K 1/4W Resistors
R2_______________1K 1/4W Resistor
R3______________50K 1/2W Trimmer Cermet or Carbon
R4,R6,R7,R14___100K 1/4W Resistors
R5______________47K 1/4W Resistor
R8______________68K 1/4W Resistor
R9_______________2K2 1/2W Trimmer Cermet or Carbon
R11_____________33K 1/4W Resistor
R12_____________18K 1/4W Resistor
R13_____________15K 1/4W Resistor

C1,C2,C3,C8,C9_100nF 63V Polyester Capacitors
C4______________10µF 25V Electrolytic Capacitor
C5_____________220nF 63V Polyester Capacitor (Optional, see Notes)
C6_______________4n7 63V Polyester Capacitor
C7______________10nF 63V Polyester Capacitor
C10____________220µF 25V Electrolytic Capacitor

IC1___________LM358 Low Power Dual Op-amp
IC2_________TDA7052 Audio power amplifier IC

MIC1__________Miniature electret microphone

SPKR______________8 Ohm Small Loudspeaker

SW1____________DPDT Toggle or Slide Switch
SW2,SW3________SPST Toggle or Slide Switches

J1____________6.3mm or 3mm Mono Jack socket

B1_______________9V PP3 Battery (See Notes)

Clip for PP3 Battery

Comments:
Although this kind of voice effect can be obtained by means of some audio computer programs, a few correspondents required a stand-alone device, featuring microphone input and line or loudspeaker outputs.
This design fulfills these requirements by means of a variable gain microphone preamplifier built around IC1A, a variable steep Wien-bridge pass-band filter centered at about 1KHz provided by IC1B and an audio amplifier chip (IC2) driving the loudspeaker.

Notes:
The pass-band filter can be bypassed by means of SW1A and B: in this case, a non-manipulated microphone signal will be directly available at the line or loudspeaker outputs after some amplification through IC1A.
R3 sets the gain of the microphone preamp. Besides setting the microphone gain, this control can be of some utility in adding some amount of distortion to the signal, thus allowing a more realistic imitation of a telephone call voice.
R9 is the steep control of the pass-band filter. It should be used with care, in order to avoid excessive ringing when filter steepness is approaching maximum value.
P1 is the volume control and SW2 will switch off amplifier and loudspeaker if desired.
C5 is optional: it will produce a further band reduction. Some people think the resulting effect is more realistic if this capacitor is added.
If the use of an external, moving-coil microphone is required, R1 must be omitted, thus fitting a suitable input jack.
This circuit was intended to be powered by a 9V PP3 battery, but any dc power supply in the 6 - 12V range can be used successfully.

Telephone call Voice Changer from http://www.redcircuits.com/

Portable 9V Headphone Amplifier

2009-11-14T03:35:00.000-08:00

Parts:

P1______________22K Dual gang Log Potentiometer

R1,R5___________18K 1/4W Resistors
R2,R3,R4,R6_____68K 1/4W Resistors

C1,C2,C6_________4µ7 25V Electrolytic Capacitors
C3,C7___________22pF 50V Ceramic Capacitors
C4,C5,C8_______220µF 25V Electrolytic Capacitors

IC1__________NE5532 Low noise Dual Op-amp

J1____________3.5mm Stereo Jack Socket

SW1____________SPST Slide or toggle switch

B1_______________9V PP3 Alkaline battery

Clip for PP3 Battery
Comments:
After several requests by correspondents, the decision of designing a 9V powered Headphone Amplifier was finally taken. The main requirement was to power the circuit by means of a common, PP3 (transistor radio) alkaline battery.
So, implementing a low current drawing circuit was absolutely necessary, though preserving a High Quality performance.
The appearance of the 5534 low-noise op-amp at a reasonable price was much appreciated by audio designers. It is now difficult or impossible to design a discrete stage that has the performance of the 5534 without quite unacceptable complexity. 5534 op-amps are now available from several sources, in a conventional 8-pin d.i.l. format. This version is internally compensated for gains of three or more, but requires a small external capacitor (5-15pF) for unity-gain stability. The 5532 is a very convenient package of two 5534s in one 8-pin device with internal unity-gain compensation, as there are no spare pins.
The 5534/2 is a low-distortion, low-noise device, having also the ability to drive low-impedance loads to a full voltage swing while maintaining low distortion. Furthermore, it is fully output short-circuit proof.
Therefore, this circuit was implemented with a single 5532 chip forming a pair of stereo, inverting amplifiers, having an ac gain of about 3.5 and capable of delivering up to 3.6V peak-to-peak into a 32 Ohm load (corresponding to 50mW RMS) at less than 0.025% total harmonic distortion (1kHz & 10kHz).
If we consider that the mean current drawing at a power output of 15mW per channel is around 12-13mA (both channels driven), this Headphone Amplifier will become a 'must' for many DIY enthusiasts needing a High Quality, High Performance portable device.

Technical data
Sensitivity:
200mV RMS for 15.6mW RMS output
350mV RMS for 50mW RMS output
Maximum undistorted output: 3.6V Peak-to-peak

Frequency response: flat from 40Hz to 20KHz; -2.3dB @ 20Hz

Total harmonic distortion @ 1KHz: <0.025% at all power outputs up to 50mW RMS

Total harmonic distortion @10KHz: <0.02% at all power outputs up to 50mW RMS

Total current drawing @ 9V supply (both channels driven):
Standing current: 8.5mA
Mean current drawing @ 15mW RMS per channel: 12mA
Mean current drawing @ 35mW RMS per channel: 17mA

Portable 9V Headphone Amplifier from http://www.redcircuits.com

Speech Amplifier Box

2009-11-14T03:33:00.000-08:00

Small portable device - 6V battery operation. Suitable for teachers, lecturers, tourists' guides etc.

Parts:

P1______________22K Log. Potentiometer

R1_______________1M 1/4W Resistor
R2______________15K 1/4W Resistor
R3_____________470R 1/4W Resistor
R4______________47K 1/4W Resistor
R5,R6____________4K7 1/4W Resistors (Optional, see Notes)

C1,C2,C4_______100nF 63V Polyester or Ceramic Capacitors
C3______________10nF 63V Polyester or Ceramic Capacitor (See text)
C5_____________220µF 25V Electrolytic Capacitor
C6______________10µF 25V Electrolytic Capacitor (Optional, see Notes)

Q1____________BC547 45V 100mA General purpose NPN Transistor

IC1_________TDA7052 Audio power amplifier IC

J1______________3mm or 6mm Mono Jack socket

SW1____________SPST Slider Switch fitted in the microphone (Optional, see text)
SW2____________SPST Toggle or Slider Switch

SPKR______________4-8 Ohm Loudspeaker (See Notes)

B1_______________6V Battery (4 x AA or AAA 1.5V Cells in series
or any 6V rechargeable battery pack etc.)

Comments:
This circuit is intended to be placed in the same box containing the loudspeaker, forming a compact microphone amplifier primarily intended for speech reinforcement. A device of this kind is particularly suited to teachers, lecturers, tourists' guides, hostesses and anyone speaking in crowded, noisy environment.
The circuit's heart is formed by the TDA7052 Audio power amplifier IC, delivering a maximum output of 1.2W @ 6V supply. An external microphone must be plugged into J1, its signal being amplified by Q1 and fed to IC1. R1 acts as a volume control and C3 tailors the upper audio frequency band, mainly to reduce the microphone possibility of picking-up the loudspeaker output, causing a very undesirable and loud "howl", i.e. the well known Larsen effect.
Therefore, C3 value can be varied in the 4n7 - 22nF range to ensure the best compromise from speech tone quality and minimum Larsen effect occurrence. For the same reason, the use of an uni-directional (cardioid) dynamic or electret microphone is warmly recommended.
Most of these microphone types are usually fitted out with a slider switch: this is an useful feature that can be used to momentarily mute the microphone. Some microphone types use a separate jack for connection to the muting circuit, some others use a stereo jack or different plug types. In any case, the connection of this switch to the circuit is shown as SW1 in the diagram.

Notes:
Please note that hands-free, uni-directional headset or earclip microphone types are very well suited for this device, as also are Clip-on Lavalier or Lapel microphones.
If a small electret capsule is used for the microphone, R5, R6 and C6 must be added to the circuit to provide power supply.
Choose a loudspeaker as large as possible, in order to increase circuit performance.
You can use also two 4 Ohm loudspeakers wired in series or two 8 Ohm types wired in parallel in order to obtain better results.
The box containing the amplifier and loudspeaker(s) can be fitted out with a belt and carried like a shoulder-bag or, if you build a smaller unit, it can be used as a Pick & Go Belt Clip Speaker.

Speech Amplifier Box from http://www.redcircuits.com

Audio Clipping Indicator

2009-11-14T03:25:00.000-08:00

Detects clipping in preamp stages, mixers, amplifiers etc.Single LED display - 9V Battery supply unit

Parts:

R1_______________1M 1/4W Resistor (See Notes)
R2,R3,R8_______100K 1/4W Resistors
R4,R6___________10K 1/4W Resistors
R5_______________5K 1/2W Trimmer Cermet or Carbon
R7_______________2K2 1/4W Resistor
R9______________22K 1/4W Resistor
R10______________1K 1/4W Resistor (See Notes)

C1,C4__________220nF 63V Polyester Capacitors
C2_______________4p7 63V Ceramic Capacitor (See Notes)
C3_____________220µF 25V Electrolytic Capacitor
C5______________10µF 25V Electrolytic Capacitor (See Notes)

D1,D2________1N4148 75V 150mA Diodes
D3______________LED (Any dimension, shape and color)

Q1____________BC547 45V 100mA NPN Transistor

IC1___________TL062 Dual Low current BIFET Op-Amp (or TL072, TL082)

SW1____________SPST Toggle or Slide Switch (See Text)

B1_______________9V PP3 Battery (See Text)
Comments:
This circuit was intended to be used as a separate, portable unit, to signal by means of a LED when the output wave form of a particular audio stage is "clipping" i.e. is reaching the onset of its maximum permitted peak-to-peak voltage value before an overload is occurring. This will help the operator in preventing severe, audible distortion to be generated through the audio equipment chain.
This unit is particularly useful in signaling overload of the input stages in mixers, PA or musical instruments amplification chains, but is also suited to power amplifiers.
A careful setting of Trimmer R5 will allow triggering of the LED with a wide range of peak-to-peak input voltages, in order to suit different requirements. Unfortunately, an oscilloscope and a sine wave frequency generator are required to accurately setup this circuit.
Obviously, the unit can be embedded into an existing mixer, preamp or power amplifier, and powered by the internal supply rails in the 9 - 30V range. The power supply can also be obtained from higher voltage rails provided suitable R/C cells are inserted. SW1 and B1 must obviously be omitted.

Circuit operation:
The heart of the circuit is a window comparator formed by two op-amps packaged into IC1. This technique allows to detect precisely and symmetrically either the positive or negative peak value reached by the monitored signal. The op-amps outputs are mixed by D1 and D2, smoothed by C4, R7 and R8, and feed the LED driver Q1 with a positive pulse. C5 adds a small output delay in order to allow detection of very short peaks.

Notes:
With the values shown, the circuit can be easily set up to detect sine wave clipping from less than 1V to 30V peak-to-peak (i.e. 15W into 8 Ohms). If you need to detect higher output peak-to-peak voltages, R1 value must be raised. On the contrary, if the circuit will be used to detect only very low peak-to-peak voltages, it is convenient to lower R1 value to, say, 220K omitting C2. In this way, the adjustment of R5 will be made easier.
Using a TL062 chip at 9V supply, stand-by current drawing is about 1.5mA and less than 10mA when the LED illuminates. With TL072 or TL082 chips, current drawing is about 4.5mA and 13mA respectively.
When using power supplies higher than 12V, the value of R10 must be raised accordingly.
When using power supplies higher than 25V, the working voltage value of C5 must be raised to 35 or 50V.

Audio Clipping Indicator project from http://www.redcircuits.com

Pure Class-A Headphone Amplifier

2009-11-14T03:22:00.000-08:00

400mW RMS into 32 Ohm load .Single-rail Supply - Optional Tilt Control

Parts:

P1_____________22K Dual gang Log Potentiometer (ready for Stereo)

R1_____________15K 1/4W Resistor
R2____________220K 1/4W Resistor
R3____________100K 1/2W Trimmer Cermet
R4_____________33K 1/4W Resistor
R5_____________68K 1/4W Resistor
R6_____________50K 1/2W Trimmer Cermet
R7_____________10K 1/4W Resistor
R8,R9__________47K 1/4W Resistors
R10,R11_________2R2 1/4W Resistors
R12_____________4K7 1/4W Resistor
R13_____________4R7 1/2W Resistor
R14_____________1K2 1/4W Resistor
R15,R18_______330K 1/4W Resistors (Optional)
R16___________680K 1/4W Resistor (Optional)
R17,R19_______220K 1/4W Resistors (Optional)
R20,R21________22K 1/4W Resistors (Optional)

C1,C2,C3,C4____10µF 25V Electrolytic Capacitors
C5,C7_________220µF 25V Electrolytic Capacitors
C6,C11________100nF 63V Polyester Capacitors
C8___________2200µF 25V Electrolytic Capacitor
C9,C12__________1nF 63V Polyester Capacitors (Optional)
C10___________470pF 63V Polystyrene or Ceramic Capacitor (Optional)
C13____________15nF 63V Polyester Capacitor (Optional)

D1_____________5mm. or 3mm. LED
D2,D3________1N4002 100V 1A Diodes

Q1,Q2_________BC550C 45V 100mA Low noise High gain NPN Transistors
Q3____________BC560C 45V 100mA Low noise High gain PNP Transistor
Q4____________BD136 45V 1.5A PNP Transistor
Q5____________BD135 45V 1.5A NPN Transistor

IC1____________7815 15V 1A Positive voltage regulator IC

T1_____________220V Primary, 15 + 15V Secondary (30V center-tapped)
5VA Mains transformer

SW1____________4 poles 3 ways rotary Switch (ready for Stereo)
SW2____________SPST slide or toggle Switch

J1_____________RCA audio input socket
J2_____________6mm. or 3mm. Stereo Jack socket

PL1____________Male Mains plug
Comments:
This design 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.

Pure Class-A Headphone Amplifier from http://www.redcircuits.com

Battery-powered Headphone Amplifier

2009-11-14T03:18:00.000-08:00

Low distortion Class-B circuitry powered by 6V Battery Supply.

Parts:

P1_____________22K Dual gang Log Potentiometer (ready for Stereo)

R1_____________15K 1/4W Resistor
R2____________100K 1/4W Resistor
R3____________100K 1/2W Trimmer Cermet
R4_____________47K 1/4W Resistor
R5____________470R 1/4W Resistor
R6____________500R 1/2W Trimmer Cermet
R7______________1K 1/4W Resistor
R8,R9__________18K 1/4W Resistors
R10,R11_________2R2 1/4W Resistors
R12____________33R 1/4W Resistor
R13_____________4K7 1/4W Resistor

C1,C2__________10µF 25V Electrolytic Capacitors
C3,C5_________100nF 63V Polyester Capacitors
C4,C6_________220µF 25V Electrolytic Capacitors

Q1,Q2,Q5______BC560C 45V 100mA Low noise High gain PNP Transistors
Q3,Q4_________BC550C 45V 100mA Low noise High gain NPN Transistor
Q6____________BC327 45V 800mA PNP Transistor
Q7____________BC337 45V 800mA NPN Transistor

SW1____________SPST slide or toggle Switch

J1_____________RCA audio input socket
J2_____________6mm. or 3mm. Stereo Jack socket

B1_____________6V Battery (4xAA or AAA Alkaline or rechargeable cells, etc.)
Comments:
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.

Notes:
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

Battery-powered Headphone Amplifier from http://www.redcircuits.com

Car Subwoofer Driver

2009-11-14T03:13:00.000-08:00

This sub woofer driver can deliver 22W to 4ohm speaker.

Parts:

P1_____________10K Log Potentiometer
P2_____________22K Dual gang Linear Potentiometer

R1,R4___________1K 1/4W Resistors
R2,R3,R5,R6____10K 1/4W Resistors
R7,R8_________100K 1/4W Resistors
R9,R10,R13_____47K 1/4W Resistors
R11,R12________15K 1/4W Resistors
R14,R15,R17____47K 1/4W Resistors
R16_____________6K8 1/4W Resistor
R18_____________1K5 1/4W Resistor

C1,C2,C3,C6_____4µ7 25V Electrolytic Capacitors
C4,C5__________68nF 63V Polyester Capacitors
C7_____________33nF 63V Polyester Capacitor
C8,C9_________220µF 25V Electrolytic Capacitors
C10___________470nF 63V Polyester Capacitor
C11___________100nF 63V Polyester Capacitor
C12__________2200µF 25V Electrolytic Capacitor

D1______________LED any color and type

Q1,Q2_________BC547 45V 100mA NPN Transistors

IC1___________TL072 Dual BIFET Op-Amp
IC2_________TDA1516BQ 24W BTL Car Radio Power Amplifier IC

SW1____________DPDT toggle or slide Switch
SW2____________SPST toggle or slide Switch capable of withstanding
a current of at least 3A

J1,J2__________RCA audio input sockets

SPKR___________4 Ohm Woofer or two 8 Ohm Woofers wired in parallel
Comments:
This unit is intended to be connected to an existing car stereo amplifier, adding the often required extra "punch" to the music by driving a subwoofer. As very low frequencies are omnidirectional, a single amplifier is necessary to drive this dedicated loudspeaker.
The power amplifier used is a good and cheap BTL (Bridge Tied Load) 13 pin IC made by Philips (now NXP Semiconductors) requiring a very low parts count and capable of delivering about 22W into a 4 Ohm load at the standard car battery voltage of 14.4V.

Circuit description:
The stereo signals coming from the line outputs of the car radio amplifier are mixed at the input and, after the Level Control, the signal enters the buffer IC1A and can be phase reversed by means of SW1. This control can be useful to allow the subwoofer to be in phase with the loudspeakers of the existing car radio.
Then, a 12dB/octave variable frequency Low Pass filter built around IC1B, Q1 and related components follows, allowing to adjust precisely the low pass frequency from 70 to 150Hz.
Q2, R17 and C9 form a simple dc voltage stabilizer for the input and filter circuitry, useful to avoid positive rail interaction from the power amplifier to low level sections.

Notes:
IC2 must be mounted on a suitable finned heatsink
Due to the long time constant set by R17 and C9 in the dc voltage stabilizer, the whole amplifier will become fully operative about 15 - 30 sec. after switch-on.
Technical data:
Output power (1KHz sinewave):
22W RMS into 4 Ohms at 14.4V supply
Sensitivity:
250mV input for full output
Frequency response:
20Hz to 70Hz -3dB with the cursor of P2 fully rotated towards R12
20Hz to 150Hz -3dB with the cursor of P2 fully rotated towards R11
Total harmonic distortion:
17W RMS: 0.5% 22W RMS: 10%

Car Subwoofer Driver from http://www.redcircuits.com

Modular Preamplifier Control Center

2009-11-14T03:08:00.000-08:00

Preamp for Volume and Loudness controls CD and Aux inputs

Parts:

P1______________47K Log. Potentiometer
(twin concentric-spindle dual gang for stereo)

R1,R2,R4_______100K 1/4W Resistors
R3,R14_________560R 1/4W Resistors
R5_______________1K 1/4W Resistor
R6,R7,R10_______10K 1/4W Resistors
R8,R9___________22K 1/4W Resistors
R11_____________68K 1/4W Resistor
R10,R13________220R 1/4W Resistors
R12______________1K5 1/4W Resistor
R13_____________12K 1/4W Resistor

C1_______________1µF 63V Polyester Capacitor
C2,C3__________100pF 63V Polystyrene or Ceramic Capacitors
C4______________47nF 63V Polyester Capacitor
C2,C6____________1µF 63V Polyester Capacitors
C5______________22nF 63V Polyester Capacitor
C6_____________220pF 63V Polystyrene or Ceramic Capacitor
C7,C10_________100nF 63V Polyester Capacitors
C8,C11___________4µ7 25V Electrolytic Capacitors
C9,C12________2200µF 25V Electrolytic Capacitors

IC1___________TL072 Dual BIFET Op-Amp
IC2___________78L15 15V 100mA Positive Regulator IC
IC3___________79L15 15V 100mA Negative Regulator IC

D1,D2________1N4002 200V 1A Diodes

SW1____________DPDT Toggle Switch
SW2____________2 poles 3 ways Rotary Switch

J1,J2,J3,J5____RCA audio input sockets
J4_____________Mini DC Power Socket

Comments:
This is the first article of a five-part series describing a complete audio preamplifier formed by five Mini-Modules, namely: Control Center, Switching Center, Phono Preamplifier, Tone Control and Headphone Amplifier. A suitable Power Amplifier module will be presented later.
The arrangement of these modules is similar to a late-1980's commercial production, the Thorens Restek Mini-Modules. Obviously, all the circuits of this Modular Preamplifier are original designs and have no relationship with the Thorens Modules.

The modular arrangement allows the amateur to choose only the modules more suited to his requirements in order to build a chain one to five modules long.
For the minimalist, the Control Center module described in this page will be most probably the only useful module, allowing the choice of two input sources, e.g. a CD player and an Aux input (Tuner or iPod etc.).
The purist can also omit the Loudness control available there: the 2 poles 3 ways Rotary Switch used for this control (SW2) can be converted into a three-input selector switch. Therefore, the two-input selector SW1 at the center of the front panel, can be substituted by a 3mm stereo mini-jack socket, allowing, for example, the quick and easy plugging of an iPod.

Each module, excepting the Switching Center that is a passive circuit, incorporates its own separate power supply rectifiers and regulators and requires only an external 15 - 18V ac (50mA minimum) Power Supply Adaptor.
In a chain formed by several modules, the use of a series of Power Supply Adaptors may be considered excessive. In such cases, the dual ±15V dc stabilized supply can be carried from a main module to the others by means of a three-wire cable and suitable connectors. Or the ac output of a single Power Supply Adaptor can be routed to several modules by using two Mini DC Power Sockets in each module wired in parallel, allowing to use a two-wire cable interconnection.

Each electronic board can be fitted in a standard enclosure: Hammond extruded aluminum cases are well suited to host the boards of this preamp. In particular, the cases sized 16 x 10.3 x 5.3 cm or 22 x 10.3 x 5.3 cm are the more appropriate and can be stacked with advantage.

Control Center circuit description:
This circuit features two high-level inputs switched by SW1, followed by the unity-gain high input impedance buffer IC1A. The output of this buffer drives the passive network Loudness circuit. Its control switch SW2A allows the choice of two different frequency compensation curves (see graph below) to be used when the sound programme is reproduced at low levels. Curve I should be used with low to mid reproduction levels, in practice when the volume control knob is set around the second quarter of its travel. Curve II is best suited to very low levels, i.e. when the volume control knob is set around the first quarter. To obtain a perfectly flat frequency response, the Loudness control must be set in the OFF position.

The following Op-Amp (IC1B) provides all the gain required by the preamplifier, featuring 166mV RMS input sensitivity at 1.5V RMS output with very low distortion. Therefore it is capable of driving low input sensitivity power amplifiers.

The dual rail power supply necessary for this circuit is drawn from the single 15 - 18V ac voltage provided by a suitable external Power Supply Adaptor. D1 and D2 rectify respectively the positive and the negative half wave in order to obtain a dual opposite polarity rail voltage referred to ground. IC2 and IC3 provide a well regulated ±15V dc supply to the Op-Amps.

Notes:
The circuit diagram shows the Left channel only and the power supply.
Some parts are in common to both channels and must not be doubled. These parts are: P1 (if a twin concentric-spindle dual gang potentiometer is used), IC2, IC3, C7, C8, C9, C10, C11, C12, D1, D2, SW1, SW2 and J4.
This module requires an external 15 - 18V ac (50mA minimum) Power Supply Adaptor.
Technical data:
Input sensitivity:
166mV RMS for 1.5V RMS output
Maximum output voltage:
9.5V RMS into 10K load
Frequency response:
flat from 20Hz to 23KHz
Total harmonic distortion @ 1KHz and 10KHz:
less than 0.002% at all levels up to 9.5V RMS (0.0017% typical)

Modular Preamplifier Control Center from http://www.redcircuits.com

George N. Fursey, Field Emission in Vacuum Microelectronics

2009-11-13T03:56:00.000-08:00

Field emission is a phenomenon described by quantum mechanics. Its emission capability is millions times higher than that of any other known types of electron emission. Nowadays this phenomenon is experiencing a new life due to wonderful applications in the atomic resolution microscopy, in electronic holography, and in the vacuum micro- and nanoelectronics in general. The main field emission properties, and some most remarkable experimental facts and applications, are described in this book.

download Field Emission in Vacuum Microelectronics link 1