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1) Wireless Headphone Receiver

IR detector diode D1 intercepts the IR signal at around 40 kHz and feeds it from U1, a high-gain preamp, to PLL, U2, a 4046 configured to serve as an FM detector. U3 is an audio amplifier that feeds a pair of headphones or a speaker

2) Power Amplifier - 12W, Low-Distortion

3) Power Amplifier - 20 Watts

This circuit will add 20 Watts of power to your audio signal.

4) Radio Control Receiver/Decoder

5) 1.5V LED Flashers

The LED flasher circuits below operate on a single 1.5 volt battery. The circuit on the upper right uses the popular LM3909 LED flasher IC and requires only a timing capacitor and LED.

The top left circuit, designed by Andre De-Guerin illustrates using a 100uF capacitor to double the battery voltage to obtain 3 volts for the LED. Two sections of a 74HC04 hex inverter are used as a squarewave oscillator that establishes the flash rate while a third section is used as a buffer that charges the capacitor in series with a 470 ohm resistor while the buffer output is at +1.5 volts. When the buffer output switches to ground (zero volts) the charged capacitor is placed in series with the LED and the battery which supplies enough voltage to illuminate the LED. The LED current is approximately 3 mA, so a high brightness LED is recommended.

In the other two circuits, the same voltage doubling principle is used with the addition of a transistor to allow the capacitor to discharge faster and supply a greater current (about 40 mA peak). A larger capacitor (1000uF) in series with a 33 ohm resistor would increase the flash duration to about 50mS. The discrete 3 transistor circuit at the lower right would need a resistor (about 5K) in series with the 1uF capacitor to widen the pulse width

6) A / D Converter - 8Bit with Output Current-To-Voltage Conversion

7) HF Broadband Antenna Preamp7) HF Broadband Antenna Preamp

The HF/SW receiver preamplifier is comprised of broadband toroidal transformer (L1-a and L1-b), LC network (comprised at 1600-kHz, high-pass filter and 32-MHz, low-pass filter), L2 and L3 (26 turns of #26 enameled wire wound on an Amidon Associates T-50-2, red, toroidal core), a pair of resistive attenuators (ATTN1 and ATTN2), and a MAR-x device .

Shown here is the composition of basic 1-dB pi-network resistor antenuator. This is the method of supplying dc power to a preamplifier using only the RF coax cable.

8) Amateur Radio Linear Amplifier

The amplifier operates across the 2-30 MHz band with relatively flat gain response and reaches gain saturation at approximately 210 W of output power. Both input and output transformers are 4:1 turns ratio (16:1 impedance ratio) to achieve low input SWR across the specified band and a high saturation capability. When using this design, it is important to interconnect the ground plane on the bottom of the board to the top, especially at the emitters of the MRF454s.

9) SSB AF Filter

10) Amateur Radio Transmitter - 80M

This transmitter consists of a keyed crystal oscillator/driver and a high efficiency final, each with a TMOS Power FET as the active element. The total parts cost less than $20, and no special construction skills or circuit boards are required. The Pierce oscillator is unique because the high Crss of the final amplifier power FET, 700-1200 pF, is used as part of the capacitive feedback network. In fact, the oscillator will not work without Q2 installed. The MPF910 is a good choice for this circuit because the transistor is capable of driving the final amplifier in a switching mode, while still retaining enough gain for oscillation. To minimize cost, a readily-available color burst TV crystal is used as the frequency-determining element for (Q1). . An unusual 84% output efficiency is possible with this transmitter. Such high efficiency is achieved because of the TMOS power FET's characteristics along with modification of the usual algorithm for determining output matching

11) CW Transmitter - Low-Power, 40 Meter

This CW transmitter has an output of up to 3 W. By using 24 V on Q2, up to 10 W output can be obtained, If a 24-V supply is used, Q1 must not see more than 12V. Connect 12V between junctions C3, R2 and L2, and remove L5. L1 should be a low-Q 18- to 20-uH inductor. R6 can be used (up to 47 ohm) to reduce the Q further

12) Amplifier - 8 Watts

13) Amplifier - 22W

The IC is TDA1554

14) Audio and video amplifier

The Audio / Video Distribution Amplifier 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 helpfull when used in conjuction 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 increass the recorded audio which typically becomes poor when makeing tape copies

Circuit operation is straight forward for amplifier circuits. The second channel for the audio amplifer is made up of the same componets except the other half of IC1 is used. Pin 6 & 5 are inputs and 7 is the output

15) Differential Amplifier

16) DC to DC converter

17) Simple Field Strength Meter

This is a simple field strength meter that can be used to verify that you antenna is in fact radiating energy. It's based on one from the ARRL UHF/Microwave Projects Manual, Volume 1 and can be used from 30 MHz to well over 2 GHz if properly constructed

18) Attenuator Pads

19) LED RF Signal Meter

Notes: All parts should be SMT 5.1 volt zener is 1N5231Get the AD8313 from Analog Devices, www.analog.com Refer to AD8313 reference design schematic for more information Note 1 Optional bandpass filter for your desired band to measure Note 2 Optional RF input protection, two 1N5711 diodes Another circuit diagram

20) Spectrum Analyzer

21) Frequency divider (down 3.5 GHz to 3.5 MHz)

22) Frequency divider (down 3.5 GHz to 55 MHz)

23) Audio Amplifier with Tunable Filter (500 to 1500)Hz

24) Audio F ncy Meterreque

The meter uses time averaging to produce a direct current that is proportional to the frequency of the input signal

25) Headlight Flasher

It will allow your car headlights to flash time or it will cause them to flash alternately. The circuit is based on the 555 timer. It is used in the astable mode. The 555 timer output will go high for an adjustable period of time and then turn off. It will then repeat the procedure. The time is adjusted by R1. To hook up the circuit to your car you must locate the positive wire from the fuse box to the headlights. Cut the wire and insert the relay contact and bypass switch. The bypass switch will allow you to bypass the relay contact for normal headlight operation. In the alternating headlight configuration you must cut the positive wire to each headlight and wire in the relay contact.

on and off at the same

26) Car Voltage Gauge

The Car Voltage Gauge is based on 3 parts. The input circuit is an Analog to Digital Converter (IC2 CA3162E). The purpose of this chip is to sample an analog voltage and convert it to a decimal value which is read by a Display/Decoder Driver (IC1 CA3161E). This chip will turn each seven segment display on through the driver transistor Q1 - Q3. The power is derived from the car and is converted to 5 volts by the 5 volt regulator. The circuit works as follows: The 10uf capacitor is charged up by the cars voltage. Its value is then read by IC2 and a decimal value of that voltage is provided to IC1 which multiplexes the three display units. Each display is turned on sequentially with its appropriate value displayed. The transistors Q1 through Q3 control the drive to each seven segment display. By monitoring the cars voltage with an accurate multimeter you can adjust the "Zero Adj." pot and the "Gain Adj." pot for accurate readings. LED 1 and 2 are optional. They can be used to indicate power on or can light up a cut out display that says "Volts". This can be made by a plastic module that has a thin plastic cover on it with the word "Volts" cut into it. The LED's would be mounted inside the module.

27) Lights-On Reminder for Autos

When ignition is off, BZ1 w are on. With the ignition

nic Combination Lock

ill sound if the headlightson, BZ1 receives no voltage

28) Electro

, a positive voltage fed through Rl appears at g it on. When Ql is conducting, pin 1 of Ul is ttery's negative terminal. With pin 1 low, two (+ 9 volts dc), turning on LED 1-indicating that

on its base in order to conduct. It also needs a positive voltage on voltage on the collector. As long as the door switch (Sl5) remains

e volt appears at the gate of SCR1. That's enough voltage to

When button S12 (#) is pressedthe base of transistor Ql, turninbrought to ground (low) or the bathings occur: Pin 8 of Ul goes high the circuit has been armed-and pin 13 goes from high to low. Transistor Q2 requires a low signal or negative voltage

its emitter and a negative open (with the door itself closed), Q2's

emitter will not receive the necessary positive voltage. If, however, an unauthorized person opens the door, thus closing switch S15 and placing a positive voltage on the emitter of Ql, the following sequence occurs: 1) Transistor Q2 conducts, receiving the necessary biasing current through a current-divider network consisting of resistors R3 and R4. 2) As Q2 conducts, a voltage drop is developed across the voltage dividers made up of resistors R5 and R6. With R5 at 10,000 ohms and R6 at 1000 ohms, approximately ontrigger the SCR's gate

29) DC motor speed control

29) DC motor speed control

30) 300W Subwoofer Power Amplifier (Updated)

Introduction

There are some important updates to this project, as shown below. Recent testing has shown that with the new ON Semi transistors it is possible to obtain a lot more power than previously. The original design was very conservative, and was initially intended to use 2SA1492 and 2SC3856 transistors (rated at 130W) - with 200W (or 230W) devices, some of the original comments and warnings have been amended to suit.

30 Jul 2003 - OnSemi has just released a new range of transistors, designed specifically for audio applications. These new transistors have been tested in the P68, and give excellent results. As a result, all previous recommendations for output transistors are superseded, and the new transistors should be used.

The output devices are MJL4281A (NPN) and MJL4302A (PNP), and feature high bandwidth, excellent SOA (safe operating area), high linearity and high gain. Driver transistors are MJE15034 (NPN) and MJE15035 (PNP). All devices are rated at 350V, with the power transistors having a 230W dissipation and the drivers are 50W.

23 Sept 2003 - The new driver transistors (MJE15034/35) seem to be virtually impossible to obtain - ON Semi still has no listing for them on the website. The existing devices (well known and more than adequate) are MJE15032 (NPN) and MJE15033 (PNP), and these will substitute with no problems at all. It is also possible to use MJE340 and MJE350 as originally specified (note that the pinouts are reversed between the TO-126 and TO-220 devices).

Note that some component values have been changed! The layout is the same, but the changes shown will reduce dissipation in Q7 and Q8 under light load conditions.

Having built a couple of P68 amps using these transistors, I recommend them highly - the amplifier is most certainly at its very best with the high gain and linearity afforded by these devices. Note that there are a few minor changes to the circuit (shown below).

With 70V supplies, the input and current source transistors must be MPSA42 or similar - the original d age! Note that the MPSA42 pinout is differ ecified. Full details of transistor pinouts are shown in the construction article (available to PCB purchasers only).

evices shown will fail at that voltent from the BC546s originally sp

High power amps are not too common as projects, since they are by their nature normally difficult to build, and are expensive. A small error during assembly means that you start again - this can get very costly. I recommend that you use the PCB for this amplifier, as it will save you much grief. This is not an amp for beginners working with Veroboard!

The amplifier can be assembled by a reasonably experienced hobbyist in about three hours. The metalwork will take somewhat longer, and this is especially true for the high continuous power variant. Even so, it is simple to build, compact, relatively inexpensive, and provides a level of performance that will satisfy most requirements.

WARNINGS:

This amplifier is not trivial, despite its small size and apparent simplicity. The total DC is over 110V (or as much as 140V DC!), and can kill you.

The power dissipated is such that great care is needed with transistor mounting.

The single board P68 is capable of full power duty into 4 Ohm loads, but only at the lower supply voltage.

For operation at the higher supply voltage, you must use the dual board version.

There is NO SHORT CIRCUIT PROTECTION. The amp is designed to be used w s not been included. A short on the output

DO NOT ATTEMPT THIS AMPLIFIER AS YOUR FIRST PROJECT

e ELF principle - see the Project Page or the info on this circuit). Where continuous high power is required, another 4

nd

s),

ithin a subwoofer or other speaker enclosure, so this ha will destroy the amplifier.

Description

Please note that the specification for this amp has been upgraded, and it is now recommended for continuous high power into 4 Ohms, but You will need to go to extremes with the heatsink (fan cooling is highly recommended). It was originally intended for "light" intermittent duty, suitable for an equalised subwoofer system (for example using thfoutput transistors are recommended, wired in the same way as Q9, Q10, Q11 aQ12, and using 0.33 ohm emitter resistors.

Continuous power into 8 ohms is typically over 150W (250W for 70V supplieand it can be used without additional transistors at full power into an 8 ohm load all day, every day. The additional transistors are only needed if you want to dothe same thing into 4 ohms at maximum supply voltage! Do not even think about using supplies over 70V, and don't bother asking me if it is ok - it isn't!

The circuit is shown in Figure 1, and it is a reasonably conventional design. Connections are provided for the Internal SIM (published elsewhere on the Project Pages), and filtering is provided for RF protection (R1, C2). The input is

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via a 4.7uF bipolar cap, as this provides lots of capacitance in a small size. Because of the impedance, little or no degradation of sound will be apparent. A polyester cap may be used if you prefer - 1uF with the nominal 22k input impedance will give a -3dB frequency of 7.2Hz, which is quite low enough for asub.

The input stage is a conventional long-tailed pair, and uses a current sink (Q1the emitter circuit. I elected to use a current sink here to ensure that the amp would stabilise quickly upon application (and removal) of power, to eliminate the dreaded turn on "thump". The amp is

) in

actually at reasonably stable operating conditions with as little as +/-5 volts! Note also that there are connections for

15.

iver is again conventional, and uses a Miller stabilisation cap. This component should be either a 500V ceramic or a polystyrene device for best

ollector load uses the bootstrap principle rather than an active current sink, as this is cheaper and very pri ip

All rshould be in good thermal contact with the driver heatsink. Neglect to do this and the result will be thermal runaway, and the amp will fail. For some reason,

the SIM (Sound Impairment Monitor), which will indicate clipping better than any conventional clipping indicator circuit. See the Project Pages for details on making a SIM circuit. If you feel that you don't need the SIM, omit R4 and R

The Class-A dr

linearity. The creliable (besides, I like the bootstrap

nc le :-)

th ee driver transistors (Q4, 5 & 6)must be on a heatsink, and D2 and D3

thebelow, k, 3 driver transistors, and a white "bl "presse the heatsink with thermal grease. C11 do"misla til someone asked me where and what it was supposed to be. Sorry about that.

tput stage that the power capability of this amp is revealed. The main output is similar to many of my other designs, but with a higher value than

rsion of d in

302A output transistors, because they are new most constructors will find that these are not as easy to get as

2SC3281 are now obsolete - if you do find them, they are almost certainly 2000.

ent

carbon

.

Because this amp operates in "pure" Class-B (something of a contradiction of terms, I think), the high frequency distortion will be relatively high, and is probably unsuited to high power hi-fi. At the low frequency end of the spectrum, there is lots of negative feedback, and distortion is actually rather good, at about 0.04% up to 1kHz. My initial tests and reports from others indicate that there are no audible artefacts at high frequencies, but the recommendation remains.

last statement seems to cause some people confusion - look at the photo and you will see the small heatsin

ob (just to the left of the electrolytic capacitor), which is the two diodes d against

es not exist on this schematic, so don't bother looking for it. It was id" when the schematic was prepared, and I didn't notice un

It is in the ou

normal for the "emitter" resistors (R16, R17). The voltage across these resistors is then used to provide base current for the main output devices, which operate in full Class-B. In some respects, this is a "poor-man's" vethe famous Quad current dumping circuit, but without the refinements, anprinciple is the same as was used in the equally famous Crown DC300A power amps.

Although I have shown MJL4281A and MJL4

they should be. The alternatives are MJL3281/ MJL1302 or MJL21193/ MJL21194.

Note: It is no longer possible to recommend any Toshiba transistors, sincethey are the most commonly counterfeited of all. The 2SA1302 and

fakes, since Toshiba has not made these devices since around 1999~

Use a standard green LED. Do not use high brightness or other colours, as they may have a slighty different forward voltage, and this will change the currsink's operation - this may be a miniature type if desired. The resistors are all 1/4W (preferably metal film), except for R10, R11 and R22, which are 1Wfilm types. All low value resistors (3.3 ohm and 0.33 ohm) are 5W wirewound types

Power Dissipation Considerations I have made a lot of noise about not using this amp at 70V into 4 ohms without the extra transistors. A quick calculation reveals that when operated like this, the worst case peak dissipation into a resistive load is 306W (4&Omega/ 70V supplies). The four final transistors do most of the work, with Q7 and Q8 having a relatively restful time (this was the design goal originally). Peak dissipation in the 8 output devices is around 70W each.

Since I like to be conservative, I will assume that Q7 and Q8 in the updated schematic shown contribute a little under 1A peak (which is about right). This means that their peak dissipation is around 18W, with the main O/P devices dissipating a peak of 70W each. The specified transistors are 230W, and the alternatives are 200W, so why are the extra transistors needed?

The problem is simple - the rated dissipation for a transistor is with a case temperature of 25C. As the amp is used, each internal transistor die gets hot, as does the transistor case - the standard derating curves must be applied. Add

to this the reactive component as the loudspeaker drives current back into the amp (doubling the peak dissipation), and it becomes all too easy to exceed the device limits. The only way that this amp can be used for continuous high power duty with 70V supplies and a 4 loudspeaker load is to keep the working temperature down to the absolute minimum - that means four output devices perside, a big heatsink and a fan

Figure 1A shows the doubled output stage, with Q9, Q10, Q11 and Q12 simply repeated - along with the emitter resistors. Each 1/2 stage has its network and bypass caps as shown, as this is the arrangement if the dual PCB

own zobel

version is built. When you have this many power transistors, the amp will happilydrive a 4 ohm load all day from 70V - with a big enough heatsink, and forced cooling. Over 500W is available, more than enough to cause meltdown in maspeakers!

A Few Specs and Measurements

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The following figures are all relative to an output power of 225W into 4 ohms, o30V RMS at 1kHz, unless otherwise stated. Noise and distortion figures are unweig

r

hted, and are measured at full bandwidth. Measurements were taken using

t ge. Figures shown are measured with 56V nominal, with the figure

in (bra

istortion 0.4% 0.4% Distortion (@ 4W) 0.04% (1 Khz) 0.04% (1 Khz)

ere

tful that any deficiencies would be readily apparent, except perhaps at frequencies above 10kHz. While the amp is certainly fast enough (and yes, 3V/us

is available up to 30kHz), the distortion may

pply voltage with zero power

measured exactly 56V, and collapsed to 50.7V at full power into 8 ohms, and

a 300VA transformer, with 6,800uF filter caps.

Mains voltage was about 4% low when I did the tests, so power output will normally be slightly higher than shown here if the mains are at the correcnominal volta

ckets) estimated for 70V supplies.

8 4 Voltage Gain 27dB 27dB Power (Continuous) 153W (240W) 240W (470W) Peak Power - 10 ms 185W (250W) 344W (512W) Peak Power - 5 ms 185W (272W) 370W (540W) Input Voltage 1.3V (2.0V) RMS 1.3V (2.0V) RMSNoise * -63dBV (ref. 1V) -63dBV (ref. 1V)S/N Ratio * 92dB 92dB D

Distortion (@ 4W) 0.07% (10 kHz) 0.07% (10 kHz) Slew Rate > 3V/us > 3V/us Power Bandwidth 30 kHz 30 kHz

These figures are quite respectable, especially considering the design intent forthis amp. While (IMO) it would not be really suitable for normal hi-fi, even thit is doub

actually is fast enough - full powerbe a bit too high.

Note that the "peak power" ratings represent the maximum power before the filter caps discharge and the supply voltage collapses. I measured these at 5 milliseconds and 10 milliseconds. Performance into 4 ohm loads is not be quite asgood, as the caps discharge faster. The su

47.5V at full power into 4 ohms.

I hope to be able to publish the full test results of the 70V version soon

Photo of Completed Prototype

The photo does not show the silk screened component overlay, since this is the prototype board. The final boards have the overlay (as do all my other boards). The observant reader will also see that the 5W resistor values are different from those recommended - this was an early prototype using 130W transistors.

As can be seen, this is the single board version. The driver transistors are in a row, so that a single sheet aluminium heatsink can be used for all three. Holes are provided on the board so the driver heatsink can be mounted firmly, to prevent the transistor leads breaking due to vibration. This is especially important if the amp is used for a powered subwoofer, but will probably not be

rd

ply

needed for a chassis mounted system.

The driver and main heatsinks shown are adequate for up to 200W into 4 ohmswith normal program material. The power transistors are all mounted underneath the board, and the mounting screw heads can be seen on the top of the boa

Power Sup

WARNING: Mains wiring must be performed by a qualified electrician - Do not attempt the power supply unless suitably qualified. Faulty or incorrect mains wiring may result in death or serious injury