Free Electronic Circuit | Energy Saving lamps

Ballast for energy-saving lamps

This compact ballast is intended for driving a 20-watt ‘bare’ Compact Fluorescent Lamps (CFL) tube or bulb, that is, one without a driver circuit built into its socket that makes it ready to screw into an existing lamp socket. Pin-base CFLs are designed to be used with a separate-ballast. As with a linear fluorescent system, the lamp and ballast must be compatible. Pin-base CFLs are available in low-power versions to replace incandescent light bulbs and in medium- and high-power versions to take over from linear fluorescent lamps or even high-intensity discharge (HID) lamps.

Making a pin-base CFL light

The circuit shown in Inductor picture uses a dedicated integrated circuit type FAN7710 from our friends at Fairchild. As illustrated in Figure 4, this device combines one high-side 625-V gate driver circuit, two 550-V MOSFETs, a frequency control circuit and a shunt regulator –– plus active ZVS control and an open lamp detection function, all crammed into one ultra-compact 8-way DIP package. Its high functionality and built-in protection features save board space, reduce power dissipation and guarantee enhanced reliability in end systems. Good!

The AC line input voltage (here, 230 VAC 50 Hz) is rectified to provide a bus voltage of approximately 320 volts DC. Start-up resistor R1 supplies initial (micro-) power to the FAN7710 IC. The IC begins to oscillate and the charge pump circuit consisting of C2, D2 and D7 supplies the current to the VDD pin, which gets regulated through the internal 15-V shunt regulator.

The FAN7710’s oscillator circuitry employs three discrete frequencies: one to pre-heat the CFL gas; one to ignite it and one for the on state — see the inset for the associated (simple) maths. In addition to this, it protects the ballast circuitry from low AC as well as lamp removal conditions.

Making the inductor

The bare PCB, FAN7710N IC and the 2.5-millihenryinductor used in the circuit come as a set from the Elektor Shop. However we would not discourage anyone from purchasing the inductor parts and making it yourself.

Let’s first carefully write down the specifications:

Inductance: 2.5 mH
Core material: Epcos N19 or equivalent
Core size: 20 / 10 / 6
Bobbin: E19
Gap: 1.5 mm
Wire gauge: 0.2 mm (SWG #32)
Number of turns: 280

Now look at the construction details.

First, wind the 280 turns of enameled copper wire (ECW) on the E19 bobbin. Bare the wire ends for about 5 mm by scratching with a scalpel, then pre-tin. Check continuity of the coil. Put the Ecore halves over the bobbin as shown, then insert and adjust the spacers to get the required air gap of 1.5 mm which is essential to achieve the required inductance. The final step is to wrap electrical isolation tape around the core frame.

Ballast for Energy-Saving Lamps Printed Circuit Board (PCB)

Elektor labs have designed a circuit board for the project; the component mounting plan is shown in PCB. The copper track layout is available as a free .pdf file from our website at Elektor for those wishing to etch their own circuit board. Reflected and non-reflected artwork is included in the .pdf file for your convenience. Component stuffing is a breeze as only normal size leaded components are used on a spacious board. The wiring to the mains and the lamp, and all connections and connectors in between, should comply with electrical safety guidelines. (Author: T. A. Babu, Elektor Magazine, 2008)

Caution!

The circuit is connected directly to the mains and presents lethal voltages. Relevant electrical safety precautions must be observed to prevent any component being touched while the circuit is in operation.

Free Electronic Circuit | Oxygen Sensor Simulator

Oxygen Sensor Simulator The oxygen sensor simulator as built on a protoboard. Note the cigarette lighter plug used for power source. The adjustment knob is at the left, and the switch is on the right. The red indicator LED is in the middle. Only use red, because the voltage drop of the LED is part of the circuit! The schematic diagram for the simulator. Closing the switch engages the simulator. Turning the knob clockwise simulates a lean condition, turns the LED off, and the car should start running rich to compensate. The big "V" is a digital voltmeter(not shown in the pictures). Using a smaller value for C1, perhaps 4.7 uF, will make the circuit oscillate faster and might be more like a real oxygen sensor(a new sensor switches more often than an old one). The adapter cable. Note the connector recycled from an old oxygen sensor. Hard to see under the black tape: 100K resistor. The schematic diagram of the adapter cable and oxygen sensor. Note the heater is shown as a resistor, mine measured about 7 ohms. Previous page... Frequently Asked Questions:

Q: Will you build one of these for me, or sell me the one you built? A: No, I won’t do that. If there is a community college or high school near you with an electronics class, you should contact the instructor and ask if there are students looking for a small job. This project is simple enough it should not pose a problem. Q: I built the project but I have to fiddle with the knob all the time. A: The car eventually will get too rich or too lean because it isn’t using the oxygen sensor anymore. This is a diagnostic aid, not a long-term replacement for an oxygen sensor. Q: I do racing on the weekends with my street car. Will this project help me tune the car to different conditions? A: If you do drag racing, yes. The races are short enough you can set a mixture and it will hold long enough. Each time you start the car it will go to the mixture you set. Other forms of racing take too long, and the mixture will creep towards very rich, you’d have to adjust the knob while driving.

Free Electronic Circuit | Infra-red Level Detector

Useful for liquids level detection and proximity devices

Up to 50 cm. range, optional relay operation

Circuit diagram:

Parts:

R1_____________10K   1/4W Resistor R2,R5,R6,R9_____1K   1/4W Resistors R3_____________33R   1/4W Resistor R4,R8___________1M   1/4W Resistors R7_____________10K   Trimmer Cermet R10____________22K   1/4W Resistor   C1,C4___________1µF  63V Electrolytic or Polyester Capacitors C2_____________47pF  63V Ceramic Capacitor C3,C5,C6______100µF  25V Electrolytic Capacitors  D1_____________Infra-red LED D2_____________Infra-red Photo Diode (see Notes) D3,D4________1N4148  75V 150mA Diode D5______________LED  (Any color and size) D6,D7________1N4002  100V 1A Diodes  Q1____________BC327  45V 800mA PNP Transistor  IC1_____________555  Timer IC IC2___________LM358  Low Power Dual Op-amp IC3____________7812  12V 1A Positive voltage regulator IC  RL1____________Relay with SPDT 2A @ 220V switch                Coil Voltage 12V. Coil resistance 200-300 Ohm  J1_____________Two ways output socket 

---

Device purpose:

This circuit is useful in liquids level or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam. It can safely detect the level of a liquid in a tank without any contact with the liquid itself. The device's range can be set from a couple of cm. to about 50 cm. by means of a trimmer.
Range can vary, depending on infra-red transmitting and receiving LEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device's sensitivity.

Circuit operation:

IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the target on the same line, a couple of centimeters apart, on a short breadboard strip. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting input of the voltage comparator IC2B. This comparator switches on and off the LED and the optional relay via Q1, comparing its input voltage to the reference voltage at its non-inverting input set by the Trimmer R7.

Notes:

• Power supply must be regulated (hence the use of IC3) for precise reference voltage. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.
• Current drawing: LED off 40mA; LED and Relay on 70mA @ 12V DC supply.
• R10, C6, Q1, D6, D7, RL1 and J1 can be omitted if relay operation is not required.
• The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.
• Avoid sun or artificial light hitting directly D1 & D2.
• Usually D1-D2 optimum distance lies in the range 1.5-3 cm.
• If you are needing a similar circuit driving 3 LEDs in sequence, also suitable as a parking aid

Free Electronic Circuit | Car Parking Sensor

Three LEDs signal bumper-barrier distance

Infra-red operation, indoor use

Circuit diagram:

Parts:

R1_____________10K   1/4W Resistor R2,R5,R6,R9_____1K   1/4W Resistors R3_____________33R   1/4W Resistor R4,R11__________1M   1/4W Resistors R7______________4K7  1/4W Resistor R8______________1K5  1/4W Resistor R10,R12-R14_____1K   1/4W Resistors   C1,C4___________1µF  63V Electrolytic or Polyester Capacitors C2_____________47pF  63V Ceramic Capacitor C3,C5_________100µF  25V Electrolytic Capacitors  D1_____________Infra-red LED D2_____________Infra-red Photo Diode (see Notes) D3,D4________1N4148  75V 150mA Diodes D5-7___________LEDs  (Any color and size)  IC1_____________555  Timer IC IC2___________LM324  Low Power Quad Op-amp IC3____________7812  12V 1A Positive voltage regulator IC 

---

Device purpose:

This circuit was designed as an aid in parking the car near the garage wall when backing up. LED D7 illuminates when bumper-wall distance is about 20 cm., D7+D6 illuminate at about 10 cm. and D7+D6+D5 at about 6 cm. In this manner you are alerted when approaching too close to the wall.
All distances mentioned before can vary, depending on infra-red transmitting and receiving LEDs used and are mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device sensitivity.
Obviously, you can use this circuit in other applications like liquids level detection, proximity devices etc.

Circuit operation:

IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the car on the same line, a couple of centimeters apart, on a short breadboard strip fastened to the wall. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting inputs of three voltage comparators. These comparators switch on and off the LEDs, referring to voltages at their non-inverting inputs set by the voltage divider resistor chain R7-R10.

Circuit modification:

A circuit modification featuring an audible alert instead of the visual one is available here:Park-Aid Modification

Notes:

• Power supply must be regulated (hence the use of IC3) for precise reference voltages. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.
• Current drawing: LEDs off 40mA; all LEDs on 60mA @ 12V DC supply.
• The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.
• Avoid sun or artificial light hitting directly D1 & D2.
• If your car has black bumpers, you can line-up the infra-red diodes with the (mostly white) license or number plate.
• It is wiser to place all the circuitry near the infra-red LEDs in a small box. The 3 signaling LEDs can be placed far from the main box at an height making them well visible by the car driver.
• The best setup is obtained bringing D2 nearer to D1 (without a reflecting object) until D5 illuminates; then moving it a bit until D5 is clearly off. Usually D1-D2 optimum distance lies in the range 1.5-3 cm.
• If you are needing a simpler circuit of this kind driving a LED or a relay, click Infra-red Level Detector

Free Electronic Circuit | 20 Watt Automotive Power Amplifier

20 Watt Automotive Power Amplifier - LM2005

The high current capability of the LM2005 allows it to continuously endure either AC or DC short circuit of the output with a maximum supply voltage of 16V. This will protect the loudspeaker in a bridge mode, when a DC short of the output occurs on one side of the speaker.

The device will prevent the speaker from destruction by reducing the DC across the load (bridge mode) to typically less than 2 VDC(VSe14.4V, RLe4X), by an internal current pullback method.

The LM2005 can withstand a constant 28 VDC on the supply with no damage (maximum operating voltage is 18V). The device is also protected from load dump or dangerous transients up to 40V for 50 ms (every 1000 ms) on the supply with no damage.



The LM2005 is a dual high power amplifier, designed to deliver optimum performance and reliability for automotive applications. High current capability (3.5A) enables the device to deliver 10W/channel into 2X (LM2005T-S), or 20W bridged monaural (LM2005T-M) into 4X, with low distortion.



Features

• Wide supply range (8V±18V)
• Externally programmable gain
• With or without bootstrap
• Low distortion
• Low noise
• High peak current capability
• PO=20W bridge
• High voltage protection
• AC and DC output short circuit protection to ground oracross load
• Thermal protection
• Inductive load protection
• Accidental open ground protection
• Immunity to 40V power supply transients
• Pin for pin compatible with TDA2005 (Datasheet)

Free Electronic Circuit | AC Ohmmeter - ESR Meter

AC Ohmmeter - ESR Meter

The ESR Meter is basically an AC Ohmmeter with special scales and protective circuitry. It provides a continuous reading of series resistance in electrolytic capacitors. It operates at 100 kHz to keep the capacitive reactance factor near zero. The remaining series resistance is due to theelectrolyte between the capacitor plates and indicates the state of dryness. Capacitor termination problems also show up plainly due to the continuous ohmic reading.

The ESR meter uses 8 operational ainplifiers. An op-amp is an idealized basic amplifier with two inputs. The non-inverting input (+) has an in-phase relationship with the op-amp output, and the inverting input (-) an out-of-phase relationship. Op-amps are usually used with negative feedback and reach a stable operating condition when their two inputs are equal in voltage.





Op-amps IA & 1B form a regenerative 100 kHz oscillatnr circuit. Capacitor C1 is the basic tiiningcapacitor and RI is selected to set frequency. Diodes D2 & D3 clip the bottom and top of the output waveform so that the output level and frequency are resistant to battery voltage changes.



The oscillator output of op-amp 1B drives 10-ohm source resistor R8F. The test-capacitor, thru the test leads, couples this 100 kllz signal to 10-ohm load resistor R9F. The amount of voltage developed here is indicative of the capacitors ESR value. (The 10-ohm resistors determine the basic iieter scaling.)



Capacitor C3 blocks any DC voltage present on the test-capacitor. Diodes D4 & D5 protect the ESR Meter from any initial charging current to C3. Resistor R7 discharges C3 after test.



A DC operating bias of 0.55 V is established by diode D1 for the oscillator stage and for all subsequent stages, which are DCcoupled and operated class A. DC bias from D1 and ESR signal from R9F are combined at the input of op-amp 1D. Both voltages are amplified by 1D, 1C, & 2A. Each of these three stages has an amplification factor of about 2.8 due to the ratio of output-voltage to feedback~voltage at the (-) input, which is determined -by feedback resistors R13F & R14F, etc.



Op-amp 2D is configured as a peak-to-peak detector. when the in-corning AC signal goes more positive than the normal bias level of about 0.77 Volt, the output of 2D also goes positive. But it must go positive enough to overcome the voltage drop across diode D6 before a fully equalizing positive voltage can be fed back to the -(-) input thru R20 to stabilize the op-amp.



-Capacitor C4 is charged to the peak value of the AC signal and accurately represents the peak of the incoming AC signal. The voltage drop across the diode becomes almost inconsequential due to the feedback process, and the circuit works down to a few mV.



A similar action occurs during the negative peak, using D7 & C5.



Resistor R21 provides a constant minimum amount of negative feed--back around op-amp 2D. The negative feedback increases the op-amp bandwidth which, most importantly, keeps theamplifier input-to-output phase-shift low enough for proper circuit operation.



The two outputs from the peak-to-peak detector are connected to two high-input-impedance unity-gain DC amplifiers, which drive the 1 mA meter movement differentially.

Free Electronic Circuit | A Tiny pH Meter

A Tiny pH-Meter

This electronic circuit is a tiny pH-meter. It is very tiny: 11cm2 including the PSU circuit! The schematic is shown below. It is basically a simple gain/offset circuit with a high impedance input (several giga-Ohm) and frankly the explanation could stop here: anyone with an background in electronics can understand this. But I started to write a webpage about this, so let's try to do it right and describe the schematic.

Juste because it's damn small does not mean that you have to settle down for second best when it comes to performance. The repeatability is around 0.01 pH and the accuracy, while depending on how well you will calibrate it, is around 0.02 pH. The main characteristics are:

• very small footprint (11cm2)


• very lightweight


• pluggable module for easy replacement


• requires only an external transformer and a display unit to work


• slope/offset settings


• repeatability 0.01 pH


• accuracy 0.02 pH


• low power


• low-cost single-sided PCB


• total unit price (including case and display unit): less than 100 euros.

The circuit input is pin 15 of K1. The probe signal enters IC1 via an RC circuit designed to allow only relatively slow signal variations (and avoid getting parasite HF signals). IC1 is a CMOS op-amp and thus has a very high impedance. The gain of IC1 is adjusted with the potentiometer R14. C2 is there for the amplifier stability. The R5/R11 circuit is the adjustment of the amplifier offset which is necessary for a high-precision application like this (see calibration below).

Once the signal has been amplified it enters an offset circuit built around IC2. IC2 is a more classic TL081 op-amp commonly found in audio devices, among others. The offset is defined by two potentiometers R12 and R13. The first one is on the PCB and the second one on the front panel. This improvement on the original design (single pot) allows the range swept by R13 to be symmetric, albeit smaller than without R12. It can be skipped if you wish (those small SMD trimmers can be damn expensive...). The circuit is designed to provide an average offset of 2V.

After the offset circuit the signal passes through a voltage divider before reaching the display unit. The divider roughly changes the signal range to something that is acceptable for the display. The real setting will be done on the display itself which contains a multiturn trimmer to precisely adjust its input gain.

The voltages for the signal evolve in the circuit as follows:

• Before IC1: -0.414/+0.414V (this might depend on the electrode used and its age, hence the gain/offset control)


• After IC1: -2/+2V


• After IC2: 0-4V


• After the voltage divider: 0-140mV (roughly)


• After the on-display trimmer: 0-140mV


• On the display: 0.00 - 14.00 pH (the display measures mV but the decimal point is placed accordingly to show a 0-14pH range)

As you can see the electrode voltage is symmetric and must undergo a linear transformation to fit the 0-14 pH range. This is all very classic stuff... Note that even if the supply rails are at +/-5V the circuit can cope with a 0-4V signal because the output swing is almost equal to the rails (no 0.7V drop, more around 0.3V IIRC).

A little remark concerning the integrated power supply circuit: it is a very small circuit that supplies a maximum of 50mA. Be careful of you want to add a power LED or something like that as it might be too much for the circuit. Check the total power used by the circuit before adding extras.PCB

The PCB is very small and you are advised to build it with through-hole mounting components if you're not familiar with SMDs. That means start the PCB design from scratch. I personally think that it looks much cooler with a small footprint... No other special remarks concerning the PCB, except that the PCBs that were manufactured were slightly different (see the photos below). This is actually also true for the schematic. No functional difference, but I changed from Protel to Eagle for designing the circuit so I had to reenter the schematic and PCB manually. Hence some differences in layout but this is not a big deal.



Component list

This is the list of components used in this circuit. I only mention the display and probe at this time as the other components are generic. Maybe more info will follow in the future.



A little link to the display unit used in this project. I chose this one because it has a nice 'pH' unit that can be activated on the display.



Another link to the probe used with this circuit (IIRC). Most probes should work but I only testedthe circuit with this one.

Construction



Random remarks: start with the smallest components, go slow, don't forget to set all the solder bridges correctly on the display unit (what you want is a 0-200mV range, an appropriately set dot and 'pH' shown as the unit). Check your cables,... before powering up.



The cabling diagram of K1 is:

* 1: AC 1

* 2: GND

* 3: +5v OUT (to display)

* 4: SIGNAL OUT (to display)

* 5: R13 / 2

* 6: R14 / 1

* 7: -5V OUT

* 8: R14 / 3

* 9: AC 2

* 10: GND (from transformer)

* 11: GND (to display)

* 12: GND (to BNC input)

* 13: R13 / 1

* 14: R14 / 2

* 15: INPUT

Free Electronic Circuit | The Leach amp 200W amplifier

The Leach amp 200W amplifier

Menu

• Introduction
• Schematics diagram
• Components
• Component prepairing
• Circuit board
• Assembling
• Heat sink
• Mechanical construction
• Chassis wiring
• Clipping indicator
• Testing
• Photo gallery

Introduction

This article descripts, how I built amplifier from Mr. Marshall Leach known like "The Leach Amp". I built amplifier from the original instructions on these pages:http://users.ece.gatech.edu/~mleach/lowtim/. Article about bulding of this amplifier I found later in journalA_Radio Praktická elektronika 11/2002. For many years I looked for construction of HiFi amplifier wit a good parameters, enough power reserve and simple construction. I built a couple of amplifiers with integrated circuits MBA810, TDA2005, LM3886, but I was disappointed by their output quality and noise. I decide to built a classic construction with discrete components and bipolar transistors. Construction from Mr. Dudek was interesting, but I didn't like used components and complexity. All of my requirements satisfied construction of theLeach Amp. Circuit author publicates in a February 1976 in american journal. From these days circuit was not practically changed. Little changes are descripted on authors page.

Link to original schematics diagram: http://users.ece.gatech.edu/~mleach/lowtim/graphics/ckt.pdf

Local copy: ckt.pdf

Redrawed schematics diagram for use with NJL transistors with added component values:

Schematics in Eagle5 format: leachamp4_5.sch

Components

I succeeded to find almost all original components on our local market, which was a miracle. Only a bigger problem was a power transformer and filter capacitors. Recommended toroid transformer for power 200W to 4 ohms is 230V/2x 42V. I succeeded to find in a GM Electronic a toroid transformer 2x36V, 300W. Output power will be a little lower, but for home use it will be more than enough. Voltage after rectification and filtering without load will be about +51V and -51V. I couldn't find capacitors with a 10000uF or 20000uF for 75V. I decided to buy electrolytic capacitors 4700uF/63V and place four pieces parallely on positive voltage and 4 on negative voltage. I was thinking about other option to place 3 pieces of 6800uF/63V on power lines. Mica capacitors are not available at all. I used ceramic instead. Someone said, that ceramic capacitors can "play", but I didn't found any problems. Carbon resistors are allegedly better for Hifi because lower noise, but I hear it after I buyed metalised resistors. I used normal electrolytic capacitors, but probably LowESR types will be better. Power transistors are not original Motorola, or today ON semiconductor, but I didn't found any problem.

Part list for two channels

number	name	value
Transistors
12x	Q1, Q2, Q5, Q7, Q9, Q10	MPSA 06
10x	Q3, Q4, Q6, Q8, Q11	MPSA 56
4x	Q13, Q14	2N 3439
4x	Q12, Q15	2N 5416
2x	Q16	MJE 15030
2x	Q17	MJE 15031
4x	Q18, Q20	MJ 15003 (NJL3281D)
4x	Q19, Q21	MJ 15004 (NJL1302D)
Diodes
12x	D1, D2, D3, D4, D11, D12	1N4007
12x	D5, D6, D7, D8, D9, D10	1N4148
8x (15x)	D13, D14, D15, D16	20 V Zener +5% tolerance, 0.5W
Capacitors
2x	C1	390 pF mica
14x	C2, C3, C15, C16, C23, C24, C25	100nF/100V film
8x	C7, C12, C17, C18	100nF/50V film
12x	C4, C5, C13, C14, C21, C22	100uF/63V radial electrolytic
2x (4x)	C6a, C6b	220uF/16V bi-polar electrolytic (4x 330uF/16V)
2x	C8	180pF mica
2x	C9	47pF mica
4x	C10, C11	10pF mica
4x	C19, C20	10nF/50V film
Rezistors
All resistors are 1% carbonic or metalised 0,5W if not noted otherwise
2x	R1	20 kohm
2x	R2	2 kohm
16x	R3, R4, R5, R6, R7, R8, R9, R10	300 ohm
6x	R11, R12, R27	1.2 kohm
4x	R13, R14	2.2 kohm
4x	R15, R16	12 kohm
4x	R17, R18	11 kohm
2x	R19	1.1 kohm
2x	R20	22 kohm
4x	R21, R22	30 ohm
4x	R23, R24	360 ohm
4x	R25, R26	1 kohm
4x	R28, R29	270 ohm
4x	R30, R31	3.9 kohm 1/2 W
6x	R32, R33, R51	82 ohm
4x	R34, R35	330 ohm
2x	R36	220 ohm
8x	R37, R38, R39, R40	680 ohm
8x	R41, R42, R43, R44	10 ohm 1/2 W
8x	R45, R46, R47, R48	0.33 ohm 5 W wire-wound
4x	R49, R50	10 ohm, 2 W
Other
2x	P1	2 kohm more turn cermet trimmer
1x	T1	Toroid power transformer SEC 2x40V AC 300W
8x	C1P, C2P	4700uF/63V (6x 6800uF/63V 4x 10000uF/63V)
8x	C3P	100nF/200V
1x	D1P	Bridge rectifier 35A/200V
5x		Fuse casing
1x	F1	Fuse 3.15A T
4x	F2, F3, F4, F5	Fuse 5A F
8x		Insulative bed under transistors + screw insulatives 16x
20x		Solder eye M4
2m		Shrinking spaghetti 4mm

Component prepairing

To prevent DC offset problems is needed to match transistors Q1-Q4 and zener diodes. In original article is a deep description how to do it. With transistors I had not any problems at all. Probably today is their producing more precise, when they are from identical series. With zener diodes it is worse. We connect 20V zener diode in a series with a resistor on the voltage power supply that to set diode current to a 3.3mA. I discovered, that zener voltage changing according to temperature and term of connection to voltage. During measuring I tried to keep identical conditions for all diodes and I waits for steady of value after about 1 minute. I buyed more zener diodes and every piece I measured three times and write down their values. After measuring I collected diode pairs for match voltages on each board.

Next was needed to wind L1 around R49. First I doesn't know which select wire and how their best wind on the resistor. I used lacquered wire from output inductor from an old PC power supply with diameter about 1mm. I wounded 11 turns on a screwdriver with a similar diameter like a R49. Finished inductor I placed on R49, turn their ends and solder them on the resistor terminals. Resistor with an inductor is normally soldered to board.

Circuit board

circuit board layout version 4.5 which looks perfectly suitable. Circuit board is one sided, nice symmetrically designed and all components fits to them perfectly. Only one little problem was small solder spots. It's not possible to drill a little bigger holes. First piece of circuit board I redrawed to an Eagle and consequently plot it on cuprextit and etch it. Next I leave them to make at Mr. Kohout which makes simple circuit boards by photo path. I only tell him page, where was circuit board published in Aradio magazine. Concretly "Praktická elektronika A Radio - 11/2002 page 13". Because he already had film negative, that curcuit board was cheaper. Circuit board was varnished to prevent oxidation and better soldering. Before assembling is suitable to check, that all holes are sufficient for components and wires. When I increased hole on an assembled board, I little damaged a case of one electrolytic capacitor.

Original printed circuit board with heatsink drilling: http://users.ece.gatech.edu/~mleach/lowtim/graphics/layouts.pdf

Local copy:layouts.pdf

Rearranged PCB for direct assembling NJL transistors. I had to make smaller PCB than original thanks to limited Light version of Eagle, but I hope that it is OK.

Assembling

Its good to begin assembling of circuit board from the smallest components to largest. First I soldered short-circuit jumper. Next I assembled all small resistors and after them diodes. I checked resistor values and diode polarity with a multimeter before assembling. Next I assembled small capacitors and smallest, middle and largest transistors. Specially I doublechecked their position. There remaining only big resistors and electrolytic capacitors, where I specially check polarity. It's needed to right turn pins on Q16 and Q17 in line with hole position and thickness of small heat sink.

Heat sink

I couldn't find suitable heat sink for a long time. I found perfect profile at small vendor, but it was much shorter than I needed it. Finally I obtained contact on a company ALUPA, which has in their list aluminium profile which fits exactly for our amplifier. Profile has marking ZH-2476. Unfortunately I doesn't know exactly required size, that I had to cut them with a circular saw, which going very badly, because aluminium "flows". Finally I cut heat sink to lenght 15cm and drilled to them holes according to original PDF document by 4mm drill except diodes. Holes for diodes I drilled to their tight contact with heat sink. Collector of power transistors I connected from upper side with help of solder eye and thick wire. I drilled holes for wires between transistors, but it was not a good idea, because I had to a little nibble mica beds. Better will be to make holes on the side of transistors.

Transistors are attached this way: First I spread his inner side with a thin layer of silicon vaseline. Next I attached on them mica bed. Next I soldered two thicker wires long 10cm, attached a piece of shrinkage spaghetti and shrink with lighter. Wires to collectors must be longer for about 5cm. Next I spreaded mica bed from the other side too. Layer must be very thin, because vaseline tried to push out. Finally I gave transistor on his place on the heat sink, in to the holes I placed screw isolant, under one I gave solder eye with soldered thicker wire and I screw up M3 15mm screws. In to the heat sink I placed and solder up 4 diodes according to original document and I drop them with glue. I drilled a small holes in a corners of the heat sink and I made worm with a M3 screw-cutter. I placed 5mm M3 spacer leg. For better heat removal is good to place blacked heat sink vertically, but I was limited by space and technological possibilities. However I didn't see any problems with overheating.

Mechanical construction

In construction I comes again from original organization. I had available old casing from some device with height 12cm, width 48cm and depth 25cm. On the front panel is placed only power switch and four diodes. Two for positive and negative supply and two for clipping indicator of the left and right channel. Front panel from aluminium I polished, that now it looks almost like a mirror. On them is placed logo made from cuprextit and glued with both sides sealing tape. But it doesn't look much good.

• Logo in a Eagle fromat
• Logo in a PDF format

Toroid transformer is placed in a center close to front panel far from electronics due to interference reason. He is attached with a bigger screw to base of the chassis. Nearby is central isolated ground point and bridge rectifier. Protective ground wire is connected from the power plug to the metal chassis. Ground from plug is not connected with a central amplifier ground for preventing ground loops and interference problems.

On the left and right side from the transformer are located filter capacitors placed vertically. Between them is longer screw with a female screw and plastic hose for preventing of wearing through capacitor insulation. On the top of the screw is placed bigger rubber pad with a female screw. Capacitors are binded together. Strong power wires are from one piece of wire and goes from rectifier over all filter capacitors to fuse holders. Maybe is better to connect all capacitors with same long wires to star, but I haven't idea how to do it mechanically. Identically is made second power line and groud line from central ground point.

Circuit boards are placed in a case vertically about 3cm from back side components backward. Originally i want to place boards with components to front, but it is much difficult to solder wires to boards. Circuit boards and transistors on heat sinks are placed mirrored that input of the amplifier has very short connection wires. Boards are placed on the longer distance legs. I hadn't them, that I used longer screws with female screws. Under two female screws I had to place insulation pads, because one of wires was too close screw. All ground wires are leaded independently to central ground point.

Back panel has on one side power plug connector and fuse holder. I made mistake here, because socket is in line with speaker connector, that can conflicts with speaker wires. Beside is speaker terminal and next heat sink of the right channel screwed with four screws on the distance legs. In the middle are two gilded input cinch connectors. They must be isolated from case! Next is heat sink of the left channel and again speaker connector. R50 and C25 are soldered directly on the speaker terminals. I founded only nickeled terminals not gilded, but they are enough massive for big power. TO3 bases or insulation covers are not available on our market.

Chassis wiring

On the circuit we can see connecting of individual components in a chassis. After power socket is connected EMI filter, which reduce interference between amplifier and neighbourhood. It can be seen in compact version in the power socket. In original amplifier I haven't them. In circuit is indicated which wires are thicker. Concrete component placing is seen on photos.

Clipping indicator

It's possible to build a clipping indicator like accesory for amplifier which detects amplifier limitation, when output transistors are fully opened and signal is cutted close to power supply voltage. In this case is acoustic signal distorted in a power amplifier. Circuit as usually is from authors pages. I redraw them in a Eagle and I designed circuit board for two channels. I added place for two LEDs for power supply voltage indicators. This board have small pads, which is not much good. Eagle has these pads too small in default state.

Schematics diagram

• Schematics in an Eagle

Circuit board

• Circuit board in an Eagle
• Circuit board in a PDF

Partlist for clipping indicator

number	name	value
2x	Q1, Q3	BC639
2x	Q2, Q4	BC640
6x	D1-D6	1N4148
2x	LED1, LED2	LED 2mm flat face, red
2x	LED3, LED4	LED 2mm flat face, green
2x	C1, C2	10uF/100V
4x	R1, R2, R8, R9	12k
4x	R3, R4, R10, R11	16k
4x	R5, R6, R12, R13	1k5 2W
2x	R7, R14	220R
2x	R15, R16	22k

Testing

First we must to test power supply part. Fuses F2 to F5 we leave out and for sure we check again circuit of rectifier and capacitor polarity. a zkontrolujeme pro jistotu zapojení usměrňovače a polaritu kondenzátorů. Possible error can be fatal. If is all OK, that on capacitors will be voltage about 51V. Exact voltage depends on used transformer and power line voltage. After disconnecting will be voltage on capacitor for a long time. We can discharge them with a resistor 100R 2W. It's possible, that with power-on blows fuse F1 even all is OK. In my situation is charging current too big, that I had place NTC thermistor in a series with primary transformer side. I get them from old PC power supply, where it has identical function. Better idea is to use "soft start" circuit, which is made from big resistor on primary side of transformer and relay, which short-circuit resistor after few seconds. I didn't found any circuit which I liked it.

When the power supply works correctly, we can go to test amplifier. First we set trmmer P1 to one end position with maximum resistance. In to the fuse holders for one channel we place resistors 100R 1/4W. With disconnected output and input we can power-on amplifier. On the resistor we would measure maximally 2.5V, which matches current 25mA. If is everything allright, we wait for discharging after power-off and replace resistor with fuses. Initially for testing we can use smaller values. I had switched two wires from power transistors on one channel and resistors smokes and smells. Really is better to everything double check.

Now we must set the bias current. Use amperemeter in place of F2. Turn the trimmer P1, until is current 100mA. How amplifier warming-up current is changing. Regulate current value when it is stabilized, which can be after 15 minutes. Identical procedure repeat for second channel.

With disconnected input we can measure DC offset on the output. In my example I measured 19mV on left channel and 22mV on right channel.

Now we can made regular tests and connects speakers and signal source. I tested with connecting of the amplifier input directly on the output of soundcard. You must carefully increase volume, because amplifier has enough power to destroy small speakers.

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