Text preview for : AV800.pdf part of usilvatel za manqcy-800W



Back to : AV800.rar | Home

1

Construction Notes for the AV 800 watt MOSFET Power Amplifier
Introduction The 800 Watt AV amplifier is based on My 1kw Amplifier and shares the same topology and basic PCB layout. The only real difference is the number of Output devices that the unit uses. The 1kw design has 20 O/P devices, while the AV amplifier has 14 O/P devices. This amplifier can be used for practically any application that requires High power, low noise, distortion and excellent sound. Examples would be Sub-woofer amp, FOH stage amplifier, One channel of a very high-powered surround sound amplifier etc. The AV amplifier has four main stages of amplification. We will begin by looking at each stage in reasonable detail. The Error Amp Stage The first stage is what I call an asymmetrical balance input error amplifier. It is a design, which allows only one single differential stage and yet has the ability to accept a balanced I/P source. An unbalanced source can be used if either the inverting or noninverting I/P is tied to signal ground. Now I will explain how each device in this stage works together. Q20, Q21, R51- R54, form the main differential error amplifier, which then has its collectors connected to a cascode load. Q18, Q19, R49 and ZD2 form the cascode stage which provides a constant 14.4 volts on the collectors of Q20, 21. Q17, R48, R50, ZD1 and C12 form a constant current source, which supplies 1.5milliamps to the first differential stage. These modules form the first stage of the amplifier and basically set up how the whole amplifier is biased from front to back. The Voltage Amplification Stage This next stage provides most of the voltage amplification that the next stage needs to drive the o/p stage to full power. Q22, 23, Q15, Q16, R34, R35, R36, R42, C7, C26, C27 form the second differential voltage amplification stage. Q15 and Q16 form what is known as a current mirror load for the second differential stage and basically force this stage to share the current supplied from R36, which is about 8milliamps. The remaining components, namely the caps provide local frequency compensation for this stage. The Bias and Buffer stage As the name suggests Q24, 25, 26, R15, 32, 33, 37, 43, 47, C6, ZD5, ZD6, form the Bias and buffer stages. Its main purpose is to provide the MOSFET Gates with a stable and compensated supply voltage and Buffer the Voltage amp stage from the high Gate Source capacitance. Which would without this stage cause the frequency response and slew rate to be very poor indeed. The down side of this is the extra stage does introduce an extra dominant pole in to the amplifiers feedback loop.

2

The Output Stage or Current Amplification Stage Once again as the name suggests this stage converts the voltage developed in the VAS and provides all the amperes needed to drive 8 or 4 Ohm loads. 2-Ohm loads are possible for several minutes at a time. In fact I have tested the 1kw amplifier to over 1600 watts RMS into 2 Ohms. But this would not be recommended as a long-term load at all. As it does exceed the SOA figures of the output stage. Power supply requirements for the 800 AV Amplifier The power supply components for this amplifier are as follows and are expressed for One Channel or One power module only. 1 x Toroidal Transformer with a Core rating of 1KVA. Primary windings are made to suit your local mains supply. eg: for Australia One single primary winding with a 240VAC rating. For USA, 110VAC, 115VAC and I believe there is a 220-Volt AC mains supply in some areas of the United States. For the UK it would be 220 VAC to 240 VAC. The secondary windings are as follows. 2 x 65 volts AC at full load. One 400 Volt 35 Ampere, Bridge rectifier. 2 x 4.7K 5 Watt ceramic resistors Minimum filter capacitor requirements would be 2 x 10,000uf 100 volt electrolytic. Ideal capacity would be 40,000uf per voltage rail. For stereo or dual mono operation the following power supply will be required. 1 x 2kva toroidal transformer with a core rating of 2kva 2 x 400 volt 35 amp bridge rectifier 4 x 10,000uf 100 volt electrolytic capacitors 2 x 4.7K 5 Watt ceramic resistors
1 2 3 4 5 6

D

Suggested power supply for Mono
T1 Local Mains Supply 47uf 390
+

D

BD1 Bridge Rectifier

+90 Volts DC 15k

Toroidal Transformer

C1 10,000uf 100 Volt

+

C3 10,000uf 100 Volt

R2 10k 5 watt Power GND R1 10k 5 watt -90 Volts DC

1uf AV800 Amp 15k
C

+ C

C2 10,000uf 100 Volt

+

C4 10,000uf 100 Volt

Suggested power supply for Stereo
+90 Volts DC BD2 Bridge Rectifier
+

C1 10,000uf 100v

+

C2 10,000uf 100v

B

R1 10k 5 watt

47uf 390 1uf

15k
B

T2 Local Mains Supply AV800 Amp 15k

Power GND
Toroidal Transformer Bridge Rectifier BD3
A +

C3 10,000uf 100v

+

C4 10,000uf 100v

R2 10k 5 watt -90 Volts DC
Title Size B Date: File: 6-Feb-2001 C:\WINNT\..\av800psu.Sch Sheet of Drawn By: 6 Number Revision

A

1

2

3

4

5

3

Assembling the Printed Circuit Board
One of the first things to do is to look at the PCB and see if all of the holes on the board are of the correct size for the components you wish to insert. The holes that have been drilled into the PCB should be OK. However it does pay to check before you start. If you find that some of the holes are not big enough then you will need to drill them out to the correct size. The standard holes sizes used for most electronic components are as follows. ¼ watt ½ watt resistors = 0.7mm to 0.8mm 1­watt resistors = 1.0mm ¼ watt to 1-watt zener and normal power diodes = 0.8mm Small signal transistors such as BC546 of the TO-92 pack = 0.6mm Medium signal transistors such as MJE340 of the TO-220 pack = 1.0mm Power Output devices such as the IRFP240 require a hole size of 2.5mm However on this PCB these devices are mounted on the copper side of the PCB facing down flat. The next thing that needs to be done is the cutting out of the PCB section, which has the output stage devices screen-printed on top of the PCB. This needs to be done so the mounting of the o/p devices can be properly clamped to the main heat sink. The best way of cutting this section out is to either use an electric router or drill 5mm holes in each corner and use a coping saw to remove the unwanted fibreglass and file the inside edges clean. Start constructing the PCB by inserting any wire links, which are shown on the component overlays as R5, R23, R41, and R45. The wire links are made from spare component leads such as from 5-watt ceramic resistors or ¼ watt resistor leads. Once the links have been taken care of the insertion of all the resistors is next, followed by the capacitors and then the small signal semiconductors. You will need to cross-reference the parts list with the white screen component overlay on the PCB to see where to insert the required component. Be careful to always insert the polarised components in the right way as shown on the screen-printed overlay. Failure to do this will most likely result in the module not functioning properly or damaging one or more of the components in the module. The output stage transistors and Q8, which is the IRF610 device, are to be left till last. The buffer stage transistors are to be mounted on 10 degrees/watt heats sinks with a one inch pitch mounting.

The buffer stage devices do not need insulating from the heat sinks, but please be aware that once the module is powered up. 90 volts DC will be present on the heat sink. So don't go touching it, as it will give you a shock.

Pre-flight test OK at this stage I am assuming you have populated all of the PCB except Q8 and the main output stage devices IRFP240's and IRFP9240's For the time been temporarily insert and solder Q8 into its position located in the middle of the PCB.

4

Pre-flight test continued It is important to test the function of the amplifier at this point in time so as to make sure it is working properly. This is achieved by soldering a 10-Ohm ¼ watt resistor from the output of the amplifier PCB to one side of the 330 Ohm 1W resistor found at R38 On the screen-printed side of the PCB. What this does is to connect the feedback resistor R37 to the output of the buffer stage. In doing so it bypasses the output stage and turns it into a very low powered amplifier, which can be tested without damaging the expensive output stage. Assuming you have connected the resistor from o/p to the buffer stage. It is now time too connect the +-90 volt supply to it and power it up. Be sure to have 4k7 Ohm 5-watt bleeder resistors across the power supply capacitors. Now assuming that there was no smoke, with a multimeter on volts. Measure the following voltage drops across these resistors locations marked in blue and if they match to within +-10% then you can be sure that the amplifier is OK. When you have done the checks, be sure to power down and remove the 10 Ohm resistor. R1~1.6 volts R2~1.6 volts R3~1.0 volts R55~500mv R56~500mv Offset voltage at R37 should be close to 0 volts, but can be as high as 100mv.

Now we have come to the soldering in of the output devices. It is assumed at this point that you have all ready matched the output stage devices as outlined in the accompanying document on How to match output devices. If this is already done then you can proceed by getting the PCB and flipping it over so the copper side of the board is facing you. Now identify which is the positive supply side of the PCB and start soldering the IRFP240 devices face down on the appropriate pads so the metal tabs on the back of the power MOSFET's are facing you. Once all of the N-channel devices are done proceed with the IRFP9240 P-channel devices, in the same way. After completing this task the module for the most part is completed. The only other thing you will need to decide is wether to use PCB stakes to solder the external wiring too or solder the cable directly into the PCB pads. Now there is one device that requires some special attention. This is Q8 and this device is the Vbe multiplier or bias compensation device, which needs to be mounted off board on a strip of 10cm x 2cm x 4mm thick piece of aluminium and it is this piece of aluminium that will clamp down the output stage. Q8 will need to be insulated with a TO-220 micawasher kit from this piece of metal and flying leads need to be soldered from the Gate, Source and Drain pins of the IRF610 to the appropriately marked pads on the PCB shown as Q8. One other thing that needs to be done is to mount some 3mm high rubber feet on copper side of the front and back of the PCB. This is to hold the PCB off the heat sink, so as not to allow the PCB to touch the heat sink in any way.

Completing the Module

5

Now having completed the power module and tested the Error, VAS and Buffer stages and you are confident that it is working OK. Its time to bolt it down to a suitable heat sink. Remember that all of the o/p devices must be insulated with either silicon rubber washers or mica ­washers and heat sink compound. The type, size and shape of heat sink are left up to you and the local availability of heat sinks. But be sure to have a heat sink rated at 0.2 degrees/watt or 0.5 degrees/watt with fan cooling.

Completing the Module Continued

So we have come to the point where we need to do a full test on the amplifier module. There are a few checks that need to be done first. · The Drain pins on all the o/p devices need to be checked for S/C to the heat sink. · The power supply wiring has been checked for correct polarity to the PCB. · The Multi-turn pot P1 has been turned back to 0 Ohms, so that a measurement of approximately 4.7k is measured across the Gate and Drain pins of Q8 IRF610. · When wiring up the power supply, be sure to have 8 amp fuses inserted on each of the supply lines. · Connect a multimeter on DC volt range to the o/p of the amplifier. Ok now that you are happy that the module is setup correctly apply power via a VARIAC if you have access to one, otherwise just power the amplifier up. Looking at the voltmeter you should get from 1mv to 50mv offset voltage. If this is not the case then power the amplifier down and check your work. Assuming all is well then power the amplifier down and find a small flat blade screwdriver so you can be ready to adjust P1 for the biasing of the o/p stage. But first connect the voltmeter across one of the o/p stage Source resistors using Alligator leads. Now reapply power to the amplifier and slowly adjust P1 while watching the voltmeter, for a reading of 18mv. Now check across the rest of the Source resistors and find the one, which has the highest reading, and adjust P1 till 18mv is read. Now connect a load and signal source to the amplifier and with a CRO if you have access to one observe that the waveform is clean and free from noise and distortion. If you don't have a CRO and Signal generator, connect a pre-amp and loudspeaker and have a good listen. The sound should be very clean and dynamic. Congratulations, the amplifier is complete. Best Regards Anthony Eric Holton 8th February 2001 www.aussieamplifiers.com

Testing the module

6

Specifications for the AV800 MOSFET Amplifier

All measurements were taken at an AC Mains input of 240 volts. And with a 2kva Toroidal Transformer powering the Amplifier module. Filtering with only 10,000uf per voltage rail One channel only was been driven. Frequency response 10hz to 100khz THD measured at 100 watts into 8 Ohms 0.01% @1khz Power Output into 8 Ohms = 450 Watts RMS Power Output into 4 Ohms = 820 Watts RMS Damping Factor = 400

7

Component List for the AV800 MOSFET Amplifier
All Resistor values unless otherwise specified are ¼ watt 1% metal films Designators
C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 D1 D2 HS1 HS2 LD1 LD2 P1 Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 Q19 Q20

Component Value
100uf 160v RB 10PF Ceramic 47UF/100V RB 47UF/100V RB 47UF/100V RB 47UF/100V RB 47UF/100V RB 47UF/100V RB 10pf Ceramic 1uf MKT 2n2 MKT 68pf Ceramic 2n2 MKT 220uf 25v RB 47uf Bipolar 100nf MKT 100nf MKT 47uf Bipolar 47uf 25v RB 47UF 100V RB 47UF 100V RB 47UF 100V RB 47UF 100V RB 47UF 100V RB 47UF 100V RB 100uf 160v RB 100nf-x2/250vac Mains Rated 1N4007 1 amp diode 1N4007 1 amp diode 1 inch pitch, Min 10 Degrees/Watt 1 inch pitch, Min 10 Degrees/Watt LED any colour LED any colour 5K POT Multi turn or 10 turn 2SC2240 TO-220 2SC2240 TO-92A 2SA1306 TO-220 2SA1306 TO-220 IRF610 TO-220 BC546 TO-92 BC546 TO-92 IRF610 TO-220 IRFP240 TO-3P IRFP240 TO-3P IRFP240 TO-3P IRFP240 TO-3P IRFP240 TO-3P IRFP240 TO-3P IRFP240 TO-3P IRFP9240 TO-3P IRFP9240 TO-3P IRFP9240 TO-3P IRFP9240 TO-3P IRFP9240 TO-3P

8

Q21 Q22

IRFP9240 TO-3P IRFP9240 TO-3P

Designators
Q23 Q24 Q25 Q26 R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22 R23 R24 R25 R26 R27 R28 R29 R30 R31 R32 R33 R34 R35 R36 R37 R38 R39 R40 R41 R42 R43 R44 R45 R46 R47 R48 R49 R50 R51 R52 R53

Component Value
BD681 TO-126 2SC3298 TO-220 2SC3298 TO-220 IRF9610 TO-220 2k2 2k2 120 100 Wire LINK2 0.22 3 WATT 0.22 3 WATT 0.22 3 WATT 0.22 3 WATT 0.22 3 WATT 0.22 3 WATT 0.22 3 WATT 10k 1watt 470 470 470 470 470 470 470 47K 100 Wire LINK4 100 4k7 4k7 4k7 47 47 4k7 4k3 10 Ohm 1watt 1k 100 470 390 15k 330 470 10k 1 Watt Wire LINK3 10k 1watt 100 100 Wire LINK5 470 470 470 470 470 470 470 470

9

R54 R55

10k 100

Designators
R56 R57 R58 R59 R60 R61 R62 R63 R64 R65 ZD1 ZD2

Component Value
100 100 0.22 3 WATT 0.22 3 WATT 0.22 3 WATT 0.22 3 WATT 0.22 3 WATT 0.22 3 WATT 0.22 3 WATT 10 OHM 5 WATT 15v 1watt Zener Diode 15v 1watt Zener Diode

10

Component Value Misc
1 Inch pitch 10 Degree/watt heat sink Wire Links

Quantity
2 4 14 8 1 1 3 1 1 1 1 2 1 1 2 17 1 1 4 1 1 1 1 1 1 1 2 1 1 2 12 1 2 1 1 1 2 2 2 2 2 1 2 1 7 7 2

Resistors
0.22 Ohm 3 Watt Resistor 100 Ohm Resistors 100 Ohm Resistors 10k Ohm Resistor 10k Ohm 1watt Resistor 10 Ohm 1watt Resistor 120 Ohm Resistor 15k Ohm Resistor 1k Ohm Resistor 2k2 Ohm Resistor 330 Ohm Resistor 390 Ohm Resistor 47 Ohm Resistor 470 Ohm Resistor 47K Ohm Resistor 4k3 Ohm Resistor 4k7 Ohm Resistor 10 Ohm 5 Watt Resistor 5K multi turn POT

Capacitors
10PF Capacitor 10pf Capacitor 100nf MKT Capacitor 100nf MKT Capacitor 100nfx2 250vac Capacitor 100uf 160v Capacitor 1uf MKT Capacitor 220uf 25v Capacitor 2n2 MKT Capacitor 47UF 100V Capacitor 47uf 25v Capacitor 47uf BP Capacitor 68pf Capacitor

Semiconductors
15v 1watt Zener Diode 15v 1watt Zener Diode 1N4007 1 amp Diode 2SA1306 Transistor 2SC2240 Transistor 2SC3298 Transistor BC546 Transistor BD681 Transistor IRF610 Transistor IRF9610 Transistor IRFP240 Transistor IRFP9240 Transistor Light Emitting Diodes

11

How to match Hexfet MOSFETs
When using this type of MOSFET in the AV800 amplifier is strongly recommended that the output stage devices be matched. As it has been found that if this is not done then there is no guarantee that they will share the current under load. The Source resistors provide only a bit of local feedback and don't in any way force the devices to current share. The best method I have found to work very well utilises just a 150 Ohm 1 watt resistor and a +15 volt DC power supply. If you look at the schematic below it shows how to connect and measure the N-channel devices and the P-channel devices. With the devices connected, as shown measure across R1 with a multimeter set to DC volts and measurement of between 3.8 volts and 4.2 volts will be shown. Simply match the device in-groups to a tolerance of +-100mv. Please note that you only have to match the n-channel to the n-channel devices and the p-channel to the p-channel devices, not the N-channel devices to the P-channel devices.

1

2

3

4

5

6

D

D

+15 VOLTSVCC DRAIN
C

GND Q2 P-channel MOSFET
C

M1 DC VOLTMETER

R1 150 Ohm 1 watt DRAIN GATE Q1 N-channel MOSFET SOURCE M1 DC VOLTMETER

GATE SOURCE R1 150 Ohm 1 watt

B

B

GND

VCC

+15 VOLTS

A Title Size B Date: File: 1 2 3 4 5 6-Feb-2001 C:\WINNT\..\FET_MATCH.Sch Sheet of Drawn By: 6 Number Revision

A

12

AV800 Schematic Build 22022001
To see this schematic in more detail use the zoom option in Acrobat 4.0.

1

2

3

4

5

6

C1 220uf 100v

C3 R4 100 D1 1N4007 47uf 100v

C4 47uf 100v

C5 47uf 100v

C6 47uf 100v

C7 47uf 100v

C8 47uf 100v

+ 92V

R1 2k2

R13 10k 1 Watt

R2 2k2

R3 100

D

D

R20 470 Q3 2SA1306 Q4 2SA1306 C2 10pf R19 470

Q15 IRFP240

Q1 2SC2240

Q2 2SC2240

C9 10pf

Q14 IRFP240

C-mount1 68pf Q6 BC546B Con? SOCKET C15 33uf R35 470 R26 4k7 Q7 BC546B

R18 470

Q13 IRFP240 D6 1N4936 (Opti onal)

ZD1 1N4744

R17 470

Q12 IRFP240

R16 R27 4k7 C11 470 R28 100 R29 100 Q5 IFR610 R24 100 ZD3 1N4737 C13 2n2 R25 4k7 P1 Q8 R38 330 IRF610 R22 100 ZD5 6.8 Volt D3 DIODE R14 470 R6 0.22 R7 0.22 R8 0.22 R9 0.22 R15 470

Q11 IRFP240

C

Q10 IRFP240

C

2n2

Q9 IRFP240

R10 0.22

R11 0.22

R12 0.22

Feed b ack

Con? SOCKET

C18 33uf

R39 470

R30 4k7 Q23 BD681 ZD2 1N4744 R31 C-mount2 4k3 68pf

C16 100nf

R40 10k 1 Watt

C10 1uf MKT

Con? SOCKET R58 0.22 R47 470 R59 0.22 R60 0.22 R61 0.22 R62 0.22 R63 0.22 R64 0.22 R65 5.6 Ohm 5 Watt

5k

D4 DIODE R34 100 ZD4 1N4737 Q26 R48 IRF9610 470 R44 100

R42 10k 1 Watt C19 47uf

R33 1K

ZD6 6.8 volts

R54 10k

C12 68pf

R43 100

Q22 IRFP9240

C27 100nf MKP x2

B

Q21 IRFP9240

B

R37 15k

Feed b ack

R49 470

Q20 IRFP9240 D5 1N4936 (Opti onal) Q19 IRFP9240

R36 390

R50 470

C17 C14 100nf MKT 220uf

Q24 2SC3298

Q25 2SC3298

R51 470

Q18 IRFP9240

R52 470 R54 100 R55 100 R53 470 R57 100 C26 220uf 100v D2 1N4007 C20 47uf 100v Q16 IRFP9240

Q17 IRFP9240

A

A

C21 47uf 100v

C22 47uf 100v

C23 47uf 100v

C24 47uf 100v
Title

C25 47uf 100v
- 92V

800 Watt Power MOSFET Amplifier
Numb er Revision

S iz e C Dat e: File: 1 2 3 4 5

22- Feb - 2001 D:\Client98\AVA MP.S CH

S h eet of Anthony E Holton Dr aw n By: 6