Saturday, January 22, 2011
The 300W Amplifier circuit is shown it is a reasonably conventional design. Connections are provided for the Internal SIM, and filtering is provided for RF protection (R1, C2). The input is 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 any sub.
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| Rangkaian 300W Power Amplifier For Subwoofer |
Continuous power into 8 ohms is typically over 150W (250W for ±70V supplies), and 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 do the same thing into 4 ohms at maximum supply voltage
Although I have shown MJL4281A and MJL4302A output transistors, because they are new most constructors will find that these are not as easy to get as they should be. The alternatives are MJL3281/ MJL1302 or MJL21193/ MJL21194.
Because this amplifier circuit 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.
Circuit from: www.sound.westhost.com
The amplifier circuit uses the basic circuitry of the 70W power amplifier, but modified for true Class-A operation - it should be pretty nice! This amp has been built by several readers, and the reports I have received have been very positive.
With simulations, everything appears to be as expected, but although I have yet to actually build it and test it out thoroughly, no-one has had any problems so far. Using +/-20 Volt supplies - either conventional, regulated or using a capacitance multiplier, it should actually be capable of about 22 W before clipping, but expect to use a big heatsink - this amp will run hot.l.)
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| Rangkaian 20 Watt Class-A Power Amplifier |
The current sink shown should have very high linearity, since it is based on the same concept as the output stage devices. The 0.25 Ohm resistor should cause little grief (4 x 1 Ohm 1W resistors in parallel), but some experimentation may be needed here, since the base-emitter voltage of the BC549 determines the current. This circuit works by using the BC549 to steal any excess base current from the compound pair. As soon as the voltage across the 0.25 Ohm resistor exceeds 0.65V, the transistor turns on and achieves balance virtually instantly.
The 1k trimpot in the collector of the first LTP transistor allows the DC offset to be adjusted. The nominal value is around 400 ohms, but making it variable allows you to set the output DC offset to within a few mV of zero.
The 70 watt amplifier circuit is pretty much original, and with a +/-35V supply as shown, will provide 70W into 8 Ohms quite happily. In its lifetime, many of the mods mentioned above were made anyway, since I could never find the circuit diagram when I needed it, so often made it up as I went along! It is a fair testament to the amp that all sorts of resistor and capacitor substitutions can be made, and it still works fine.
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| Skema Rangkaian 2N30055|MJE2955 70 Watt Power Amplifier |
This amplifier is fairly well behaved for turn on, and should issue (at worst) the smallest click as power is applied. When power is removed, after about 5 seconds or so, there will normally be a low level thump - this is not dangerous to speakers, unless used in tri-amp and directly connected to the tweeters - DO NOT DO THIS - not with any amp. Always use a capacitor in series with tweeters (see Bi-Amplification, Some thoughts on Tri-Amping).
Circuit from: www.sound.westhost.com
The TDA7293 Power Amplifier circuit is conventional, and is very simple because all additional internal functions are unused. The LED is optional, and if you don't think you'll need it, it may be omitted, along with series resistor R3. All connections can be made with plugs and sockets, or hard wired. In most cases, I expect that hard wiring will be the most common, as the connectors are a pain to wire, and add unnecessary cost as well as reduce reliability.
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| Skema Rangkian 100Watt Power Amplifier TDA7293 |
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| TDA7293 Pin Out |
The TDA7293 amplifier specifications might lead you to believe that it can use supply voltages of up to ±50V. With zero input signal (and therefore no output) it might, but I don't recommend anything greater than ±35V if 4 ohm loads are expected, although ±42V will be fine if you can provide good heatsinking. In general, the lower supply voltage is more than acceptable for 99% of all applications, and higher voltages should not be used unless there is no choice. Naturally, if you can afford to lose a few ICs to experiments, then go for the 42V supplies (obtained from a 30+30V transformer).
This is a simple microphone preamplifier circuit which you can use between your microphone and stereo amplifier. This circuit amplifier microphone suitable for use with normal home stereo amplifier line/CD/aux/tape inputs.
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| Skema Rangkaian Simple Microphone Preamplifier |
The circuit is based on a low noise, high gain 2 stage PNP and NPN transistor amplifier, using DC negative feedback through R6 to stabilize the working conditions quite precisely. Output level is attenuated by P1 but, at the same time, the stage gain is lowered due to the increased value of R5. This unusual connection of P1, helps in obtaining a high headroom input, allowing to cope with a wide range of input sources (0.2 to 200mV RMS for 1V RMS output).
List Component of Microphone Preamplifier Circuit
P1 : 2K2 Potentiometer
R1,R2,R3 : 100K
R4 : 8K2
R5 : 68R
R6 : 6K8
R7,R8 : 1K
R9 : 150R
C1 : 1µF/63V
C2,C3,C4 : 100µF/25V
C5 : 22µF/25V
Q1 : BC560C
Q2 : BC550C
This circuit is derived from the Portable Headphone Amplifier featuring an NPN/PNP compound pair emitter follower output stage. An improved output driving capability is gained by making this a push-pull Class-A arrangement. Output power can reach 427mW RMS into a 32 Ohm load at a fixed standing current of 100mA. The single voltage gain stage allows the easy implementation of a shunt-feedback circuitry giving excellent frequency stability.
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| Skema Rangkaian Class-A Headphone Amplifier |
The above mentioned shunt-feedback configuration also allows the easy addition of frequency dependent networks in order to obtain an useful, unobtrusive, switchable Tilt control (optional). When SW1 is set in the first position a gentle, shelving bass lift and treble cut is obtained. The central position of SW1 allows a flat frequency response, whereas the third position of this switch enables a shelving treble lift and bass cut.
Note:
- Before setting quiescent current rotate the volume control P1 to the minimum, Trimmer R6 to zero resistance and Trimmer R3 to about the middle of its travel.
- Connect a suitable headphone set or, better, a 33 Ohm 1/2W resistor to the amplifier output.
- Connect a Multimeter, set to measure about 10Vdc fsd, across the positive end of C5 and the negative ground.
- Switch on the supply and rotate R3 in order to read about 7.7-7.8V on the Multimeter display.
- Switch off the supply, disconnect the Multimeter and reconnect it, set to measure at least 200mA fsd, in series to the positive supply of the amplifier.
- Switch on the supply and rotate R6 slowly until a reading of about 100mA is displayed.
- Check again the voltage at the positive end of C5 and readjust R3 if necessary.
- Wait about 15 minutes, watch if the current is varying and readjust if necessary.
P1 : 22K Dual gang Log Potentiometer
R1 : 15K
R2 : 220K
R3 : 100K
R4 : 33K
R5 : 68K
R6 : 50K
R7 : 10K
R8,R9 : 47K
R10,R11 : 2R2
R12 : 4K7
R13 : 4R7
R14 : 1K2
R15,R18 : 330K
R16 : 680K
R17,R19 : 220K
R20,R21 : 22K
C1,C2,C3,C4 : 10µF/25V
C5,C7 : 220µF/25V
C6,C11 : 100nF
C8 : 2200µF/25V
C9,C12 : 1nF
C10 : 470pF
C13 : 15nF
D1 : LED
D2,D3 : 1N4002
Q1,Q2 : BC550C
Q3 : BC560C
Q4 : BD136
Q5 : BD135
IC1 : 7815
T1 : 15CT/5VA Mains transformer
SW1 : 4 poles 3 ways rotary Switch
SW2 : SPST slide or toggle Switch
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