灌水，几款放大器电路。

chenang39

Audio Line Driver
　　Notes:
　　This preamplifier has a low output impedance, and is designed to drive long cables, allowing you to listen to a remote music source without having to buy expensive screened

cables. The very low output impedance of around 16 ohms at 1KHz, makes it possible to use ordinary bell wire,loudspeaker or alarm cable for connection. The preamplifier must be

placed near the remote music source, for example a CD player. The cable is then run to a remote location where you want to listen. The output of this preamp has a gain of

slightly less than one, so an external amplifier must be used to drive loudspeakers.



Hi-Fi Preamplifier
　　Design: Graham Maynard
　　Email graham.maynard1@virgin.net
　　
　　Notes:
　　This circuit was submitted by Graham Maynard from Newtownabbey, Northern Ireland. It has an exceptionally fast high frequency response, as demonstrated by applying an 100kHz

squarewave to the input. All graphs were produced using Tina Pro.

　The Preamp's Bode Response

　Squarewave Response with 100kHz Input Signal Applied

Total Noise at Output Measured with 600R Load

Signal to Noise Ratio at Output





2 Watt Audio Amplifier
　　Circuit : Andy Collinson
　　Email : anc@mitedu.freeserve.co.uk
　　
　　Description:
　　A 2 Watt audio amplifier made from discrete components.

　　Notes:
　　This was one of the earliest circuits that I ever designed and built, in Spring 1982. At that time I had only an analogue meter and a calculator to work with. Although not

perfect, this amplifier does have a wide frequency response, low harmonic distortion about 1.5%, and is capable of driving an 8 ohm speaker to output levels of around 5 watts

with slightly higher distortion. Any power supply in the range 12 to 18 Volts DC may be used.
　　
　　Circuit Description
　　The amplifier operates in Class AB mode; the single 470R preset resistor, PR1 controls the quiescent current flowing through the BD139/140 complimentary output transistors.

Adjustment here, is a trade-off between low distortion and low quiescent current. Typically, under quiescent conditions, current is about 15 mA rising to 150 mA with a 50 mV

input signal. The frequency response is shown below and is flat from 20Hz to 100kHz:

　　The circuit is DC biased so that the emitters of the BD139 and BD140 are at approximately half supply voltage, to allow for a maximum output voltage swing. R9 and R10

provide a degree of temperature stabilisation which works as follows. Ifthe output transistors are warm, the emitter currents will increase. This causes a greater voltage drop

across R9 and R10 reducing the available bias current. All four transistors are direct coupled which ensures:-
　　(i) A good low frequency response
　　(ii) Temperature and bias change stability.
　　
　　The BC109C and 2N3906 operate in common emitter. This alone will provide a very high open loop gain. The output BD139/140 pair operate in emitter follower, allowing the

amplifier to drive low impedance speakers. The signal to noise ration is shown below:

　　This amplifier has a S/n ratio of 115dB at 1kHz. Overall gain is provided by the ratio of the 22k and 1k resistor. A heat sink on the BD139/140 pair is recommended but not

essential, though the transistors will run "hot" to the touch.
　　
　　Original March 1999
　　Last Revision 26-6-06 by ANC



Headphone Amplifier

　　Circuit : Andy Collinson
　　Email: anc@mitedu.freeserve.co.uk
　　
　　Description:
　　An amplifier to drive low to medium impedance headphones built using discrete components.

　　Notes:
　　Both halves of the circuit are identical. Both inputs have a dc path to ground via the input 47k control which should be a dual log type potentiometer. The balance control

is a single 47k linear potentiometer, which at center adjustment prevents even attenuation to both left and right input signals. If the balance control is moved towards the left

side, the left input track has less resistance than the right track and the left channel is reduced more than the right side and vice versa. The preceding 10k resitors ensure

that neither input can be "shorted" to earth. Amplification of the audio signal is provided by a single stage common emitter amplifier and then via a direct coupled emitter

follower. Overall gain is less than 10 but the final emitter follower stage will directly drive 8 ohm headphones. Higher impedance headphones will work equally well. Note the

final 2k2 resistor at each output. This removes the dc potential from the 2200u coupling capacitors and prevents any "thump" being heard when headphones are plugged in. The

circuit is self biasing and designed to work with any power supply from 6 to 20 Volts DC.



Low Voltage Preamplifier
　　Circuit :Andy Collinson
　　Email :anc@mitedu.freeserve.co.uk
　　
　　Description:
　　A low voltage preamplifier optimised for 3 Volt operation.


　　Notes:
　　This is a special low voltage version of my audio preamp. T1's emitter voltage is biased close to half supply voltage (1.5V) to allow for maximum output voltage swing. Both

transistors are direct coupled and have closed loop feedback to aid temperature stability.
　　
　　T2 realises the amplifiers full voltage gain, and for low noise operation, T2 collector current is about 70uA. T1 merely buffers T2 and operates in emitter follower mode

providing a good low output impedance. The overall S/N ratio measured at the output is shown below:
　　Signal to Noise Ratio

　　Capacitor C3 decouples the emitter resistor of T2. Without C3 the gain of T2 would be approximately R1 / R4. With C3 the gain of T2 is now R4 in paralell with the input

impedance of T1 / the small signal emitter resistance of T2. The overall voltage gain of the circuit is around 28 times as shown below. Harmonic distortion is about 8%.
　　Harmonic Distortion

　　Frequency response is flat from 50Hz to around 200KHz. Phase change across this range varies little, see bode plot below.

　　One drawback of this circuit is that the input impedance is fairly low. This is because the input of T2 is low and has C3 decoupling the emitter. The inclusion of R7 in

series with the base of T2 raises input impedance slightly. A plot of input imedance versus freqency response is shown below.
　　Input Impedance

　　The output impedance is very low, around 66 ohms as shown in the plot below. Note that this is a preamp and therefore designed to feed into a power amplifier not drive

direct loads directly.
　　Output Impedance





24 Watt Class A Amplifier
Circuit :Marc Klynhans
　　Email : Marc Klynhans
　　
　　Description:
　　A 24 Watt Class A Amplifier made from discrete semiconductors, built and tested by Marc Klynhans from South Africa.
　　
　　Specifications:
　　Here are the specifications:
　　24W Class A into 8 Ohm
　　100mHz - 100kHz flat
　　305mV input for 24W into 8 Ohm (33dB gain)
　　THD is very low, although I have not been able to measure it properly
　　
　　Notes:
　　The supply voltage can be between 34V and 46V and the quiescent current should be set to 1.7A measured through R25 (a voltage of 0.75V must be measured over R25 for a

quiescent current of just under 1.7A). R23 is a trimmer and must be set to maximum resistance (10kOhm) when powering up. Then the resistance of R23 must be decreased until the

the quiescent current is achieved. If the amplifier is mounted on a big enough heatsink ( 0.6K/W at most) then the amplifier is very safe from thermal runaway. Intelligence must

be used when choosing power and voltage ratings of resistors and capacitors.
　　
　　I have been using this amplifier with a pair of Celestion F20's and the sound is unbelievable!
　　
　　Marc's website may be found at: http://mrcshobbies.blogspot.com

chenang39

Class-A//AB Amplifier
　　Circuit :Graham Maynard
　　Email :graham.maynard1@virgin.net
　　
　　Webmasters Note
　　Graham would be interested to hear from anyone who has built this amplifier, please use the email address above to contact Graham.
　　
　　Description:
　　A Class A // Class AB amplifier rated 100 Watts when driving a 4 ohm loudspeaker.

　　Notes:
　　This circuit developed out of my 30+ years of JLH class-A based investigations.
　　
　　The original 'simple' 1969 JLH class-A design provided excellent first cycle accuracy through mid and high frequencies (dynamic clarity) because there were no stabilisation

components nor a series output choke, whilst the NFB error correction was established via the input emitter (some describe this as current feedback).
　　
　　However it did generate rather a lot of heat, the damping was 'soft' at lower frequencies and the positive slew was weaker in the presence of loudspeaker system generated

back-EMF at higher audio frequencies. I was eventually able to improve upon the original JLH circuit by;-
　　
　　1) adding a 'helper' class-AB output stage to substantially increase power and efficiency, but leave sufficient class-A bias for real-time control maintenance through phase

shifted zero current class-AB crossovers;
　　
　　2) adding a differential input stage for zero output voltage control, but also fit a 10nF base-emitter capacitor for differential voltage operation at audio frequencies,

though with leading emitter routed feedback to maintain circuit stability and NFB control above 20kHz;
　　
　　3) adding a current mirror to obviate power-up thump, but also fit a 220nF base-emitter capacitor to ensure stable 'source only' operation above audio frequencies.
　　
　　Thus, when compared to conventional circuits, one complete high frequency phase change has been removed from the closed feedback loop in order to minimise need for any

additional stabilisation components that would otherwise render the circuit inductive at audio frequencies. The original JLH hf (current feedback) stability and simultaneously

phase coherent class-A control are retained.
　　
　　This circuit was intended for 2SC5200 operation, yet it has been successfully constructed using other device types, including a single Sanken 2SA1216+2SC2922 pair in place

of the paralleled ABs. Keep VAS, Zobel and output related wires 5cm/2" away from input devices and wiring. Use a star earth from the input location. Use star power distribution

from each fused 10mF at the pcb. Use star output node connections. Parallel all large Cs with smaller ones. Do not twist any extender e-b-c wires that might be used out to

heatsink mounted output stage devices. Mount the Vbe multiplier on the output heatsink for automatic temperature compensation. Adjust the class-AB pre-set to 50%, but adjust the

class-A pre-set to be a short circuit before the initial switch-on. I recommend 22 ohm per rail in place of the fuses in case of error at initial power-up, but do not try to set

any bias with them in circuit.
　　
　　100W-4ohm (conservatively rated) is 50W-8ohm. For 70W/35W use 30V rails. For 50W/25W, 25V. For 100W-8ohm with higher voltage rails try a 47pF Miller connected C.dom to the

VAS, it should compensate for device/stability changes with increased voltage, yet not adversely affect the class-A operation in maintaining crossover continuity. Always bias

from zero current if you increase the rail voltage. Insert a 0.22 ohm series output resistor to maintain stability when driving purely capacitive loads, and don't forget to bi-

or tri-wire out to composite loudspeaker system sections and drivers in order to obviate single cable developed dynamic voltage drops with varying loudspeaker system generated

back-EMFs, no matter how expensive your loudspeaker cable might be.
　　
　　Graham Maynard.




Buffer Amplifier
Description:
　　A hifi preamplifier designed to convert high output impedance amplifiers to 600 ohm outputs.

　  Notes:
　　A PCB layout for this circuit has been designed by Graham and is available for download by clicking this link.
　　Finished Buffer Amplifier




Audio Notch Meter
　  Description:
　　A variable notch filter with both high and low pass filters.

　　Notes
　　At first glance this circuit looks fairly complex, but when broken down,can be divided into high pass and low pass filter sections followed by a summing amplifier with a

gain of around 20 times. Supply rail voltage is +/- 9V DC. The controls may also be adjusted for use as a band stop (notch) filter or band pass filter.

蟋蟀的帅

不知道效果如何。

chenang39

原帖由 蟋蟀的帅 于 2008-6-24 20:37 发表
不知道效果如何。

试试就知道，呵呵

独钓火星鱼

这不是灌水,这是灌精~!

chenang39

原帖由 独钓火星鱼 于 2008-6-24 22:07 发表
这不是灌水,这是灌精~!

分明是灌水，没几个看。

l275319932

看不懂吧。。。

楼主应该英汉夹杂的来就好了。。。。

收藏了，说不定哪天用得到。

dfyl

不知道效果如何。