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AUDIO CIRCUITS I have design some power amplifier and many more base on my own basic electronic knowledge. The aim for this circuit is to give DIY fan a chances in making own power amplifier. The circuit originally design by myself therefore some of the result may not satisfied the specifications of HiFi lovers. I use for very cheap material in building the circuit. Please BE CAUTION some of the circuit using our main 230V/110v, please get and advice from an authorize electrician. BEE POWER AMPLIFIER CLASS- A 25W RMS After a long test and burning seeking for a best power amplifier I then realized that what a such of variety of power amplifier. I have build 3 prototype of power amplifier that is a 20W Class A (project 10 a 20W class A power amplifier). Class B (blameless power amplifier by Douglas Self) and 60W class AB (Project 3A a updated 60W to 80W power Amplifier) The true result is a class A are choice of mine with a low and nice detail songs. I then decided to build my own power amplifier that is in class A topology. I found that the better solution is not the true class A power amplifier. It will required a regulated power supply and monster heatsink. It will cost me a lot and I cannot afford it. I found that a basic of class AB can be set into class A by bias it to reach at nearly 1.5A for the quiescent current. Of course a big heatsink will be used here. The push-pull concept of class AB will make it efficient of my Class A boost into 50%. A basic low noise devices and circuit topology will make it ultra low noise. Here is my basic circuit of class A that I have design.
Fig1-Bee Amplifier Full Circuit (click to bigger view) Bee amplifier is normal mode in Class AB. The power are at 60W. When it bias so high it will be limited to 25W of class A operation. My heat sink cannot cover the whole heat generated by the power transistor if I drive it high. The bigger heat sink is needed here for 30W of heat to be cool down by the air. A small fan can be put in the heat sink but you will hear small air blowing. Design Details The Bee Power Amplifier follow the generic power amplifier topology. The topology is basic compound power amplifier that other what they call symmetrical power amplifier. I do prefer the compound power amplifier then the symmetrical one. The component that use is moderate then the other type. The limitation of the component will save my money. The input impedance of Bee Amplifier are set using R1 of 220K. The value are so high to make this Bee amplifier compatible to use a tube type pre-amplifier. The C1, R2, C2, R3, R4, value will make the amplifier band width from 15Hz to 30KHz. I set to 15Hz to make it an ideal power amplifier for the turntable. The CD player limited for 20Hz to 22Khz. I heard that the turntable do not limited the band width. I love an analog, an old technology that hard to beat. The gain of "Bee Power Amplifier" is 22dB. The value of the R14 and R15 will provided the 22dB. The gain will make the input minimum of 1Vpp to gain the 22Vpp at the output. The supply to run the power amp is around 35V. The used of a regulated power supply not needed for this power amplifier. The Red LED will provide Vref for the constant current (Q3) for the input pair transistor (Q1 ,Q2). I choose around 2mA. From my experiment the value of the constant current changes the high frequency respond at the end stage. The lower the smoother in the treble. I like a bit or higher then a smooth one. I found that a value of 2mA is very ideal with my taste. It been set to 2mA using the R8 at 510R. The input pair type is a high gain (hFE) therefore a R7 at 1K required. The input pair then been connected to a current mirror (Q4,Q5) that will improve the CMRR of the "Bee Power Amplifier". The Q7 is Voltej Amplifier Section (VAS) get the current from a constant current source transistor (Q6). The Vref share a same node with the RED LED. This will make it share a same voltej drop if the input pair have a drop to. This will improve stabilization of the Bee Power Amplifier. I choose a nearly 11mA for my VAS current source using the value of R16 that will be 100R. A basic value of 100pF for the Cdom (C7) seems work fine. I try from 50pF to 220pF and still the sound better when I choose 100pF. I found many value share a same value for the C7 a 100pF. A type of ceramic disc will improve. A MKT or Polyester maybe will be a better but I to lazy to change it. At last the most distortion will come from the Output Stage. I had to choose between a Compound Darlington or Emitter Follower Darlington topology. I read that a Compound better then Emitter follower. Thus an Emitter Follower will make the Collector of the power transistor share a same node and make the mounting process easily but the heat not very linear and keep on reaching and the solution is to put Q8 mounted on a same heat sink. I really do not like this type of configuration and my Q8 is a TO92 package. A big change is to use a TO220 package to mount it on a same heat sink. I choose the compound Darlington configuration and the value of R19 and R20 will be form 100R to 220R. I choose a 220R, I just take the original copy of the compound Darlington. The Power transistor that I will used is a slow switch type of 3MHz. This is to prevent a internal oscillation because it will be run at high bias current (1.5A). I tried to use a fast switch type that have a great of 30MHz and it run very hot and get burn easily. A C8 is to make any small oscillation from not happed to the power transistor. It originally to use for a fast power transistor when bias at class AB or B. I do not omit it just in case of protection the power transistor even a slow one. The gain is set by from a configuration of the R14, R15 with a caps of 100uF (C5). This make the Bee power amplifier of a 22dB in gain. Power Supply I use unregulated power supply. A 25V for each real will provided a 25W of output in the speaker. It need a big power toroidal type transformer of 70VA for a mono. I built a mono block to get a higher stereo separation at end result. The 150VA of 18Vpp will enough to drive the Bee power Amplifier in stereo. If you want to use an unregulated power amplifier, you must use at least 46,000uF/50V for the power capacitor. Do not forget to put a small heat sink at the 35A bridge diode. This Class A will run very hot. The best result you will find when you get a regulated power supply circuit. You can get it www.sound.au.com . I will not provide this circuit. This power supply will help you get rid of all small hum from the power amplifier. Be ready your budget because it will cost you a lot. Test Result I started to play a love songs. A love songs have a small music instrument that naturally seems hard to be heard in a normal amplifier. I found that Bee Power Amplifier very audioable for this small music instrument, this mean the Bee Power Amplifier have a better details. I playing Out of Reach-Gabrielle a small of a violin getting out clearly and fly free from my loudspeaker. The vocal from the singer natural with slow ambiance of a backup singer. I then increase the volume until 1/2 of the turn, the result still impressive bass and treble a big control from the Bee Amplifier. I will never go over loud in overall respond from the bass, mid-bass, mid and treble. A control mean more power in our hand. I had to change the track to Hero-Mariah Carey. The singer have high loud voice but still with a small air like from her voice. I feel the Bee Amplifier still very great in the performance even I increase the volume to nearly 1/2 of the turn. The voice still the control of the Bee Amplifier. I had in my mind that this is the true control for most power amplifier fails. I change it to a new type of songs. The power of bass and treble from this type of song., what I have in the list ok Mason's Violin-DJ MASON. The test found that it have a big bass with a solid one. The violin are very details full of nutrition. This Class-A better then the class AB that I have made before. The total feel in listening to this music changes to a great deal. The treble are very on my taste. I cannot accept a to smooth of treble. A bit of enough in the treble what I'm aiming one. A great deal of my sensitive ears. I wanted more in the list of hours of listening test. I play the hardest songs. I choose Phantom of the Opera. I found that this is the critical music with a orchestra instrument and a Pavarotti singer. A melody of glass broken type make it a big test. I started to play. I found what the thing I really want, an open crystal clear in the vocal and the big small details sound come out freely into my room. I love this music before this it such a shy singer with a dull treble. bass and orchestra instrument. A live concert from the famous theater in my small room. This Bee Amplifier have all the control for the sound. Never been to over blown in the music. I love the performance a big high-quality for a simple circuit. I still love the overall performance. This will be my best ever amplifier that I had built and design love the result. Overall this is a big changes of the feels of my instrument. I still use a non High-End test system. Pictures of my Bee Amplifier in class A.
Fig1-Bee Power amplifier Class A (Mono) Component list
The Component have many substitute. Send me an email if you find a problem in finding the component. The Bee Amplifier have a kits and can be order from me at nanhifi@hotmail.com Test Setup
Sound Track of testing
nanhifiŽ June 2003 |
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