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I have put the amp circuit in post 162 by itself so that we can refer to it simply, as APA162.
It is a simple, very good amp.
Treat it as a model for you to work on. Don't worry about the power line voltages or transistor types. They can be changed to suit what you want.
So far your requirements are 40W into 8 Ohms and 2N3055/MJ2955 output transistors. The next thing is to know what other transistors you want to use.
Once you give that. I will let you know where to go from there.
In the mean-time, you could start assembling the other components and even start building without risk.
Notice that APA162 is divided into three stages: Input Stage, Voltage Amplification Stage (VAS), and Output Stage. This is more or less standard. The way that the three stages are designed has been proven many times to give excellent fidelity: high current output, low distortion, high slew rate, wide frequency reponse, good frequency stability. It was designed by Douglas Self*, one of the best audio amp designers in the world.
Once you get the layout and power supplies sorted out you will have an ideal facility for future improvements. The first thing would be to use the output power transistors that I reccommended in post 126 (MJL3281A_MJL1302A).
If you have any questions please ask.
* Audio Power Amplifier Design by Douglas Self, Sixth Edition, Page 382, Published by Focal Press.
You are too kind MrAl- I find most people intresting on ETO. I'm slowly reading the past posts. One member in particular, won't say who, really understands electronics, and has a way of explaining it so that others can understand too.
The self book is a nice book. There aren't a lot of amplifier design books. I'd like to find one on FET current sources, electrometer amps and nulling input bias currents.
Hmm, interesting! Never checked the opamp's performance with 5V between the rails, mostly 12V up, although I have used the amp for non linear applications at 5V.
While I'm on air, can I ask a question about one of your previous posts:
... EDIT: I am in Canada (not the OP) and the weather is lovely today, no frost and no snow (yet). The trees are dropping brightly colored leaves all over the place...
The self book is a nice book. There aren't a lot of amplifier design books. I'd like to find one on FET current sources, electrometer amps and nulling input bias currents.
I want to use 2n3055 on output stage but, I can't find 2955, I have call to stores but no stores have MJ2955 or sth. 2955. May I have to use TIP34-35 or some other complementaries? Or use only 2n3055?
I small signal transistor low noise is available, BC549 and PN2222. MPSA18 MPSA42 2SK170
Wow, that is one disturbing depiction of some nasty crossover distortion, which i am sure can be heard very well by any listener if used as an audio amplifier.
I very rarely use bold text, but that is also a very very good illustration of how NOT to bias the output stage into class A (class A is always conducting). If we think about it for a minute, if the amplifier is class A then how can it have crossover distortion? Class A means the transistor is conducting 100 percent of the time unlike class AB and so there can not be any crossover distortion.
To PROPERLY bias the output of that amplifier into class A, the output resistor can not go to ground, it must go to the NEGATIVE supply rail. If the resistor instead goes to ground (as that test picture shows) then the output stage is still working in class AB so nothing at all has been done to reduce the crossover distortion. This is very important, and makes all the difference how that output resistor is connected. This is required because the LOWEST power supply to the amplifier is a negative voltage, not ground, had it actually been ground, then connecting the resistor to ground would have worked. Since the lowest voltage is lower than ground, connecting that resistor to ground will NOT help the crossover distortion.
I want to use 2n3055 on output stage but, I can't find 2955, I have call to stores but no stores have MJ2955 or sth. 2955. May I have to use TIP34-35 or some other complementaries? Or use only 2n3055?
I small signal transistor low noise is available, BC549 and PN2222. MPSA18 MPSA42 2SK170
I have been meaning to ask about your component buying situation. Where can you get components from? Can't you buy by mail order from RS, Farnell Mouser, Rapid etc? Please let me know, not only because it would be interesting, but also it would also help to understand what the component selection constraints are- I don't mean to pry into your affairs.
I will have a look at TIP33C_TIP34C & TIP35C_TIP36C. Take note of the 'C' on the end of the part number- that is very important.
I will also have a look at the other transistors that you mention and get back.
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Thks.
