Another question about class A.

[boxedin]

Hello peeps,

I am kind of stuck in my simulation. I am facing two problems.

1. AC coupling between stages. (how i can avoid single ended CLASS A type circuit.).
2. THD problem (50% ). (this can be fixed with feedback but i don't like to do feed back). So i will figure this one out by trial and error method.

2. Dc coupling needs isolation , ac coulpling well i don't like capacitor filtering my signal frequency.

I will figure a way out. I intend to finish my simple 1-5 w class A single ended (no feedback, THD 1%) in 3 months.

It is all learning process. Thanks again for all the people who replied in this threads.

Alexk
Toronto

 

[Gandalph]

Greetings from Nortfolk

Come on boxedin, don't be shy, show us your circuits.

You make a lot ofstatements about THD, feedback, capacitors, AC coupling, but do not explain what you are doing or what the circuit is that you are working on.

A lot of people have commented on your posts, so lets see what you are up to !

Richard

 

[ilimzn]

I am kind of stuck in my simulation. I am facing two problems.
1. AC coupling between stages. (how i can avoid single ended CLASS A type circuit.).

Why would single ended necessairly mean AC coupling between stages? In fact, doing it AC coupled between stages almost presents a small challenge of sorts. And obviously, there are other topologies except single ended, so the way to avoid single ended is rather obvious?

2. THD problem (50% ). (this can be fixed with feedback but i don't like to do feed back). So i will figure this one out by trial and error method.

How about replacing trial and error with some simple math? The grocery shop + - * / type should do just fine. Your 50% problem points in two directions: either you are misinterpreting the results (50% distortion is quite obvious on a sinewave to anyone who has seen a sinewave), and/or your DC conditions are completely wrong and the amp is clipping.

2. Dc coupling needs isolation , ac coulpling well i don't like capacitor filtering my signal frequency.

Ever seen multiple supply rails used in an amplifier? Or, failing that, a choke or transformer?

I will figure a way out. I intend to finish my simple 1-5 w class A single ended (no feedback, THD 1%) in 3 months.
It is all learning process. Thanks again for all the people who replied in this threads.

There has been a lot of oportunity to learn in the many posts in this thread. Yet, it seems you are still at the same place when you started. If you insist on continuing by trial and error, I fear 3 months will not be enough. But then, I make my living designing circuits, what do I know...

 

[boxedin]

Hi,

Ok then, design a single ended two stage power amp without capacitor, no feedback what so ever, no push pull , High input impedence , low output impedence 5-10 W pure Class A single ended amplifier using BJT only.

Also it has to have max of .5% thd.

if you have one , show me the circuit, i do simulation if it matches the parameters then i buy the pcb from you.

Actually i am listening to every one suggestion. I will find things which suits my ideal goals. There are 1000's of designs for CLASS A amplifier. Each has its own advantages and disadvantages.

I have nothing to show until my simulation works. i work only weekends on the circuit simulation. so my next questions will be after saturday.

Thanks once again

Alexk

 

[ilimzn]

Hi,
Ok then, design a single ended two stage power amp without capacitor, no feedback what so ever, no push pull , High input impedence , low output impedence 5-10 W pure Class A single ended amplifier using BJT only.
Also it has to have max of .5% thd.

Hold on, why are the your requests to me suddenly much stricter than your own design goals?
1) No capacitors whatsoever? (you only wanted to avoid an interstage cap, which is a trivial problem)
2) No form of feedback at all - good luck doing that with a BJT. Before you mention Susan Parker (and you should search the forum for her work, you might find it interesting), even her amplifier employs 100% degenerative AC feedback using it's transistor as a follower.
3) Suddenly less than 0.5% THD is needed when you wanted up to 1% in the previous post?

But OK. It is doable. You need 2 BJTs, a battery (say 12V), one resistor, one trimpot, and two transformers, or one transformer and one autotransformer. For ideas on how to connect it, look up Susan Parker's work. Simulation might prove difficult, good transformer models are hard to find. Distortion largely depends on the quality of the transformers.

 

[boxedin]

oh i forgot. No transformer also.

 

[ilimzn]

Well then, good luck. Without them, you need some form of feedback to set the gain, or you need a type of transistor that is no longer in production (hasn't been for 25 years) but then that has a form of intrinsic feedback within it. Further, if you want to cancel feedback at AC, then you need capacitors. I hope you are aware that capacitors in the power supply are also in the signal path. Oh, and differential designs are actually a form of push-pull, just in case you want to go there

 

[Gandalph]

I look forward to seeing this design, it will be something of a landmark in electronics !

No capacitors, no transformers, no feedback, no pus-pull, high input impedance, low output impedance WOW !

I look forward to this with bated breath !

PS. can you use batteries ? They, and resistors, seem the only 'passive' component you have not thrown out ?

Richard

 

[lineup]

oh i forgot. No transformer also.

I think you are a big joker, boxedin


If we could be allowed to use a little bit of feedback
and maybe 3 stages to make this bipolar class A creation ...

Input and output caps, would make it even more possible.
After all, you have capacitor(s) in your loudspeaker cossover, havent you?
Or you maybe want a loudspeaker system WITHOUT crossover ....


Nelson Pass is known to have special demands and ideas when making amp.
But he sure doesnt come near to you, when making it difficult!

 

[boxedin]

Ok, you can have input and output capacitors.
No feedback though.

 

[Gandalph]

"Ok, you can have input and output capacitors.
No feedback though. "

So how do you propose to set the gain ? Typical transistors have a gain variation of about 5 times or more - i.e. a transistor of one type could have a gain of between15 and 75 (power transistors) and for small signal transistors, which often have a larger variation, between 50 and 500 !

Richard.

 

[boxedin]

we can think about gain later. Do a fixed gain first.

start with smal and simple then we can add complexities(features).

thanks for the reply.

 

[ilimzn]

we can think about gain later. Do a fixed gain first.
start with smal and simple then we can add complexities(features).

Either you don't understand the language, or you don't understand the concept of gain in an amplifier. Given the length of this topic, you seem to be doing a lot to label yourself as a troll.

And BTW capacitors are NOT required. Some form of feedback is - wonder if you can recognise it when you see it...