Metropol

Got a message asking for my help. I've forwarded it to people who know a little more than me, and thought you might be able to help too...

I need to analyse a microphone pre-amplifier circuit, in order to show how it operates.  At present I have not got the ability to do that, but it is imperative that I do do it.  I don't know whether you can help, but it's certainly worth a try. 

Basically the circuit is a balanced input, single ended output microphone amplifier, which is made up of two main stages.  The first of the stages is made up from a combination of transistors(which I just can't understand at present), and this is followed by a differential amplifier (op-amp) with a fixed gain. Sounds simple enough!?

What I really need to do is show how it works from principles (i.e. ohms law, kirchoffs laws etc.??).  I've attached a copy of the circuit.... 

And I've uploaded that copy. It would be great if you can help.

If I was going to give somebody the answer to their homework (which I won't anyway - if your mate isn't going to learn the basics of electronics {and that circuit really is basic electronics} I don't think he should get any kind of qualification that suggests he has learnt it), you'd need a better circuit diagram than that. There are a few lines missing where the image has apparently been resized or maybe scanned.

In it's present form, a circuit made from that diagram won't work!

Ebeneezer Scrooge wrote:If I was going to give somebody the answer to their homework (which I won't anyway - if your mate isn't going to learn the basics of electronics {and that circuit really is basic electronics} I don't think he should get any kind of qualification that suggests he has learnt it), you'd need a better circuit diagram than that. There are a few lines missing where the image has apparently been resized or maybe scanned.

In it's present form, a circuit made from that diagram won't work!

Thanks for that....

Is there anybody who is not on such a high horse, which has so proudly galloped to the moral high-ground, and has the ability to help out more constructively?

If that is being on my high horse, then more people should be - there are enough people in industry who don't know what they are doing!

Maybe you'll understand when you become mature and wise like me.

Ebeneezer Scrooge wrote:If that is being on my high horse, then more people should be - there are enough people in industry who don't know what they are doing!

Maybe you'll understand when you become mature and wise like me.

Think I might be a few steps already, thank you.

Well aside from the glaring negative feedback for the op amp and the fact you can use a complex analysis of potential dividers for at least one part of it, I'd say that your friend needs to sit and do it himself.

I think it's unlikely that they would learn anything (I assume of course that is it academic) if they hand it to others to think about for them. In my experience it's getting to the answer that counts, being shown the answer really won't help - no matter how descriptive it is.

Ebeneezer Scrooge wrote:I don't think he should get any kind of qualification that suggests he has learnt it)

Hey, that's not quite fair... I think Sony are looking for employees!

I agree with Ebeneezer Scrooge, though; if he hasn't learnt it then he shouldn't be qualified to say he has... in some circumstances that could even be dangerous. If this is a simple knowledge-gap his tutor should have no quarms whatsoever about explaining parts of it to him.