1. Home
  2. Hobby Electronics Basics
  3. class A amplifier

class A amplifier

Hello,

First, I must say that I have not done analog electronics since a long time. So please be indulgent !

I want to do a small class-A music amplifier + preamp. I want to find the best trade-off between simplicity and sound quality.

My approach is very incremental. I have started with one old 2N3055, polarized with voltage divider composed of 2 resistors.

As the gain of the transistor is to low I finally put a (too?) small BC546 in front of the 2N3055 (Darlington). See schema:

formatting link

As I need a preamp for the volume control, I have add another BC546 to amplify the input signal. See schema:

formatting link

The DC is provided by a lab power supply (0-30V, 0-3A). I use from 5V to 12V as the 2N3055 heatsink is to small.

When I first test it, I was expected to have a crappy and plastic sound, and even smoke, but I was very surprised. The sound is clean and contains a lot of details (speaker: B&W DM110).

What I want to do now is to improve:

- the schematic (there are certainly mistakes ...)

- the component choice (better capacitor ? , better transistor ?)

Any remarks and suggestions are welcomed !

Thanks very much,

Olivier

Reply to
olivier.scalbert
Loading thread data ...

For a starter, increase C1 to 1000uF. 'T'll get the response down to about

20Hz.
Reply to
john jardine

Stop mucking about with stuff you don't understand and simply buy a modern hi-fi amp. Power amps are a real speciality (especially if you want them to be stable). It's no place for a beginner.

Do you understand stabilty criteria for example. What's a Bode plot ? etc

Graham (designer of stable pro-audio power amps since 1980)

Reply to
Eeyore

Come now Graham, he didn't mention he wants to become an EE... why be so mean?

Olivier, why not try this one?

formatting link

2SK1058 lateral mosfets can be hard to find however.

Michael

Reply to
mrdarrett

The passive pull-down resistor really limits the negative swing into the speaker. A constant-current sink would be better.

John

Reply to
John Larkin

Late at night, by candle light, Eeyore penned this immortal opus:

Hey, he's having fun, and it's not like it would go into production or anything.

- YD.

--
Remove HAT if replying by mail.
Reply to
YD

Thanks ! Done. I will try to find high quality capacitors later ...

Reply to
Olivier Scalbert

Ok, I will try it. Thanks.

Reply to
Olivier Scalbert

. . .

--- Mean Mister Mustard sleeps in the park Shaves in the dark trying to save paper Sleeps in a hole in the road Saving up to buy some clothes Keeps a ten-bob note up his nose Such a mean old man Such a mean old man

His sister Pam works in a shop She never stops, she's a go-getter Takes him out to look at the queen Only place that he's ever been Always shouts out something obscene Such a dirty old man Such a dirty old man

Mean Mister Mustard Such a dirty dirty Mean Mister Mustard Such a dirty dirty Mean Mister Mustard

Mean Mister Mustard sleeps in the park Shaves in the dark trying to save paper Sleeps in a hole in the road Saving up to buy some clothes Keeps a ten-bob note up his nose Such a mean old man Such a mean old man

JF

Reply to
John Fields

Simple facts though and a BC546 is way too tiny to drive a 2N3055.

Essentially impossible since Hitachi stopped making them. I know a company in the UK than can provide equivalents though.

That's a truly horrible circuit too.

Graham

Reply to
Eeyore

Just simple facts John.

Graham

Reply to
Eeyore

The 'quality' of capaciors is an entire irrelevance with something so primitive. In fact it's almost a complete irrelevance completely unless you buy Asian junk.

I take it you've been 'Audiophooled' by reading magazines written by wholesale fraudsters. Audiophile was it ?

Graham (pro-audio designer since 1971)

Reply to
Eeyore

primitive.

junk.

Graham, why are you so aggressive with me ? What is your problem ?

I have read it in Farnell catalog.

Olivier

Reply to
Olivier Scalbert

I have studied Bode, Nyquist, Smith diagrams, Z, Laplace, Fourier transformations and their digital implementations, ...

So I think I can read technical answers to my "beginners" questions.

Oh, by the way, I must admit that I have miss the training "how to become arrogant".

Olivier

Reply to
Olivier Scalbert

Thanks for the link Michael. I do not want to become EE ! At least good EEs should respect IEEE Code of Ethics (point 5).

formatting link

;-)

Olivier

Reply to
Olivier Scalbert

5).
formatting link

Oh that's good to know.

And to think, some people will sell amplifiers out of a van, with horrible distortion, that can even destroy your speakers...

formatting link

Michael

Reply to
mrdarrett

--- You're a goddam liar.

You know very well that this is seb and that instead of just putting the guy down by puffing yourself up as an "expert" (implying that he's a virtual nonentity) you should be helping him understand where his deficiencies lie, like Larkin did.

But no, you always have to try to make yourself feel important by trying to make it seem like everyone is less important.

JF

Reply to
John Fields

primitive.

junk.

wholesale

Oh, don't mind Graham, he's still working up the courage to ask a girl out for drinks.

formatting link

He does know his audio stuff though.

Welcome to Usenet.

Michael

Reply to
mrdarrett

primitive.

junk.

--
I believe both of his parents died when he was very young and he\'s been
angry and taking it out on the whole world ever since.

JF
Reply to
John Fields 

--
Since John Jardine suggested that he increase the _capacitance_ of C1 to
1000µF, I\'m sure Olivier took that to mean the capacitor would be higher
quality since it would extend the audio response of the amp down to
about 20Hz.

He\'s already said he\'s a newbie and just starting out, so why do you
beating him up instead of showing him the right way to do it?

Because you\'re a real shit, that\'s why.
Reply to
John Fields

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.