How to build a class A - Class AB amplifier? / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

How to build a class A - Class AB amplifier?

1 2 next

Move Thread

LAN_403

Inducktion

Mon Sept 26 2011, 02:03AM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

I understand the basic concepts behind building these amplifiers, and I have quite a few complementary pairs of power transistors (with 80 gain!) and was wondering, what's a good schematic to start with for a simple 1 transistor Class A amplifier, and then a complementary pair class AB amplifier?

And the reason I ask here, and not just google it, is it seems that a few schematics out there are created by .... people who don't really know what they're doing, so I was hoping someone could point me to a schematic that's proven and working by someone on here.

I appreciate it!

Sulaiman

Mon Sept 26 2011, 04:41AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

What transistors do you have ?

A class-AB is quite straightforward,
A class-A requires a good heatsink (less than 50% efficient)
and commonly a very expensive output transformer.

I have built and designed a few audio amplifiers,
If this is a 'learning exercise' then it's ok,
if you want a hi-fi amplifier then you'd be better off buying one.

101111

Mon Sept 26 2011, 05:41AM

Registered Member #575 Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263

I would check out Rod Elliot website. He has allot of general information about amplifiers and amplifier topologies, he also has a few robust designs that you could port to fit your parts and needs.

If you are aiming at something that is somewhat usable I would check out Nationals LM3886, a high power opamp specificly designed for audio use which would give a rather decent result that involving less effort and knowledge.

If you are interested in audio you should read one of Douglas Self books.

Inducktion

Mon Sept 26 2011, 02:39PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Sulaiman wrote ...

What transistors do you have ?

A class-AB is quite straightforward,
A class-A requires a good heatsink (less than 50% efficient)
and commonly a very expensive output transformer.

I have built and designed a few audio amplifiers,
If this is a 'learning exercise' then it's ok,
if you want a hi-fi amplifier then you'd be better off buying one.

To both, yes, it's a bit of a learning experience, which is why I don't want to just buy a power op amp and call it a day...

I would love to see my own amplifier working that I made with discrete parts!

Austin the Ozone

Mon Sept 26 2011, 05:33PM

Registered Member #3989 Joined: Thu Jul 07 2011, 05:10PM
Location: In a van down by the river.
Posts: 52

I'm doing the same thing only with tubes, Here are some great links that might help you: http://www.thermionic.info/

http://www.pmillett.com/tubebooks/technical_books_online.htm

The second link has some good transistor books at the bottom.

You probably already know that transistors and tubes are basically very similar tho they sometimes use different names for the same thing so alot of the tube related stuff is still useful as they do some clever tricks that can sometimes be applied to solid state. I relate with you on wanting to do it without just buying a $2 IC chip, I feel the same way.

haxor5354

Mon Sept 26 2011, 11:14PM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

i've made a class A sound amplifier from a darlington NPN pair.(only 5 components if I remember correctly)
it sounds ok and no visible clippings for a 1KHz sinewave.
only problem with it was that it always outputs DC voltage even when its not suppose to.
so the speaker coil heats up quite a bit. i've tried connecting a 100uF cap in series with the speaker but then no sound would come out of the speakers :(

google would provide you a basic schematic of a sound amp, but all the component values would differ from different transistor.
so you might need to play around with different component values to get it right (unless if you have the exact same transistors and other parts)
BRO TIP: use pots to determine the right resistor values

Sulaiman

Tue Sept 27 2011, 05:39AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Inducktion; what transistors do you have

haxor5354;
put an inductor as the collector load and connect the speaker via a capacitor.
(e.g. take apart an E I laminated core transformer,
put all the 'E' together and all the 'I' together
and make a 1mm gap between the 'E' and 'I' cores.
use the original low voltage winding as the inductor.)

Inducktion

Tue Sept 27 2011, 02:28PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Sulaiman wrote ...

Inducktion; what transistors do you have

haxor5354;
put an inductor as the collector load and connect the speaker via a capacitor.
(e.g. take apart an E I laminated core transformer,
put all the 'E' together and all the 'I' together
and make a 1mm gap between the 'E' and 'I' cores.
use the original low voltage winding as the inductor.)

and it's complement,

Experimentonomen

Tue Sept 27 2011, 06:14PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

This is the schematic for the amplifier i use daily:

And some pics of the prototype:

Sulaiman

Tue Sept 27 2011, 10:43PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Inducktion .... nice transistors, much better than what was available when I was experimenting with audio P.A.s
I've looked through some of my older notes and can't find a single high power audio PA circuit diagram
... I lost interest as my ears are no longer 'hi-fi'

The circuit diagram posted by Experimentonomen looks ok.

You should definately look here

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob