Biasing a NPN Transistor

Hello all, i have set myself the task of designing from scratch at Transistor Amplifier.

I hope to be able to create an amplifier capable of providing 1 Watt into 8 Ohm from a Transistor Based amplifier.

I intend it to be based around an mp3 player, mainly because of what i have read there is a standard headphone output allowing my amp to be used on a varying array of sources (im dreaming i know)

but im having a few issues:

1) What is the source impedance, I know for example when i put my multimeter across the output of my Ipod i get 3800 Ohm (Left Channel to Ground), is this the Source/Input Impedance?

2)How do you determine what the Impedance of the actual amplifier will be once completed?

3)For a Pre-Amp stage i planed on using a BC547, now looking on the graphs i see it shows the Vce and Ib at a particular Ic at "Saturation", now how do you use these graphs to determine the BC547's Q point and how to appropriately bias the Transistor so it is not in "Cut-off" nor in "Saturation"?

BC547 Datasheet with graphs:
http://www.datasheetcatalog.org/datasheet/mcc/548B.pdf

4) Also concerning the Graphs it states the relevant values at for instance when the Ic is 10mA, or Ic is 1mA, but they only show when the Vce is 5V, how do you calculate a Vce its position relevant to the Q point to see if it is in Saturation or Cut-off?


Please help and explain as simply as possible (i struggle to make sense of things without someone talking me through it)

Many thanks and regards in advance

Can anyone please help?

Read this whole thread: https://www.electro-tech-online.com/threads/my-first-class-ab-amplifier.113558/

You will need to specify which class of amplifier that you want to build

Amplifier classes:
A /most common
B /most common
AB /most common
C
D /most common
E
F
G
H
and others such as class T

A good amount of info about them here: Electronic amplifier - Wikipedia, the free encyclopedia

Hope that helps!

-Ben

Ah yes, i forgot to mention i would prefer it to be a Class A amplifier

Warlord_1011 said:

Ah yes, i forgot to mention i would prefer it to be a Class A amplifier

Click to expand...

So you know that class A amplifiers are inefficient, but their sound quality is amazing!?
They are the simplest of them all too.

-Ben

An example class A amplifier circuit:

ben7 said:

An example class A amplifier circuit:

Click to expand...

hi ben,
I would suggest for a earpiece load it should be capacitor coupled, dont want DC flowing in the earpiece coil

ericgibbs said:

hi ben,
I would suggest for a earpiece load it should be capacitor coupled, dont want DC flowing in the earpiece coil

Click to expand...

Oh yeah good catch

-Ben

Despite how useful this has been so far (thank you ben for your input) i still haven't found out how to appropriately bias the transistor at a certain Vce, for instance on the datasheet it gives the performance of a transistor when Vce is at 5 Volts, but i dont want that i would prefer a Vce of 3 Volts instead, but then how do i determine what base and collector current would be reqired to ensure the transistor is not in either Cut-off or Saturation

Warlord_1011 said:

Despite how useful this has been so far (thank you ben for your input) i still haven't found out how to appropriately bias the transistor at a certain Vce, for instance on the datasheet it gives the performance of a transistor when Vce is at 5 Volts, but i dont want that i would prefer a Vce of 3 Volts instead, but then how do i determine what base and collector current would be reqired to ensure the transistor is not in either Cut-off or Saturation

Click to expand...

hi,
Look at this web tutorial.
**broken link removed**

Thanks ericgibbs, that site has helped SO MUCH, thank you