Hi all

Just to know my knowledge level in electronics, I'm now taking electronic circuits II in the university (second year electronics engineering student)...

What I want to do is a simple audio amplifier of power not less than 20W, for now let the input be a mic. I want to make it using very widespread parts that are almost available in most stores... I prefer to use the 2N3055 power transistor to make the power amplifier and to use an LM741 for the preamplifier...

Can this be done in a simple circuit?? any tips?

 

Hello,

Is this something you are looking for ?
http://www.elecfree.com/circuit/power-amplifier/2n3055-power-amplifier/
Try to figure out how it works.

It is better to look at some theory before.
This will give you some background information.
http://www.educypedia.be/electronics/amplifiers.htm

Greetings,
Bertus

 

Hello bertus,
This is a very good circuit for me...I searched a lot and didn't found audio power amplifier circuits with 2n3055... I recently took the classes of power amplifiers so I have some theory... this is not a problem for me. I am deciding to use an op-amp with the circuit..this is the point, op-amp with power transistors without much accessories (I can use universal transistors but not those BCXXX transistors in the circuit in the first link)

 

I am trying to build my own circuit but I need some help..I don't want to build ready circuits

 

I am trying to build my own circuit but I need some help..I don't want to build ready circuits

If you want help, you need to design something and then post it here for review. If we design it for you, you may as well build a "ready circuit".

 

Hello,

I think you should take a look at this :
http://www.eng.warwick.ac.uk/staff/elh/elh_es261_notes/notes3_m_2000.htm
It comes from the page I already gave you.

There are more pages on audio subjects over there :

Audio: General overview Amplifiers Audio compression techniques Digital audio Midi Amplifier classes Audio file formats DSP MP3

Greetings,
Bertus

 

For a first project I would seriously recommend finding better transistors than the 3055.

The 3055 transistor is horrendously unsuitabe for audio applications for many reasons Certainly, 2nd year Students could do better in 1968, in my university.

Firstly a practical objection - TO3 transistors are more difficult to mount and connect to, especially without creating unwanted earthing problems.

Secondly two electrical specification objections.
These transistors were designed for DC power supplies and low frequency servo amps. Their very poor frequency response leads to the horrendous distortion so evident in many 1970's commercial and cheapo magazine designs.
These transistors also have unsuitable gain verses output current characteristics for the power levels your are talking about.

 

He is using lousy old 2N3055 transistors with a lousy old 741 opamp.
Then the amplifier will be lousy and old.

 

He is using lousy old 2N3055 transistors with a lousy old 741 opamp.
Then the amplifier will be lousy and old.

I think 2N3055s and 741s grow on trees in the Middle East and other farflung locations. Why else would anyone use them?

 

The 2N3055 transistor has changed several times since the 1970's. The original RCA device was used in power supplies and many amplifiers. RCA published circuits using transistors like 40363 which appear to be in-house versions of the 2N3055. Many seem to agree that this transistor really is not the best for audio amps. But the RCA transistor is no longer available because RCA sold out in 1988.

ON semi and ST provide epitaxial transistors which are faster (typically 2 to 4x which makes them acceptable), and there is a PNP complement (MJ2955). The gain non-linearity is still present, but circuits like Self's "Blameless" using high open loop gains can offset this, so this is not a problem. These epi devices are not so good for linear supplies over about 40V unless used with good protection because they do not quite have the second breakdown rating of the original 2N3055.

But it seems you can still make good amplifiers with 2N3055/MJ2955 up to about 50W /8 ohm (single pair) with low distortion. The newer "linear gain" transistors give an order of magnitude reduction in distortion, but cost a lot more. Depends what you want.

As for 741's -I've never regarded these good for audio amps. Ever. Much better IC's are available -or use discretes.

If any of you have old Quad303's, try replacing the old 2N3055's with new 3055's and you can then reduce the capacitors (and a bit of jiggerypokery) to give a doubled bandwidth. Performance is impressive.

-neonstrobe