puzzled

[sam18]

ah yes, just done that, i still get the boom, when it first has power but that is expected but it is working a lot smoother now

 

[Osvaldo de Banfield]

Sorry, but I go again: is the final stage working of properly?

 

[sam18]

yes its working much better now ive placed that decoupling capacitor in, but how would u test the power amp if it needs a pre amplifier to work?

 

[Osvaldo de Banfield]

It is simple: put a sine signal gen at a level sufficient to get the top and bottom of the sine cut or flattened. Then, check if its level is the desired. If not, add a preamp with sufficient gain to cover the remaining need.

 

[currentflow]

Hi sam18,

Looking at your circuit, IC1 output (pin 1) will slowly rise from 0V to 12V after power on due to the time constants of R1-R3 and C1 and C2. In turn, this will cause the amplifier output to be offset by 12V. Nico's advice (insert capacitor in series with R9) will prevent this happening.

Why not supply IC1 from a regulated split rail supply and connect its non-inverting input to signal ground?

 

[sam18]

okay this is with no preamp just a signal gen plugged into the power amp.
http://i1094.photobucket.com/albums/i452/Sam_Burridge/test.jpg

 

[sam18]

and @currentflow ive pm you

 

[sam18]

looking at it now guys, do you think it would need a preamp?

 

[DF96]

can anyone tell me why my amplifier i have built is doing this when it starts up?

this is just a simulation, im hoping to build this circuit soon.

Which of these two statements is true?

My impression is that you are well out of your depth. Try to build and debug a nice simple circuit. Much more educational than simulating a more complicated circuit.

 

[DRC]

The opamp based preamp is dc coupled to the power amp but its output is NOT ground referenced - if im not mistaken it will sit at +12V. You could either use a coupling capasitor at its output OR use a 12-0-12 supply for the opamp. Actually, i would do both since you do not have a dc servo ...

dc

EDIT
ooops, Nico already said that !

 

[sam18]

even with no pre amp connected, it is still doing this

http://i1094.photobucket.com/albums/i452/Sam_Burridge/stillnotworking.jpg

 

[Nico Ras]

This may sound stupid, but did you phase the AC input signal correctly (what you use to simulate the transformer). Sometimes the obvious causes the most confusion.

 

[sam18]

http://i1094.photobucket.com/albums/i452/Sam_Burridge/transformersim.jpg

 

[Nico Ras]

I mean turn one of the AC sources up-side-down. If they are phased correctly your voltage build-up across the capacitors will be symetrical, if not the one will lag the other.

 

[sam18]

ive also found that if increase them to 50hz it dosnt do it? do you think this could of been the problem?

 

[Nico Ras]

Definitely it is. What you see in a simulator is the results from the data you enter into it. You selected 1 Hz for the mains frequency, the UK mains frequency is 50 Hz.

 

[Nico Ras]

Which of these two statements is true?

My impression is that you are well out of your depth. Try to build and debug a nice simple circuit. Much more educational than simulating a more complicated circuit.

At least you figured him out early, I did his homework.

 

[DF96]

If so, I hope he gives you a proper citation in his write-up.

 

[wahab]

The differential VAS has 180uA current per leg , a value quite low
since it drives directly the output mosfets capacitances ,
this should be increased ten folds at least.

This make me wonder if the original schematic used the ubiquitous 2N5401/
2N5551 pair instead....

The BD139/140 are well within power spec but are out of spec for Vce...

 

[DF96]

Someone needs to invent a simulator with a little bottle of blue smoke, so that excursions outside safe operating regions are more like real life!