opamp plus driver stage and output stage with its own supply, what could happen?

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#124
I never got on with SketchUp when it first came out, but that drawing looks like it's up there with SolidWorks. (That would have been a great Christmas present - along with a new Macbook that isn't running out of memory and space, like mine is!) It's not New Year yet, but I must take some time out to learn what Solidworks can really do, so I'm going to make that a resolution. Happy Xmas!
 
#131
Still waiting for HV opamps... Happy new year everyone 😀 it has been 2014 here for 30 minutes only.
I smoked 2 pairs of outputs yesterday, somehow I managed to connect the supply backwards. Stupid bulb tester bulb was blown 🙁
I was going to rebuild the amp but then I got high...
From silicon smoke.

I have to continue with single pair. But...
With single pair, at +-15V regulated I heard something WONDERFUL.
I tried with output transistors only but then it started to distort the audio at around 1-1,5W just sounded really wierd.
Im still listening to it, Its pretty loud at +-15V I belive the output power reaches nearly 20W But that could be a lie.

The one on picture has a design failure, those diodes did nothing, I dont know why maybe one or more of them were blown. Didnt check tho
Next one was hard wired and Its still working like a charm.

I bought 20 pairs of those drivers and outputs, for testing porpouses...
Yet I will build one 150W amp for my subwoofer in next few days if they open the damn store so i could buy some more solder, I always run out of solder before i finish my project.

A bit drunk too, must get some sleep. Tomorrow I might talk about it longer.
 
#132
Getting the supply the wrong way round will do it every time! It's great fun when you have op amps with tants around them - they explode quite spectacularly! It really is worth putting in diodes, if only to avoid this. I have managed to get things the wrong way round even when I have had everything colour coded in red and blue. (somehow one's in a bit of a haze, imagining you are doing everything right, and you just go on and do something stupid.)
 
#134
My opamp as very weird sound... outputs are biased to 0,003V on the output with 850mA on both sides at +-18V regulated opamp is OPA27GP and used 100k 1k 47uF on feedback...
Theres - supply voltagge 18V on the output...
Weird.. Like poorly biased class B
 
#135
You may need to double up on the diodes.
They may not be raising the voltage on the bases high enough to keep the transistors turned on.
It is good to match up the Vfr (diode forward voltage drop) as well.
Diodes are typically .67v for the 1N4148 that I just measured.
Some transistors may require as much as .8V or more if you are using a darlington configuration.
Just be sure that the diode is rated for the base current that is flowing through them.
Else use a higher current diode like a 1N4001 or something.

jer 🙂
 
#136
The configuration in the link you posted is the same configuration I used in post #40.
Only I used a darlington output configuration, and, The two extra diodes were required as I mentioned in the previous post, else I got distortion.

FWIW

jer 🙂
 
#137
If you are using the circuit in the article, with no drivers, then you are going to be hard pressed to get enough current from the OP27. But it shouldn't sound too bad, even if you don't have enough diodes. There are plenty of (usually early) op amps which just go into a push pull pair. I guess your problem is with how you have built the circuit.
 
#138
Parasitic oscillations comes to mind as well.

Do you have any small capacitance in parallel with the feedback resistor?
If not try adding some say 20pf to 100 pf ( or more) or so.

Or from the +input to ground works sometimes as there are a few different methods to solve such issues.
I think that is what the .01uf in my schematic was used for, But I am not positive since I tried many power supply configurations as well.

jer 🙂
 
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