Ok so what’s the most accurate way to check for oscillation since my scope only goes up to 50mhz
Use the scope but connect it correctly.
You said:
You said:
You should never connect the scope ground to the main amplifier output. The scope ground connects to the amplifiers power supply ground (the zero volt line). You then connect the scope probe tip to whatever you want to look at such as the output of the amplifier.
Ok thank you I’ll have an update for you guys by Monday I’m waiting on parts to arrive and I have good news I was able to find the tweeter for my vintage ads speakers I’ll definitely will be installing a 1 amp fast blow fuse to the tweeter to save it from blowing again !
You could always test the amp with a dummy load resistor first. In fact the amp should be stable with no load and so you could look with the scope before ever connecting any load to the output.
I would also still recommend using a bulb tester at first.
I would also still recommend using a bulb tester at first.
You guys think 1 amp is a good size to protect the tweeter ? Or should o go with 0.5 amp it’s a 4ohm tweeter !
I have a 8 ohm resistor I could try it’d a 100w but I think I’ll just hook up to scope directly to the amp like you said it should be stable enough
I’m not so much worried about the amp burning as much I am with the speakers they are very valuable to me !
Tweeters can't handle much power with their very thin and small voice coil, typically its just a few watts at most so 0.5 amp should be plenty, I bet you could even go lower for normal programme listening like an F315ma. If you blow the fuse there is no harm done.
That should be OK for normal volume levels but it isn't very large in the scheme of things. If it gets to hot to comfortably hold your hand or fingers on (like a hot radiator) then you need larger. With no signal it should stay quite cool.
Alright another problem I accidentally shorted the amplifier positive output with the ground it was a split second and I mean a split second but the transistor still blow there was no input why should they blow if there is no input ?!?
You're not having much luck with this are you 🙁
If there is no signal and if the DC offset is low then I think it all comes down to how low the output impedance of the amp is at the terminals. If there is a series output inductor and/or a series low value resistor then that should save it from disaster.
Without any significant resistance the amp sees not only a short but also a collapse of the feedback loop which would then most likely turn on the output stage harder and with it working into a short the transistor fail.
A transistor junction can fail 100's or 1000's of times faster than a normal fuse.
If there is no signal and if the DC offset is low then I think it all comes down to how low the output impedance of the amp is at the terminals. If there is a series output inductor and/or a series low value resistor then that should save it from disaster.
Without any significant resistance the amp sees not only a short but also a collapse of the feedback loop which would then most likely turn on the output stage harder and with it working into a short the transistor fail.
A transistor junction can fail 100's or 1000's of times faster than a normal fuse.
Dam so I need to keep a lot of these transistor in stock cause what if someone else is using the amp and they by accident short the output and boom ! Are all amps like that ? If you short the output they fail?
Not all amps, many do have electronic protection to monitor the current (in those low value white 'emitter' resistors).
Commercial amps usually have some of these safeguards, diy ones not always.
If yours is like the one in post #13 then it has no protection and also no series output inductor (which can add enough series resistance to stop this happening)
Commercial amps usually have some of these safeguards, diy ones not always.
If yours is like the one in post #13 then it has no protection and also no series output inductor (which can add enough series resistance to stop this happening)
I see so an inductor on the output stage could mitigate the short circuit ! Yes mine actually has 0.1 ohm resistors on the output stage like the post 13 . Got to say I’ve learned so much from this stupid amp lol 😂
The crucial part is to have a little series resistance from the output of the amp to the speaker sockets. An inductor can do that and tbh most amps include one for stability.
The 0.1 ohm resistors in your circuit are not in series with the output... its a subtle difference.
Look at this output stage. The speaker terminal is shorted and the dissipation in the output transistor is well over 600 watts.
Now we add a low value resistor at the output and then apply a short. The amp can maintain the main output at what is the normal DC offset of the amp and the 0.1 ohm does not remove the feedback. The output stage operates normally and in fact 40ma bias current is flowing normally. The same transistor is just dissipating 1.6 watts. All good in this state.
If any signal was present the amp would try and drive that signal into the 0.1 ohm and that would draw excess current. That is where electronic protection would come into play and also rail fuses if fitted.
The 0.1 ohm resistors in your circuit are not in series with the output... its a subtle difference.
Look at this output stage. The speaker terminal is shorted and the dissipation in the output transistor is well over 600 watts.
Now we add a low value resistor at the output and then apply a short. The amp can maintain the main output at what is the normal DC offset of the amp and the 0.1 ohm does not remove the feedback. The output stage operates normally and in fact 40ma bias current is flowing normally. The same transistor is just dissipating 1.6 watts. All good in this state.
If any signal was present the amp would try and drive that signal into the 0.1 ohm and that would draw excess current. That is where electronic protection would come into play and also rail fuses if fitted.
Wouldn’t that 22ohm resistor affect the impedance of the speaker? You would be basically attenuating the output volume !
Also the 100pf caps I orderd arrived today but they all measure 116pf is that fine or will I run into trouble ?
Also the 100pf caps I orderd arrived today but they all measure 116pf is that fine or will I run into trouble ?
Also I orderd a 2w 10ohm resistor instead of a 1w 10ohm is that a problem? It’s for the zobel network !
All the R's are just component designators. There is no 22 ohm 🙂
R20 and R21 are 0.22 ohm and the normal 'emitter' resistors seen in most amps.
R22 is the load (speaker if you like) and with it set even as low s 0.1 ohm the amp will set all the DC conditions correctly.
Should be fine. Also unless you have a way of checking the calibration of the meter then don't assume they are wrong. The extra 16pF could be little more than stray lead capacitance adding to the result.
2W is fine. It will withstand an overload better should it ever need to.