Is there a coupling capacitor at the amp's input? Can you validly exclude driver or output power device failure? If not,...
Best regards!
Best regards!
Yes a 2.2µf mkt type capacitor, when I deactivate the loudspeaker safety I can obtain a signal of 100 Watts on 4 ohms without difficulty with my lab power supply set to -+32 V the signal is good and without distortions! If there was a failure in the preamplifier stages it would show on the output signal! Especially since I wired 2 similar modules and the 2 behave exactly the same way. I think from the beginning that it is a problem of loudspeaker security which is oversimplified! But it bothers me to add an additional protection module because there is not much space inside the box.
Neither 😉
* 0.65V positive turns T2 base ON , so it discharges 220uF cap, so T3/T4 get unbiased and release relay cutting speakers OFF
* 0.65V negative pull T1 emitter below zero, so its base is more positive and it turns ON, again discharging 220uF cap, so T3/T4 get unbiased and release relay cutting speakers OFF
* no rectification, since input resistor feede two opposite polarity BE junctions .... just not the usual way.
Clever and simple trick.
First time I saw this kind of circuit I also said "WTF?".... until it finally clicked 🙂
I guess circuit is not "broken", simply too sensitive.
I would experiment by adding two series but opposite polarity 3.3V or 4.7V Zeners between 220uF first cap and the junction of T1 Emitter/T2 Base.
That will turn trigger voltage from 0.65V to 4-5V DC, either polarity, which is still a useful DC protection sensitivity.
If amp blows it will put way more than that anyway, up to 80V DC with the amp fully built as expected.
4 or 5 V DC will NOT burn those voice coils, in any case relay will cut them off within seconds.
Try it, and if it solves the problem, leave the Zener MOD in, in any case it is way safer than no protection at all.
Almost 😉
This way new "DC trigger" level is about 6V, which clearly indicates a serious DC problem.
Original threshold was 0.65V ... too sensitive.
It does work, sort of, and I´ve seen similar ones used by many, but from what you say it´s subject to "nuisance triggering", similar to specifying a too tight Mains fuse ... sometimes blowing on "normal" turn-on.
Ok, try it and you tell us.
2 tests :
1) play amp LOUD, to clipping, it "should" not trigger.
2) with R1 NOT connected to speaker out but "floating": apply 9V or 12V or any voltage in that range to R1 now floating end, protection should trigger after a very short pause.
R1 C1 time constant is
20k - 220uF : 4.4 seconds.
meaning with 9V DC, relay will click in 4.4 seconds
I find it uncomfortably long (previous trigger time was shorter because C1 had to charge only up to 0.65V) so I would try lowering C1 to 47uF ... always bipolar of course.
Then it would trigger in slightly over a second which I like better.
As always, testing rules [tm] so please do.
This way new "DC trigger" level is about 6V, which clearly indicates a serious DC problem.
Original threshold was 0.65V ... too sensitive.
It does work, sort of, and I´ve seen similar ones used by many, but from what you say it´s subject to "nuisance triggering", similar to specifying a too tight Mains fuse ... sometimes blowing on "normal" turn-on.
Ok, try it and you tell us.
2 tests :
1) play amp LOUD, to clipping, it "should" not trigger.
2) with R1 NOT connected to speaker out but "floating": apply 9V or 12V or any voltage in that range to R1 now floating end, protection should trigger after a very short pause.
R1 C1 time constant is
20k - 220uF : 4.4 seconds.
meaning with 9V DC, relay will click in 4.4 seconds
I find it uncomfortably long (previous trigger time was shorter because C1 had to charge only up to 0.65V) so I would try lowering C1 to 47uF ... always bipolar of course.
Then it would trigger in slightly over a second which I like better.
As always, testing rules [tm] so please do.
Hi All
I was on vacation abroad so I couldn't handle it! So I tried modifying the Zener diodes but it does exactly the same thing! I came to the solution of the resistance in parallel on the non-polarized capacity see assembly! I manage to minimize the sensitivity but it's still far too sensitive for this kind of amp! So I looked at the resistor values triggering the relay in case of clipping! At 560 Ohms it triggers well before clipping! with 100 Ohms it's OK!!! I think if the final transistors explode with 80V power supply it will still work! At least it allows me to keep this shitty montage! without too many modifications!!! Which is normal given the origin of this thing! These chintoks really suck at engineering!
I was on vacation abroad so I couldn't handle it! So I tried modifying the Zener diodes but it does exactly the same thing! I came to the solution of the resistance in parallel on the non-polarized capacity see assembly! I manage to minimize the sensitivity but it's still far too sensitive for this kind of amp! So I looked at the resistor values triggering the relay in case of clipping! At 560 Ohms it triggers well before clipping! with 100 Ohms it's OK!!! I think if the final transistors explode with 80V power supply it will still work! At least it allows me to keep this shitty montage! without too many modifications!!! Which is normal given the origin of this thing! These chintoks really suck at engineering!
I have seen automatic torches, those switch on at mains failure, controlled by capacitors, 1 uF/50 V is common, sometimes a 1/63 does not work.
Try changing the capacitor, that might have some effect.
Try changing the capacitor, that might have some effect.