OK. Lets keep the two caps shorted for now. That means you have 0.00 volts on the + input of A3 and 0.00 volts on the - input of A4. Measure on the pins to confirm that is happening. The plus 0.6 volts on D5 needs measuring on the - input of A3. Measure it on the pin to be sure. Do the same for the minus 0.6 on the + input of A4.
In that condition A3 and A4 outputs should equal almost the same voltage as the negative rail. What do the outputs measure ? and what does the negative rail measure ?
Question ? Have you used the correct opamp here. No substitution.
Next, if you remove D7 and D8 the led MUST be off. Is it ?
The voltages I mention for you to check are all critical. I suspect the output from the opamp isn't swinging low enough tbh to turn off the LED etc.
In that condition A3 and A4 outputs should equal almost the same voltage as the negative rail. What do the outputs measure ? and what does the negative rail measure ?
Question ? Have you used the correct opamp here. No substitution.
Next, if you remove D7 and D8 the led MUST be off. Is it ?
The voltages I mention for you to check are all critical. I suspect the output from the opamp isn't swinging low enough tbh to turn off the LED etc.
the opamp is LM324N, when I remove it from socket the LED goes off and after 6sec relay works,
1thing that in the pack of kit I bought instead of 4 x R47k (R14...R17) 4 x 51k was in the box, coud this be the damn problem?🙂 I need time to apply the changes you said
1thing that in the pack of kit I bought instead of 4 x R47k (R14...R17) 4 x 51k was in the box, coud this be the damn problem?🙂 I need time to apply the changes you said
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I do suspect a problem like you describe.
R14 and R15 should be OK at either 47k or 51k I think. R7 is a critical one. What value have you got fitted ? You could try lowering it to something like 10k as a test. The circuit relies on R7 to "pull down" the bases of the transistors. When the trip operates the opamp outputs swinh high (+ rail) and overcome the negative bias provided by R7.
Try that first, lowering R7.
R14 and R15 should be OK at either 47k or 51k I think. R7 is a critical one. What value have you got fitted ? You could try lowering it to something like 10k as a test. The circuit relies on R7 to "pull down" the bases of the transistors. When the trip operates the opamp outputs swinh high (+ rail) and overcome the negative bias provided by R7.
Try that first, lowering R7.
I replaced 10k that you suggested as R7, I don't understand when you're saying lower r7 because R7 is 8.2k and you suggested 10k, by the way I tried 10k then 18k then lowerized it with 5.8k then 3.9k and the LED stil on, with R7 disconnected too, can this kit take +/- 15v? the amps ps has this output for pre (7815 and 7915), is this logic to use this for both pre and protection?
I was guessing at the value R7 and what it might be. Refit the correct value back in place.
Yes, -/+15 volt should be OK, its well within the limits of what the opamp can take. If its a 12 volt relay then it will over run it slightly but probably within tolerance. You could always add a small resistor in series with the relay once its all fixed.
So back to the problem... I think you have to do as I suggested in post #23 and work through it seeing where its going wrong. We need to know the voltages I mention. If that's not conclusive then it could be an AC issue (oscillating).
Yes, -/+15 volt should be OK, its well within the limits of what the opamp can take. If its a 12 volt relay then it will over run it slightly but probably within tolerance. You could always add a small resistor in series with the relay once its all fixed.
So back to the problem... I think you have to do as I suggested in post #23 and work through it seeing where its going wrong. We need to know the voltages I mention. If that's not conclusive then it could be an AC issue (oscillating).
If you understand how it works it will help 🙂
T1 and T2 are biased OFF via R7. That ties the base of the transistors to the -V rail ensuring both transistors are fully non conducting.
Lets look at A3. Its used as a comparator. There is a fixed voltage of 0.6 volts on the - input. When the voltage on the + input exceeds this 0.6 volts then the opamp output swings high (to + rail). When the voltage on the + input is lower than 0.6 volts the opamp output is close to the -V rail. That is all the opamp outputs do, they are either at +V or -V.
A4 works the same way except the reference voltage and input are reversed. A4 output should still normally be at -V and only go to +V when triggered.
If the opamp outputs are not swinging down far enough (say they only reach -10 volts on a 12 volt supply) then there is enough voltage (the 2 volts difference) to cause D7 or D8 to conduct and still turn on the LED .
So the vital information is how close are the opamp outputs getting to the negative rail. They must get within a volt or so for the circuit to work.
T1 and T2 are biased OFF via R7. That ties the base of the transistors to the -V rail ensuring both transistors are fully non conducting.
Lets look at A3. Its used as a comparator. There is a fixed voltage of 0.6 volts on the - input. When the voltage on the + input exceeds this 0.6 volts then the opamp output swings high (to + rail). When the voltage on the + input is lower than 0.6 volts the opamp output is close to the -V rail. That is all the opamp outputs do, they are either at +V or -V.
A4 works the same way except the reference voltage and input are reversed. A4 output should still normally be at -V and only go to +V when triggered.
If the opamp outputs are not swinging down far enough (say they only reach -10 volts on a 12 volt supply) then there is enough voltage (the 2 volts difference) to cause D7 or D8 to conduct and still turn on the LED .
So the vital information is how close are the opamp outputs getting to the negative rail. They must get within a volt or so for the circuit to work.
before that isn't it better to use 47k resistors? are they causing problem? (R14...R17 51k)
or the ps I'm using (12vdc) instead of 8.5vdc?
or the ps I'm using (12vdc) instead of 8.5vdc?
R14 and 15 aren't very critical. They just limit base current to the transistor.
R16 partly determines the delay time. Higher value gives longer delay.
R17 I can't find on the diagram 🙂
What does the kit say the supply voltage should be ? although it should not be that critical. What is the coil voltage of the relay ?
R16 partly determines the delay time. Higher value gives longer delay.
R17 I can't find on the diagram 🙂
What does the kit say the supply voltage should be ? although it should not be that critical. What is the coil voltage of the relay ?
The critical thing is that opamp A3 and A4 MUST have their output within a volt or so of the -rail. If they are higher than that then the led light and the circuit won't work.
That is the critical relationship between all the voltages.
That is the critical relationship between all the voltages.
thank you mooly for your time
your description was very helpfull
I'm on it
wanna make its ps, should buy 6-0-6 trans first
your description was very helpfull
I'm on it
wanna make its ps, should buy 6-0-6 trans first
Your welcome 🙂 Hope it helps.
(Depending on current consumption (the relay) it might even work of two 9 volt batteries for testing. Connect in series, ground is the centre point giving -/+ 9 volts. If the relay draws a lot of current you could replace with a 2k2 resistor for testing. Also if you have a -/+15 volt supply available then its easy to drop it for the circuit. Even a couple of zeners, one in series in each rail should work)
(Depending on current consumption (the relay) it might even work of two 9 volt batteries for testing. Connect in series, ground is the centre point giving -/+ 9 volts. If the relay draws a lot of current you could replace with a 2k2 resistor for testing. Also if you have a -/+15 volt supply available then its easy to drop it for the circuit. Even a couple of zeners, one in series in each rail should work)
This design lack reversed diodes, preferably Schottkys, across the power supplies. If for some reason, one of the rails got reversed at power on/off, the LM324 is likely to have blown
Can't Recommend This Kit
Based on my experience I wouldn't recommend using this kit for loudspeaker protection. I am using it in a 100W per channel power amp and on two separate occasions it has failed spectacularly to do its job. On the first occasion one channel failed, the contacts on the Velleman relay instantly welded together and the coils on two $200 tweeters acted as very efficient fuses! I repaired the power amp and replaced the relays (and the tweeter coils!). The power amp was in use for a couple of years when one channel failed again. Same result, relay contacts welded together and full current delivered to the voice coils. Fortunately this time I was using the amp to drive two fairly robust woofers which managed to handle the current long enough for me to switch the amp off, so no further damage. Consequently I won't be using this kit again. For what it's worth I have used the Signal Transfer Co Doug Self amplifier and loudspeaker protection kit without any problems. In saying that the amps I use them in haven't failed to date so they haven't been tested yet but the relays are larger and much better quality than the Velleman units.
Based on my experience I wouldn't recommend using this kit for loudspeaker protection. I am using it in a 100W per channel power amp and on two separate occasions it has failed spectacularly to do its job. On the first occasion one channel failed, the contacts on the Velleman relay instantly welded together and the coils on two $200 tweeters acted as very efficient fuses! I repaired the power amp and replaced the relays (and the tweeter coils!). The power amp was in use for a couple of years when one channel failed again. Same result, relay contacts welded together and full current delivered to the voice coils. Fortunately this time I was using the amp to drive two fairly robust woofers which managed to handle the current long enough for me to switch the amp off, so no further damage. Consequently I won't be using this kit again. For what it's worth I have used the Signal Transfer Co Doug Self amplifier and loudspeaker protection kit without any problems. In saying that the amps I use them in haven't failed to date so they haven't been tested yet but the relays are larger and much better quality than the Velleman units.
the same result for me .
I ended up mounting relays with gold-plated contact and they do not carbon and do not stick at all.
I ended up mounting relays with gold-plated contact and they do not carbon and do not stick at all.
To my point of view all relay based protections are suitable for speaker connection delay only.
Nothing more.
To be worthwhile, the relay has to have a high current rating at a rail level dc voltage. Most do not, what is the Vellemann model?
Vellemans technical specs for this unit are ; DC protection:+1V/-1V. Max. input voltage:200VPP+DC. Max. switching current:10A.
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