I modified the circuit in post #7. I lower the value of the resistors and increase the value of the capacitors. I have two extra transistors to separate the two channels better. I don't like the voltage divider effect of the RC filter, I want to keep the trigger threshold at close to 0.7V.
I use a big MOSFET just because I ordered for the SS relay already.
I use a big MOSFET just because I ordered for the SS relay already.
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With my protection on post#17...
I touch the input with my finger that leads to noise in the speakers, and within few seconds, the relay disconnects the speakers. This was discovered accidentally.
I think the polycarbonates in the low pass are responsible for this. This may be due to their poor DA.
Gajanan Phadte
I touch the input with my finger that leads to noise in the speakers, and within few seconds, the relay disconnects the speakers. This was discovered accidentally.
I think the polycarbonates in the low pass are responsible for this. This may be due to their poor DA.
Gajanan Phadte
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You have schematic?
Without looking at the schematic and knowing more, my first guess is the impedance of the circuit is too high. That's what I try to avoid by taking the circuit n post 7 and lower the impedance of everything, raise the current so the circuit is less sensitive to static, touching and susceptibility to noise.
I did not post it as I have mentioned the Hafler amp model (Hafler DH500) in that post and can be found on the net.
I am not touching the circuit but my amp input.
Gajanan Phadte
Edit: A film capacitor lives more than any electrolytic.
I am not touching the circuit but my amp input.
Gajanan Phadte
Edit: A film capacitor lives more than any electrolytic.
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Sounds like your input filter is not low enough then. You touch the input, you induce 50 or 60Hz continuously.
In my circuit, the RC input low pass is 20K and 100uF. This gives -3dB at 0.08Hz. Sounds like it's very low, too low already. BUT this is the corner frequency that the amplitude drops to 0.7071 of the original amplitude. Problem is if you have a 40Vpeak sine wave, 0.707 of the amplitude is 28.3Vpeak after the filter at the corner frequency!!
So in order to make sure a 40V wave to not trigger at 0.7V detector, you have to make the lowest possible frequency of the signal to be less than 0.7V after the filter. That is over 30dB down from the -3dB point. So the actual lowest frequency for 20K and 100uF is 31 X 0.08Hz= 2.5Hz.
That's why 20K and 100uF is not over kill at all. Or else, high amplitude bass signal can trigger the relay.
In my circuit, the RC input low pass is 20K and 100uF. This gives -3dB at 0.08Hz. Sounds like it's very low, too low already. BUT this is the corner frequency that the amplitude drops to 0.7071 of the original amplitude. Problem is if you have a 40Vpeak sine wave, 0.707 of the amplitude is 28.3Vpeak after the filter at the corner frequency!!
So in order to make sure a 40V wave to not trigger at 0.7V detector, you have to make the lowest possible frequency of the signal to be less than 0.7V after the filter. That is over 30dB down from the -3dB point. So the actual lowest frequency for 20K and 100uF is 31 X 0.08Hz= 2.5Hz.
That's why 20K and 100uF is not over kill at all. Or else, high amplitude bass signal can trigger the relay.
Attached is the layout. All the unconnected pins are grounded as I have a ground plane.
The board is 1.7" X 1.05". I am waiting for the quote. This is the last pcb for the amp. I have 4 pcbs all together....OPS, IPS/VAS, Filter and this Speaker Protection. The OPS should arrive any day now.
The board is 1.7" X 1.05". I am waiting for the quote. This is the last pcb for the amp. I have 4 pcbs all together....OPS, IPS/VAS, Filter and this Speaker Protection. The OPS should arrive any day now.
You should select the RC time constant so that the highest voltage of the lowest frequency signal you WANT to pass through does not trigger the DC detection.
eg, a 100W into 8ohms amplifier designed for wideband duty must be able to pass 28.3Vac @ 20Hz and NOT trigger the protection. You may want to change those values to suit what YOU decide would be appropriate.
You can test this safely with the finished power amplifier by passing a real sinewave and adjusting the RC until the signal passes without triggering.
Then check that it actually detects and triggers with a DC of BOTH polarities. You can also check how quickly it detects small DC and medium DC and how DC. You NEED fast detection of high DC, since this is what causes damage. LTspice can do this for you.
Finally you should at least try a few voltages and very low frequencies to see the detection threshold at 10Hz and 5Hz and maybe even at 2Hz.
I don't think that doing this by normal Filter calculations gets to the answers you need.
A simulation like LTspice can do this, but as I said it (in my hands) indicated that some odd combinations of VLF gave oscillation of the detector & trigger signal.
eg, a 100W into 8ohms amplifier designed for wideband duty must be able to pass 28.3Vac @ 20Hz and NOT trigger the protection. You may want to change those values to suit what YOU decide would be appropriate.
You can test this safely with the finished power amplifier by passing a real sinewave and adjusting the RC until the signal passes without triggering.
Then check that it actually detects and triggers with a DC of BOTH polarities. You can also check how quickly it detects small DC and medium DC and how DC. You NEED fast detection of high DC, since this is what causes damage. LTspice can do this for you.
Finally you should at least try a few voltages and very low frequencies to see the detection threshold at 10Hz and 5Hz and maybe even at 2Hz.
I don't think that doing this by normal Filter calculations gets to the answers you need.
A simulation like LTspice can do this, but as I said it (in my hands) indicated that some odd combinations of VLF gave oscillation of the detector & trigger signal.
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