Hi everyone.
I've recently built an active crossover system using a high pass filter board that goes to my stereo active speakers and a low pass - sub filter that goes to a mono LM 3886 and that goes to a 5'' 8ohm passive speaker.
The system is powered with a 4A triple secondary transformer.
3A 19-0-19 ACV for the LM38886. After rectifier 3A 26-0-26 DCV
0.5 A 12-0-12 ACV for the high pass. 0.5A 12-0-12 DCV after rectifier.
0.5A 12-0-12 ACV for the low pass without any rectifier.
Switches on all parts of the system.
Unfortunatelly I haven't placed any delay relay between the LM3886 out and the sub speaker yet, so whenever I turn on the amp there is a momentary loud pop, movement of the woofer. I think it's because of DC. I 've already ordered a relay circuit to add there.
I alway turn on the pre amp first, then the crossover power supply, after the high pass board , then the low pass board and finally the LM 3886.
The high pass stereo active speakers part works perfectly well always
The low pass, LM 3886 mono speaker have a very erratic behaviour. Whenever I don't allow more than 10minutes between the switching of each stage the subwoofer doesn't play and it gives a faint distorted signal if I max its level. But if I allow 10 minutes of switching between the low pass and LM3886 and about 15minutes before I play anything through the system, then it plays well.
What could the problem be? Any ideas?
Thanks in advance
I've recently built an active crossover system using a high pass filter board that goes to my stereo active speakers and a low pass - sub filter that goes to a mono LM 3886 and that goes to a 5'' 8ohm passive speaker.
The system is powered with a 4A triple secondary transformer.
3A 19-0-19 ACV for the LM38886. After rectifier 3A 26-0-26 DCV
0.5 A 12-0-12 ACV for the high pass. 0.5A 12-0-12 DCV after rectifier.
0.5A 12-0-12 ACV for the low pass without any rectifier.
Switches on all parts of the system.
Unfortunatelly I haven't placed any delay relay between the LM3886 out and the sub speaker yet, so whenever I turn on the amp there is a momentary loud pop, movement of the woofer. I think it's because of DC. I 've already ordered a relay circuit to add there.
I alway turn on the pre amp first, then the crossover power supply, after the high pass board , then the low pass board and finally the LM 3886.
The high pass stereo active speakers part works perfectly well always
The low pass, LM 3886 mono speaker have a very erratic behaviour. Whenever I don't allow more than 10minutes between the switching of each stage the subwoofer doesn't play and it gives a faint distorted signal if I max its level. But if I allow 10 minutes of switching between the low pass and LM3886 and about 15minutes before I play anything through the system, then it plays well.
What could the problem be? Any ideas?
Thanks in advance
Since it's not that easy for me to try this let's talk hypothetically.
In case the problem stop, the sub start functioning immediatelly, what can we assume?
And in case the problem persist even through the other amp and speaker (immediate faint distorted signal when the sub pre is maxed, or proper function after a long waiting and orderly switching). In that case what can we assume?
In case the problem stop, the sub start functioning immediatelly, what can we assume?
And in case the problem persist even through the other amp and speaker (immediate faint distorted signal when the sub pre is maxed, or proper function after a long waiting and orderly switching). In that case what can we assume?
Thanks a lot. The power supply provides 0.5A of 2 x 12VAC and 0V. The pcb demands VAC since it rectifies the power on board (no external rectifier needed).
According to the designer it draws around 300mA. So that side of the supply is enough. Maybe 3A of 19VAC are not enough for the LM3886 and the 8 ohm speaker. And the whole combination of being powered from the same transformer may cause some problems.
I doubt grounding problems since all the boards have a common ground in a quite small aluminum case and there are no shorts or something. The power supply and all the rectifier boards are in a different plastic box.
According to the designer it draws around 300mA. So that side of the supply is enough. Maybe 3A of 19VAC are not enough for the LM3886 and the 8 ohm speaker. And the whole combination of being powered from the same transformer may cause some problems.
I doubt grounding problems since all the boards have a common ground in a quite small aluminum case and there are no shorts or something. The power supply and all the rectifier boards are in a different plastic box.
All I can say is that in order to troubleshoot it, you have to go step by step and test each function separately.
For instance, find out if the dedicated sub lm3886 is working fine. Disconnect active circuit and bring the signal from outside source and feed it directly to the amp. If you get nice clean powerful undistorted sound, all is good, you move on. And do on.
Otherwise I can not help. Good luck.
For instance, find out if the dedicated sub lm3886 is working fine. Disconnect active circuit and bring the signal from outside source and feed it directly to the amp. If you get nice clean powerful undistorted sound, all is good, you move on. And do on.
Otherwise I can not help. Good luck.
Thanks Adason for your help anyways.
I have tried the amp on its own with just line signal, everything fine. Then I have tried the amp and the low pass with everything disconnected, everything fine. Combined with the high pass, and the problem occurs (and its gradual solution). High pass on its own perfectly fine always.
High pass and low pass share the same input jacks. Common ground for the whole circuit. No ground for the power supply. 3 different 0V lines from the power supply secondaries. The red light on the amp rectifier board takes a long time to fade out completelly.
I guess it's something with the power supply current capacity or something. I think all three combined draw a lot of current (since the sub and the amp play at their limits because the voltage and the 5'' speaker are quite small for 8ohm sub duities ).
Also could be something with the LM3886 chip (mute etc.) or even a bad cap or something on the sub board.
PS. I beleive strongly that if something's not broken don't fix it, that's why in this case I don't try to improve blindly something that works (even somehow eratically).
Only if somebody has sorted out a similar issue and has a positive answer that the problem is at a specific part of the circuit I would do the disconnections and follow the steps suggested.
I have tried the amp on its own with just line signal, everything fine. Then I have tried the amp and the low pass with everything disconnected, everything fine. Combined with the high pass, and the problem occurs (and its gradual solution). High pass on its own perfectly fine always.
High pass and low pass share the same input jacks. Common ground for the whole circuit. No ground for the power supply. 3 different 0V lines from the power supply secondaries. The red light on the amp rectifier board takes a long time to fade out completelly.
I guess it's something with the power supply current capacity or something. I think all three combined draw a lot of current (since the sub and the amp play at their limits because the voltage and the 5'' speaker are quite small for 8ohm sub duities ).
Also could be something with the LM3886 chip (mute etc.) or even a bad cap or something on the sub board.
PS. I beleive strongly that if something's not broken don't fix it, that's why in this case I don't try to improve blindly something that works (even somehow eratically).
Only if somebody has sorted out a similar issue and has a positive answer that the problem is at a specific part of the circuit I would do the disconnections and follow the steps suggested.
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After a bit of experimentation I realized that the problem lies on the power supply section.
What I did was just firing up the transformer and leave it for about 10min on, then switch on the low pass and seconds later switch on the LM 3886. I left it like this for about half a minute more and then by just fading in a healthy preamped sound everything works properly. Tried this several times with the same good result.
When I try without having the transformer warmed up properly (or when I leave it on overninght), then the problem occurs. So I guess it's either the rectifier board of the amplifier (filter cap charging, discharging or something around there) or the transformer itself (because it works at its limit).
Another suspect could be that I'm using xlr to unbalanced (pin 1 and 3 to ground) connections on the inputs so some DC issue may happen there.
What I did was just firing up the transformer and leave it for about 10min on, then switch on the low pass and seconds later switch on the LM 3886. I left it like this for about half a minute more and then by just fading in a healthy preamped sound everything works properly. Tried this several times with the same good result.
When I try without having the transformer warmed up properly (or when I leave it on overninght), then the problem occurs. So I guess it's either the rectifier board of the amplifier (filter cap charging, discharging or something around there) or the transformer itself (because it works at its limit).
Another suspect could be that I'm using xlr to unbalanced (pin 1 and 3 to ground) connections on the inputs so some DC issue may happen there.
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