I have added one of these to a dual mono class D amp I built with 2 mono IRS2092 boards. I have tried to check that these work if DC is present by attaching a 1.5v battery to the speaker OUT terminals but the relays are not doing anything. Have I got the wrong idea of how to check that they will work if there is DC present?
Attachments
Thanks for your reply. Having read a little bit more since I posted I see that DC is likely to be induced by a blown output stage or over driving (clipping)
So was I right to input DC by way of a battery into the speaker out to check the relay?
So was I right to input DC by way of a battery into the speaker out to check the relay?
I wouldnt put voltages into the output of the amp, it might damage something.
The DC detect is there in case of output transistors blowing and outputting dc to the speaker.
The speaker is a low impedance to dc and it often fries the voice coil.
I designed my own dc detect. It works at about 2 volts if the dc level is there for more than 500mS.
The DC detect is there in case of output transistors blowing and outputting dc to the speaker.
The speaker is a low impedance to dc and it often fries the voice coil.
I designed my own dc detect. It works at about 2 volts if the dc level is there for more than 500mS.
If you are just trying to test, put an 8 ohm R at the speaker terminal and put the battery on the channel input terminals. You could go up to two 1.5V batteries in series if 1.5V does not trigger. I'd also check both directions, IE battery + to channel in+ and battery- to channel in- and vice versa to verify both directions are caught. Don't hook the board to speakers or amp for testing. As Nigel says, putting a battery on the amp out terminals is not good.
Yes, just use a higher voltage as a test (9 volt battery) and also try it both ways around as a DC offset can be either polarity.
On another practical note...
Class D amps usually use a BTL type output stage with the speaker driven between two out of phase amp outputs. That means the speaker out terminals would both be at a high DC voltage (but zero between the two) and depending on the design of the relay board might throw up issues. If your amp is of that type then you must not ground either speaker terminal and neither must any termianl from one channel be in contact with a terminal on the other... in other words there is no common ground. So this is something you need to check.
I can see from the replies that there is much more to this than I evisaged. Thanks for all the replies and I will check whether my boards are BTL. I thought as Ihad a couple of these relay boards kicking around I would use one in this amp.......we will see.
The link is to the thread about the amps the subject of this thread. There was no information with the amps as to whether or not they are BTL. Would the fact that the relays latch mean that they are happy with the amp topology and if not would they fail to latch?
Hi!
The thread talks about an amplifier fed by symmetrical power supply, so it can be single ended or BTL. If it was just a single power supply, since there are no large output capacitors looking at the PCB, it would be for sure BTL.
1) Find if you amp is BTL or not. Very simple: check the negative (and also positive just in case) output speaker lead if it is connected to GND. If yes, it is not BTL. If there is no GND connection, turn on the amp, see if it is playing something, remove input signal and check the voltage from GND to the output speaker leads. If you find zero volt on both, this is not BTL. But if you find some relevant DC level, then is BTL. In this case, check voltage across the ouput speaker leads, you should find zero (from GND to any output lead a DC leve, and from ouput lead to lead zero).
2) Now check your DC protection PCB if the input leads have GND as common. If yes, this PCB is not suitable for BTL amps. For BTL amps, you need a kind of differential input signal with no GND connection. Or you need to use 2 separate and galvanic isolated PCB's (so different transformer windings to feed them) for each channel.
3) If your AMP is not BTL, then you can use your DC protection PCB. In this case, test the protection circuit isolated from the AMP. Feed it with AC, and insert a DC level in the INPUT leads, since is through these leads that failed DC siganl will eventually come. It must work.
The thread talks about an amplifier fed by symmetrical power supply, so it can be single ended or BTL. If it was just a single power supply, since there are no large output capacitors looking at the PCB, it would be for sure BTL.
1) Find if you amp is BTL or not. Very simple: check the negative (and also positive just in case) output speaker lead if it is connected to GND. If yes, it is not BTL. If there is no GND connection, turn on the amp, see if it is playing something, remove input signal and check the voltage from GND to the output speaker leads. If you find zero volt on both, this is not BTL. But if you find some relevant DC level, then is BTL. In this case, check voltage across the ouput speaker leads, you should find zero (from GND to any output lead a DC leve, and from ouput lead to lead zero).
2) Now check your DC protection PCB if the input leads have GND as common. If yes, this PCB is not suitable for BTL amps. For BTL amps, you need a kind of differential input signal with no GND connection. Or you need to use 2 separate and galvanic isolated PCB's (so different transformer windings to feed them) for each channel.
3) If your AMP is not BTL, then you can use your DC protection PCB. In this case, test the protection circuit isolated from the AMP. Feed it with AC, and insert a DC level in the INPUT leads, since is through these leads that failed DC siganl will eventually come. It must work.
