It's wound on a double stacked torrid. I had to rewind this one. It had burned and cooked the output caps, too. What's funny is that only one runs hot. The other doesn't.
It's a Boss Audio NXD5500. I'm out of the house for a bit, today. I will post a picture when I get back.
There are several things that could be the reason for it to run hot.
If the other inductor is shorted, all of the load is being put on the one you re-wound. You can look at the signal on the point where the two inductors connect and you should see 1/2 of the rail-rail voltage swing if both inductors are working as they should.
Another issue could be the cores. If the cores were heated too much, their properties may have changed and could cause the inductor to heat up. Again, if both inductors are equal, you should see 1/2 of the r-r waveform where the inductors connect.
If the other inductor is shorted, all of the load is being put on the one you re-wound. You can look at the signal on the point where the two inductors connect and you should see 1/2 of the rail-rail voltage swing if both inductors are working as they should.
Another issue could be the cores. If the cores were heated too much, their properties may have changed and could cause the inductor to heat up. Again, if both inductors are equal, you should see 1/2 of the r-r waveform where the inductors connect.
Perry, I had a feeling that about the core being damaged. The one I wound was shorted and had been hot to begin with. The other showed no signs and even now, runs cool. But it did blow the caps, too. I'm thinking I need 2 cores and some more wire. Just start from scratch with both. I will check the voltage swing first.
Andrew, they are inductors. Lower left in the picture.
Andrew, they are inductors. Lower left in the picture.
Either the core is damaged/wrong one or the wire you used is too resistive.
I had trouble when I designed my first class d amp and used the wrong inductor core.
The core reached 120 degrees C !
Changed the core to t106-2 and it barely gets warm now.
I had trouble when I designed my first class d amp and used the wrong inductor core.
The core reached 120 degrees C !
Changed the core to t106-2 and it barely gets warm now.
I checked the r-r swing. I do have half the voltage at the point that they meet. Nice clean square wave. Going into the first, I have the same pattern and voltage as at the FETs. Half that at the second inductor. Leaving the second inductor, I get a distorted triangle wave. It stays the same through the caps and to the positive speaker post. But it plays well with no audible distortion.
A slight residual carrier waveform can be expected at high sensitivity settings. If you don't see the triangle waveform at 5v/div, it's likely OK.
If you power the amp up when everything is cold and start to monitor the temperature of the windings around the hot inductor, do the windings all of the way around heat up at the same rate?
If you power the amp up when everything is cold and start to monitor the temperature of the windings around the hot inductor, do the windings all of the way around heat up at the same rate?
You can get replacement cores from CWS Bytemark. I typically use the molypermalloy but they're expensive. I'm not sure what the inductance is for each of those inductors. It's probably in the 50-90uH range. If you make up two new inductors that are each about 75uH, you should be OK. Ask for tech-support from CWS Bytemark and they should be able to tell you exactly what you need.
Yeah, I think its time to make new ones. It just worries me that this one had overheated before and is running hot again. I would feel a lot better if I could find the cause of its original failure. Unfortunately, I'm at a point where I either have to fix it and take a hit on it. Or, buy it from the owner and still take the hit. This guy brings me too much work not to take care of this one.
Could 1 shorted output FET have caused it to cook an inductor and blow the caps? I've never seen it, myself. Have you?
Could 1 shorted output FET have caused it to cook an inductor and blow the caps? I've never seen it, myself. Have you?
Last edited:
Why would an inductor get hot?
1.) the dcr times the output current is too high.
2.) the impedance times the rms current (minus the DC current) is too high.
The first implies that the output current is too high.
The second implies that the wrong ferrite has been chosen.
1.) the dcr times the output current is too high.
2.) the impedance times the rms current (minus the DC current) is too high.
The first implies that the output current is too high.
The second implies that the wrong ferrite has been chosen.
- Status
- Not open for further replies.