HammerTech LCA 600.1 not oscillating

[Lingo]

The first thing you need to do is to make sure that the rail voltage cannot go above ±50v. Adjust the DC output of your power supply to at least 14v to see how high the rail voltage goes. If nothing over that, something like the IRF3710Z may be better. If the rail voltage goes above ±50v, something like the IRF3415 may be better.

By better, I mean more rugged. If the amp won't be abused, the 640s may be OK. The 640Ns may be somewhat better.

For the 'right' resistor, when you find the FETs that you will leave in the amp, you would use a potentiometer to adjust the resistance and adjust for the value that just makes the amp start to draw current. Start with the pot reading approximately and adjust carefully from there.

This is much like setting the bias on a class AB amplifier. Bear in mind that the amp must be oscillating when finding the value. If it doesn't want to oscillate, drive a low-level signal into the amp (no speaker/dummy load) to encourage it to oscillate.

Thank you for your reply 🙏

The rail voltage goes up to 106V when the input voltage is 14V.

I did install 640Ns on it. The amplifier is rated for 600 W into 1 Ohm. Maybe it will be alright, I guess. Also, the two other part numbers cost three times as much as the 640N here.

What if I lower the oscillation frequency? Would it be able to improve the waveform?

I've seen some amplifiers using a similar circuit design with a 47 kHz oscillation frequency, and the waveform was much better.

For the resistor, I will do as you suggested.

Thank you very much for your time and attention 🙏🙏🙏

 

[stuparumihairadu]

The first thing you need to do is to make sure that the rail voltage cannot go above ±50v. Adjust the DC output of your power supply to at least 14v to see how high the rail voltage goes. If nothing over that, something like the IRF3710Z may be better. If the rail voltage goes above ±50v, something like the IRF3415 may be better.

By better, I mean more rugged. If the amp won't be abused, the 640s may be OK. The 640Ns may be somewhat better.

For the 'right' resistor, when you find the FETs that you will leave in the amp, you would use a potentiometer to adjust the resistance and adjust for the value that just makes the amp start to draw current. Start with the pot reading approximately and adjust carefully from there.

This is much like setting the bias on a class AB amplifier. Bear in mind that the amp must be oscillating when finding the value. If it doesn't want to oscillate, drive a low-level signal into the amp (no speaker/dummy load) to encourage it to oscillate.

I am sorry to off topic this post. It's been a while since I wrote here. I am so very happy to see you are still active. I remember and very much happily so, your help on my car amp problems in the past. I shall pe putting a help request soon enough and this time (since I've grown up a bit) I will be sending some Guinness down your route for the help given. Again, happy to see you're still active here. Have a good Sunday

 

[Perry Babin]

If you drive the amp hard while watching the carrier frequency, you should see the frequency drop significantly from idle to when it's driven hard. If you have a low idle frequency, the high-power frequency may be too low. I'd prefer that the high-power carrier be up around 80kHz.

The wave shape isn't all that critical as long as the outputs have a good drive signal amplitude and shape.

If that's a handheld (battery-powered scope), you can check the drive signals by placing the probes on the gate ans source of the FETs.

When you get the amplifier fully assembled and during testing, confirm that the output stage part of the heatsink is relatively slow to heat up.