Hey everyone,
I’ve built a 1000W RMS amplifier designed to drive a 2Ω load. I'm supplying it with ±80V rails. However, when I check the output voltage (without any load connected), the signal starts clipping at only 55V peak.
I was expecting a higher swing, given the rail voltage. Could this be due to a weak driver ? Would adding a predriver help improve the voltage swing?
Any insights or suggestions would be appreciated
I’ve built a 1000W RMS amplifier designed to drive a 2Ω load. I'm supplying it with ±80V rails. However, when I check the output voltage (without any load connected), the signal starts clipping at only 55V peak.
I was expecting a higher swing, given the rail voltage. Could this be due to a weak driver ? Would adding a predriver help improve the voltage swing?
Any insights or suggestions would be appreciated
Actually R5 is liniting the current in Q3. It is a common current generator that should leave 6 mA.
That current should be amplified by Q10 and the output transistors. No load does not take much current so the signal out should be able to get near the 80 volts. The schematic seems to be correct so there is probably a faulty component or self oscillation.
Check if it gets hot when you drive it to the max output. That is an indication of self oscillation. With fast transistors lead lenght and drawing is critical so that cam be the reason.
That current should be amplified by Q10 and the output transistors. No load does not take much current so the signal out should be able to get near the 80 volts. The schematic seems to be correct so there is probably a faulty component or self oscillation.
Check if it gets hot when you drive it to the max output. That is an indication of self oscillation. With fast transistors lead lenght and drawing is critical so that cam be the reason.
It should see about 80v as drawn , possibly
Q3 or Q10 are defective
If you place a 10k resistor across Q3 it should hit 80v no load.
Q3 or Q10 are defective
If you place a 10k resistor across Q3 it should hit 80v no load.
No 10k there wouldn't change anything. Q10 will easilyi compensate that.
If you lift out Q10 it should be near + 80v out with no load.
Can you see anything of self oscillation? Does the amplifier get hot?
If you lift out Q10 it should be near + 80v out with no load.
Can you see anything of self oscillation? Does the amplifier get hot?
Check resistor values to make sure you didn’t accidentally put one in with the wrong multiplier so it’s off by a few orders of magnitude. Ask me how I know this can happen. 😆
Also check the current through your VAS by measuring the voltage at the lower leg of R5 and applying ohms law. I believe you should have about 5-10mA, which translates to 80-100*0.005=79.5V or thereabout. Put a scope on that same node. The current should not bog down when you’re running signal through it. You will see ripple, but it shouldn’t change in any meaningful way
Also check the current through your VAS by measuring the voltage at the lower leg of R5 and applying ohms law. I believe you should have about 5-10mA, which translates to 80-100*0.005=79.5V or thereabout. Put a scope on that same node. The current should not bog down when you’re running signal through it. You will see ripple, but it shouldn’t change in any meaningful way
no faulty component here , amp is working fine . Its giving >800w rms at 2 ohm load ,,, but only issue is why its not going above 55v even without any load ,
nothing is defective as the amp is working ,,,, only problem is its not going above 55v even without any load
Ok. Have you checked your power supply? What happens if you put a scope on the rails? Does it bog down?If it’s running fine at 800W, that’s kind of the only place left to look.
If it is not going over 55v something is wrong. Agree?
It can be a self oscillation that appears at 55v. Not likely as the output transistors dont get hot. Agree?
It can be a faulty component. Agree?
For instance if you have got a fake Q8. Where did you buy it? A 100v transistor can have a breakdown at 135v.
If you glue a coin as a cooler on a 2n 5551 it can do the job.
It can be a self oscillation that appears at 55v. Not likely as the output transistors dont get hot. Agree?
It can be a faulty component. Agree?
For instance if you have got a fake Q8. Where did you buy it? A 100v transistor can have a breakdown at 135v.
If you glue a coin as a cooler on a 2n 5551 it can do the job.
Then again, since it clips at no load, it’s probably not the power supply. I’m siding with Stig: You probably have a faulty component somewhere. The schematic is standard blameless style and the component values seem fine, so it would perform well!