Anyone have a recommendation on how to fix low output level and severely distorted waveform on one side of my amp? The right side looks great, but the left looks terrible and is quiet. Not sure how to isolate the problem?
Sounds ok believe it or not, but quiet.
New Guy, so be gentle. Thank you all!
A 1V, 1kH, sine wave was put in.
Here's left side (bad):
Here's the right side (Notice the voltage peak differences):
Sounds ok believe it or not, but quiet.
New Guy, so be gentle. Thank you all!
A 1V, 1kH, sine wave was put in.
Here's left side (bad):
Here's the right side (Notice the voltage peak differences):
Yes, pictures please. The pictures of the original post are not viewable. It's best to upload the pictures directly to diyAudio.
On the bad channel, what is the voltage at the drain of Q1 relative to Gnd? Were you able to adjust P1 to get the voltage to 10V?
What is the voltage across R9? It should be somewhere around 4V or higher.
On the bad channel, what is the voltage at the drain of Q1 relative to Gnd? Were you able to adjust P1 to get the voltage to 10V?
What is the voltage across R9? It should be somewhere around 4V or higher.
I may not be able to upload pics yet...new member. I got this message after trying again.
" Your post is invisible to others until a moderator approves it. After a few quality posts you will be able to post freely."
" Your post is invisible to others until a moderator approves it. After a few quality posts you will be able to post freely."
Have you compared your wiring to the guide? Have you compared the two boards to see if there are any differences?
Here's the left side (bad) board and wiring pics. I have tested all components for loose solder joints as best I know how. I'm building version 1.8.
I have checked the wiring diagram closely, but I of course could have missed/reversed something. Don't think so however.
I have adjusted P1 to have 12 volts at the drain of Q1 on both channels. This is the 24 volt version (1.8)
I measure 4.32v (left) and 4.63v (right) across R9.
I have checked the wiring diagram closely, but I of course could have missed/reversed something. Don't think so however.
I have adjusted P1 to have 12 volts at the drain of Q1 on both channels. This is the 24 volt version (1.8)
I measure 4.32v (left) and 4.63v (right) across R9.
Two things to check:
1. Voltage drop across R3 or R4. R3 and R4 are parallel for a resistance of 0.34 Ohm. That will give Iq of Q1. Compare bad left to good right.
2. Use oscilloscope to view signal at output of Q4 buffer. Output is across R9.
1. Voltage drop across R3 or R4. R3 and R4 are parallel for a resistance of 0.34 Ohm. That will give Iq of Q1. Compare bad left to good right.
2. Use oscilloscope to view signal at output of Q4 buffer. Output is across R9.
I get .5vdc drop across R4 on the right and a .35vdc drop on the left. Signal looks distorted on left, good on right.
Signal across R9 is GOOD on the left (1.38v pp) but crazily BAD on the right. Again, the left channel is the bad one. Very confusing? See attached photos.
Right side across R9:
Left Side across R9:
Generally speaking, would a severely distorted wave form like that (attached) ever be caused by a resistor? A short? Diode?
In my days and days of experience, I would think only a capacitor, transistor, or Mosfet/Jfet would cause that? Interesting how the trough of the waveform is good but the peak is flat? I'm trying to learn more how to troubleshoot vs. just replace stuff randomly to see if it fixes it.
Here is the left side with a 2V input:
In my days and days of experience, I would think only a capacitor, transistor, or Mosfet/Jfet would cause that? Interesting how the trough of the waveform is good but the peak is flat? I'm trying to learn more how to troubleshoot vs. just replace stuff randomly to see if it fixes it.
Here is the left side with a 2V input:
It may just be an illusion but your power resistors appear to be soldered on one side only. Also check the two resistors at the top right of the board.
shine a flashlight on the holes if it shines thru to the heat sink you just skipped them. I did that once.
shine a flashlight on the holes if it shines thru to the heat sink you just skipped them. I did that once.
Good idea. I added some solder to all those resisters an no luck. Same distorted output.
What is the input voltage in all of the tests?
The amplifier is supposed to have a gain of 14 dB which is 5X voltage amplification.
Are you sure that your oscilloscope shots of the buffer output are not reversed? Assuming that you used the same input signal voltage in all of the tests, the "left" buffer output was 1.38 Vpp or 0.69Vp and the "right" mosfet output was 3.20Vp. That is a gain of close to 5X. However the "right" buffer output was 0.32 Vp. If this was compared to the "right" mosfet output, the gain is 10X, which is double the expected value.
Perhaps you have a bad mosfet or bad jfet. Were the jfets matched? Were the mosfets matched or tested?
What happens if you adjust the trimmer of the bad left channel so that the voltage across R9 is equal to 4.63V of the right channel? What does the buffer output look like? What is the mosfet drain voltage?
The amplifier is supposed to have a gain of 14 dB which is 5X voltage amplification.
Are you sure that your oscilloscope shots of the buffer output are not reversed? Assuming that you used the same input signal voltage in all of the tests, the "left" buffer output was 1.38 Vpp or 0.69Vp and the "right" mosfet output was 3.20Vp. That is a gain of close to 5X. However the "right" buffer output was 0.32 Vp. If this was compared to the "right" mosfet output, the gain is 10X, which is double the expected value.
Perhaps you have a bad mosfet or bad jfet. Were the jfets matched? Were the mosfets matched or tested?
What happens if you adjust the trimmer of the bad left channel so that the voltage across R9 is equal to 4.63V of the right channel? What does the buffer output look like? What is the mosfet drain voltage?
Can we back up a minute and look at the test procedure? Where are you connecting your scope probes? Remember the ground of the scope probe goes to the RED output terminal.
Correction: Original Amp Camp gain was 14 dB. ACA 1.6/1.8 is 10 dB or 3.2X.
- 2V p-p, 1 kHz Sine wave
- I get 6.2V p-p on the right and 920mV p-p on the left. The left has a Vmax of 380mv and a Vmin of -540mv. So the left is severely clipped on the top side and symmetrical on the bottom, as well as 1/6 the total output voltage.
I double checked it and no change. ????
I never tested them myself. Don't know how. They just came in the kit.
Making them even didn't change anything. The signal on the left (across R9) is good (perfect sine wave) and the one on the right looks like noise? Baffling? I assume AC coupling on the scope is appropriate?
Ben, appreciate the help!
Absolutely. For the overall output test, I am connecting the negative scope lead to the ground bus bar (red inputs) and the scope probe to the black speaker terminal, for each channel.