I received an email today from DIYAudio staff saying M2x boards are expected in stock by February. I’ve got a B1Korg to assemble first, and plan to start work on the PSU and 4U 300 chassis elements as part of an F6. Then I’ll see which I prefer when the M2 boards become available.
I've run both M2x amp boards with Tucson DBs for over an hour to start the off-set process.
The left channel readings are perplexing. I'm using the 5K trimpots (858-64WR5KLF), and I get 0.095 V DC and it is steady there. I'm unable to adjust it at all. And when I switch to mV I get OL. I've tried several different DMMs.
The right side reads around close to 0 for both mV and V DC. The trimpot does not appear to have an effect when adjusting.
The trimpot I used does not have the 3 leads in line. The middle lead I had to bend to get it in to solder. I was told this should work, but now I'm skeptical. Plus #3 from post 3 suggests using a 20K RV1 for greater adjustability.
Should I switch to the 20K and would this part work: 3296W-1-203RLF?
Both heatsinks warm up nicely, so that is working.
Thanks for the assistance.
The left channel readings are perplexing. I'm using the 5K trimpots (858-64WR5KLF), and I get 0.095 V DC and it is steady there. I'm unable to adjust it at all. And when I switch to mV I get OL. I've tried several different DMMs.
The right side reads around close to 0 for both mV and V DC. The trimpot does not appear to have an effect when adjusting.
The trimpot I used does not have the 3 leads in line. The middle lead I had to bend to get it in to solder. I was told this should work, but now I'm skeptical. Plus #3 from post 3 suggests using a 20K RV1 for greater adjustability.
Should I switch to the 20K and would this part work: 3296W-1-203RLF?
Both heatsinks warm up nicely, so that is working.
Thanks for the assistance.
You can bend the leg, I did the same, so that's not the issue. Is the offset Pos or Neg?
If it's neg post 3 is right on and helped me... it's not just changing the pot though.
JT
If it's neg post 3 is right on and helped me... it's not just changing the pot though.
JT
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Something seems amiss with the pots, potentially. 😀
Turning RV1 should alter the voltage at the gate of Q1 => Change the current through Q1 relative to Q2 => change the offset. You said that you've got heat on the outputs, and the M2x is autobiasing, soooo...
On both boards, measure the voltage between the rail side of R6 and either side of R8. Turn the pot and see if the voltage changes. If not, something may not have gone well with your re-alignment of the legs.
Clearly, I am not an expert. I think that's how it works and could point things in the right direction. Others, please chime in if that's way off base.
Turning RV1 should alter the voltage at the gate of Q1 => Change the current through Q1 relative to Q2 => change the offset. You said that you've got heat on the outputs, and the M2x is autobiasing, soooo...
On both boards, measure the voltage between the rail side of R6 and either side of R8. Turn the pot and see if the voltage changes. If not, something may not have gone well with your re-alignment of the legs.
Clearly, I am not an expert. I think that's how it works and could point things in the right direction. Others, please chime in if that's way off base.
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Ok. Current readings:
Right side: output = jumps around from +001.8 ish and -024.3 ish V DC.
I get the same readings in m V DC.
reading from R6 to R8 -40.3 V DC Turning the trimpot changes values at the resistors, but not the output
Left side: Output is a 0.946 V DC
I get OL when measuring mV DC. ????
Resistors R6 to R8 ~ 16.38 + V DC
The values change when Ii turn the trimpot for both output and resistors, but I can't get the output lower than 0.946 V DC.
So weirdly performing trimpots or something else?
Right side: output = jumps around from +001.8 ish and -024.3 ish V DC.
I get the same readings in m V DC.
reading from R6 to R8 -40.3 V DC Turning the trimpot changes values at the resistors, but not the output
Left side: Output is a 0.946 V DC
I get OL when measuring mV DC. ????
Resistors R6 to R8 ~ 16.38 + V DC
The values change when Ii turn the trimpot for both output and resistors, but I can't get the output lower than 0.946 V DC.
So weirdly performing trimpots or something else?
The 0L in mV range may just be an "overload" indication until you get below 500 mV or so?
Wait setting the range to mV until normal range shows 0.010V DC or so.....
The jumping around from 1.8 to 24.3 V DC.....is not so good......
Seems the amp is not in a working condition where it makes sense to adjust offset......
Wait setting the range to mV until normal range shows 0.010V DC or so.....
The jumping around from 1.8 to 24.3 V DC.....is not so good......
Seems the amp is not in a working condition where it makes sense to adjust offset......
Those values are off from my basic calcs. That could be just me doing it incorrectly or misinterpreting your readings.
If the pot is altering the voltage across R6 to R8, then the pot is functioning.
For clarity and just to be absolutely sure, can you confirm what you mean by output - is that between the black and red speaker terminals - i.e. you're measuring the offset? Before you were saying one channel was stable at 0V and the other was only at 0V095. That seems to have changed.
Please confirm decimal places. "001.8 ish and -024.3"
For future, I've found it helpful to note 24V3 for 24.3 volts. 0V0243 or just 24.3 mV for 24.3 millivolts. Always use units, and please continue to note the polarity. 🙂
Your DMM is behaving normally. Many DMMs will read OL (Over Limit) at anything over 200mV or so depending on the model when set to mV. Leave it on VDC if it's auto-ranging until you're stable under 0V100. If it's not auto-ranging, set it to your 2V, 20V or 200V setting depending on your readings and if it goes over limit. It will be close enough for now.
Perhaps someone that knows this circuit a bit more intimately can chime in. I'll continue thinking over it, but I don't want to lead you down the wrong path. I can't make the numbers work. It does not seem to be wildly performing pots, but I could be incorrect.
If the pot is altering the voltage across R6 to R8, then the pot is functioning.
For clarity and just to be absolutely sure, can you confirm what you mean by output - is that between the black and red speaker terminals - i.e. you're measuring the offset? Before you were saying one channel was stable at 0V and the other was only at 0V095. That seems to have changed.
Please confirm decimal places. "001.8 ish and -024.3"
For future, I've found it helpful to note 24V3 for 24.3 volts. 0V0243 or just 24.3 mV for 24.3 millivolts. Always use units, and please continue to note the polarity. 🙂
Your DMM is behaving normally. Many DMMs will read OL (Over Limit) at anything over 200mV or so depending on the model when set to mV. Leave it on VDC if it's auto-ranging until you're stable under 0V100. If it's not auto-ranging, set it to your 2V, 20V or 200V setting depending on your readings and if it goes over limit. It will be close enough for now.
Perhaps someone that knows this circuit a bit more intimately can chime in. I'll continue thinking over it, but I don't want to lead you down the wrong path. I can't make the numbers work. It does not seem to be wildly performing pots, but I could be incorrect.
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Right channel:
Offset = 0.000 V DC +
Resistors = -4.912 V DC
Left channel:
Offset = 0.939 V DC +
Resistors = 16.12 V DC +
Sorry for the confusion.
Thanks
Offset = 0.000 V DC +
Resistors = -4.912 V DC
Left channel:
Offset = 0.939 V DC +
Resistors = 16.12 V DC +
Sorry for the confusion.
Thanks
Resistors = -4.912 V DC......if you mean across R6 to R8.....you can't have a negative voltage there. It can only be positive if you have +probe at R6 (VPOS) and -probe at R8?
Have you connected power supply correct to right channel?
Have you connected power supply correct to right channel?
Happy New Year!
@Chiptech - I pondered over this a bit longer while attempting to learn this circuit more in-depth with a few fresh cups of coffee. I'm afraid my meager troubleshooting skills are no match for what you're encountering. What I'd do to mine to get to the root of the problem could lead to the demise of your M2x at worst or a lot of needless/frustrating measurements at best. I hope it is something simple. I can understand if your pot is not providing the range you need to move the offset to 0V0, but I can't get my doodlings to indicate why the offset on either channel won't move AT ALL and why it seems to be so unstable. The things I can imagine do not follow Occam's razor.
The best suggestion I have at the moment is to post some well-lit photos and wait for an expert to chime in. Good Luck! It's a marvelous project, and I hope it's making beautiful music soon.
@Chiptech - I pondered over this a bit longer while attempting to learn this circuit more in-depth with a few fresh cups of coffee. I'm afraid my meager troubleshooting skills are no match for what you're encountering. What I'd do to mine to get to the root of the problem could lead to the demise of your M2x at worst or a lot of needless/frustrating measurements at best. I hope it is something simple. I can understand if your pot is not providing the range you need to move the offset to 0V0, but I can't get my doodlings to indicate why the offset on either channel won't move AT ALL and why it seems to be so unstable. The things I can imagine do not follow Occam's razor.
The best suggestion I have at the moment is to post some well-lit photos and wait for an expert to chime in. Good Luck! It's a marvelous project, and I hope it's making beautiful music soon.
Chiptech, I second my friend ItsAllInMyHead's suggestion of posting well-lit,
in focus photos of your boards.
in focus photos of your boards.
Good evening gentlemen and best wishes 2021 .
What is the value of the bias current in IRF240/9240 in M2X?
By thanking you in advance.
JC
What is the value of the bias current in IRF240/9240 in M2X?
By thanking you in advance.
JC