I had the pleasure of listening on the phone while Jim/6L6 troubleshooted garyalex's PCBs. There was quite a loud "Eureka" (the actual utterance was not G-rated) when he found the exact place where the signal path changed from "Perfectly Correct" to "Defecating The Bedsheets." That's how debug works folks, you hunt around in the dark and suddenly you step on a liquid phosphorous grenade.
This would be good information for everyone to use. Let's see it. Pretty please!
Russellc
Last edited:
I have been listening to the M2x with the Mountain View input boards for several days now, after swapping out the Ishikawa boards. Subjectively, the different boards sound very similar. There is a slight improvement in spatial presentation with the Mtn View, but this could very well be due to the extra 470 uF of capacitance between VPOS and VNEG that is added by these boards. Perhaps the Mtn View boards have a more organic sound quality to them, but it is really difficult to tell exactly what is different besides the imaging. This is good news, as it indicates that there is at least one discrete transistor implementation of an input stage that is a viable and worthy replacement for the increasingly expensive and occasionally tricky to source k170/j74 JFets used in the original M2.
I built my Mtn View boards almost exactly as the original BOM indicated, including the infamous "do not substitute" red LEDs. The only substitution I made was a PET film 470 nF capacitor for the 0.1 uF ceramic capacitor in the C3 position. I do have some ideas for other substitutions that might be made, and will eventually report on those after I've had a chance to build up to prototype vero boards and listen to them for a while.
I built my Mtn View boards almost exactly as the original BOM indicated, including the infamous "do not substitute" red LEDs. The only substitution I made was a PET film 470 nF capacitor for the 0.1 uF ceramic capacitor in the C3 position. I do have some ideas for other substitutions that might be made, and will eventually report on those after I've had a chance to build up to prototype vero boards and listen to them for a while.
Absolutely!
This is one of hose cases where a photo would be worth significantly more than 1000 words, and yet I took exactly zero photos. Sorry...
Both channels were inoperative, although with different symptoms.
Channel one -
Issues reported; no output, some smoke reported, source resistors getting really hot.
On examination the 0.47R 3W output source resistors were discolored and cracked, they were removed and measured at 0.33R, and replaced with new. The mosfets were removed and tested, both were fine, and subsequently replaced.
Further examination found there to be a 100K resistor in position R12 on the mainboard (which should be 100ohm ) - that would explain the heat as the bias circuit was turning full on and only the LM385s keeping it from burning up straight away. The proper value was installed.
With the daughter card removed I powered it up and it biased up nicely and seemed to be behaving. (It was)
Reason for problem? Miss-stuffed board. Easy and honest mistake, the only damage was the source resistors.
Reinstallation of the daughter card (SMD Tucson) proceeded and a signal was applied, and nothing happened. The output stage was still working, but no signal was getting to the speakers. Hmmm... So I applied a 1000hz test tone and started poking around with the oscilloscope probe.
Interestingly, (which is to say, "confusingly") the signal essentially disappeared as soon as the probe was downstream of R1. That is, as soon as the signal touched anything remotely attached to ground, it was gone. Nothing looked amiss on the daughter card, the soldering looked good and there was no visible damage.
The obvious answer would be that R2 was bad or the wrong value, but it was properly installed and correct. Huh. Mark suggested that perhaps the opamp had failed to a short, and it would be worth trying a different daughter card. So I grabbed a Tucson from my little box full of M2x stuff, the one in the photo below, and installed it. Everything worked great! Horray! Channel fixed.
Reason for problem on the daughter card? Unknown. Replaced the card, problem fixed.
Channel two -
Issues reported - very low (quiet) output, sounded distorted.
Initial examination didn't reveal much, the only obvious thing was the nuts/bolts holding the daughter card were a bit loose. Everything was snuggles up but it didn't change anything. The output stage was biasing properly and appeared to be functional. (it was)
Looking more closely (necessitating removal of the board and lifting some resistor leads, I found the culprit - remember how there was a resistor in the wrong spot on the other channel? Well, I found the one that should have been there. Where there should have been 100K there was 100ohm, and the bulk of the signal was just wasting away to ground.
The proper value was installed in that position and everything behaved properly. Yay! Channel 2 fixed.
Reason for problem? Mis-stuffed board. Again, easy and honest mistake.
In an interest of symmetry, and because I don't have any OPA1611 on hand nor the ability to rework SMD, I just sent the boards home with the green Tucsons.
One thing I learned and want to pass on - the lockwashers on the daughter card supports are very important.
None were installed, so I just squared everything up and snugged things down nicely thinking that would be sufficient, and rapidly found that no, it wasn't. the posts loosened up immediately after moving the daughter card once. This required taking the big board off to get to the screw heads, and attaching the lock washers as shown in the photo. I was quite surprised with how loose they got with removing the daughter card once.
Use the lock washers. Very important.
The Dale RN- and CMF- resistors have their value printed on the side, the code is 3-digit + multiplier at values greater than 100ohm, and below 100ohm the "R" is the decimal.
So, from top to bottom, you see;
10K (100+2 zeros, 10000ohm)
1K (100+1 zero, 1000ohm)
100 ohm (100+0 zeros, 100ohm)
10.0 ohm (10R0, 10.0 ohm)
This is one of hose cases where a photo would be worth significantly more than 1000 words, and yet I took exactly zero photos. Sorry...
Both channels were inoperative, although with different symptoms.
Channel one -
Issues reported; no output, some smoke reported, source resistors getting really hot.
On examination the 0.47R 3W output source resistors were discolored and cracked, they were removed and measured at 0.33R, and replaced with new. The mosfets were removed and tested, both were fine, and subsequently replaced.
Further examination found there to be a 100K resistor in position R12 on the mainboard (which should be 100ohm ) - that would explain the heat as the bias circuit was turning full on and only the LM385s keeping it from burning up straight away. The proper value was installed.
With the daughter card removed I powered it up and it biased up nicely and seemed to be behaving. (It was)
Reason for problem? Miss-stuffed board. Easy and honest mistake, the only damage was the source resistors.
Reinstallation of the daughter card (SMD Tucson) proceeded and a signal was applied, and nothing happened. The output stage was still working, but no signal was getting to the speakers. Hmmm... So I applied a 1000hz test tone and started poking around with the oscilloscope probe.
Interestingly, (which is to say, "confusingly") the signal essentially disappeared as soon as the probe was downstream of R1. That is, as soon as the signal touched anything remotely attached to ground, it was gone. Nothing looked amiss on the daughter card, the soldering looked good and there was no visible damage.
The obvious answer would be that R2 was bad or the wrong value, but it was properly installed and correct. Huh. Mark suggested that perhaps the opamp had failed to a short, and it would be worth trying a different daughter card. So I grabbed a Tucson from my little box full of M2x stuff, the one in the photo below, and installed it. Everything worked great! Horray! Channel fixed.
Reason for problem on the daughter card? Unknown. Replaced the card, problem fixed.
Channel two -
Issues reported - very low (quiet) output, sounded distorted.
Initial examination didn't reveal much, the only obvious thing was the nuts/bolts holding the daughter card were a bit loose. Everything was snuggles up but it didn't change anything. The output stage was biasing properly and appeared to be functional. (it was)
Looking more closely (necessitating removal of the board and lifting some resistor leads, I found the culprit - remember how there was a resistor in the wrong spot on the other channel? Well, I found the one that should have been there. Where there should have been 100K there was 100ohm, and the bulk of the signal was just wasting away to ground.
The proper value was installed in that position and everything behaved properly. Yay! Channel 2 fixed.
Reason for problem? Mis-stuffed board. Again, easy and honest mistake.
In an interest of symmetry, and because I don't have any OPA1611 on hand nor the ability to rework SMD, I just sent the boards home with the green Tucsons.
One thing I learned and want to pass on - the lockwashers on the daughter card supports are very important.
None were installed, so I just squared everything up and snugged things down nicely thinking that would be sufficient, and rapidly found that no, it wasn't. the posts loosened up immediately after moving the daughter card once. This required taking the big board off to get to the screw heads, and attaching the lock washers as shown in the photo. I was quite surprised with how loose they got with removing the daughter card once.
Use the lock washers. Very important.
The Dale RN- and CMF- resistors have their value printed on the side, the code is 3-digit + multiplier at values greater than 100ohm, and below 100ohm the "R" is the decimal.
So, from top to bottom, you see;
10K (100+2 zeros, 10000ohm)
1K (100+1 zero, 1000ohm)
100 ohm (100+0 zeros, 100ohm)
10.0 ohm (10R0, 10.0 ohm)
Are these PassLab amps Current sources or Voltage sources ?
Knowing nothing about electronic I try to deep my nose into theory a bit and get an idea of the relation between amps and speakers.
You see when I read Nelson's papers, I understand nuts, and that is rather frustrating.
Please don't point me to a book of some kind that I won't read anyway, I no intention to become proficient, I am far too old for this.
I understand that Tube amps are generally Current sources and Solid amp being Voltage sources, Mac Intosh being an exception may be Nelson's amps are exceptions as well ?
This could help me understand the difference between the ACA I built and my Nait2 pairing with different speakers.
Knowing nothing about electronic I try to deep my nose into theory a bit and get an idea of the relation between amps and speakers.
You see when I read Nelson's papers, I understand nuts, and that is rather frustrating.
Please don't point me to a book of some kind that I won't read anyway, I no intention to become proficient, I am far too old for this.
I understand that Tube amps are generally Current sources and Solid amp being Voltage sources, Mac Intosh being an exception may be Nelson's amps are exceptions as well ?
This could help me understand the difference between the ACA I built and my Nait2 pairing with different speakers.
Have a look at the First Watt M2 Manual found HERE on First Watt's website
Look at the spec called "Damping Factor". This is simply (8 ohms) divided by (amplifier output impedance). An ideal current source has an output impedance of Infinity ohms. An ideal voltage source has an output impedance of zero ohms.
Take the M2's output impedance and compare to infinity, and compare to zero. There's your answer!
Look at the spec called "Damping Factor". This is simply (8 ohms) divided by (amplifier output impedance). An ideal current source has an output impedance of Infinity ohms. An ideal voltage source has an output impedance of zero ohms.
Take the M2's output impedance and compare to infinity, and compare to zero. There's your answer!
Tooppy - You asked "Are these PassLab amps Current sources or Voltage sources ?" And the answer depends on which of these amplifiers you are specifically referring to...
Please look at the chart on this page - FIRST WATT PRODUCTS
And note the column marked "Output Ohms"
Using Mark's information in the above post, you can determine from Nelson's chart that the F5 amp will be the strongest voltage source, and the F1 the strongest current source, and where the rest lay along that spectrum.
Please look at the chart on this page - FIRST WATT PRODUCTS
And note the column marked "Output Ohms"
Using Mark's information in the above post, you can determine from Nelson's chart that the F5 amp will be the strongest voltage source, and the F1 the strongest current source, and where the rest lay along that spectrum.
I read this Manual a few times already, OK Damping factor (I know the word but don't know what it means, I am going to search) is 20, I do not find the amp's output impedance but lets take the speakers one which is 8 ohms, we got 2.5 so this is a Voltage source.
Thanks Mark
It's a math problem. We know that (8 / X) equals 20 and we wish to solve for X.
(8 / 0.1) equals 80 ... too high!!
(8 / 1.0) equals 8 ... too low!!
Since X=0.1 gives an answer that's too high, while X=1.0 gives an answer that's too low, we know for certain that the correct value of X is somewhere between 0.1 and 1.0. Maybe that's all we really need.
Also try X=0.4 and X=0.5.
(8 / 0.1) equals 80 ... too high!!
(8 / 1.0) equals 8 ... too low!!
Since X=0.1 gives an answer that's too high, while X=1.0 gives an answer that's too low, we know for certain that the correct value of X is somewhere between 0.1 and 1.0. Maybe that's all we really need.
Also try X=0.4 and X=0.5.
Absolutely!
This is one of hose cases where a photo would be worth significantly more than 1000 words, and yet I took exactly zero photos. Sorry...
Both channels were inoperative, although with different symptoms.
Channel one -
Issues reported; no output, some smoke reported, source resistors getting really hot.
On examination the 0.47R 3W output source resistors were discolored and cracked, they were removed and measured at 0.33R, and replaced with new. The mosfets were removed and tested, both were fine, and subsequently replaced.
Further examination found there to be a 100K resistor in position R12 on the mainboard (which should be 100ohm ) - that would explain the heat as the bias circuit was turning full on and only the LM385s keeping it from burning up straight away. The proper value was installed.
With the daughter card removed I powered it up and it biased up nicely and seemed to be behaving. (It was)
Reason for problem? Miss-stuffed board. Easy and honest mistake, the only damage was the source resistors.
Reinstallation of the daughter card (SMD Tucson) proceeded and a signal was applied, and nothing happened. The output stage was still working, but no signal was getting to the speakers. Hmmm... So I applied a 1000hz test tone and started poking around with the oscilloscope probe.
Interestingly, (which is to say, "confusingly") the signal essentially disappeared as soon as the probe was downstream of R1. That is, as soon as the signal touched anything remotely attached to ground, it was gone. Nothing looked amiss on the daughter card, the soldering looked good and there was no visible damage.
The obvious answer would be that R2 was bad or the wrong value, but it was properly installed and correct. Huh. Mark suggested that perhaps the opamp had failed to a short, and it would be worth trying a different daughter card. So I grabbed a Tucson from my little box full of M2x stuff, the one in the photo below, and installed it. Everything worked great! Horray! Channel fixed.
Reason for problem on the daughter card? Unknown. Replaced the card, problem fixed.
Channel two -
Issues reported - very low (quiet) output, sounded distorted.
Initial examination didn't reveal much, the only obvious thing was the nuts/bolts holding the daughter card were a bit loose. Everything was snuggles up but it didn't change anything. The output stage was biasing properly and appeared to be functional. (it was)
Looking more closely (necessitating removal of the board and lifting some resistor leads, I found the culprit - remember how there was a resistor in the wrong spot on the other channel? Well, I found the one that should have been there. Where there should have been 100K there was 100ohm, and the bulk of the signal was just wasting away to ground.
The proper value was installed in that position and everything behaved properly. Yay! Channel 2 fixed.
Reason for problem? Mis-stuffed board. Again, easy and honest mistake.
In an interest of symmetry, and because I don't have any OPA1611 on hand nor the ability to rework SMD, I just sent the boards home with the green Tucsons.
One thing I learned and want to pass on - the lockwashers on the daughter card supports are very important.
None were installed, so I just squared everything up and snugged things down nicely thinking that would be sufficient, and rapidly found that no, it wasn't. the posts loosened up immediately after moving the daughter card once. This required taking the big board off to get to the screw heads, and attaching the lock washers as shown in the photo. I was quite surprised with how loose they got with removing the daughter card once.
Use the lock washers. Very important.
The Dale RN- and CMF- resistors have their value printed on the side, the code is 3-digit + multiplier at values greater than 100ohm, and below 100ohm the "R" is the decimal.
So, from top to bottom, you see;
10K (100+2 zeros, 10000ohm)
1K (100+1 zero, 1000ohm)
100 ohm (100+0 zeros, 100ohm)
10.0 ohm (10R0, 10.0 ohm)
Great work! Best way to avoid this going forward is to recommend measuring all resistors with a DMM prior to stuffing them?
For the initial powering up of the amp boards I do not see the steps in this thread. Do I need to follow the original M2 build thread? I have finished my amp boards and would like to power up one channel at a time and set it up. I am going to use the Ishikawa first as I had the alweit's jfets matched with me since longtime. Let me know where can I read on the powering/biasing/offset on the M2X amp boards.
Thanks in advance.
Thanks in advance.
