My build in post #2938 is quiet—and compact—not sure it could be more compact actually without some crazy rogue layout—there are a few up on this forum—the creativity here is nuts. Be concerned about noise of course... just saying—I'm seeing plenty of room in your cases—and I hear Dual Mono is a thing—but I just went to straight mono blocks. If you have the cases and don't mind the sizes—just build mono blocks IMO. I used Antek 300VA 2x18s and was getting +/-26.5VDC on the rails unloaded.
I've since added Mark's ACPR circuit to both of them, mounted on the back panel under the IEC—still quiet even with the primaries getting quite long. Interestingly—my M2Xs had some interesting behavior—they were absolutely ghostly into 97db speakers when cold—but when warmed up you could hear a faint buzz from both amps—I mean faint—ear right on the cone faint. That seems to be gone now—only change was adding Marks boards....cable routing?
I've since added Mark's ACPR circuit to both of them, mounted on the back panel under the IEC—still quiet even with the primaries getting quite long. Interestingly—my M2Xs had some interesting behavior—they were absolutely ghostly into 97db speakers when cold—but when warmed up you could hear a faint buzz from both amps—I mean faint—ear right on the cone faint. That seems to be gone now—only change was adding Marks boards....cable routing?
Perfect. I think I’m going the mono block route since I have two chassis already put together as monoblocks. What are the ACPR circuits you are referring to? Because I have the room, I would love to work them into my build.
PCB: low voltage On-Off switch drives AC mains relay \ includes soft start .. H9KPXG
This also eliminates the whole barrier block and CL-60 routine that most of us do for inrush countermeasures. So in some ways it simplifies layout. But really you can now use any silly button you like for power—safely. Plus more stuff to build—which is what I love—I have made four of those boards so far. Did a run of 10 from the PCB house.
This was my first time taking some gerbers and having boards made. Couldn't have been easier. The thread is short so far—all the info is there (Read the whole thing—the cart I made evolved....).
This also eliminates the whole barrier block and CL-60 routine that most of us do for inrush countermeasures. So in some ways it simplifies layout. But really you can now use any silly button you like for power—safely. Plus more stuff to build—which is what I love—I have made four of those boards so far. Did a run of 10 from the PCB house.
This was my first time taking some gerbers and having boards made. Couldn't have been easier. The thread is short so far—all the info is there (Read the whole thing—the cart I made evolved....).
ACPR = Alternating Current Power Relay circuit board (free download)
Lets you use a low-voltage, low-current switch for front panel on-off control. This switch activates a large & robust relay which connects and disconnects the AC mains to your amplifier's power transformer. It also implements inrush current limiting aka soft start.
Lets you use a low-voltage, low-current switch for front panel on-off control. This switch activates a large & robust relay which connects and disconnects the AC mains to your amplifier's power transformer. It also implements inrush current limiting aka soft start.
Mid way on the first of the Monos, still early, but I like what I'm seeing so far. This will be a clean build, no frill black face with a lighted power button.(maybe a temp sensor and fan speed indicator) It will also have active cooling. I have an idea this one will run cool, but it's my first active, so it remains to be seen.
I had a couple of gotchas, so far and I'm sure there are more. A couple buddies wanted to go for drinks, I demurred because I was on a roll... I told them honey said no. The are good friends, but they think a resistor is someone that doesn't cooperate.
These are going in the dedicated room with the ANs. I love the M2 so much, I refused to move the dual mono out of the lab and decided to build a true mono to go in the other room.
Favorites so far for SS are:
M2X
AN
J2
Depending on speakers and music any one of those is best. I didn't get long enough with the F5T I built for a friend. I might have to bring it in for, "service" this winter.
I had a couple of gotchas, so far and I'm sure there are more. A couple buddies wanted to go for drinks, I demurred because I was on a roll... I told them honey said no. The are good friends, but they think a resistor is someone that doesn't cooperate.
These are going in the dedicated room with the ANs. I love the M2 so much, I refused to move the dual mono out of the lab and decided to build a true mono to go in the other room.
Favorites so far for SS are:
M2X
AN
J2
Depending on speakers and music any one of those is best. I didn't get long enough with the F5T I built for a friend. I might have to bring it in for, "service" this winter.
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my M2X amplifier’s output offset voltage - all over the place and not stable. what could be the issue? I did go with 20K VR and 37.5k (two 75k parallel) for R6.
I could tune it down either side of zero but this value is oscillating between negative and positive values of a few mv (typically -80 to +140mv) over time.
There is music from both channels, no hum, no unusual heat up of components. My rails are 24v and the voltage across 0.47R is about 610mv.
I initially thought my LM385 1.235v reference voltage parts are faulty and got them replaced with genuine ones. Also replaced 4N35 ics. no change in outcome. Resistors R10, R12, R11 are .1% and rest are 1% precision. R13, R14 (0R47) are Panasonic sourced from mouser and used the ones closely measuring.
What else I can check to debug this and arrive at a stable offset, what risk am carrying if i continue to use with dc offset of under +/-120mv.
s
Thanks for reading and looking forward to your support.
I could tune it down either side of zero but this value is oscillating between negative and positive values of a few mv (typically -80 to +140mv) over time.
There is music from both channels, no hum, no unusual heat up of components. My rails are 24v and the voltage across 0.47R is about 610mv.
I initially thought my LM385 1.235v reference voltage parts are faulty and got them replaced with genuine ones. Also replaced 4N35 ics. no change in outcome. Resistors R10, R12, R11 are .1% and rest are 1% precision. R13, R14 (0R47) are Panasonic sourced from mouser and used the ones closely measuring.
What else I can check to debug this and arrive at a stable offset, what risk am carrying if i continue to use with dc offset of under +/-120mv.
s
Thanks for reading and looking forward to your support.
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I can see that 88 db speakers min rating is 30W and the F5 is 25W. You could do the F5T V2 50W or V3 100W and I think you would be pleased.
The M2, F5 and other N. Pass Class A amplifiers are known for hitting well above their weight class. My M2x, with its 23V power rails is quite satisfactory driving my old Vandersteen 2C speakers, which are rated for 87 dB sensitivity. It is still fun to rotate through my system, especially when I have a new input stage concoction to try.
Does my Aleph J get more playing time? Yes it does. So does my F6, for different reasons between the two of them.
Does my Aleph J get more playing time? Yes it does. So does my F6, for different reasons between the two of them.
Can someone here, give this guy some help? I don't know enough to help, or I would... Mark? Someone?
JT
The first thing to do is find out exactly how other M2x amplifiers behave, amps which are known/believed to be working well. It's important that all of these measurements are made after the same length of warm up time, so all amplifiers are approximately the same distance from thermal equilibrium. I suggest 3 hours, which might be excessive but is on the right side of too aggressive / too conservative. It's also important that all of these measurements be made with the same input signal and the same output loading and the same completely-closed-and-screwed-together chassis plates.
Since no one knows whether the problem originates in the power supply rather than the amplifier channel PCBs, it may be crucially important for all of these M2x owners to make all of these measurements, using TWO high accuracy DVMs, one per channel. Record the offset voltage of each M2x channel at the same instant. See whether Left-Offset and Right-Offset fluctuate up and down in unison (suggesting a common root-cause (perhaps the power supply??)), or whether they fluctuate up and down independently from each other and seemingly at random.
_
Since no one knows whether the problem originates in the power supply rather than the amplifier channel PCBs, it may be crucially important for all of these M2x owners to make all of these measurements, using TWO high accuracy DVMs, one per channel. Record the offset voltage of each M2x channel at the same instant. See whether Left-Offset and Right-Offset fluctuate up and down in unison (suggesting a common root-cause (perhaps the power supply??)), or whether they fluctuate up and down independently from each other and seemingly at random.
_
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I would like to built the ishikawa M2x version but I have an question. I have some pairs of 2sj74v and 2k147v that are bang-on Idss 16.5mA but when I checked the input capacitance and found that the J74 has less than half the input capacitance (30 vs 75pf) than the k147. What is the effect of having such input cap mismatch on the input fets AFA distortion? It is unity gain stage so does it affect the freq response?
I have 2sk170BL but the Idss is 7.7mA, the Idss mismatch is too much.
thanks
I have 2sk170BL but the Idss is 7.7mA, the Idss mismatch is too much.
thanks
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Using a N-channel / P-channel pair of JFets that are significantly mismatched in either gate capacitance or Idss is not a recipe for success. You may be able to get music to play, but might be better off getting that used Akai instead
There are good sources of properly matched JFets, both the original Toshiba parts and the newer Linear Systems parts. Either of those would be a much better solution than trying to use mis-matched parts. Spend a little money.
There are good sources of properly matched JFets, both the original Toshiba parts and the newer Linear Systems parts. Either of those would be a much better solution than trying to use mis-matched parts. Spend a little money.