Transformers are really at their best being driven by something with really low output impedance. I would try to get rid of the 100 ohm output resistor of the Nutube if I could. The amp in my signature has a BJT follower with a series resistor at 22 ohms driving the Cinemag transformer. The coupling cap needs to be much larger also. Look at some of Mark Johnson's front end circuits that have the EDCOR and also the lottery VFET amps to see what values those guys are using there.
Maybe I should reduce the series 100 ohms? How much does this affect the other parameters?
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I recommend you build one of the five input stage daughter card designs that are supplied in the M2x PCB set from the diyAudio Store. Ishikawa has the fewest components to solder but the K170 and J74 JFETs are expensive & difficult to source. Tucson is the second simplest PCB and all of its parts are widely available and low cost. The other three are very lovely too but they require more assembly time and purchasing effort than Tucson or Ishikawa.
You can now listen to your M2x, verify its correct operation, and get accustomed to its sonic signature with an official diyAudio Store input stage card installed. Later, if you're still curious, you can remove the input stage card and connect a Korg NuTube directly to the daughter card output post (i.e. the input to the M2x Edcor transformer). Now you can hear for yourself how much better or worse the sound has become.
You can now listen to your M2x, verify its correct operation, and get accustomed to its sonic signature with an official diyAudio Store input stage card installed. Later, if you're still curious, you can remove the input stage card and connect a Korg NuTube directly to the daughter card output post (i.e. the input to the M2x Edcor transformer). Now you can hear for yourself how much better or worse the sound has become.
I built the M2x with Ishikawa 🙂 I'm curious if it's possible to skip it and use it with the Korg Nutub 😉 What does it do to the sound.
Thank you for the encouragement!
Can I reduce the Korg Nutube B1 output serial 100 ohms or not necessary?
Question - what is an acceptable amount of hum? Obviously zero is best, but I think I am close, and see what others get their builds.
After a 6+ month rotation of other amps, I put the M2x back in the system, which is when I remembered I needed to fix a hum issue. I could hear hum ~2-3 feet away with music paused. My fix was to re-routed input and speaker outputs wiring and successfully (IMO) reduced the hum significantly.
Now I need to put my ear 2-3 inches from the woofer to hear any hum. Wondering if that's still sub-par results and I need to keep working on the wiring.
Also - I'm sure I've said it before, but @Mark Johnson @Nelson Pass, this is a truly magical amp - so easy to listen to, the hours fly by, enjoying every kind of music I throw at it.
My current combination - M2x with Norwood card.
After a 6+ month rotation of other amps, I put the M2x back in the system, which is when I remembered I needed to fix a hum issue. I could hear hum ~2-3 feet away with music paused. My fix was to re-routed input and speaker outputs wiring and successfully (IMO) reduced the hum significantly.
Now I need to put my ear 2-3 inches from the woofer to hear any hum. Wondering if that's still sub-par results and I need to keep working on the wiring.
Also - I'm sure I've said it before, but @Mark Johnson @Nelson Pass, this is a truly magical amp - so easy to listen to, the hours fly by, enjoying every kind of music I throw at it.
My current combination - M2x with Norwood card.
I stop worrying about hum when it is necessary to have my ear within a hand’s width away from the speaker to hear it.
I finally achieved this with my M2x when I rebuilt the power supply, going from a single Antek 400VA transformer to a pair of Triad 250VA transformers (dual-mono). This placed the Edcor signal transformers farther away from the power transformers. I also switched to CLC filters.
I finally achieved this with my M2x when I rebuilt the power supply, going from a single Antek 400VA transformer to a pair of Triad 250VA transformers (dual-mono). This placed the Edcor signal transformers farther away from the power transformers. I also switched to CLC filters.
Thank Nelson Pass who created the M2 and without whom, M2x obviously would not and could not exist.
Thank 6L6 who passionately believed the M2 was absolutely spectacular, thus we NEED to somehow get it into the diyAudio Store so DIYers can build and enjoy it. Immediately!!
My own modest contribution was to observe that M2's out of production, obsolete Toshiba JFETs could be moved onto a field swappable daughter board, and therefore replaced by other circuits whose components are all in active production. Thus were Tucson, Mountain View, Austin, and Norwood born. Ishikawa is the original Nelson design, unchanged.
The whole story is in post #1 of this thread. Thank goodness BAF1997 was in San Francisco (north of the airport) and I lived in Silicon Valley, south of the airport. Driving home from Fort Mason, I was happy to give 6L6 a ride to the airport, it was literally right on my way home. During that 20 mile trip, the key requirements for M2x were hammered out.
Thank 6L6 who passionately believed the M2 was absolutely spectacular, thus we NEED to somehow get it into the diyAudio Store so DIYers can build and enjoy it. Immediately!!
My own modest contribution was to observe that M2's out of production, obsolete Toshiba JFETs could be moved onto a field swappable daughter board, and therefore replaced by other circuits whose components are all in active production. Thus were Tucson, Mountain View, Austin, and Norwood born. Ishikawa is the original Nelson design, unchanged.
The whole story is in post #1 of this thread. Thank goodness BAF1997 was in San Francisco (north of the airport) and I lived in Silicon Valley, south of the airport. Driving home from Fort Mason, I was happy to give 6L6 a ride to the airport, it was literally right on my way home. During that 20 mile trip, the key requirements for M2x were hammered out.
Great to hear that you are enjoying the music - at the end of the day, that is the most important thing. 🙂 The DIY M2 gets a lot of praise from happy builders, thanks to Mr. Pass for sharing the design with the DIY community! 6L6 has been a champion for DIY, and his build-guides act as reference for most of us. And MJ's coming up with the M2X has possibly resulted in a lot more people going for the build, and actually building this amp.
If you don't mind, can you share some more details about your system - source, preamp, speakers?
I have a modest set-up in a small office (10’x13’). Desktop PC usually running Spotify premium, with optical output to an Outlaw 975 pre-amp, with analog outputs to the M2x, playing my own DIY SB Acoustics 2-way creation (5” woofer, 1” dome tweeter), sometimes supplemented with DIY 10” ported sub.
Hi,
New member here (although registered a long time ago), although this thread already has a lot of information, I'm sharing my build experience from someone who doesn't have a lot of experience in electronics.
My last build was a Dynaco ST70 tube amp back in 2015
Planning:
1. Study the project, the schematic and the BOM for each PCB, take your time, I took three weeks in this process constantly reviewing my Mouser shopping cart and replacing/removing/adding parts; (read all the posts on this thread and you'll be able to anticipate and avoid a lot of issues on what parts to use and how to solder and wire things)
2. Choose a chassis for your build.
3. In your planning include also the bits and pieces needed to assemble the pcb's to the chassis, cables, switchs, jacks, tabs, screws, etc...
(aliexpress is a good source for this small hardware bits and pieces
4. Order everything
Assembling:
1. Be methodical, measure every component before soldering, make sure you're soldering the correct component on the correct place and with the correct orientation (polar capacitors and transistors)
DO NOT ASSEMBLE IRFP240 and IRFP9240 at this stage
After the boards are complete (minus IRFPs), clear solder flux with isopropil alcohol and a toothbrush.
2. Take photos, the ones I share below helped me identify that I missed some connecting tabs and also check resistor color codes when testing:
2. I ordered a Mini Dissipante 4U300 with pre drilled holes, it only has 240mmx300mm useful space inside, not much space to work after every parts are assembled,
3. Plan your chassis layout for the bottom plate and do all the drilling beforehand, plan the cable routes, attach the mounting tabs, etc... this is the order I did things:
a. Power switch clearance (mine is front mounted)
b. Transformer;
c. Rectifier bridges:
d. PSU Board;
e. Junction tab
f. Wiring and grounding scheme
3. Assembled transformer, rectifier bridges (I used thermal paste between the bridge and the bottom plate, works quite good), psu pcb and junction tab, connect trafo to bridges and bridges to psu, prepared all the primary connections (CL60, .0033 cap) on the junction tab.
4. PSU test OK, 25.3V unloaded.
5. Amp Boards assembly: start by assembling the IRFP240 and 9240 to heatsinks, I used AAVID 4180G thermal pads and Genesis Silicon 851 thermal paste, I applied paste between tab and heatsink and between IRFP and tab. Attach firmly to heatsink and use your DVM to make sure there's no continuity between each leg and the mounting screw.
6. Attach the Amp Boards and solder the IRFPs from above. Make sure everything is OK, you want to avoid removing the IRFPs from now on.
Now let's to do some smoke tests:
1. Insert your choosen output board;
2 Shunt the input with input ground;
3. Connect V+, V- and ground to PSU;
4. Breed in, breed out and connect your trafo to mains (make sure you use a fuse in case something goes wrong)
Test one side, if no smoke and everything measures OK, disconnect and test other side.
Key points to measure:
1. V+/V- when loaded are around +- 23/24V
2. V on R13 and R14 is around 610mV, monitor this value when connecting, if it rises way above this value, turn off immediately.
3. Check DC offset and try to get it to 0V by turning Rv1 one side or another.
In my case everything went fine, did 30m smoke test on each side with no major issue, the only issue I have so far is I cannot set DC offset to 0V.
After some inspection I found the culprit, I went for R6/Rv1 combination of 37K/20k but mistakenly soldered 47K instead of 37K
(I failed miserably my recommendations 1 and 6 above)
To avoid removing the Amp Boards and IRFPs from the heatsink I soldered a 100k resistor in paralell with R6 (47k) all of this from above, this gave me around 32k on R6 which was enough to allow the DC offset to be set to 0V
Now that everything is tested, on the next few days, I'll put the chassis together and finish all the connections.
New member here (although registered a long time ago), although this thread already has a lot of information, I'm sharing my build experience from someone who doesn't have a lot of experience in electronics.
My last build was a Dynaco ST70 tube amp back in 2015
Planning:
1. Study the project, the schematic and the BOM for each PCB, take your time, I took three weeks in this process constantly reviewing my Mouser shopping cart and replacing/removing/adding parts; (read all the posts on this thread and you'll be able to anticipate and avoid a lot of issues on what parts to use and how to solder and wire things)
2. Choose a chassis for your build.
3. In your planning include also the bits and pieces needed to assemble the pcb's to the chassis, cables, switchs, jacks, tabs, screws, etc...
(aliexpress is a good source for this small hardware bits and pieces
4. Order everything
Assembling:
1. Be methodical, measure every component before soldering, make sure you're soldering the correct component on the correct place and with the correct orientation (polar capacitors and transistors)
DO NOT ASSEMBLE IRFP240 and IRFP9240 at this stage
After the boards are complete (minus IRFPs), clear solder flux with isopropil alcohol and a toothbrush.
2. Take photos, the ones I share below helped me identify that I missed some connecting tabs and also check resistor color codes when testing:
2. I ordered a Mini Dissipante 4U300 with pre drilled holes, it only has 240mmx300mm useful space inside, not much space to work after every parts are assembled,
3. Plan your chassis layout for the bottom plate and do all the drilling beforehand, plan the cable routes, attach the mounting tabs, etc... this is the order I did things:
a. Power switch clearance (mine is front mounted)
b. Transformer;
c. Rectifier bridges:
d. PSU Board;
e. Junction tab
f. Wiring and grounding scheme
3. Assembled transformer, rectifier bridges (I used thermal paste between the bridge and the bottom plate, works quite good), psu pcb and junction tab, connect trafo to bridges and bridges to psu, prepared all the primary connections (CL60, .0033 cap) on the junction tab.
4. PSU test OK, 25.3V unloaded.
5. Amp Boards assembly: start by assembling the IRFP240 and 9240 to heatsinks, I used AAVID 4180G thermal pads and Genesis Silicon 851 thermal paste, I applied paste between tab and heatsink and between IRFP and tab. Attach firmly to heatsink and use your DVM to make sure there's no continuity between each leg and the mounting screw.
6. Attach the Amp Boards and solder the IRFPs from above. Make sure everything is OK, you want to avoid removing the IRFPs from now on.
Now let's to do some smoke tests:
1. Insert your choosen output board;
2 Shunt the input with input ground;
3. Connect V+, V- and ground to PSU;
4. Breed in, breed out and connect your trafo to mains (make sure you use a fuse in case something goes wrong)
Test one side, if no smoke and everything measures OK, disconnect and test other side.
Key points to measure:
1. V+/V- when loaded are around +- 23/24V
2. V on R13 and R14 is around 610mV, monitor this value when connecting, if it rises way above this value, turn off immediately.
3. Check DC offset and try to get it to 0V by turning Rv1 one side or another.
In my case everything went fine, did 30m smoke test on each side with no major issue, the only issue I have so far is I cannot set DC offset to 0V.
After some inspection I found the culprit, I went for R6/Rv1 combination of 37K/20k but mistakenly soldered 47K instead of 37K
(I failed miserably my recommendations 1 and 6 above)
To avoid removing the Amp Boards and IRFPs from the heatsink I soldered a 100k resistor in paralell with R6 (47k) all of this from above, this gave me around 32k on R6 which was enough to allow the DC offset to be set to 0V
Now that everything is tested, on the next few days, I'll put the chassis together and finish all the connections.
^ Some fantastic stuff! Thanks for sharing your experience.
Not second guessing ... b/c it sounds like you've read everything and made informed choices.
With that said, I'm not saying you will experience hum, but consider the relationship / proximity of the signal transformers (the Edcors) to your power transformer (the Toroidy).
Many people choose to put their power transformer at the front of the chassis to assist.
Maybe I've misinterpreted your layout... that's also been known to happen. 🙂
Either way... lovely, just lovely!
Congratulations and enjoy the tunes!
Edited to add - you specifically call out that your power switch is front mounted... yep... I misinterpreted by only looking at the picture. See... LOL! 🙂
Not second guessing ... b/c it sounds like you've read everything and made informed choices.
With that said, I'm not saying you will experience hum, but consider the relationship / proximity of the signal transformers (the Edcors) to your power transformer (the Toroidy).
Many people choose to put their power transformer at the front of the chassis to assist.
Maybe I've misinterpreted your layout... that's also been known to happen. 🙂
Either way... lovely, just lovely!
Congratulations and enjoy the tunes!
Edited to add - you specifically call out that your power switch is front mounted... yep... I misinterpreted by only looking at the picture. See... LOL! 🙂
hehe, That's correct, the transformer is front mounted, the fact that the heatsink on the right side is on the wrong side (for testing purposes) might be what caused the confusion.
I left some space between the transformer and the rectifiers so that I can use a transformer cover in case of HUM.
I left some space between the transformer and the rectifiers so that I can use a transformer cover in case of HUM.
I recommend using a dim bulb tester for first power-ups. It may help to keep the smoke in if there is a mistake somewhere. If there is a short in the circuit, sometimes a fuse or human reaction on the power switch is not fast enough to prevent catastrophic failure of a component. If the dim bulb test is successful, then power up with the dim bulb tester removed.
Thanks Ben, that's a really good advice.
Yesterday evening assembled front, heatsinks and bottom plate and did another 1h smoke test.
My notes:
1st attached heatsinks to front plate
2nd attached bottom plate to heatsinks
3rd did the internal wiring
After 1h on, re-measured bias and it was stable around 1 or 2mV, heatwise, the heatsinks get really hot but I'm able to keep my hand on the fins for quite sometime, need to get a thermometer to check temps.
Yesterday evening assembled front, heatsinks and bottom plate and did another 1h smoke test.
My notes:
1st attached heatsinks to front plate
2nd attached bottom plate to heatsinks
3rd did the internal wiring
After 1h on, re-measured bias and it was stable around 1 or 2mV, heatwise, the heatsinks get really hot but I'm able to keep my hand on the fins for quite sometime, need to get a thermometer to check temps.
And it’s working, trying Mountain View it’s a bit to clinical for my taste, waiting for parts to try Tucson and Ishikawa.
Thanks to the community for all the shared knowledge.
Thanks to the community for all the shared knowledge.
