The diyAudio First Watt M2x

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#6,001
Hi checkulater,

yes, if you only have two wires coming out of the transformer on the primary side - just connect the CL-60 in series with mains.
I usually put it after the mains fuse, and in the hot line instead of neutral.

Best regards,
Claas
 
#6,005
No need to update any values to use 2SK1530/2SJ201 right? I read somewhere that 0r33 was used by some people but that it would change the damping factor. I'd rather leave that alone, if possible.

I already have a fistful of 0R47, leftover from other projects, so using those would be better.
 
#6,006
I want to follow up on my issue where an output mosfet burned out. Initially I suspected that I hadn't provided enough clearance for the cooling fins on one side of the amp but also wondered if the transistors were being clamped adequately against the heat sink. So I moved the amp, snugged up the M3 clamping screws, and have been listening happily for the last six months. Recently I checked the screws again and was surprised to find them 3 of 4 loose enough to allow spinning the large clamping washer! The clamping hardware is an M3 screw with a split washer, flat washer (small), and drilled penny against the mosfet case. There are Wakefield thermal pads between the mosfets and the heatsink.

My best guess is the thermal cycles and the expansion/contraction of the heatsink has slowly loosened the clamping screws (the amp is turned on/off several times a day). Since split washers haven't been able to maintain the clamping force I've replaced them with two Belleville washers, oriented like: (). I'm hoping they will do better.
 
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#6,007
A few suggestions...

  • the wiring can have one side soldered, and the other crimped with lugs. This reduces the potential of developing hot spots by 50% and you can still remove the modules/PCBs. Not to mention the reduction in contact resistance by 50% as well - your ears will like that. I check the lugs in my amp every 2 years to ensure a good grip - there's a lot of current running through a few of those wires at all times (!).
  • you could use low-noise fans to cool down the interior. They are usually 12V, but if you power them up with let's say external 10V DC, they will be completely silent. You can leave them on at all times... and maybe replace them every 2-3 years.
  • you've chosen TO220 diodes... make sure they are not running hotter than 100 deg C.
  • re: MOSFETs and how to mount them on the heatsink... my suggestion is to go with these: https://diyaudiostore.com/collections/frontpage/products/keratherm-transistor-insulators. You could polish the heatsink and make the surface completely smooth. I tighten my MOSFETs with a fair amount of torque... the Keratherm actually injects into micro-imperfections on both sides (heatsink and MOSFETs), and makes an excellent heat transfer. Of course, the downside is... the new Keratherm set will be required if I decide to remove the amp PCBs... very often. I re-tightened my MOSFET screws a few times over the period of 1 year, and now all I do is check sporadically the quiescent current and DC offset. I used a large flat washer & a smaller spring washer.
  • the way you placed the mains wiring is not ideal. It runs in parallel with one AMP PCB. What you should definitely do, at the very least, is to move the mains wiring away from the audio transformer. It would be better to run the mains wiring underneath the PS PCB.


1663644412666.png


Aleph J.JPG
 
#6,009
delecoy said:
No need to update any values to use 2SK1530/2SJ201 right? I read somewhere that 0r33 was used by some people but that it would change the damping factor. I'd rather leave that alone, if possible.

I already have a fistful of 0R47, leftover from other projects, so using those would be better.
Click to expand...
The 2SK1530 / 2SJ201 have lower gm than the IRFPs. Using less source resistance partly works against this, but even with 0R33, if I remember correctly, damping factor will still be lower than IRFP / 0R47. I don't recall everything of it, but it should have been discussed in one of the original M2 threads in fairly good detail.

I have built mine with 2SK1530 / 2SJ201 and lower source resistors, but the lower source resistors lead to a higher idle current through the output MOSFETs because you get less voltage at the optocoupler diode. You can lower the idle current by replacing R11 (221R) (schematic post #1) with a jumper, if I remember correctly, but idle current is still about 1.8A in my case. Again, there should be more info in the M2 threads.

I did like the sound with the 2SK1530 / 2SJ201 very much 🙂

Best regards, Claas
 
#6,010
M2.jpg


Just making sure I'm not missing anythign between the teabag version and the DIYA store boards 😉

Ill bypass R11 ( 221 ohm ), which connects to pin 2 of the 4N35, with a jumper.

4N35.PNG


Then R13 and R14 will get 0R33 instead of 0R47.

And thatll make it ready for 2SK1530/2SJ201.

Thank you for the help! I'm still very much painting by numbers here...

🙂
 
#6,011
Hi delecoy, that's it, looks good to go.

Just be advised that this mod will have the amp run at a bias of approx. 1.8A. That is not a problem for the Toshiba outputs, as long as you use mica & goop, Keratherm 86/82 or ceramic pads with goop between the Toshibas and the heatsink.
A 4U/400 works well for dissipating the heat of this combination. If you would like to lower the bias further, probably Zen Mod is the right guy to ask if there is an easy way for that.

I'm at home now and found my posts in the M2 threads about the M2 with 2SJ201 / 2SK1530:

https://www.diyaudio.com/community/threads/an-all-toshiba-amp-after-papas-hint.371817/#post-6642641

https://www.diyaudio.com/community/threads/official-m2-schematic.281520/page-157#post-5597309

https://www.diyaudio.com/community/threads/official-m2-schematic.281520/page-121#post-5337548

Best regards,
Claas
 
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#6,012
Zen Mod said:
Keratherm 86/82, Alumina pads + goop, Mica + goop

always big washer + split washer

squishy silicon pads are big no-no for FW form factor amps
Click to expand...

Thanks ZM. This is the heat transfer pad product I used which seems similar (almost identical?) to the Kernatherm pads:
ulTIMiFlux Dielectric Phase Change Thermal Material
https://www.mouser.com/datasheet/2/...tric_Phase_Change_Thermal_Materia-2933390.pdf

I also have some of the Aluminum Oxide Ceramic pads but I haven't installed them since I'd have to resolder the mosfets since the pads are thicker.

Big washer and split washer since day 1. When I replaced the one mosfet that burned out six months ago I used two split washers, with a flat washer between them, plus the big washer (drilled penny). That's the one that was still tight when I checked all four a couple days ago. But since I now have some M3 Belleville washers I installed those and will be checking the clamping screws every few days for awhile.
 
#6,014
Zen Mod said:
on the paper that phase change thingie is ok, but as you found, it has some problems nonexistent with other options

anyway, now you know, your call what to do
Click to expand...

I'm curious, what do you think its problems are? Do you think it may not transfer heat as well as the other options? Or somehow contribute to the screws loosening? The heatsinks on my amp do get quite warm so as far as I can tell the pads are working.
 
#6,015
I have some leftover keratherm pads form the store I can use, so will go with those.

It'll be going in a 4U from the store, so should be good there.

Once that's done I'll pack up the family and move to a climate more amenable to hot amplifiers. Perhaps Canada.

🙂

Thank you @chede!
 
#6,016
slk23 said:
I'm curious, what do you think its problems are? Do you think it may not transfer heat as well as the other options? Or somehow contribute to the screws loosening? The heatsinks on my amp do get quite warm so as far as I can tell the pads are working.
Click to expand...

as I said in first reply - it is squishy, evidently running from pressure**

you can try to tighten it by recommendation from datasheet ( if there is number) and see/check few times did it squished to permanent state

though, you'll need torque screwdriver for that

**proper examination of thermal transfer , even if pressure from screw is lost, can be verified with contact thermometer; if you see few C of difference between mosfet case and heatsink ditto to mosfet, no worries;

though, why wasting your energy to observe for prolonged time, something which can be solved for good, with little work
 
#6,017
Zen Mod said:
as I said in first reply - it is squishy, evidently running from pressure**

you can try to tighten it by recommendation from datasheet ( if there is number) and see/check few times did it squished to permanent state

though, you'll need torque screwdriver for that

**proper examination of thermal transfer , even if pressure from screw is lost, can be verified with contact thermometer; if you see few C of difference between mosfet case and heatsink ditto to mosfet, no worries;

though, why wasting your energy to observe for prolonged time, something which can be solved for good, with little work
Click to expand...

I don't think I said the pads were squishy; they are only 0.003" (0.076mm) thick. It's the M3 screws that are loosening, perhaps due to thermal expansion cycles or the thick washer (penny) deforming from the heat.

I do notice a significant temperature difference when I touch the screw head vs. the heatsink close to the mosfet. I guess I'll bite the bullet and resolder the mosfets so I can try using the aluminum oxide ceramic pads + thermal transfer grease.
 
#6,018
sorry, my bad - that I got impression of pads being softy

though, if you did torque screws properly, with split washers, something i not adding

taught by bad experience, I'm always using stainless screws and split washers, easiest way to get M3 in guaranteed quality in my neck of wood
 
#6,020
Put the transformer right next to the IEC socket/switch. This will minimise the high voltage wiring length.
Rotate the PS PCB 180 deg, so that the DC wiring to AMP PCBs is minimal length.

The mains' wiring length could be as short as 10cm, including the NTC, if you mount the NTC on the IEC socket lugs.

The longest wiring would actually be the 2 x 20V AC, stretching from the transformer towards the "front" of the PS PCB, running underneath, and coming from the bottom of the PCB.
 
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