How to Pass a little time ...cont

Discussion in 'DIY' started by dBel84, Oct 22, 2018.

  1. dBel84

    dBel84 Friend

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    seems I don't have access to the original thread so posting an update or perhaps an appropriate new start to the story :)

    .....

    My first foray into Pappa's world. ( as long as you don't count modifying old ADCOM mosfet amps )

    A good story always starts at the begining, which in my case started with a pair of HK775's which I bought to tinker with and was curious how they sounded.

    HK775
    [​IMG]

    After replacing one of the push buttons and trying to clean up the amp, I ended up giving them a face lift
    = much to some purists distress.

    [​IMG]

    I have been lurking the PASS forum for a very long time, but most of my DIY endeavors have been headphone oriented which is no news to most here and I browsed more out of curiosity. Then while working late one night I happened to stumble on an add for a set of M2x boards - I had been toying with buying the First Watt M2 and just never pulled the trigger and had let the original GB pass me by as I had too many other things going on at the time, so this was a momentary lapse of reason and a little late night weakness/delirium

    [​IMG]

    This weakness had mostly been spurred on by ZenMod's fantastical thread "Most Greedy Boy, of them all... or (there is no) DEFiSIT of Papa's Koans" and a few others of the same ZM ilk.

    I then enquired from the person that I bought the M2X from as to what had driven him to unload this precious cargo and the next thing I knew .... M25 boards on the way and these arrived in the mail

    [​IMG]

    tested them to make sure they were good

    [​IMG]

    these SIT devices were made to start iron forge furnaces and power elevators - major cojones ...but that remains for another day.

    I guess I have become a little derailed in my story telling as not soon after had I refurbished the HK's and had them singing some fairly impressive tunes, one died with the release of special faerie dust never to be rescussitated . Now that I had a set of boards, I got to thinking , would they fit ? The heatsinks are thick solid blocks of aluminum so I gutted the original carcass and voila , a near perfect fit.

    [​IMG]

    As the chassis is mono, I did some patching and modified it to stereo

    [​IMG]

    I by this time had gradually paged through all of the M2 and M2x threads on DIYaudio and became aware of a theme that was a little concerning - noise in the signal , most likely being picked up by the edcor transformer that the M2 uses. Hum has been a point of sore contention recently as I have spent most every free minute trying to kill an annoying hum that has plagued the stacker since starting it's new voyage.

    I recalled that Alex had designed a current limiter and noise cleaner for a power amp project that never got off the ground before CA closed down and I had the perfect pair of smps supplies.

    [​IMG]

    I tested it bolted to external heatsinks and it worked perfectly. I needed to reseat the mosfets under the board as the rig with the heatsinks didn't fit in the case - got it looking good with a nice tight fit and tested again - nothing, for some reason the Fets would not activate - they test well out of the board but something else must have happened and I was getting inpatient with it all - probably a good time to stop and take a breather but instead I rigged up a little CRC and wired it up for testing.

    [​IMG]

    I built 3 of the little input daughter boards - turns out I didn't have suitable NPN transistors for mountain view, so waiting on another mouser order and I thought I had the correct brass nuts to seat the input board but alas - nothing in my parts bin would fit. Probably a good thing as this will afford me time to go over the build once more before I power it up.

    Still a lot to do for the final amp but almost at a point ready to test.

    ..dB
     
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  2. Cspirou

    Cspirou They call me Sparky

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    Nice! I noticed the new M2 boards at the diyaudio store
     
  3. dBel84

    dBel84 Friend

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    Well it works - very elegant design . The mosfets come up slowly - must have to do with the way the optocoupler sets the bias between the devices.

    [​IMG]

    just plugged it in briefly to make sure it plays music , always such a eureka moment no matter how often it happens.

    I just built the simple opamp input boards to make sure it worked, now need to build the jfet board and possibly the diamond buffer too.

    then of course to get the little dials working in the front and case finish the case once I am sure it will tolerate the heat - plan to leave it cooking for at least a few hour before moving it upstairs into the main rig.

    ..dB
     
  4. dBel84

    dBel84 Friend

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    Let the beastie run last night

    [​IMG]

    It gets hot but within reason and without any real air moving - 52deg C on the heatsinks, running dual 18.5 V rails. No noise detected.

    I have to admit that the initial power up and one or 2 tunes was rather unimpressive from the first night but I didn't let it run . Last night I set it up and put on Roger Water's Amused to Death and hit replay

    Once this amp gets to operating temp it really sings, even on the crappy bose test speakers ( that I don't care if I destroy a driver and have done so once before ) . This is pretty much what I expect from a classA amp and it delivers that in spades. Once I have the rest fine tuned and it has spent a few more hours cooking in the test rig, I will move it up and try with the maggies and OB's

    ..dB
     
  5. dBel84

    dBel84 Friend

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    Still working on beautifying the M2x and will post updated pics and impressions sometime but was majorly impressed when my heatsinks arrived for the SIT version of the M2

    relative to M2X

    [​IMG]

    with transformers

    [​IMG]

    I picked them up from a surplus supply store and am busy thinking about what I want the final amp to look like so that I can get the necessary parts to complete the build

    ..dB
     
  6. dBel84

    dBel84 Friend

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    Bought some bling for the front of the chassis

    [​IMG]

    Amp sounds really very good , need to do a little fixing as I glitched something in the bias network when I changed out the front end daughter boards - always let big caps discharge :)

    Now I need to get the OB's tuned a little better so that I can run them SE without too much Hi/Lo driver disparity

    ..dB
     
  7. dBel84

    dBel84 Friend

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    Final update .. Replaced the fets and it powers up, biases and zeroes perfectly

    EDIT: added a pic

    [​IMG]

    Going to let the new bits burn for a while and then plug it in.

    Because the amp sits in a console, I built a sensor controlled fan base with a clc filter to kill the the power supply noise and a temp probe to control the fan speed = will snap a few pics when I pull out the old amp and replace it with the M2. Total noise from fans is 9dB something I can live with for a little piece of mind.

    .. dB
     
    Last edited: Nov 15, 2018
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  8. dBel84

    dBel84 Friend

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    My saga continues - left it burning in only to come back to find another FET in smoke - this is not making any sense, so going to dig deep and see if there might be something that is causing some intermittent failure.

    BUT....

    the real beast continues and while I wait for the SIT based boards to arrive, I am slowly sourcing pieces to make a suitable chassis for the 40W beast.

    [​IMG]

    [​IMG]


    The heatsinks are recycled from some energy fan farm, the "perforated" aluminum plate is from a supplier of folk art metalwork and I have some corner alu blocks en-route from the far east. The big plate will become the front and rear plate, still deciding whether to fit the back plate flush or bolt onto the outside .

    Also deciding on finish ... just polish the pieces I have, anodize it all or use some high heat paint

    ..dB
     
  9. dBel84

    dBel84 Friend

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    Just a small update - no music yet but I am reminded why I hate case work - that is with only a dremel , angle grinder and tapping threads by hand.



    I took a little time over the holiday break to get a few of the more manually challenging things taken care of.



    progress thus far



    [​IMG]



    a few steps along the way



    [​IMG]



    [​IMG]



    [​IMG]



    Assembled an AMBLABS e24 to use as a trigger for powering up the transformers



    [​IMG]





    still a LONG way to go but this was one of the major obstacles to a functional product - if there is ever a next time, an off the shelf chassis is without question the option I will take.



    ..dB
     
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  10. dBel84

    dBel84 Friend

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    Got my M2X working and sounding amazing ---- finally!

    [​IMG]

    to think this happened at least 3 times to different mosfets but on the same channel!!

    thermal insulation pad arc

    [​IMG]

    I couldn't find any pointy bits that might have instigated this and the pads themselves are rated for temp and current , just serious bad luck. They have now all been replaced by ceramic jobbies .

    this amp runs hot - about 55 deg in the open but closer to 65 on the fan base in the rack.


    and added more pics of the beastie

    wiring up the power supply

    [​IMG]


    [​IMG]



    ..dB
     
  11. dBel84

    dBel84 Friend

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    Took a little break from chassis work and decided to take another look at the OB speakers

    I picked up a pair of Linaeum drivers a little while ago and have been toying with adding them into the OBs

    Top hat installed

    [​IMG]


    took a little fiddling to get the ribbon integrated with the full range ( RAAL ) is disconected

    [​IMG]


    throws a very wide stage and complements the set up very well - all drivers are not optimally integrated - this is going to take some time tweaking but it is very listenable.


    and just because I ended up being home alone last night

    [​IMG]

    Nelson Pass's B1 NuTube buffer - only electronically tested thus far, needs volume etc to be tested in a system.

    ..dB
     
  12. Cspirou

    Cspirou They call me Sparky

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    Hey, where did you get a NuTube B1?
     
  13. Thad E Ginathom

    Thad E Ginathom Friend

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    Small thing in passing. Love the wire-clover-leaf multiple-probe attachment point! Clever! And good-looking :)


    .
     
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  14. Walderstorn

    Walderstorn Friend

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    Technical knowledge aside (that i don't own by looking at those pics) they look beautiful.
     
  15. dBel84

    dBel84 Friend

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    Have been following its development on DIYA and Nelson ran a small proto batch which he then released to those interested as an Xmas gift to the community. The even cooler surprise was that he threw in matched Jfets with every board.

    I had already bought some hard to source matched Jfets which will now have to wait for another project. I bought the nutube off ebay and have a muses volume controller coming in (actually PCB arrived yesterday from Germany but chip is still inbound from the UK) This should allow for remote controlled volume with decent fidelity. It was intended for Alex's bootstrapped tube buffer (silver box on top of adcom harkes from Headwize days, but is the best pre I have ever heard) So the jury is out as to which will ultimately end up in daily use.

    The OPPO is just sooo convenient and doesn't sound terrible

    .. dB
     
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  16. dBel84

    dBel84 Friend

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    Tell me again why I didn't just buy a chassis from ebay or one of the ones designed specifically for DIYA.

    Drilled out the mounting holes so that the screws sit flush. Also rendered some customized artwork

    [​IMG]

    Close to a point where I can set up the test rig to bias up the input Jfets then the output devices. Might be easier to dismantle it and have them loose and easily accessible

    .. dB

    seems I didn't add in the other pics

    boards assembled

    [​IMG]

    had to switch gears as the boards didn't allow much room for binding posts , so picked up an L-Bracket and after much cussing - had them mounted

    [​IMG]
     
    Last edited: Jan 16, 2019
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  17. dBel84

    dBel84 Friend

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    Most of the finicky wiring done - still need to find the smaller Molex connectors I bought for the input and then I will be ready to fire it up and set bias/offset and ultimately give it a first listen, plan to leave the chassis unfinished until I am sure everything is working 100% as I will be painting the panels and they will just get beat up with repeated disassembly.

    [​IMG]

    but for now, have to get some real work done for tomorrow

    ..dB
     
  18. dBel84

    dBel84 Friend

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    Inspired by @JeffYoung 's post with his immaculate F3 , I decided to plunge back into the SIT abyss.

    I ran into a few issues of not being able to bias the channels nor set the offset to zero and then one of the input buffers didn't bias up at all - so many many hours of tracking traces and checking parts, I am back on track.

    I switched out a few resistor values in the amp , replaced all the active elements in the bias circuit and managed to set the offset to zero. The bias is still higher than desired and I suspect that my SITs are not in the optimal range for the bias circuit - based on VGS it should be but life is stranger than truths. JFET buffer was a malfunctioning BJT in the power supply - replaced and working

    so now have some ( surprisingly good sounding ) music coming out of crappy sacrificial Bose speakers.

    [​IMG]

    just going to let it burn for a few days before doing anything else

    ..dB
     
  19. JeffYoung

    JeffYoung Friend

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    I can't believe I missed out on the NuTube offer. How's it sound?
     
  20. dBel84

    dBel84 Friend

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    I am a little embarrassed to admit this but I still don't have a volume pot for it. I bought a muses kit and everything finally arrived a week ago but the preamp is just silently waiting
     
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