DIY talk

Discussion in 'DIY' started by Cspirou, Jul 25, 2021.

  1. Armaegis

    Armaegis Friend

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    Or you do what Jan Meier does and cobble together the "active balanced ground". Somewhere in a dusty notebook I did sketch out how to hack the M3 board to do this. I wish I could find it...
     
  2. Cspirou

    Cspirou They call me Sparky

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  3. TomB

    TomB MOT: Beezar

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    No "kinda" about it - nwavguy was fulll of it. His problem was that he never knew to lift the ground lead when testing a three-channel amp. If not, it shorts the ground channel to ground, which completely defeats the purpose. It was why it was extremely important to isolate the ground connections on the input/output connectors of a three-channel amp

    IMHO, ground channel topology has a lot of merit, but as Beefy said, going balanced is not a much bigger step anyway. The issue with balanced back in the day was not necessarily the parts cost, but finding a four-channel volume pot. I think the availability of those have increased over the years (and for attenuators), but they still remain quite expensive, comparatively speaking. I would guess that besides the casework, it's the single most expensive item in the Jotunheim, for instance.

    I don't have all the history correct, but I believe the three-channel configuration was the original idea of PPL, otherwise known as Phil Larocco. The Larocco headphone amplifiers were among the finest commercial headphone amplifiers of their day and some (all?) used the three-channel topology. PPL teamed up with Morsel and Tangent to produce the PPA. Technically speaking, the M3 is a MOSFET version of the PPA. AMB came along later and teamed up with Morsel to design the M3 by using the three-channel topology on Sheldon Stoke's MOSFET-output headphone amplifier, originally published on Headwize:
    SDS Labs Headphone Amplifier. – HeadWize Memoria (wordpress.com)

    Here's Morsel's original web page on the M3 design:
    M³ Headphone Amplifier (elvencraft.com)

    No offense to Beefy, but I don't agree that the Sigma power supplies make the M3 so quiet. It's really the opamp input and feedback that can be optimized for low noise. (Which is what nwavguy exploited for his O2 design.) The M3 and the PPA were super-quiet long before AMB ever developed his Sigma power supplies. Most were powered by Tangent's STEPS or TREAD power supply. In fact there was quite a bit of discussion about the S/N capability when AMB came out with his B22 design. The B22 was the better headphone amp with fully discrete circuitry, but it was not as quiet as the M3. I'm guessing again here, but I think that's why AMB developed the Sigma power supplies next, because there was some talk at the time that the B22 would not make a great pre-amp, especially compared to his own M3.

    Keep in mind that both the M3 and PPA are somewhat difficult DIY builds, especially for newcomers, because the PCBs have no power supply or casework design. It means you have to fiddle with line power, a power transformer, a choice of an audiophile-quality power supply, and then come up with your own casework design. You have to fiddle with line power and a power transformer with the Crack, too, However, it's much more cookbook and included in the overall design/kit. The issue in building the Crack is that it's point-to-point wiring, not a paint-by-numbers PCB. The M3 and PPA are also much more versatile with headphone impedances, whereas the Crack is very limited to the Sennheiser 300 ohm sweet spot. (What Beefy has said.)
     
  4. 3l3tric

    3l3tric Rando

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    Thank you so much for the writeup, I never realized just how related these projects all were. I've seen a bunch of these projects around but never understood how the history all fit together.

    That point on the low-noise design is pretty fascinating too. I'd always kinda assumed you HAD to assemble a regulated design like the sigma if you wanted that truly silent noise floor, so it's interesting to hear the design itself is already pretty low noise. Almost makes me want to just get a wallwart when I build the thing and maybe build a sigma at some point down the road.

    I should be fine with the difficulty curve of the M3, given I assembled a sigma25 and gamma2 a few years back. I'll definitely need to read through the documentation thoroughly and go slowly since it'll be my first big project in a long time, and I always exercise due caution when working with line voltages. The casework will be a challenge but luckily I know a few people that could provide assistance. I may just end up with an all wood enclosure M3, hehe
     
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  5. TomB

    TomB MOT: Beezar

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    Just an FYI, but the STEPS and TREAD were state-of-the-art before the Sigma power supplies. So, neither one were slouches when it came to low noise.

    The STEPS and TREAD (which Tangent unfortunately removed from his website) were rated at about 58-60 micro-volt ripple. The Sigmas brought that down to single digits of micro-volt ripple. Honestly, once you get to less than 0.1 milli-volt ripple, you're probably not going to hear the difference in going lower. (JMHO)
     
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  6. Armaegis

    Armaegis Friend

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    Wow, thanks to @TomB for the trip down memory lane this morning. Those are some pages I haven't seen since... well, the first time they were around.
     
  7. M3NTAL

    M3NTAL Friend

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    Hopefully this is the right thread for this. I see a lot of the newer "DIY" guys working with headphones as their first foray into speakers. This neat little video popped up on my youtubez recommendations and thought it covers some things that don't always get explained easily. The part where he is running a compression driver without the horn is a bit annoying, but still something that most people don't often get to see/hear.

     
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  8. Cspirou

    Cspirou They call me Sparky

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    As far as casework goes, M3 seems pretty forgiving. Heatsinks are stock and PCB mounted so no need for custom heatsinks with tapped holes. Case width and length don't need to be precise as long as they surpass a minimum. Only the front panel has PCB mounted components which is the one part you need to be careful with. The back is wired parts and pretty forgiving of placement.

    panels can be done at FPE which are nice and expensive. However since this amp has been developed we've had the rise of another DIY hobby, mechanical keyboards. Because of keyboards we've had a various different layouts that all use a metal plate for stability. The components for a keyboard rarely need a round hole, more often needing some kind of modified square fitting for switches. Precision lasercutting is necessary to do this which used to be expensive, but due to high demand has made available many online lasercutting services for the hobbyist.
     
  9. Cspirou

    Cspirou They call me Sparky

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  10. randytsuch

    randytsuch Facebook Friend

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    I decided to post here instead of the deals page because only DIYers will care about this.

    Modushop.biz is having a black friday sale, say 20% off on almost all products.

    BLACK2021 is the code

    I'm still deciding on my next project, guess I need to decide and buy a chassis for it now.
     
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  11. dBel84

    dBel84 Friend

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    I found the 3U/400 is extremely versatile (if we are talking power amps)
     
  12. Beefy

    Beefy Almost "Made"

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    Ooooh, might be a good time to buy a chassis for a First Watt clone. Tempting, tempting.....
     
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  13. randytsuch

    randytsuch Facebook Friend

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    The actual email with dates at end:

    This year at Modushop enjoy whopping discounts of 20% on almost all our products for even more than a whole week! Unlike previous years, this time the discount will be applied on customizations as well!

    Make sure you use the coupon "BLACK2021" before checking out and paying for your order.
    This percentage is added to the already existing 6% off for 2 equal pieces and 10% off for 3 equal pieces

    But hurry! This offer only lasts from 19/11 until 29/11 included!
     
  14. Cspirou

    Cspirou They call me Sparky

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    goddamn

    i got some aleph boards and now would be good to case it. i also want to recase my gainclone
     
  15. Pancakes

    Pancakes Friend

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    Ah, this explains why the code didn't work last night.
     
  16. Garns

    Garns Friend

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    Not strictly DIY but... spitballing some thoughts for an eventual endgame 2A3 amp to replace my Aficionado.

    My system is widebanders + active sub. Both the speakers and the sub are fed from the output transformers of the Aficionado (I prefer to drive the sub from the output of the tube amp to help with integration, and so I don't need a preamp.) The mains start rolling off as high as 100Hz, and are well down by 60Hz. Thinking about this, the two things I feed from the amp have very different requirements. The widebanders don't need flat response to 10Hz. The active sub doesn't need much current or to see a particularly low impedance.

    So is the following crazy? Use an OPT which starts rolling off high (e.g. 70Hz) to drive the mains, and then feed the sub from some kind of parallel output off the power tube which is, I don't know, maybe another OPT or a cap? (I have zero knowledge or understanding of what's possible). It seems that the advantages are:
    • Amp is not trying to drive a highly variable impedance load at bass freqs.
    • Reduce cone excursion and induced IMD at frequencies the mains can't reproduce.
    • Main OPT is smaller and/or fewer turns -> cheaper, better performance.
    • Bass output only needs to deliver low frequencies into a high Z load.
    Possible disadvantages:
    • I don't know what I'm talking about and this is completely not doable
    • Different characters between the two outputs (bad integration)
    • OPT may introduce added distortion and/or phase shift near the bass roll-off frequency which is now in the audible range of the mains
    • Wildly quixotic and impossible to resell.
    So is this a thing that can be done/has been done?
     
  17. Pancakes

    Pancakes Friend

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    Is the goal to here to have lf roll off on the mains without using a crossover?
     
  18. Garns

    Garns Friend

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    In effect, and it seems doing it via the transformer would avoid a (giant and expensive) cap in the signal path. Plus you have one fewer constraint the transformer performance needs to satisfy. Of course the lf couldn't then be tapped off the same transformer.
     
  19. Pancakes

    Pancakes Friend

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    Perhaps you can do the same thing using multiple secondaries off the same trafo (as opposed to multiple trafos). It would have to be a custom deal though. I dunno man, this is a pretty unique thing you're trying to do.
     
  20. Cspirou

    Cspirou They call me Sparky

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    Multiple transformers seem like it would mess with the tube impedance load a bit. A transformer that rolls off early would be a custom job for sure. Usually only cheap transformers have bass roll off as high end one almost always extend to 20Hz-40Hz.

    I would check TubeCAD since he seems to be a source of crazy ideas like this.
     

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