A DIY version of the Pass HPA-1

Discussion in 'DIY' started by JeffYoung, Sep 29, 2019.

  1. JeffYoung

    JeffYoung Friend

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    I've been working on a clone of the Pass HPA-1. Jam gave a general overview of the topology on DIYAudio, and 6Moons and Hi Fi Knights had a lot of good internal photographs in their reviews. Some of the other guys on DIYAudio also had some good insights, and I exchanged a few more emails with Jam.

    I now have a schematic and board design. I believe the PSU and audio portions are pretty true to the original, while the control logic is my own as I didn't need remote control and I didn't want to program a PIC controller.

    I'm doing casework similar to the original, with a few changes to avoid the killer setup charges for anodising one-off parts.

    Grooving the faceplate:

    progress_frontplate.jpg


    Turning the volume knob insert from Richlite:

    progress_volume_insert.jpg


    Boring the hole in the faceplate for the insert:

    progress_volume_insert2.jpg


    Tapping holes on the back of the faceplate for the PCB that holds the buttons and LEDs:

    progress_tapping.jpg


    Stuffing the board:

    board-1.jpg


    That's it for now.

    Cheers,
    Jeff.
     
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  2. skem

    skem Friend

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    That settles it. I'm going to Ireland for my next vacation.
     
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  3. JeffYoung

    JeffYoung Friend

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    Front panel:

    progress_front.jpg


    And the "button board" (it has 6 slots on the theory that I can also use it for other designs, but this one only uses 4):

    progress_buttonboard.jpg
     
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  4. fraggler

    fraggler A Happy & Busy Life

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    Insane efforts on the casework. Wow.

    If this turns out well, are you considering selling the boards?
     
  5. JeffYoung

    JeffYoung Friend

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    I just ran a Group Buy for my FirstWatt J2 boards so I might need a break from the post office runs. ;)

    But I'll be happy to post the Kicad files (and/or Gerbers) if someone else wants to do one....
     
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  6. JeffYoung

    JeffYoung Friend

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    progress_stuffed1.jpg progress_stuffed2.jpg progress_stuffed3.jpg
     
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  7. skem

    skem Friend

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    What are the output devices?
     
  8. JeffYoung

    JeffYoung Friend

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    FQP3N30 / FQP3P20.

    Front end is 2SJ74 / 2SK170; cascodes and current mirrors KSA992 / KSC1845.
     
  9. skem

    skem Friend

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    Mmmm....the coveted jfets.

    Do you prefer the 992 to the zetex devices? The zetex ZTX795A look to have a little higher bandwidth (EDIT: uniform hFE over Ic ranges). But there are no published noise figures on them.

    992s have low noise, and nowadays have very consistent hFE, so that’s an advantage.
     
    Last edited: Oct 4, 2019
  10. JeffYoung

    JeffYoung Friend

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    More just familiarity. I did try the 2SA970/2SC2240 in SPICE, but the 992/1845 performed (marginally) better.

    On the Zetex side I'm only familiar with the 450/550 (which I tend to use for general purpose stuff) and the 653/753 (with their unusually high Cob required by the Naim NAP250 topologies).

    The KSA992s are indeed consistent. I tried matching a cut tape of 20 of them, but they were all within my measurement error / repeatability.
     
  11. dBel84

    dBel84 Friend

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    Really amazing amount of work putting this together.. dB
     
  12. JeffYoung

    JeffYoung Friend

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    progress_cased1.jpg

    progress_cased2.jpg
     
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  13. LetMeBeFrank

    LetMeBeFrank Won't tell anyone my name is actually Francis

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    Wow, I really like how you sleeved and braided the wires from the input to the volume control. Very slick.
     
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  14. JeffYoung

    JeffYoung Friend

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    So how's it sound?

    I compared it to 2 other DIY builds: a Bottlehead SEX with some modifications (no CCS) and a Torpedo 3 clone (with tube and output stage CCSes). They were all built by me, so no ownership bias. I think the SEX looks the coolest, so there's a bit of bias there.

    headphone amps.jpg

    All listening was done with HD650s. The Pass was the least powerful, with the listening done at about 2 o'clock, while the other two were at 10 or 11 o'clock.

    The T3 has the punchiest bass, but only by a hair. The SEX gets a bit flabby down low, but it's nice and round and euphonic. Surprisingly, the Pass goes deeper than the other two and was more effective at getting my groove on.

    Another surprise: vocals were best on the SEX. More body, more soul.

    The SEX fell down on detail. The T3 was noticeably better while the Pass was in a different league. This was by far the largest difference between the amps.

    The Pass had a more expansive sound-stage while the other two were more similar than not. It wasn't so much that the Pass was wider or taller (although it might have been), but more that it felt like you could walk around in between the various bits.

    The SEX was more fun than the T3, but if I was listening seriously I'd be annoyed by the loss of detail. The Pass consistently gave me goosebumps where the other two didn't. For me? The Pass without a moment's hesitation.
     
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  15. skem

    skem Friend

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    Excellent builds. I’m curious what you get on measurements (despite being a subjectivist myself), if you do those sorts of things.
     
  16. JeffYoung

    JeffYoung Friend

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    I've got an old HP339 and a Tek signal generator, but I need to move my workbench to have space to set them up.

    It's worth mentioning that I'm a noob on that front, so God knows what kind of results I'll get. ;)
     
  17. skem

    skem Friend

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    Ah yes. My life on that front has been immensely improved by the QuantAsylum QA401
     
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  18. Clemmaster

    Clemmaster Friend

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    Where do I place an order? :p
     
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  19. JeffYoung

    JeffYoung Friend

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    My Audeze LCD-2 came in today. I was curious if a preference for planers in 2-channel would translate to the same for cans: it would appear to. The LCD-2 have a wide, spacious sound that the HD650 can't match (and is the same thing I love about Maggies).

    Back to the three amps. The LCD-2s accentuate the HPA-1's strengths in terms of detail retrieval and balance. The T3's bass sounds fab on them, making me want to turn it up more, but then the highs start to get uncomfortable. I don't know whether the HPA-1 is rolled off a bit or if its just less harsh, but I could play it at slightly higher volume. The highs on the SEX are definitely rolled off, but that allowed me to enjoy the bass a bit more (and detail retrieval isn't its strong suit anyway).

    I just wish the LCD-2s were as comfortable as the HD650s on the head....
     
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  20. atomicbob

    atomicbob dScope Yoda

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    This may be of some interest if not already viewed: Comparison of several audio analysis systems - technical measurements
     
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