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Pass Aleph 3

Discussion in 'classic' started by Tony L, Sep 10, 2021.

  1. Tony L

    Tony L Administrator

    Not often tidy boxed examples of this little 30 Watt single-ended class A amp come up for grabs: https://www.ebay.co.uk/itm/PASS-LAB...d=link&campid=5338728743&toolid=20001&mkevt=1

    I have to admit if I’d not just spent a simply ridiculous amount getting the bathroom sorted out I’d have maybe been tempted. Nelson Pass has a reputation of being remarkably good with sharing knowledge, service info etc, so even though it’s not a new amp (late ‘90s) servicing it shouldn’t be any issue at all.
     
    John_73 and Stuart Frazer like this.
  2. Goldenmouse

    Goldenmouse pfm Member

    Does look to be a beautiful example which probably justifies the price. Totally classic case design as well.
     
  3. earlofsodbury

    earlofsodbury Wastrel.

    Sane price for a cracking amp; if I'd not just bought the First Watt J2, I'd have had that.
     
    dan m likes this.
  4. vesuvian

    vesuvian Well-Known Member

    hifinutt likes this.
  5. Tony L

    Tony L Administrator

    I tried, I really, really tried, but I just couldn’t not push the button…
     
  6. Tony L

    Tony L Administrator

    PS Justification: I just have too much duplication at present, I certainly don’t need both the two Stereo 20s (I have a spare one), and the TL12 Plus monos, so I suspect in time (assuming I like the Pass) I’ll sell the former two and just keep the TL12+ and all the valves, and that’s the cash back. I’ve always wanted to try a proper class A amp as I’ve liked Krells, Sugdens etc, and I’d never need a really big powerful one. Nor did I want anything with a fan in it. The Nelson Pass stuff is superbly documented and serviceable and this looks to be a very simple and sustainable amp. This one is a classic, I love the brutalist look, and it is small enough to fit where I want it to fit. It is also apparently pretty insensitive so that means I’m not trapped on the lowest output setting of the Verdier (the higher, lower-feedback settings sound better as far as I can tell, so I’ll get a better sounding preamp for free!).
     
    earlofsodbury, simonheys69 and Darren like this.
  7. anotherdom

    anotherdom pfm Member

    Well justified sir - not that you need to explain yourself to us!
     
    Nytechy likes this.
  8. Fergus

    Fergus pfm Member

    I doubt it’s a purchase you’ll regret. Two of my friends used one in their very different systems and both sounded superb.
     
  9. Tony L

    Tony L Administrator

    I’ll shunt this thread across into the classic room now as hopefully it will be another interesting journey…
     
    nmtjb likes this.
  10. mandryka

    mandryka pfm Member

    The amplifier does not require any maintenance. While the design is conservative, this is a hard running amplifier, as single ended Class A operation is the least efficient operating mode. In fifteen years the electrolytic power supply capacitors will get old. Depending on usage, you will begin to have semiconductor and other failures between 10 and 50 years after date of manufacture. Later, the sun will cool to a white dwarf, and after that the universe will experience heat death.

    A3MANR0.PDF (passlabs.com)
     
  11. mandryka

    mandryka pfm Member

    Congratulations. If I'd have seen it I would have thought "I would like to have that!"
     
  12. mandryka

    mandryka pfm Member

    It looks like a hedgehog!
     
  13. Tony L

    Tony L Administrator

    There’s a service manual here with a schematic. Assuming it arrives safe and sound and works ok I’ll work on the assumption that I’ll eventually at least recap it, check the heatsink gloop is still gloop etc, and probably try and find a full set of the power mosfets to keep safe as a spare. Apparently it used very good quality Panasonic caps which seem to have lasted well/better than expectations, but even so they are likely getting tired by now. I’ve yet to find evidence of folk having issues these amps despite the age, but I’ve not read the whole internet yet. I’ll pop the lid and if nothing is obviously leaking or bulging and the DC offset looks reasonable I’ll assume it is safe for a while. I’ve also got a heat meter so I can spot if it is running too hot.
     
  14. Goldenmouse

    Goldenmouse pfm Member

    Hedgehogs are lovely, just like the amp.
     
    RJohan, nmtjb and mandryka like this.
  15. Woodface

    Woodface pfm Member

    Excellent, can’t wait to hear about this one.
     
  16. Tantris

    Tantris pfm Member

    Probably a very good partner to Quad ESL63s.
     
  17. Tony L

    Tony L Administrator

    Anyone know how to convert a ‘voltage gain of 20db’ into the more familiar input sensitivity in volts/mV etc? Spec and measurements in this old Stereophile review, but I think in terms of x volts for full output, i.e. how much do you have to squirt in to it to get 30 Watts out?

    I get the impression my Audio Synthesis passives just aren’t a contender here, but the JC Verdier valve pre certainly should be. It is a very good partner with the 303 which also has a 23k input impedance, so that bit is certainly fine. The Verdier is switchable between 0db and 20db gain over 5 steps (via internal jumper settings), this apparently done by altering the negative feedback loop. I use it on the lowest 0db setting with the 303 and Tannoys which gives a fairly typical CD listening level at around ‘quarter-to’ on the volume knobs. I can get away with a higher gain setting with the much less efficient 149s or LS3/5As (the Quad is 0.5V for full out (45 Watts)), and the preamp does seem to sound better this way. I’m assuming I’ll be able to blow the windows out as the Verdier is so versatile and configurable gain-wise, but it would be interesting to convert the Pass 20db voltage gain into a more familiar sensitivity figure if anyone knows how.
     
  18. gingermrkettle

    gingermrkettle Deep vein trombonist

    If my maths is right, 20dB gain is x10, so 30W output into 8ohms (which would be 15.5V output) would require 1.55V in. Pretty close to the top of a 0dB gain setting with a standard 2V output source, needing gain with a 300mV tuner output
     
  19. Tony L

    Tony L Administrator

    Excellent, that sounds right in range. My guess is the Verdier/Pass combo will be easy to setup optimally without being at either extreme of preamp internal settings with any of my speakers.
     
  20. Darren

    Darren All Business

    To be frank, I'm finding this unhelpful. I am currently avoiding the purchase of a large pair of speakers I've wanted forever because I desperately need a modern kitchen and this kind of willy nilly buying and justification is messing with my head.
     
    narabdela, earlofsodbury and Rug Doc like this.

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