AliExpress / eBay JL Hood 1969 Class A Amp

Discussion in 'Power Amps' started by purr1n, Apr 25, 2017.

  1. purr1n

    purr1n Finding his inner redneck

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    AliExpress / EBay John Lindsey Hood 1969 Class A Amp. I mentioned this amp in another thread.
    Hood 1969.jpg

    This is a China special based on John Lindsey Hood's Class A design from Wireless World April 1969, but with modern parts. I haven't popped the hood yet, but I just ordered my own: the one with the PNP transistors and better caps. I believe this unit (on loan from a friend), uses NPN transistors.

    Do I like this amp? Hell yeah! For just a bit more $200 shipped from China, we have something that is competitive (but different sounding) with the Hegel H2, as long as we don't need the power.* This amp is only 10 watts. (The Hegel is 150W or so). The chassis gets incredibly hot. Remember when everyone at HF was bitching how hot the Asgard 1 got? Well this amp is just like that, probably even more so. Class A baby.

    I'll write up a comparative review with other amps a bit later. Figured I'd tease you guys a bit. I'm kind of curious how it measures too. For now, I'll just say with the modern parts and built-in simple PS, great clarity, neutral, maybe a bit mid-forward, and with just the right staging. Not upfront, but also not too deep and diffuse. Sort of just right with burnished edges leading into the stage. The original version was supposedly warm sounding. I'm sure cap rolling (or adding 10uF cap in parallel) would yield interesting results.

    Here is the original schematic (from tubecad.com)
    [​IMG]

    See, totally simple. Basically three stages. Very unlike modern amps with zillions of parts and transistors. Downside might be the big cap at the output, in the feedback, and a small cap at the input. But heck, with modern parts, this the one of the best SS amps I've heard. The Epic Japanese Pioneer M-22 amp had a few caps in the signal path as well.

    I can't figure out if this is PP, or SE (if the top transistor is a current source), or maybe a bit a both. Some of these amps have two trim pots, one of which is probably bias, the other the midpoint voltage, which might set how much of the pushing and pulling the bottom transistor performs. Again, I'll pop this one I have on hand open when I have more time.

    To be continued.

    *HE-6 owners should still seek massive power. Remember, an amp that delivers 120W into 8 ohms, will deliver far less into 32 ohms (approximate impedance of HE-6). Ideally 30W, but realistically, maybe even less like 15W.

    PICTURES: http://www.superbestaudiofriends.or...ay-jl-hood-1969-class-a-amp.4308/#post-136690
    IMPRESSIONS: http://www.superbestaudiofriends.or...hood-1969-class-a-amp.4308/page-2#post-136866
     
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    Last edited: May 2, 2017
  2. ultrabike

    ultrabike Measurbator - Admin

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  3. philipmorgan

    philipmorgan Member of the month

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    I'm starting to shop around for an amp for my Overnight Sensations (nearfield in a pretty small room), and this seems interesting. I wonder about the power output though...
     
  4. purr1n

    purr1n Finding his inner redneck

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    We could buy another one for the loaner program. Let me evaluate the variations out there first. I'm making certain assumptions, but the big thing to worry about are loads less than 8 ohms.
     
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  5. Merrick

    Merrick A lidless ear

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    I'd be down for a loaner on this.
     
  6. manatworks

    manatworks Friend

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    Nice! I'm looking for planar amp (for code-X) and this looks like a simpler solution (or i will just wait for Vidar)
     
  7. frenchbat

    frenchbat Almost "Made"

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    I'd venture and say that for the he6, one would actually look for good current capability. The more amperes available the better.
     
  8. Armaegis

    Armaegis Friend

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    Although us HE-6 nutjobs should also know the difference between voltage limited or current limited amps. A low power amp that is voltage limited will not be able to push the HE-6 very hard, but a current limited one might be just fine.
     
  9. zerodeefex

    zerodeefex Grumpiest admin

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    I ordered a few variations too. Might have to experiment with some builds from scratch when I am moved into the new place and have a soldering iron again.
     
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  10. uncola

    uncola Friend

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    I support this dipping of toes into the asian clone amp scene
     
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  11. purr1n

    purr1n Finding his inner redneck

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    I wouldn't call this amp an clone. JLH published the design in the April 1969 issue of Wireless World. Everyone and anyone is free to do what they wish for the design. As far as clones of existing amps or designs which require license or permission, I won't support that.
     
  12. Grahad2

    Grahad2 Red eyes from too much anime

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  13. purr1n

    purr1n Finding his inner redneck

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    1969. The updated version is slightly more complex with more parts and the use of a bipolar power supply. Also, an update doesn't necessarily mean it sounds betterer. Nelson Pass also designed an amp, I think the Zen, based on some ideas from the JLH.
     
  14. shipsupt

    shipsupt Admin

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    Why you no get gold version?

    [​IMG]
     
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  15. spwath

    spwath Collegiate hijinks master

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  16. Cspirou

    Cspirou They call me Sparky

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    Nice to see an endorsement of Nobsound. I've seen a lot of their stuff on eBay and Aliexpress and was wondering how it holds up. Makes me a little more comfortable to try some of the tube gear I've seen.
     
  17. purr1n

    purr1n Finding his inner redneck

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    I ordered the gold version for myself!
     
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  18. Grahad2

    Grahad2 Red eyes from too much anime

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    I believe it's the PLH.
     
  19. purr1n

    purr1n Finding his inner redneck

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    Very cool. Looking at it quickly, looks like he replaced everything with FETs and eliminated the first transistor.
     
  20. purr1n

    purr1n Finding his inner redneck

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    Looks like the unit I borrowed is the same that I ordered with the same MJ2955 transistors.

    DSC_2060.JPG
    DSC_2062.JPG

    I put a cheap Audyn 10uF (whatever I could find) in parallel with the Epcos output caps (there are two of those in parallel to get a higher value) a few days ago. This amp is so incredibly simple with a primitive yet effective power supply circuit. Would be curious how a better PS with fare, but I like the fact that everything so far costs no more than $225. The chassis is one big heatsink, like the Schiit stuff. This is ChiFi done right, or how ChiFi should be. Cheap and good, not mediocre and expensive.

    Been going back and forth between this amp and the Hegel H2. Haven't had as much time as usual. Will solicit family input tonight and finally post some impressions afterward.
     
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    Last edited: May 2, 2017

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