I just finished making a headphone amp from an ebuy kit .... about 15usd for the pcb and components (incl. delivery!)
It' s the
John Linsley-Hood Class A circuit using 2 small signal transistors and a pair of output transistors (which are mounted on the underside of the pcb).
Has a gain of x8, with a stereo potentiometer at the input, unbalanced rca inputs and a stereo trs output jack.
I'm running (for now) with a Vcc +9.7Vdc - the output transistors warm up *strongly* without the heatsinks - I am using simple aly angle brackets for the heatsinks.
ANYway, apart from having a bunch SMDs in the form of resistors, the size of a grain of schmutz
, the thing all came up good.
THD is something in the region 0.001% driving my Motu (10K inputs, more or less)
NOTE - further tests at 'normal listening levels', then switched to drive 10K load does indeed show THD 0.001% rising to around 0.1% for 8Vpp output (off of a +9Vdc supply) [ just a quick test so far, so not definitive .. yet]
Considering it has just 4 active devices, and with a relatively low Vcc supply used, it is pretty good THD performance, albeit at a stupid level of power wasted as heat!
I'll wait for the properly heatsinked version before increasing Vcc to +15Vdc and beyond!
.....
So, I'm doing more tests, driving various loads, down to 60ohms (headphones!) to get more info on this neat little beasty.
But so far, it is looking good,
sounds quite good with the headphones ... well strong, *quite* hifi and very balanced in the frequency response (ie. not a fizzy schtick and with proper bass).
For use as a stereo line amp (into 300ohm and higher) loads, it seems to be working well.
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SUBjectively, as a 'born again tube guy', I'm *surprised* the sound is giving me such excitement, for such little time and cash down
Yes there's heat and power involved, but for a tube guy whose made big SE amps, it's not such a big deal!
I'm
looking forward to messing with the JLH circuit (1969), the mods from the designer himself (from 1996) and the subsequent commentary (circa 2000+).
I'm hoping that the JLH 1996 at 10Wrms per channel will be a good match for some late 70s real-wood paper-coned 'Realistic' 2 way speakers (Radio Shack for the usa folk!)
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The same design scales up to whatever class A power levels you can heat-sink! The esteemed JLHood has lots of info out there on his 10W plus version. I've seen it used up to 25Wrms into 8ohm speaker loads.
This same compact pcb, I'm using as a stereo bus driver with some haufe traffos for output balancing.
Input is stereo unbalanced mix busses.
SUper cheap and damn good performance, for mixing up a bunch of pedals and such ..