SKA Headamp Build - Pics Attached

Hi Gang,

Well I originally posted about this headphone amp to see if anyone was interested in a joint build - there were no takers so I flew solo. It's my first project from woe to go, and it was AWESOME FUN!!

It's a headphone amp from fellow Aussie Greg Ball (not sure if he is a member here) - he's a great guy who helped me through the entire build process - his site is;
SKA - Simple Killer Amplifier by Greg Ball

I've built it as per the specifications - Class A up until 10mW (which is very loud for headphones) - except changed the 10k stereo pot for an ALPS 10k stereo pot, and changed the 10uF 16v capacitor to a 470uF 25V for higher ripple rejection. Power supply at the moment is a wall wart style 24v DC 1A plug pack, so 1k5 resistors are linking + to GND and - to GND on the pcb. It's using an OPA2134, might swap a few others in after 50 hrs of burn in time, but so far (after an hour) the sound signtaure has definitely settled! There’s a huge amount of definition in the sound, and I dare say I am completely converted from my tube headphone amp – which actually sounds a bit sluggish by comparison.

That said, I'll get into some more detail about headphone types used and give more detail on the sonic signature once I've had a good chance to form an opinion.

Here's some pics;

Don't know how many people out there have built this unit - but I've basically had it on all weekend, it's running quite warm!

It's a REVELATION! I've listened over and over to my favourite albums & they sound brand new. My [guilty] pleasure is Emerson, Lake and Palmer - their Brain Salad Surgery album always sounds quite thin at the bottom end, but with this headamp there's so much definition that it gives a whole new strength to the recording

Really doubting the need to even try a different opamp (still using the OPA2134). It drives the K701 to great levels, but I think the stock build really sounds great (after 30 hrs burn in) with my Beyerdynamics.

All bias aside, I'm really starting to prefer it to my Vincent Audio tube hybrid (especially as it was 1/8th of the cost to build!) - but I'm going to do another build of it, with a dual regulated power supply, just to see how far the circuit can be pushed.

If anyone has any opamp recommendations (with a high PSRR), let me know. Or if you're keen on doing a build, tell me while my memory of all the chassis measurements is still in my head!!

I've got the Vincent KHV-1, along with the Shanling PH300 and Heed Canamp. Used to have a Firestone Little Country.

$57 for the kit
$21.50 for the chassis
rca jacks $5
headphone jack $3
knob $4
$20 wall wart
$6 LED switch

I upgraded the pot to an ALPS, which was about $20 (but you get a pot with the kit).
Total: about $130 AUD = $120 USD.

Update - some opamp rolling remarks;

I've tried the following in both headphone and preamp outputs;
OPA2228
LME49720HA (on an adapter)
TLE2142

Used each for about an hour. Preliminary remarks are that the OPA2228 sounds quite similar to the OPA2134, quite smooth - signature of most Burr Brown opamps, I'd say, but with better overall balance (meaning better detail in the top end)

The LME49720HA is in a small tin can and has a reputation that probably entails expectations that are far too high. Need some more time with this one, couldn't draw too many distinctions between it and the OPA2228.

TLE2142 was the real gem!
It took away some very subtle hissing in the speakers, and gives a beautiful sound! My mate who sent me these opamps mentioned that this one (although the single version TLE2141) was used in the iBasso headphone amps which were also biased into class A. Maybe there's something in that. Who knows, it sounds brilliant and brings real depth to some of my test recordings.

OK another weekend later, tried the TSH22IN and also the LM4562:

I have to say, the TSH22IN is a great chip! It doesn't colour the sound as much as the Burr Brown opamps, and seems to be quite neutral (no boomy lower end). Enjoy the midrange on this one - which is the heart and soul of any music, so if a chip does this well, it's a keeper!!

The LM4562 sounds quite similar to the LME49720HA - verrrry dry, probably a good reference opamp. Might test it with some string music to see how the acoustic sounds come across.

However, the one I've come back to repeatedly is the OPA2228 - it's just fantastic for rock music, but not so mellow like the OPA2134 and plus has better top end definition.

All this listening takes a LOT of time, but is well worth it.

I'd say, if you can, track down the OPA2228 for this amp.