Hi all, I've only just spotted this thread while looking for something else and it's been interesting to see what other folks have been doing with their Jaycar amps.
I'm on my third one, building my first one some years ago when the design first came out. Since moving to NZ 21 months ago, I have since constructed two more of this terrific design, since I didn't bring the original one with me. I've thought for years that this design had lots of potential and this last few months has seen me rebuild two of them, the latest one has few of the original parts on board, other than the transistors and connectors, since I haven't yet got around to putting in the higher quality parts.
I've named my amp, KHA, for Kit Headphone Amp, since I prefer to write KHA than just 'the Jaycar amp'.
. I called KHA I.5 the first upgrade from standard, which kept everything original bar the capacitors and the op-amp. It's been quite a journey for this honey of an amp, firstly just exchanging the op-amp for various other models, including OPA627, LT1028 (2 on a Brown Dog adapter) and for a short time LT1057s which was bland and boring IMO.
The best of that lot for me were the LT1028s, adding much needed body and warmth for the Senn HD540 Refs I was using at the time (Senn HD650s now). Fortunately, the Gods smiled grandly and I got to hear about the audio-gd fully discrete HDAMs from the Zero thread and all the op-amps were then kissed goodbye for ever; as good as some of them were, they couldn't hold a candle to the HDAMs, OPA Earth being the first one slotted straight into the socket, followed a month or so later by what IMO is the finest piece of add-on electronics I have come across in 35 years of audio as a hobby, the OPA Moon HDAM. This fine creation jells with KHA as if it had been specifically designed for it, turning the amp into something truly extraordinary, especially in light of the small amount of funds required to take it to this level. I have been stunned speechless countless times by this amp with the OPA's on board, the OPA Moon being the more emotionally connective of the two and OPA Earth the more neutral (slightly) and a tad less warm.
I implore any of you who wants to hear more from this great amp, please take a listen to your amp with an audio-gd OPA amp on board, you may never go back to using op-amps again .... other than the odd exceptions.
These HDAMs simply give you more of everything, speed, dynamics, dynamic contrasts, fine micro details, sound stage in 3D+ and more. The HDAMs need a decent power supply! The standard one, as many of you have, is fine for the op-amps and I upgraded mine with UF diodes, Nichicon FG caps and took off all of the excess parts. However, once I bought an audio-gd power supply, it was game on and the HDAMs never looked back, adding massive grunt, speed and dynamics again from top to bottom and utter silence between the notes, all caps bypassed with Russian PIOs.
Lastly, my third incarnation, KHA II, was fully rebuilt using Dale resistors, Nichicon Fine Gold, FA and ES caps, plus two Paper In Oil (PIO) caps for the output network and of course, an OPA Moon HDAM. I am considering taking out the output network and I see one or two of you have done so and I am curious to hear what those who have done so thought of the difference, if any?
All PS caps on the board were bypassed with the fantastic Black Gate .1uF NX series non polar caps and the same were used in place of all of the original .1uF poly box caps. I have a few pics below of the boards, KHA I.5 (with 100uF Elna Silmic IIs in place of the standard 100uF caps) and KHA II (using 100uF Nichicon FGs), plus a pic of the audio-gd PS. I'm still using the MT2086 transformer and it runs fine with the a-gd PS.
A neutrik h/phone jack is on the way and I have CMC RCA jacks ready to go as soon as I get the case finished.
The amp is often used direct from the pre-out of my FrankenZero and the two
together are way beyond anything I've ever heard from cans since 1989, a sound virtually free of any electronics in the way of the music, uncannily open and musically alive and of-a-piece from top to bottom.
I had no idea that this cracking little amp had such a following until recently, has anyone tried running the output trannies further into class A? And if so, what were the results?
The pics here were taken before the amp was mounted on it's temporary platform.
Cheers all, S-Man
