Impressions
Coming from more entry-ish amps such as the LD2++ and TW-J1, and hearing the anecdotal reports of the CKK3 being a "little" Beta22, I set out building it with sky-high expectations. I was not let down--my impressions follow, and please mind that all my impressions are relative to my (limited) experiences with h.p. amplifiers.
Before this amp I had developed a preference for the K701s over the 650s; now the old Senns are king again. As others have noted about the CKK3, there's just better synergy: the type which the 650s must have to be happy. The amp produces mids and treble with more weight and aggression, but never harshness, with a controlled bass that compliments the 650's silkiness there. The result is the most coherent, balanced and involving headphone sound I've heard. This is not to say that other HP's are not well suited to it: the AKGs are certainly enjoyable, but highly AKG-sounding, in a good way. It's all personal preference at that point. Regardless of headphones, the ultimate ecstasy is during musical complexity, where the amp could not be more sure of itself--perhaps this is the defining feature of the CKK3.
My build
Thanks to the amazing Jeff Rossell for the kit; FrontPanelExpress for the FP. The build took two days of obsessive work, something like 18 hours, excluding bias adjustment. I had to make an external PSU--though I'd initially put the tranny and board in the same case, there was a slight persistent hum. Not anymore, the amp is eerily quiet. PSU case from Context Engineering. A massive vintage heatsink I had on hand was cut and installed, providing plenty of cooling for the quiescent current of ~55ma. It's barely lukewarm to the touch, and it made bias adjustment minimally tedious. With this much heat dissipation, the transistors' QC often dropped a little during adjustment and had to be brought back up! Still, expect to spend a good afternoon adjusting the QC especially if you're OCD about getting things equal. Oh, and the zipties--probably a bad idea, but no problems yet!
My advice to prospective builders
-Use the largest heatsinks you can get ahold of, even if you plan to bias to only 30ma. My experience using smaller, individual HSs for 30ma was a pain, full of fluctuations, but doable. I cannot imagine using no heatsinks.
-Solder small leads onto the bias resistors, R23 and R47, on the sides closest to the adjacent transistors (see pic). This way, you can measure the voltage here without shorting anything--one probe at output left (or right) and the other at R23 (or R27)'s safely-distanced lead. The necessity and advantages of this will become clear once you begin bias adjustment.
-Use a separate enclosure for the transformer and mains wires if possible. I tried an all-in-one solution initially, but I was unable to eliminate all hum until the tranny was out of there. It was worth the extra effort.
-My two input grounds (L&R) had to be connected at the volume potentiometer. I don't think this was indicated on the AMB wiring diags. If you find yourself hum-busting, check here first.
-Always wear that anti-stat bracelet, all it takes is one costly zap. Also, have a heat management strategy when soldering the transistors.
Conclusion
I used to not believe different amps made a difference in SQ beyond things like distortion and SNR. I thought this amp would sound about the same as my others, and at least offer a fun DIY project. My smug convictions all changed with the CKK3, as it sounds better with less (or more musical) distortion and it sold me on DIY--it's the best bang for your buck audiophile solution that also brings a unique pride into the hobby.
Gallery
(Hey amb if you get a chance maybe you could add these to your collection
)
Great panel manufacturing from FPE.
PSU connected to the ckk3...
Silly zipties!
PSU with trans. and mains stuff
Note the lead soldered to one end of the blue bias resistor
