After receiving a prototype pre-assembled K272B cct. brd, featuring the JAN6418 pentode, I was anxious to mount it in my usual ABS plastic case and take a listen. I had just finished building two OPA2134 CMoy style HP amps, which I enjoyed thoroughly, and now keen to hear the difference. Both CMoy(ers) sold so I have none on hand for an A/B test but do remember the sound of both. In the K272B, sent to me, low grade components are used, carbon film resistors, green polyester caps etc. Normally when assembling these kits I swap out the low grade bits for better parts. I left the PT2308 HP driver chip in place. Usually I replace this with an OPA2134 but I wanted to listen to the kit "as is".
Take a look at the images below and you wee see the new "B" is a much narrower brd. I left in place most of the wiring which came with the pre-assembled and only replaced that which was required. Normally I would not use multi-strand hook-up wire but I wanted this kit up and going ASAP. I employed my "safe-on" technique of using switched HP jacks and a push-button on\off switch. With "safe-on" no power is supplied to the cct. brd. unless both plugs have jacks inserted and the power switch is on. Also in my last two builds of these portable HP amps I have a battery test point at the back near the power switch. Putting the probes of a voltmeter here (positive in the center and negative outside) and having the unit powered-up will allow you to check battery health without dissembling the case. I use two 9V batteries in parallel.
This K272B rang like hell when I had the top off and was testing it. Lid on and sitting beside me on the couched there is no ringing at all. So how does it sound? If you like a crisp, dry, clinical wholly accurate sound build a CMoy clone with the OPA2134 solely. BUT if you want a rich, full, earthy, gripping auditory headphone experience, wait for the K272B to come out in kit form. It sounds weighty and harmonically textured. From the first few seconds of FM radio from my Cowon S9 I knew this not only sounded different but was going to be a winner. Love it. While on the bench I use a test CD to get the balance between channels set. The left was well down on the right. I used central voice, a 1Khz test tone and pink noise to tweak the balance. If you build the kit upgrade all cheap parts with better parts. Mine sounds good as is but there is probably more juice in the lemon.
Attachment:
K272_New.jpg
Attachment:
K272AandNew.jpg
Attachment:
K272B.jpg
Attachment:
K272BRear.jpg
Login
Register
FAQ
Instead of a kit that is "set" to be either singularly powered or dual powered, how about making so the builder can choose how he wants to power the kit - whether to use a single source power supply or a dual source power supply. I, for one, prefer the single source power supply like the original 272 has over the dual source found on the 272A, and since I assisted another builder in finding a way to convert the "A" model to a single source model, I would seem not to be alone in this. 
