Melos SHA-1 headphone amplifier
By Corey Greenberg   •   October, 1992 "I remember Momma!"

That's what I used to yell whenever I removed my headphones after a long session of late-night Led Zep. They were Koss's big "DJ" hermetic-seal specials (footnote 1), the ones so beloved by FM DJs because the big plastic cups actually house gnarly-ass car stereo drivers that can blow your ear drums clean down into your throat with but a few milliwatts and have such a hellacious bass boost that they make even the squeakiest, wimpiest voices sound like Isaac Hayes to the tenth power.

It was that pair of Koss 'phones, plugged into a cheap JVC jambox that withstood four years of summer-camp abuse, that made up my first hi-fi rig. It wasn't much, but it was enough to instill in me a passionate dislike for headphones; when I finally got a hand-me-down all-in-one record changer, I swung those Koss headphones around by their coiled brown cord like a dead cat and smashed 'em against my bedroom wall with glee, vowing never to own another pair of headphones again.

I thought about that vow again last year while buying a pair of Joe Grado's new headphones several minutes after I first put them on for a listen. I'd heard these new Grados were good, real good even, but I was stunned at how clean and clear they sounded even when driven by an Adcom GFP-565 preamp's headphone output jack. I need a pair of headphones like I need a fourth leg, but I bought the Grados on the spot because it was obvious that these were as good or better than anything else I'd heard, the high-dollar Stax 'phones included.

Only problem is, what do you plug 'em into? Forget the headphone jacks on your preamp, CD player, tape deck, etc.; these afterthought circuits are usually built around cheap 4558 op-amps, rank resistors, and crappy caps. You wouldn't drive your Thiels with a cruddy low-end amp, would you? No, what the cool-man Grados need is a high-quality headphone amplifier.

OK, let's crack open the latest Audio Equipment Directory ish...heh heh, another fine Edward Tatnall Canby piece—how I adore that man and his wondrous tales of yore. Lessee now...[flip flip flip]...CD players...[flip flip flip]...headphones...[flip flip flip]...turntables...woops!...[pilf pilf pilf]...hmmm. No headphone amplifiers! What's a girl to do?!

They call me melos yellow (quite right-ly)
I wasn't the only one who noticed the dearth of high-quality headphone amplifiers; Melos Audio's George "Tell Sam Tellig My Name's Not Gunther" Bischoff was also mightily impressed by the Grado 'phones, so he set out to design a hybrid tube/FET circuit to drive them with; the result is the Melos SHA-1. Rather than base the circuit on op-amps, even good ones like those found in Joe Grado's own $795 HPA-1 battery-powered portable headphone amp, the Melos SHA-1 utilizes a specially selected 6DJ8 for nearly 20dB of gain, then follows it with discrete FETs to both buffer the tube and provide the current drive needed to properly drive dynamic headphones.

As befits the high quality of the Grado headphones, Melos has paid careful attention to the parts selected for the SHA-1. The audio signal is routed with both Grado's own proprietary cable as well as FMS "zero-core" hookup wire, all resistors are low-noise metal-film types, and the few caps in the audio circuit are all high-quality polypropylenes. Interestingly, the 6µF polypropylene caps that AC-couple the line outputs (the headphone outputs are direct-coupled) are contained in metal cans, giving them the appearance of sonically inferior aluminum electrolytics; George explains that these special French film caps were chosen because the metal cans minimize vibration-induced microphonics.

As I found out during the design of Aunt Corey's Homemade Buffered Passive Preamp (footnote 2), the selection of the volume control is critical when it comes to sonics; many potentially great preamps are let down by mediocre volume pots, simply because the best-sounding ones are so goldarned (footnote 3) expensive! George fits his SHA-1 with the high-grade ALPS "Black Beauty" 100k stereo volume pot, the same model used by Joe Grado in his headphone amp. The input signal is fed directly to the ALPS volume control, and the wiper/output is AC-coupled via a 1µF film cap to the grid of the 6DJ8, whose plate is then AC-coupled with two 1µF caps in parallel (2µF) to the FET buffer stage, which is DC-coupled to the ¼" stereo headphone jack.

---

Footnote 1: If you've ever owned a pair of these monsters, you can appreciate how they give new meaning to the term "Sweatin' to the Oldies."—Corey Greenberg

Footnote 2: Those interested in constructing this buffered, unity-gain preamp can check out my DIY plans in Vol.14 No.11. An update feature will appear in our November '92 issue.—Corey Greenberg

Footnote 3: 1993 Miss Audio Reviewer pageant judges, please note the lack of offensive language in this review. I'm also for world peace, an end to starvation, and a career as a model/actress. Thank yew.—Corey Greenberg