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Jim Hagerman's Octal Cornet--Can't Lose

Posted by slowburn (A) on March 3, 2007 at 18:11:55

In Reply to: Phono Preamp Suggestions? posted by Vint_age on March 1, 2007 at 09:16:03:

I was thinking about the same question a year ago. On paper, I liked JC Morrison's Siren Song, too.

Hagerman's circuit appeared the most elegant: no feedback and passive two-part RIAA filter.

The octals intruiged me. I'd renovated and used an Audio Research SP6B's well-regarded phono stage for a few years and while I think it is good, she and I never really bonded. For this, I blamed the mini 9-pinners and sand rectification. I'd replaced the primitive diodes in the 6B's PS, but I was never able to fully banish the grain. The Cornet is glass rectified and I wanted to give that a run.

I chose to tweak Herr Hagerman's PS by adding some Henrys. I had a couple nice chokes in the closet so what the heck. I figured he'd designed a nice capacitor power supply but that as a guy who has to sell kits, spec'ing expensive iron is a no-no. I don't have to sell kits, though, so what the heck. Iron's good for you.

I also use a "real" 5Y3, an old RCA, instead of the spec'd Sovtek, which is indirectly heated.

I like point-to-point so I opted to build my own turret board for the signal circuit. Used supplies from Hoffmann Amps. (great stuff!) Of course, this meant that I didn't purchase Mr. Hagerman's PCB.

I scored an NOS Stancor power trans on ebay, plenty robust and electrostatically shielded, to boot. I like old transformers.

I ordered the Hammond chassis that Jim suggests but I found it too flimsy, too cramped. I opted for a commercial cake pan, instead. They're cheaper, thicker, have square welded corners. They drill and punch like a dream and I highly recommend them. They come in many sizes, 2 and 3 inches deep.

I must've built the thing ten times before it worked right. Phono stages are a bitch. Point-to-point wiring, microphonic octals, and a single chassis are tall hurdles.

By the time I worked out all the bugs, though, the Hagerman Octal Cornet is one of the sweetest pieces of audio gear I've ever heard. It was so delightful that I wrote JH a note, sent some pictures and entered his DIYer of the Month contest. Check his January 07 post and you'll see my green monster.

It still exhibits the slightest hum with the gain pinned all the way up. I expect that when I put the power supply on a seperate chassis, it'll be just about the sweetest phono stage I've heard.

Oh. And as always, I think that as long as the designer's dialed in the operating points, by all means, forget about stocking the circuit with a couple dozen metal oxide or metal film resistors. Spend the $30 bucks already! Get yerself some Kiwames or a couple Rikens in key spots. Damn things are dead quiet and sound fantastic.

I can also tell you that the circuit is simple enough that you can actually hear the differences in parts. For instance, the coupling caps between the first and second stage absolutely affect the Cornet's sound. So you can have fun flavoring the thing. (I think that I may throw down the outrageous sum of $70 for a pair of V-caps, someday. It's the perfect spot to try them)

For the time being, I've settled on Angela tin film caps as couplers and Cardas at the outputs. Auricaps' precision worked well with Cardas flavor, too.

I tried Jupiters that I got for cheap years ago. Yuck. At first I thought that they sounded rich. When substituted the Auricap/Cardas mix, though, I realized that I can be fooled. Mud is rich.

Anyhow, ramble on, and build the octal Cornet. I'd bet that if you buy Jim's kit or half-kit, it's probably darn quiet, too.

Word to the wise: if you're using the octals, keep their sockets mounted OFF the chassis. Those 6SL7s are microphonic as hell. The good news is that there are many old ones that sound fantastic.

Thank Mr. Hagerman! Great phono stage.

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