Aunt Corey's Homemade Buffered Passive Preamplifier Mo' Better Mods, Page 2

People, people who need people
First things first: When I was wading through different pots from Penny & Giles, Bourns, Vishay, and Radio Shack, I thought I preferred the sound of the high-grade Alps pot Joe Grado sold me to the Penny & Giles pot I'd originally used. It's hard making direct comparisons between volume pots when you have to unsolder, remove, and resolder all the hookup wires each time you switch. However, Steve Giunta used the P&G in his preamp; since it appeared to be the only difference in parts between the two units, I put my P&G back in. Sure enough, the preamp sounded better, with a much cleaner and smoother high end. Vocals that sounded a bit dark through the Alps-based preamp were now more natural, with more air. Soundstaging was better, too.

Soooooo...even though I recommended the Alps "Black Beauty" pot in my original DIY article, I'm doubling back on myself; the Penny & Giles sounds better. And what's more, you can actually buy it, although it is a bit pricey at 200 clams. Hey, you want the best, you got to drop some lettuce, my man!

But even after the switchover to the P&G pot, Steve's preamp still edged mine out. I asked him if I could take a look under the hood, but the only real parts difference I could see was in the power supply: instead of the standard DigiKey-sourced rectifiers I had in my preamp, Steve had used buck-and-a-half Motorola MUR-810s, big beefy diodes the size of TO-220 voltage regulators.

"They're high-speed rectifiers," smiled Steve. "They sound better."

Sh'yeah! As if! All rectifiers do is convert the incoming AC from the power transformer's secondary windings into simple DC; how could they make a difference?

A few days later, I got a letter from Clarke Greene, a reader who seemed to know his way around a schematic: "Corey, you should try high-speed rectifiers in your power supply," he wrote.

Awright, awright! Gangin' up on me, eh boys? I tried it.

GREEN EGGS AND HAM!!! I couldn't believe it! Just substituting the high-speed rectifiers for the stock bridges in my power supply made for a huge improvement in the sound; a more significant step than most cable trade-ups I've made. The sense of inner detail coming from a black background of silence was uncanny, and the slight upper-midrange grain I heard in Santa Fe compared to the YBA 2 was gone, replaced with a vividly outlined presentation totally free of hardness and strain. All this from an octet of power-supply diodes! Makes me wonder how much better all the high-end gear that uses typical 1N4002 rectifiers in their power supplies would sound simply by switching over to high-speed jobs like the MUR-810s...

Don't argue, don't waffle, don't wait; if you built my preamp, you must install these high-speed rectifiers. This is the Linn philosophy of system hierarchy taken to the absurdist extreme: you can't go much further back than the power-supply rectifiers! Just be sure that when you replace your standard diodes with these special jobs, you install them with their correct polarity; the Motorola MUR-810s have one leg marked "K" for cathode, or "banded end." Diodes don't swing both ways, so make sure you install these special rectifiers in the right direction.

They're coming to take me away, ha-ha!
There's one sure thing about screwing around with mods: once you catch that fever, it's hard to stop! You do a mod, the sound gets better, and you think, "Hmmm, now that I've changed that, I REALLY need to change this, too!" and you end up chasing that rabbit down so many holes you wind up replacing the chassis screws with aircraft-grade Blue Devils.

Sure enough, I started getting that Modkateer Fever myself after I tried the high-speed rectifiers. I started sweating. I felt nauseated. I even tried calling my Tweak-Anon big brother Earl, but he'd fallen off the wagon too and was reflowing all the solder joints in his CD player's remote control with Wonder Solder.

"I-I wish I could h-help you," he whimpered over the phone, "b-but I need to mod my remote...it's getting slower..."

I heard some faint sobbing, and the phone went dead.

Frantically, I ran to a mirror and recited the 12 Steps of Tweak Recovery: 1) I am a Tweakaholic. 2) I need to keep improving my gear with better caps, solder, and wire. 3) I void my warranty when I do this, but I don't care. 4) If I really sat down with a calculator, I'd find that with all the money I spent on parts, I could've just bought a much better unit. 5) I justify this by claiming that it's fun to spend a beautiful sunny day indoors inhaling solder fumes. 6) It's not fun at all; I'm frightened. 7) My skin is so pale I look like Caspar The Ghost. 8) I have never kissed a woman. 9) I sleep with my eyes open. 10) I own more than one sound-effects CD. 11) I hear voices when nobody's around, which is always. 12) Ma-ma!

That didn't work either. Well, you can either ride a wave or be soaked by one, and if Modkateer Fever had me in its clutches, I was gonna hang-ten all the way back to the beach!

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