From: moskowit@tronsbox.xei.com (Len Moskowitz)
Subject: Re: a match for GRADO headphones
Organization: Xanadu Enterprises Inc.
Date: Fri, 6 Nov 1992 15:32:51 GMT

Henri Quiniou writes:

> I want to know what you are matching Grado's Signature (HP2) headphone 
> with?
> Does plugging it at the amplifier output (through a QED-like box) sounds 
>good or having a dedicated headphone amplifier is really worth it?
>
> I'm sorry, but I couldn't find headphone amp to listen to in my area
>because ... I don't know why!!! (have any idea?) Please go ahead: list
>whatever component you liked and the way the whole thing was
>connected.

I run my Grado HP-1 from a battery powered headphone amp that I built.
It's a version of Corey Greenberg's BUF-03 active pre-amp (see his
Stereophile article).

I'm appending my old headphone amp article.  Hope you enjoy it.


---

Len Moskowitz
moskowit@panix.com (preferred address)
moskowit@tronsbox.xei.com (alternate address)


------
(Repost of an old article)

I was no more than 6 years old and my father had brought me a present.
It was a small, red plastic box with a 9 Volt battery in it -- my very
first transistor radio.  I turned it on and music came out.  What
excitement!

That kind of experience doesn't happen very often but it happened once
again last night.  I plugged my Grado HP-1 headphones and Sony
D-5/D-14 portable CD player into the battery powered circuit board I'd
just cobbled together, started the CD player, and watched the Eric
Clapton disk spin up.  At first I heard nothing.  Then, out of the
velvety black silence, I turned up the volume knob and music quietly
appeared and grew louder.  And the music sounded wonderful!  

What I was listening to was my CD player's line outputs driving my new
headphone amplifier.  Why wasn't I using the CD player's headphone
jack?  I'd been having problems with my new headphones, the very
beautiful (and expensive) Grado Signature Series HP-1.  You see, the
drivers in the HP-1 have a nominal 40 Ohm impedance, much lower than
most common headphones that are nominally 600 Ohms.  When driving the
Grados from their headphone jacks, my two portable CD players would
distort horribly on sharp transients, including the initial attack
transients on piano and all manner of percussion.  Even at mild
loudness levels the sound wasn't what I'd been expecting from these
wonderful headphones -- it was veiled and lacked air and detail.  In
sharp contrast, the new amplifier's sound was clean, loud, and
transparent; truly audiophile heaven.

Still laying exposed on my kitchen table, anyone who bothered to look
would see that the new amp used a pair of Precision Monolithics
military grade BUF-03AJ precision buffers.  Unlike Sony's wimpy dime
store integrated circuit that could barely drive the CD player's
headphone jack, the BUF-03s, driven from the CD player's line level
outputs, can source enough current to effortlessly drive the Grado
HP-1s to truly prodigious sound pressure levels.  Not surprisingly,
they're expensive -- $35 each for military grade and $11.25 for
commercial grade parts (prices were quoted by Allied Electronics).

This odyssey started back in '91, when Stereophile's Corey Greenberg
published an article describing how the BUF-03 could be used as an
active buffer in a high end stereo system.  Almost in passing, he
mentioned that he also tried using it as a headphone amplifier to
drive his new Grado HP-1 'phones.

Greenberg used the robust Jung/Galo regulator circuit to power his
buffers.  With his usual macho bigger-is-better flair, he decided to
push the BUF-03s to their limit, supplying them with plus and minus 18
Volts, the absolute maximum they can tolerate.  What this bought was
the best slew rate the devices could offer: close to an amazing 300
Volts per microsecond.  Unfortunately, what it also bought was a bunch
of letters from the whole wide world telling Mr. Greenberg how he was
pushing them buffers too hard and that he shouldn't expect much of a
life out of 'em.  Those BUF-03s in Greenberg's circuit almost run hot
enough to turn hydrogen to plasma.

Oddly enough, the same Stereophile issue that carried Corey's buffer
article also carried an interview with Nelson Pass, the lauded power
amplifier designer and daddy of the Stasis circuit topology.  In the
course of his career, Pass had done some measurements and found that
even if he allowed a ten-fold error margin, a power amplifier needed
only a 50 Volts per microsecond slew rate.

A year or so later, when I had just bought the Grado headphones and
found myself dissatisfied with my CD player's on-the-road sound
quality, I re-read that issue.  50 Volts per microsecond?  The idea
light flashed brightly over my head.  I checked the data sheets: Wow,
the BUF-03s could still manage over 100 Volts per microsecond even
when powered by plus and minus 6 Volts.  Maybe I'd found the answer to
my portable headphone amplifier problem.

I started scrounging up the parts.  I lucked out: one of my analog
circuit designer friends happened to have a few surplus BUF-03s left
over.  A trip to Radio Shack provided a few film capacitors, an
electrolytic capacitor or two, a phenolic circuit board, a three
conductor stereo phone jack, a pair of nice gold plated chassis mount
phono jacks, an Alps audio taper stereo pot (with a surprisingly silky
feel), two small PC-mount variable resistors, battery connectors, a
sub-mini DPDT power switch, and some good silver content solder.
Searching through my stock of parts, I found some teflon insulated
hookup wire, a nice military-looking knob, and a black cast aluminum
chassis about the size of a pack of cigarettes.

I started the assembly.  I quickly calculated that the BUF-03s
wouldn't need heat sinks when powered by plus and minus 6 Volts so I
could feel free to really pack the parts tightly.  This I did, using
point-to-point wiring and star grounding on the very small
2-inch-by-2-inch circuit board.  The whole amplifier took only three
nights to build including the following detour into power regulator
land.

At first, I had the ultimately not-so-bright idea that maybe, instead
of using the ubiquitous three terminal voltage regulators, perhaps I
could use an elegantly simple, discrete component, constant current
supply design I'd back in my radio control airplane days.  This design
used only a single transistor, two diodes, two capacitors, and two
resistors.  I was hoping that this regulator design would offer
seriously low drive impedance and, as a result, sound wonderful.
Alas, it was not to be.  In the end, even after numerous tweaks, I
couldn't get the regulator to provide enough current without using
some seriously weird component values.  One very irritating night of
wrestling with this circuit was quite enough to convince me that I
should at least try the LM317T/LM337T combination and see if they'd do
the job.  At the very least they'd be simple to wire up, and if by
chance they didn't sound good, it wouldn't take more than a few
minutes to unsolder the things and start over.

In the end, the LM317T and LM337T worked just fine.  I assembled the
two three-terminal regulator circuits in under a half hour, set them
to deliver plus and minus 6 Volts, and wired them to feed the BUF-03
circuits.

The regulators were powered by a pair of common 9 Volt alkaline
transistor radio batteries.  At first I had my doubts whether these
mundane batteries could provide the power this amplifier needed, so I
checked the Duracell specifications: they have a capacity of 565
milli-Ampere hours.  At the 40 milli-Amperes the amplifier typically
drew, the batteries should last over 14 hours.  To assure myself that
they could provide adequate peak current, I measured the current they
delivered into a dead short.  I was very surprised to find that they
could source more than 6 Amperes for a short period.  The final proof
that they could do the job was experiential: the amplifier sounded
wonderful.  I'm not even going to bother to try the Jung/Galo
regulator circuit unless the hobby bug bites again or those rather
uncommon parts happen to fall into my lap.

So now, if you happen by as I'm sitting in Newark International
Airport waiting for my next flight to God-knows-where, you'll likely
see me with my headphones on my head, little black headphone amp on my
knee, smiling contentedly.  Am I happy?  You bet!


Len Moskowitz
-- 
---

Len Moskowitz
moskowit@panix.com (preferred address)
moskowit@tronsbox.xei.com (alternate address)