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Volume Upgrades & HeadRoom rossfeed info
Imagine you are listening to a pair of speakers. If you turn off the left speaker, both
ears hear the sound from the right speaker. But because the left ear is slight farther
away than the right ear, it hears the speaker’s sound slightly after the right ear; about
300 microseconds. This time difference is called the “inter-aural time difference” and
it is the main thing your brain listens for in order to tell where to place sound left-to-
right.
But in headphones if you turn off the left channel, only the right ear hears the sound.
In headphones, if there is any sound that is only in the left channel, or only in the
right channel, then only that ear hears the sound. This is not natural, and you brain
becomes fatigued trying to figure out where sound is coming from when only one ear
is hearing it. This tends to create an audio image that is a blob on the left, blob on the
right and a blob in the middle.
HeadRoom amplifiers cure the problem by allowing you to cross-feed a little of the
left and right channels across to each other through a short time delay using the
processor switch. The usefulness of the circuit varies depending on what type of re-
cording you are listening to; mono and binaural recordings need no processor at all.
Old studio recordings that have instruments panned hard left or right, benefit greatly
from the processor. Live and classical recordings miked from a distance benefit some-
what less, and can often be listened to without the processor quite comfortably.
Plain
Headphones
With
HeadRoom
The crossfeed switch in HeadRoom ampli-
fiers allow you to cross-feed a little of the
left and right channels across to eacho-
ther through a short time delay.
Far ear hears
slight delay.
Near ear hears
sound first.
30 degrees
off axis
Module Info & Upgrades
Our Home Line of amplifiers come standard with a very good Nobel potentiometer.
Putting a signal through the wipers and conductive element of a potentiometer, how-
ever, does slightly degrade the sound. One way to get rid of degradation from a pot is
to use a stepped attenuator, which is simply a multi-pole switch that allows you to se-
lect one of a series of resistors to adjust the volume. We built a shunt attenuator where
the voltage is divided between a single fixed resistor on the circuit board and the resis-
tor selected by the stepped attenuator. This meethod keeps the number of contacts
the audio signal has to go through to a minimum. We use parts from the well regarded
Elma Type 04, 24-position switch, but we manufacture our own Electroless Nickel/Im-
mersion Gold (ENIG) switch contact circuit boards. These boards are highly corrosion
resistant, and have a very heavy gold plating---significantly heavier than normal circuit
board gold coatings. This is important to the increased lifetime of the switch.
Volume Control Upgrade- Stepped Attenuator
About the HeadRoom Crossfeed
Max Module
The Home Module
This little blue module contains all the elec-
tronics for a Home Headphone Amp. There
are two 4-layer circuit boards (one each for
the left and right channel) that are connected
with a series of header pins used to solder
the module to the main circuit board. This
module is designed to sound great without
going up the ridiculously steep part of the
diminishing returns curve. It uses OPA2134
op-amps for the internal input buffer, cross-
feed, summer, and power amp voltage gain
stage. The output current amplifier is our ver-
sion of the highly regarded Diamond Buffer discrete transistor design by Walt Jung.
All these active circuits are forced in to class “A” bias with constant current sources.
Resistors are 1% metal thin film, and caps in the signal chain are polyphenylenesulfide
(poly film). The sound of this module is not only well balanced and punchy, it’s also
liquid and integrated. This is a sweet listen. The Home Amp and Balanced Home Amp
can be upgraded with Max modules. This is a tricky maneuver and must be executed
with exceeding care. Only those with the trickest of gear should bother as these babies
are pricy almost beyond reason; every one else should just enjoy the lovely sound of
getting it right between your ears in a less spendy module. But the Max Modules are
the real deal, and easily let you tell the difference between a $3000 and $12000 CD
player.
This little gold and black module is the real
deal. Tiny chips that cost $15 bucks apiece,
0.1% metal film resistors, and polyphenyl-
enesulfide (poly film) caps are silver soldered
to 2 oz. gold coated copper traces which
blur in a glittering haze over black solder
masked four layer circuit board. Speaking of
circuit board, this is the first time we have in-
creased the sized of our module circuit board.
Fear not, for it is still pin for pin compatible with older Home and Max units. But the
circuit boards must be mounted on edge for better heat dissipation. The Max Module
uses what many audiophiles insist is the best audio op-amp made, the OPA627, for
the internal input buffer, crossfeed, summer, and power amp voltage gain stage. The
output current amplifier is our version of the highly regarded Diamond Buffer discrete
transistor design by Walt Jung. All active stages are forced heavily into class-A bias with
coinstant current sources. Writing this copy we realized the benefit statement of the
Max module is the features statement. The quality of the entire build of this module
is out of this world, and when coupled with the finest of headphones and the finest of
front ends, the results are transcendent bliss.
Home Module
The Max Module Upgrade
