Wheatfield Audio HA-2 User`s manual

Wheatfield Audio
HA-2 Headphone Amplifier
User's Manual
Wheatfield Audio
HA-2 User's Manual
Contents
Safety ............................................................................................................................... 3
Unpacking, Setup, and Connection ................................................................................. 4
Unpacking the amplifier............................................................................................... 4
Installing the tubes ....................................................................................................... 4
Connecting the amplifier.............................................................................................. 4
Listening with the HA-2 .................................................................................................. 5
About Headphones .......................................................................................................... 5
The Tubes ........................................................................................................................ 6
Wheatfield Audio’s Warranty ......................................................................................... 6
Tweaks............................................................................................................................. 7
Specifications................................................................................................................... 8
Schematic Diagram.......................................................................................................... 9
Copyright 1999 Wheatfield Audio LLC. All rights reserved. Printed in USA 11/99
Wheatfield Audio LLC
Andale, Kansas
www.headphoneamp.com
11/19/99
Page 2
Wheatfield Audio
HA-2 User's Manual
Safety
The HA-2 is a tube headphone amplifier. As such, there are some safety precautions that
you need to observe.
! CAUTION:
DANGER:
HOT SURFACES. KEEP COMBUSTIBLES AWAY FROM TUBES.
DO NOT BLOCK AIR FLOW AROUND AMPLIFIER.
TO PREVENT ELECTRIC SHOCK, DO NOT REMOVE COVER. NO
USER-SERVICEABLE PARTS INSIDE. REFER SERVICING TO
QUALIFIED PERSONNEL.
First, the tubes are hot… really hot. The 6AS7G tube in particular is specified to operate
at up to 200° Celsius – that’s 392° Fahrenheit. If you touch the tubes when the amplifier
has been running for a while you will likely get burned.
Because of this, please, please keep small children away from the amplifier. If you have
small kids in the house, locate the amplifier out of their reach, and never leave it turned
on unattended, even for a moment.
Also, make sure that you don’t locate the amplifier near anything that could create a fire
hazard. Don’t place it near curtains, for example, or bedding, or anything else that is
flammable. Make sure that there’s nothing but air within a foot of the tubers on top of
the amplifier.
Second, there are high voltages inside the chassis of the HA-2 – really high voltages, up
to 540 Volts. Do not open the chassis of the HA-2 unless you are qualified to do so. If
you have any doubts, don’t do it – refer service to somebody that is familiar with working
on tube equipment.
Like any electronic equipment, do not operate the HA-2 near water, or in any location
where it is likely to get wet. If by some accident water or other liquid is spilled onto the
amplifier, unplug it immediately. Take it to a competent service technician and have it
checked out, dried off, and cleaned before plugging it back in.
If for some reason the fuse on the HA-2 blows, replace it only with the same type of fuse
that was originally installed. The HA-2 uses a slow-blow, 1.5A 250V, AGC-type fuse.
11/19/99
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Wheatfield Audio
HA-2 User's Manual
Unpacking, Setup, and Connection
Unpacking the amplifier
Carefully unpack your HA-2 amplifier. Inside the package, you will find the amplifier
chassis, the tubes (packed separately), a power cord, and this manual (guess you already
found that, huh?) It’s always a good idea to save the original packing material.
Installing the tubes
There are three different tubes used in the HA-2. Note the tube types, which are printed
on the tube boxes. Referring to the drawing below, remove each tube from it’s box and
install it into the corresponding socket on the amplifier. The tubes are keyed, so rotate
the tube until its key matches up with the one on the socket, and press it down into the
socket as far as it will go.
6SN7GT 6AS7G
5U4G
Make sure that the tubes are installed in the right locations. DOUBLE-CHECK! If you
turn the amplifier on with the tubes in the wrong spots, you will likely ruin the tube, and
may do damage to other amplifier components as well.
Connecting the amplifier
Plug the power cord into the amplifier, and the other end into a wall outlet. Connect the
audio inputs of the HA-2 to your CD player, pre-amp, or other source, using standard
RCA-type audio cables. Note that the input connectors are color-coded, red for the right
channel and white for the left. Plug your headphones into the connector on the front.
You’re ready to listen!
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Wheatfield Audio
HA-2 User's Manual
Listening with the HA-2
It’s best to start out with the volume control knob turned all the way down (counterclockwise) until you’re familiar with the HA-2.
Turn the amp on, using the font panel power switch. It’s OK to leave your headphones
plugged in when you turn the amplifier on and off – there is very little turn-on/turn-off
“thump” generated, since the amplifier warms up slowly.
Speaking of warm-up, the amplifier takes only a half minute or so to start working,
though you may find that it takes a couple of minutes for the sound quality to reach it’s
best.
Adjust the volume to your liking. The HA-2 doesn’t have a lot of gain, so most people
wind up listening with the volume control almost halfway up. Even with the volume
control all the way up, unless you have an unusually high-level source, you will still have
plenty of “headroom” before the HA-2 starts to distort.
All the musical detail is there, even at very low volume. Try listening in an absolutely
quiet room sometime, with the volume fairly low. It’s amazing!
About Headphones
To get good sound from the HA-2, you need good headphones. Cheap headphones
driven by the best of amplifiers will still sound like cheap headphones.
The HA-2 is designed to drive high-quality headphones of greater than 100 ohms
impedance. Pretty much all of the headphones made by Senheiser, AKG, and Beyer
Dynamic fit into this category.
The HA-2 will drive headphones of lower impedance, like those from Grado, Koss, or
Sony, but we don’t recommend it. The mismatch of impedance between the amplifier
and such headphones introduces larger amounts of distortion. Low-impedance
headphones are best driven from solid-state amplifiers, or conventional tube amplifiers
that use output transformers.
You can’t hurt the amplifier by plugging in any type of headphones.
11/19/99
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Wheatfield Audio
HA-2 User's Manual
The Tubes
Tubes don’t last forever, so you can expect to replace the tubes from time to time. If you
notice degradation of the sound, or a lowering of the volume, it may be time to replace
the tubes.
You can replace the tubes yourself. Just find a high-end Hi-Fi shop that sells tubes, or
look on the internet – there are a number of companies that sell tubes on-line for very
reasonable prices. Purchase the same tube types as what was originally supplied in the
amplifier.
You don’t have to use tubes made by the same manufacturer as those shipped with the
amplifier – any tube with the same type is OK. Also, the “style”, or glass shape of the
tube, can be different. For example, we may use a Sovtek 5U4G rectifier tube. You can
replace it with an RCA 5U4GB tube.
Wheatfield Audio’s Warranty
Your HA-2 amplifier is warranted to be free of defects for a period of one year after you
receive it. If anything fails during that time, excluding the tubes, we will fix it for free.
You will have to take it, or pay to ship it, back to where you bought it.
The tubes are warranted for a period of six months.
After the one year warranty period, contact the dealer that sold you your HA-2 if you
have a problem. He can either fix it or arrange to get it back to us to fix.
11/19/99
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Wheatfield Audio
HA-2 User's Manual
Tweaks
We think that the HA-2 is a fine amplifier, right out of the box. It was designed with
what we believe is an optimal combination of components.
That being said, many audiophiles are never satisfied with any piece of equipment until
they’ve “tweaked” it in their own special way.
We don’t recommend that you make changes to the amplifier. If you choose to modify
the amp or change any components, your warranty is void, so you’re on your own.
We will make one exception to this rule, however. That exception is the tubes.
You may replace the tubes with others OF THE SAME TYPE if you desire, without
endangering your warranty.
Since the HA-2 is a manufactured product, we have to use components that are readily
available, in quantity, month after month. That means that we use Russian tubes that are
still in production, generally from Sovtek.
Though the Russian tubes we use sound great, it is possible that the sound could be
improved by the use of NOS (New Old Stock) tubes. Good NOS tubes for audio use are
tubes made between World War II and the ‘80’s, in the USA and Europe.
The best potential for improving the sound of the HA-2 is to replace 6SN7 voltage
amplifier tube with a good NOS tube, like one from Amperex. Replacing the 6AS7 is
likely to have less of an audible affect, and replacing the 5U4 rectifier will probably have
no audible affect at all.
11/19/99
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Wheatfield Audio
HA-2 User's Manual
Specifications
Note: Specifications listed are typical,
and are derived from measurements on
actual amplifiers. There will be some
variation from one amplifier to the next.
Specifications are subject to change
without notice.
Description
Single-ended, OTL, class-A triode
amplifier
Single voltage amplifier stage, single
cathode follower stage
DC-coupled input; capacitor-coupled
output.
Tube complement
1 - 6SN7GT voltage amplifier (one
section used for each channel)
1 - 6AS7G cathode follower (one section
used for each channel)
1 - 5U4G rectifier
Power supply
Full-wave tube rectifier
Capacitor-input filter with choke, using
electrolytic and polypropylene
capacitors
AC filament supply
Dimensions
13” wide x 8.5” deep x 8” tall
(including tubes)
Fuse type
AGC-type, slow-blow, 1.5A 250V
Output Impedance
100 Ohms
Maximum output level
(1kHz, 5% THD)
620 ohm load: 13V RMS / 36V P-P
270 ohm load: 10.5V RMS / 30V P-P
Rated Maximum continuous output
power
(1kHz, 5% THD)
620 ohm load: 270mW
270 ohm load: 400mW
Total Harmonic Distortion
(1kHz, 1V RMS out)
620 ohm load: < TBD %
270 ohm load: < TBD %
Voltage Gain
620 ohm load: 17dB
270 ohm load: 15dB
Frequency Response
(+/- 3dB)
620 ohm load: ~10Hz – 75kHz
270 ohm load: ~15Hz – 75kHz
Ripple and Noise
< 3.5mV RMS
Power requirements
120VAC 60Hz only
100 Watts
11/19/99
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Wheatfield Audio
HA-2 User's Manual
Schematic Diagram
11/19/99
Page 9