Wheatfield Audio HA-1 Specifications

Wheatfield Audio
HA-1 Headphone Amplifier / Pre-Amp
Owners Manual
Wheatfield Audio
HA-1 Owners Manual
Contents
Contents....................................................................................................................... 2
Safety .......................................................................................................................... 3
Unpacking, Setup, and Connection............................................................................... 4
Unpacking the amplifier ........................................................................................... 4
Checking the tubes.................................................................................................... 4
Connecting the HA-1 ................................................................................................ 4
Listening with the HA-1 and headphones..................................................................... 5
About Headphones....................................................................................................... 5
Using the HA-1 as a pre-amp ....................................................................................... 5
The Tubes.................................................................................................................... 6
Wheatfield Audio’s Warranty ...................................................................................... 6
Tweaks ........................................................................................................................ 7
Specifications .............................................................................................................. 8
Schematic Diagram...................................................................................................... 9
Copyright 2000 Wheatfield Audio LLC. All rights reserved. Printed in USA 9/00
Wheatfield Audio LLC
Longmont, Colorado
www.headphoneamp.com
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Wheatfield Audio
HA-1 Owners Manual
Safety
The HA-1 is a tube 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, tubes get hot. Please ensure that there is adequate ventilation around your HA-1,
and never place anything directly on top of the unit. If you place the HA-1 on shelves or
in an equipment rack, make sure that there is plenty of space above it.
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 top of the
amplifier.
Second, there are high voltages inside the chassis of the HA-1 – up to 200 Volts. Do not
open the chassis of the HA-1 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.
And if you do open the chassis (to replace tubes, for example), make sure that it’s been
unplugged for at least a minute to minimize the risk of electric shock.
Like any electronic equipment, do not operate the HA-1 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-1 blows, replace it only with the same type of fuse
that was originally installed. The HA-1 uses a slow-blow, 0.63A, 250V, 5x20 MM fuse.
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Wheatfield Audio
HA-1 Owners Manual
Unpacking, Setup, and Connection
Unpacking the amplifier
Carefully unpack your HA-1 amplifier. Inside the package, you will find the amplifier, a
power cord, and this manual (guess you already found that, huh?) It’s always a good idea
to save the original packing material.
Checking the tubes
The HA-1 is shipped with the tubes preinstalled. Though we use some mighty
tight tube sockets, it is a wise idea to
check and make sure that the tubes
haven’t been jarred loose during
shipment. If you look down through the
slots on the top, you should see the three
tubes installed in their sockets. If they
look crooked (or if you just want to see
what’s inside), remove the outer case of
the HA-1 by removing the seven cover
screws, using a philips screwdriver. The
tubes should look like they do in this
picture.
Connecting the HA-1
Plug the power cord into the amplifier, and the other end into
a wall outlet. Connect the audio inputs of the HA-1 to your
CD player or other source, using standard RCA-type audio
interconnect cables. Note that the input connectors are colorcoded, red for the right channel and white for the left.
If you’re using the HA-1 as a preamp, connect your power
amplifier to the line outputs in a similar manner.
Plug your headphones into the connector on the front.
You’re ready to listen!
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Wheatfield Audio
HA-1 Owners Manual
Listening with the HA-1 and headphones
It’s best to start out with the volume control knob turned all the way down (counterclockwise) until you’re familiar with the HA-1.
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.
About Headphones
To get good sound from the HA-1, you need good headphones. Cheap headphones
driven by the best of amplifiers will still sound like cheap headphones.
The HA-1 is designed to drive any high-quality headphones of at least 30 ohms
impedance. Pretty much all of the headphones made by Sennheiser, AKG, Grado, Sony,
and Beyerdynamic fit into this category.
The HA-1 will drive headphones of lower impedance, but we don’t recommend it. The
mismatch of impedance between the amplifier and such headphones introduces larger
amounts of distortion.
You can’t hurt the amplifier by plugging in any type of headphones.
Using the HA-1 as a pre-amp
Using the line outputs provided on the HA-1, your headphone amplifier can double as an
excellent all-triode, zero-feedback pre-amp. It has more than enough gain, and a low
enough output impedance, to drive even the most difficult power amplifier.
When there are headphones plugged in to the front panel jack, the line outputs are muted.
Occasionally, the switch contacts on the headphone jack can become dirty, resulting in no
output from one or both line output with the headphones unplugged. If this happens,
blow the dust out of the jack, and repeatedly plug in and unplug your headphones. This
should remove any contamination from the switch contacts.
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Wheatfield Audio
HA-1 Owners Manual
Replacing Tubes
Tubes don’t last forever, so you can expect to replace the tubes from time to time. We
have operated the HA-1 for more than 2500 hours, with no noticeable degradation of the
tubes. We expect that the tubes will last between 4,000 and 10,000 hours before needing
replacement. That’s about an hour of listening per day, for ten to twenty years.
Of course, your mileage may vary. If you do 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.
You don’t have to use tubes made by the same manufacturer as those shipped with the
amplifier – any tube with the same type number is OK. Certain equivalent replacement
types are fine, too. For example:
7044
ECC82
can be replaced with
can be replaced with
7119, E182CC
12AU7, 12AU7A, 5814, 6189, CV4003
Wheatfield Audio’s Warranty
Your HA-1 amplifier is warranted to be free of defects for a period of one year after you
receive it. If anything fails during that time, including the tubes, we will fix it for free.
Contact the dealer from which you bought the HA-1 for directions on how and where to
return it.
After the one year warranty period, contact the dealer that sold you your HA-1 if you
have a problem. He can either fix it or arrange to get it back to us to fix.
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Wheatfield Audio
HA-1 Owners Manual
Tweaks
We think that the HA-1 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 OR ELECTRICALLY
EQUIVALENT TYPE if you desire, without endangering your warranty.
We use some very high quality tubes in the HA-1. Specifically:
The voltage amplifier tube is a JJ/Tesla ECC82, a current production type that is among
the best ECC82/12AU7 types available – better than many NOS American 12AU7’s.
However, if you are a connoisseur of 12AU7 types, or are just curious if you can hear the
difference between the JJ and a Telefunken or RCA “clear top”, go ahead and give it a
spin.
The output tubes are a special NOS computer triode, the 7044. We have secured a good
quantity of these tubes, but they are no longer manufactured. NOS 7044 tubes are
available in the marketplace from a couple of manufacturers. If you’d like to try
something different, the 7119 and E182CC tubes are acceptable substitutes, and are easier
to find than 7044’s. There is a good supply of Amperex 7119 tubes in the marketplace,
and you may find other European brands of E182CC tubes (though many will be made by
Amperex).
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Wheatfield Audio
HA-1 Owners 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.
As a Headphone Amplifier
Description
Noise: TBD
Single-ended, OTL, class-A triode
amplifier
Maximum output voltage (5% THD):
600 ohm load: 13V RMS
32 ohm load: 1.5V RMS
Single voltage amplifier stage, single
cathode follower stage
DC-coupled input; capacitor-coupled
output.
General
Input impedance: 50k ohms
Input connections: Unbalanced, goldplated RCA
Tube complement: 1x ECC82 (12AU7),
2x 7044
Power supply: Silicon rectifier, 3-stage
RC filter
Power requirement: 117V, 60 Hz, 50W
Frequency Response (+/- 3dB) :
600 ohm load: <9Hz - 250kHz
32 ohm load: 12Hz – 250kHz
THD+N (1kHz, 1V RMS out, 100 ohm
load): <0.12%
Output impedance: Approx. 35 ohms
Output connection: Standard ¼” stereo
headphone jack
As a Pre-Amp
Frequency Response (10k ohm load) :
<9Hz - 250kHz +/- 3 dB
<9Hz - 95kHz +/- 1 dB
THD+N (1kHz, 1V RMS out, 10k ohm
load): <0.18%
Noise: TBD
Maximum gain: 28 dB
Maximum output voltage (5% THD):
10k ohm load: 15V RMS
600 ohm load: 8V RMS
Dimensions: 9.5” W x 4” H x 7.5” D
Output impedance: Approx. 35 ohms
Weight: TBD
Warranty: One year on all parts,
including tubes
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Output connections: Unbalanced, goldplated RCA
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Wheatfield Audio
HA-1 Owners Manual
Schematic Diagram
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Page 9