Wheatfield Audio | HA-4 | Wheatfield HA-1.pmd

Wheatfield HA-1
HeadRoom Corp. 2002
Wheatfield Audio HA-1 Tube Amplifier
The HA-1 Headphone Amp / Pre-Amp from
Wheatfield Audio is an affordable vacuumtube headphone amplifier that is also
designed to be used as a single-source preamp to drive a power amplifier.
obsessed headphone geeks at your service.
Elegant Simplicity
We believe in simplicity. So, the circuitry employed in the HA-1 is as simple as
possible. A single-ended, class A triode gain stage is directly coupled to a singleended triode cathode follower. No negative feedback is employed. There is only
one capacitor (actually two in parallel, an electrolytic and a polypropylene) directly
in the signal path.
Good Tubes
The tube used for the gain stage is the venerable 12AU7/ECC82 medium-mu dual
triode. The output stage employs a special dual triode, the 7044. The 7044,
originally designed for computer service, makes an outstanding low-outputimpedance cathode follower. Two sections are operated in parallel in each channel
to provide an output impedance of around 35 ohms.
Good supplies of both 12AU7 and 7044 tubes are available in the marketplace. For
those that like to experiment with changing tubes, there are many good 12AU7
types to choose from, and the 7119 and E182CC can be used in place of the 7044
with no modifications.
A Fine Headphone Amplifier
First and foremost, the HA-1 is designed to be an audiophile-quality headphone
Because of it’s low output impedance, the HA-1 can drive nearly any dynamic
headphones, from 32 ohms to 600 ohms. Unlike many competing amps (both tube
and solid-state), which either lack the current drive for low-impedance headphones,
or the voltage capability for high-impedance headphones, the HA-1 can drive them
Wheatfield HA-1
HeadRoom Corp. 2002
A Zero-Feedback, Single-Source Pre-Amp
The HA-1 is an excellent single-source pre-amp to act as a line stage between a CD
player and a power amplifier. It’s ideal for use in a simple system, or to drive a
single-ended triode power amp to provide a true all-triode, zero-feedback system.
It can also be used between a source (like a CD player) and a pre-amp or integrated
amp, to provide the utmost headphone listening quality, and to add some tube
“character” to a solid-state system.
As a pre-amp, the HA-1 is very different from other tube pre-amps. Most use
several high gain tubes as gain stages, with negative feedback employed to
lower the distortion. In contrast, the HA-1 uses only one medium gain tube gain
stage, with no negative feedback.
While it’s true that the HA-1 has higher distortion figures than tube pre-amps that
use negative feedback, to many listeners it sounds better. And it’s the sound that
The line outputs are provided through gold-plated RCA jacks on the rear panel.
The line outputs are muted when you plug a pair of headphones into the front
panel headphone jack.
Quality Components, Quality Construction
High-quality yet affordable components have been chosen carefully for use in the
HA-1. Polypropylene capacitors are used alongside quality electrolytic
capacitors, like the Nichicon “Muse”. Quality carbon composition and metal film
resistors are selected for their sonic characteristics.
The tubes provided with the HA-1 include a JJ/Tesla ECC82, and NOS GE 7044
output tubes.
All components (except the power transformer) are mounted on a single PC
board. This method of construction provides superior signal integrity and
consistency from unit to unit, compared to expensive hand wiring.
The HA-1 is assembled by hand in the USA.
Important Safety Information
The HA-1 is a tube amplifier. As such, there are some safety precautions that you
need to observe.
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
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.
Wheatfield HA-1
HeadRoom Corp. 2002
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 pre-installed. 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
color-coded, 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!
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/turnoff “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.
As a Pre-Amp
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
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.
Wheatfield HA-1
HeadRoom Corp. 2002
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:
can be replaced with
can be replaced with
7119, E182CC
12AU7, 12AU7A, 5814, 6189,
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
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).
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.
Single-ended, OTL, class-A triode amplifier
Single voltage amplifier stage, single cathode follower stage
DC-coupled input; capacitor-coupled output.
Wheatfield HA-1
HeadRoom Corp. 2002
Input impedance: 50k ohms
Input connections: Unbalanced, gold-plated RCA
Tube complement: 1x ECC82 (12AU7), 2x 7044
Power supply: Silicon rectifier, 3-stage RC filter
Power requirement: 117V, 60 Hz, 50W
Dimensions: 9.5” W x 4” H x 7.5” D
Weight: TBD
As a Headphone Amplifier
Frequency Response (+/- 3dB) :
600 ohm load: <9Hz - 250kHz
32 ohm load: 12Hz – 250kHz
THD+N (1kHz, 1V RMS out, 100 ohm load): <0.12%
Noise: TBD
Maximum output voltage (5% THD):
600 ohm load: 13V RMS
32 ohm load: 1.5V RMS
Output impedance: Approx. 35 ohms
Output connection: Standard ” stereo headphone jack
And Now A Word About Your Hearing
People have a natural tendency to listen to music on headphones at much
louder levels than they would on speakers. If you hope to avoid permanent
hearing damage, it’s important to be careful not to listen at extremely loud
levels or to listen for too long at moderately loud levels. Because HeadRoom
amps must be capable of driving even the most inefficient dynamic headphones to satisfactory listening levels, the amps are able to drive headphones of average and high efficiencies to very high levels. As a result, you
may not be listening at a safe level even though the volume control on the
amp is less than half way up. Generally speaking, when listening to headphones, you should only turn up the volume to the point at which the sound
isn’t too quiet.
The most common hearing damage caused by prolonged or excessively loud
sound is called tinnitus. It manifests itself as a sustained ringing in the ears
and can become a permanent condition. If you find that your ears are ringing
or that there is a sensation of pressure or fatigue, give them a rest for a
couple of days (or until they feel fresh). These symptoms are your body
telling you that your ears need a break. Should you choose to ignore these
symptoms, you are risking permanent hearing damage. As a general rule,
sound pressure levels under 80 decibels will not damage hearing, even if
listened to continually. On the other hand, anything over 100 decibels may
cause permanent damage fast. Sound pressure levels anywhere in between
can also be damaging. The louder the sound, the shorter the exposure time
required to cause permanent damage.
Now, don’t fool yourself into thinking that you either have full-blown tinnitus or
you don’t have it at all—you can get a slight case. For example, you might only
notice your ears ringing in bed at night. Once you have a slight case of
tinnitus, your ears are much more susceptible to further damage. So, if you
get tinnitus, it’s important to be much more careful about exposure to loud
sounds. Now that we’ve told you to be careful, don’t blame us if you blow it. If
you have any more questions about hearing damage, call a doctor. Sorry to
sound so sobering, but a lifetime of musical enjoyment requires ears in tiptop
Wheatfield HA-1
HeadRoom Corp. 2002
30-day Satisfaction Guaranty
We back everything we sell with a 30-day Satisfaction Guarantee. If, at any time
during the first 30 days from the time you receive your HeadRoom product, you
decide it is not providing enough bang for your hard-earned buck, you may return it
(in a “good-as-new” condition) for a full refund. Damaged returns will be repaired
and the repair costs deducted from your refund. Shipping costs are not covered
under this guarantee. If you purchased a package system at a discount and are
keeping some of the items in the package, your refund will be adjusted based on
the retail price of the equipment you are keeping. In other words, we don’t give fullprice refunds on products purchased at a discount.
Two-Year Product Warranty
The Wheatfield HA-1 amplifier carries a two-year parts and labor product warranty,
while the tubes carry a one-year warranty. If you have any problems with your
headphone listening system, please first call us at 1-800-828-8184. We will try to
diagnose the problem over the phone, which can save both of us considerable time,
effort and money. If the equipment must be returned for repair, we will authorize a
return for you. HeadRoom is the only authorized service center for HeadRoom
products, either in or out of warranty. If a unit is under warranty, there is no cost for
the repair labor, parts, or shipping from HeadRoom back to you (i.e., You’re responsible for paying the shipping charges to get the product to us). For units out of
warranty, repairs are billed on a time and parts basis, plus shipping costs. When
we receive the equipment, we will initiate repairs quickly (usually within three
working days) and return the unit to you, or call you with an assessment of the
Contacting HeadRoom
HeadRoom Corporation
521 East Peach Street
Bozeman, MT 59715
toll free 800-828-8184
or 1+ 406-587-9466
fax to 406-587-9484
drop us an email at
sales@headphone.com or
We’re on the web
obsessed headphone geeks800-828-8184
at your service.
Download PDF