PA-4 Front-End Circuit Boards:for Hafler DH-200/220/500 and XL-280/600, plus we
do some custom installations in other MOSFET amps. —––New picture soon, picture of
earlier version shown––––-
The Design:Design simplicity has always been a trademark of Musical Concepts products.
The new PA-4 is a straightforward, effective amplifier topology with a single-ended
front-end. LED biasing is used for the current source supplying current to the differential
'front-end' to complement the LED biasing in the ultra-linear connected, cascode
What’s New in the PA-4?: So as far as the general schematic is concerned there is
evolutionary change. After all we were happy with the sound of the PA-3E. Then what
gives? Well, the layout has been changed a bit for one. P More physical space is
provided for a superb new coupling cap. New wide-band, very linear driver stage transistors
and heat sinks are used to increase quiescent Class A driver stage current providing
greater linearity and lower distortion for a cleaner, full-bodied sound quality(in
standard PA-4 and up models). The superb Dale, widely-respected 1% metal film resistors
are used in most PA-4 models. Yes, these resistors cost 5 times more depending on
wattage rating than those used in many audio products but we believe the difference
is worth every penny. They sound clearly superior in the sense of lucidity, soundstage
and overall naturalness. There is a sense of a quieter, darker background that allows
the instruments and voices to be more clearly located in transparent space. All PA-4
series driver boards,excepting the SE, have these superb sounding resistors. The
PA-4 Elite Ultra version uses the wonderfully dynamic, dimensional, rich, powerful
sounding Takman resistors. Yes, some things are worth the extra expense.
The PA-4 Sound:This is merely a Hafler you ask? No slight to Hafler, but think again.
This is a really great amplifier in a Hafler chassis. It’s not just a great solid-state
amplifier, but a great amp period! Beyond all the new technical improvements, the
sound quality is the real treat. There is a sense ultra-low distortion and a clean,
clear response to the most intense transients/crescendos. The degree of perceived
dynamic range, bass power and overall delicacy is clearly striking. You’re treated
to a tremendous sense of effortless power. The high frequency extension with delicacy,
liquidity and naturalness make you think you are listening to a vacuum tube amp.
Then along comes bass detail and overall clarity that makes you reconsider that thought.
There is a sense of solidity, accurate timbre, simple majesty and air-moving power
that must be heard. If your speaker plays really deep you’ll be thrilled. PA-4 modified
Hafler amps will easily compare to the finest sounding amplifiers available today.
New! PA-4SE: Our PA-4 mod series has been further up-scaled in quality level of individual
parts equiring a consequential price increase beyond the budget of some who wanted
to own it. We had to bring the excitement of excellent audio reproduction to more
affordable levels. The PA-4SE, still a very hi-quality product, is our answer. The
PA-4SE is shipped to you with the very latest version of the PA-4 PC board. The circuit
topology is the same but some operating points are carried over from our excellent
PA-3 series. Though many of the parts are different, we worked hard to maintain the
highest possible sound quality. We think we succeeded. You will enjoy a sound quality
well beyond what is possible with the original stock amps. The PA-4SE modified amps
will compare to amps of far higher price.
The PA-4SE Sound: After you’ve read above about the sound quality of the PA-4 imagine
a close runner-up position for the PA-4SE. Yes, in a side by side comparison the
PA-4 will finish first. Taken by itself the PA-4SE is very enjoyable. It would serve
at the heart of your audio system for many years putting a smile on your face all
Attention kit builders--- you must set the output stage bias current with a multi-meter
(digital type with 2 Amps DC or more capability preferred). Then you set the DC offset
voltage at the speaker outputs. These are simple, well-documented procedures explained
within your excellent PA-4 instructions. Your kit will have eutectic alloyed solder.
This means that the “solidus” point is the same as the melting point. When soldered
correctly this produces a solder joint that has the appearance of a drop of mercury,
a mirror like shine, while non-eutectic alloys may produce a matte finish appearance.
Eutectic properties are said to decrease the number of crystal boundaries in the
hardened solder and produce a better sounding solder joint.
PA-4SE Modification <NEW!!>
$249 kit, $399.00 installed - kit includes all items required for installation. The
hardware installation parts are of the same quality level as those provided with
the original PA-4 (with two circuit boards) including specially alloyed eutectic
solder. Only the actual driver boards have different components compared to the other
$349 kit, $499.00 installed - kit includes all items shown (with two circuit boards)
including specially alloyed eutectic solder.
---------View the installation manual!--------- This is a large file and requires
Adobe Acrobat Reader in order to view and/or print it on your computer. It's probably
already installed on your computer. If not then get Adobe Acrobat Readerhere
PA-4 Elite Modification
Superb Nichicon Muse high-end audio grade caps are used in the feedback loop and
front-end power supply positions on the PA-4 Elite for higher resolution, crystal-clear
frequency extension, clarity and just plain naturalness. PA-4 Elite has great bass,
quick powerful transients, smoothness, natural warmth and great 3D imaging. That
same word naturalness just keeps coming up.
PA-4 Elite: $449 kit*, $599.00 installed
PA-4 Elite Plus Modification
You not only want superior sound but extended reliability and confidence that you’re
getting the best from your power amplifier. You want all this at a price that Is
unmatched considering the top quality of parts and sound. This exotic modification
includes all Elite mods, described above, plus:
CMC Silver Binding Posts, beautifully made, insulation clad silver posts with connectivity
for spade lugs, banana plugs and quite thick wire - great sound - all parts are copper
with double silver plating. You’ll want these on your speakers after you hear the
Elite Plus modification. If you buy the kit you’ll have to enlarge the holes on most
amps so the connector will be electrically insulated from the chassis. A step drill
is the simplest method. Please use caution and eye protection.
CMC Silver RCA Jacks, rock solid feel, super clear sounding, supremely made silver-plated
over copper RCA jacks - all parts are copper with double silver plating. CMC is a
widely respected provider of luxury connectors. If you buy the kit you’ll will have
to enlarge the holes on most amps so the connector will be electrically insulated
from the chassis. A step drill is the simplest method. Please use caution and eye
PS-200 Power Supply - See it here. dual-mono power supply with wonderful sounding
caps and superb IXYS HyperFred rectifiers.
You will receive a PS-200 specialized for your amp, please specify your amp when
you order. See more PS-200 versions here, some of these items on Exotic Parts page.
Our latest PA-4 Elite Plus creates a truly a superb amp that demands comparison to
any amp available!
PA-4 Elite Plus: $899kit*, $1099.00 installed >>>>>>>For PS-200J luxury version,
with Jensen 4-pole caps, add $195 to either price.
PA-4 Elite Ultra Modification
Our PA-4 Elite Ultra mod is truly State of the Art and beyond State of the Art as
it is practiced by so-called high-end manufacturers. Although we at Musical Concepts
have modified many expensive well known amplifiers we've never seen build quality
even remotely close to the Ultra. The superb Takman resistor is used in nearly all
slots for all Elite Ultra driver boards. For all amps the Elite Ultra also includes
a new high in-rush current, silver-alloy power switch and a Rhodium-plated IEC power
cord socket with hi-current cord. Just imagine what this incomparable product might
sell for if it had some fancy over-hyped manufacturers name on the front panel. This
is the finest mod we have to offer.
Depending on your original amp there are some differences in the power supplies.
The DH-200/220 and XL-280 has a 625W dual-secondary toroid power transformer. The
main power capacitor supply is our PS-200J with IXYS HyperFred rectifiers and four
high-resolution Jensen 4-pole caps which are the finest you can buy for power supply
The DH-500 and XL-600 have twin 500W toroid power transformers and twin PS-200J boards
with Jensen 4-pole caps - eight of them in total. This power supply operates with
totally dual-mono performance.
PA-4 Elite Ultra modification: $2495 installed only for DH-200/220 & XL-280, $3195
for DH-500, $3395 FOR XL-600
Dual-Mono Power Supply Conversion
See our PS-200 pagefor dual-mono power supply conversions for some amps. It is recommended
for new dual-mono conversions. Improve the transparency, focus, imaging, bass solidity
and resolution abilities of your amplifier with the tried and true optimization of
your power supply for a mono amplifier level of sonic results. The ability of the
amplifier to sound more "together" and unstrained is greatly improved.
Hafler amplifiers: SE Series, DH-120, DH-240, 9000 series* - We do THX stuff, Too!
LX modification techniques include a very thorough mod with changes in the Feedback
Loop, existing RFI input filter, Bias Circuitry, Power Supply, bypassing, compensation
caps, etc. The result is a remarkable improvement in perceived wider dynamics, greater
naturalness, warmth and transparency! Save yourself from dry, bright sound today!
ELITE modification uses all the LX techniques and more. ELITE replaces your main
power supply bridge rectifiers, front-end power supply rectifiers(some amps) and
important small value electrolytic caps, such as the DC restoring cap in the FB loop.
We use the remarkably natural sounding Silmic II capacitors. Additional power supply
bypass caps linearize the highest frequency performance of the power supply.
ELITE SOUND - Picture a smooth, extended top-end, wide but perfectly scaled dynamics,
tremendous coherency and a fatigue-free listening experience. Picture cymbals with
light airy frequency extension and not a bit of harshness. Now picture yourself enjoying
instead of analyzing!
*We don’t service the 9505 amplifier.
Hafler LX Modification is $399.00/inst., Elite versions with Soft-Recovery rectifiers,
SILMIC II and more caps is $599.00
See our "Connector" page for hi-quality RCA connectors and binding posts that we
can install for you!