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
driver stage. The copper 'trace' width in signal carrying areas is narrowed for lower‘dielectric
effect' from the circuit board material.
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. Provision for dual bypass
caps on each electrolytic cap has been added for use in the highest end PA-4 versions.
More physical space is provided for a superb new coupling cap. Driver stage current
is increased providing greater linearity and lower distortion for a cleaner, full-bodied
sound quality. Even heavier wide-band driver transistors with greater linearity are
new. These new transistors have an appropriately larger heatsink for cooler operating
temperature. Another big change which started with the earlier PA-3E was the adoption
of an ultra high quality resistor for almost universal use in the mod. These 100%
tested, mil-qualified resistors are made with even higher quality materials than
the previous resistors. Those earlier resistors were already equal to parts used
in many higher end amplifiers. Yes, these resistors cost 3 to 10 times more depending
on wattage rating 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 clear located in transparent space. All PA-4 series driver boards have
superb sounding resistors. The PA-4 Elite Ultra version uses the wonderfully dynamic,
dimensional, rich, powerful sounding Takman resistors.
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: Due to the more upscale quality level of individual parts in the PA-4
series the price had escalated 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 provided
with the very latest version of the PA-4 PC board. The circuit topology is the same
but some operating points are altered. 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 multimeter
(digital type with 2 Amps DC or more capability preferred). Then you set the DC offset
voltage at the speaker outputs.
PA-4SE Modification <NEW!!>
$249 kit, $379.00 installed - kit includes all items required for installation. The
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 are different.
$399 kit, $529.00 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 SILMIC II caps (FB, power supply and current source positions on PA-4) for
higher resolution, silky frequency extension, clarity and just plain naturalness.
IXYS HyperFred rectifiers replace the standard rectifier bridge. They have great
bass, smoothness, natural warmth and great 3D imaging. That same word naturalness
just keeps coming up.
PA-4 Elite: $499 kit*, $629.00 installed
PA-4 Elite Plus Modification
This exotic modification includes all Elite mods, described above, plus CMC Silver
Binding Posts(awesome stuff), exotic CMC SilverRCA jacks(tremendous sound) and our
PS-200 power supply(standard version) board,specialized for your amp,with high-performance
capacitors and superb IXYS HyperFred rectifiers. See PS-200 here, some of these items
on Exotic Parts page, see the RCAs and binding posts on our Connectors page. Our
latest PA-4 Elite Plus is truly a superb amp that demands comparison to any amp available!
PA-4 Elite Plus: $875 kit*, $1100.00 installed (for PS-200J add $175 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: $2795 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!