A description
of the LX521 ASP Reworked PCB. The opinions expressed are my own; use at
your own risk.
Please do not copy and repost these photographs or
link directly to them from my server.
Please see here for the ASP.4 For the earlier version, see below.
Bare PCB boards are available for sale from this page. Board sets include two new ASP boards and one
set of V-scored separable Power PCBs as pictured above and described below. No components are
included; these are bare PCBs only. Prices for the full set of boards
with domestic or international shipping via regular airmail (no
tracking) is $67. The 15.09.15 LX521 ASP is a third-generation
design that is confirmed as working when constructed correctly with
the appropriate functioning parts. No individual support
is offered or implied by the purchase of these boards. Support for questions not answered by the documentation or this page will be provided through the dedicated thread at the LX521 Resources
Forum.
Please post any questions not answered on this page or within the
documentation to the dedicated thread within the LX521 Resources
Forum (restricted access, please read the posting
guidelines for access instructions). This page will be updated as
required based on forum questions raised. Do not post questions of a
commercial nature to the linked forum.
While putting together my
own LX521 build I decided to rework the ASP PCB. The intention was
to fit it inside of a DIY amplifier case. When I finished the design I
sent a completed board to Mr. Linkwitz and offered it as a replacement
to the original ASP.
Since he had decided to pursue the DSP route he declined my offer.
However, it has become evident that others prefer to retain the
all-analog signal path of the original design. Mr. Linkwitz suggested
that I offer the boards myself with the condition that I provide support
on the Oplug forum.
The LX521 ASP Reworked board is the same circuit described in the
LX521 construction plans but on a smaller scale than the original. Each
board measures 4.25 x 8.35 inches or nearly half the size of the
Linkwitz ASP. However, construction of the new ASP is simplified by the
elimination of footprints for unused parts and wire jumpers. The PDF
documentation - posted in the restricted area of
the LX521 Resources Forum - is fully searchable, allowing location
of parts by value or designation between the bill of materials and board
screen overlay. Just use [ctrl + f] and each instance of the search
string will highlight upon the press of the enter key whether in the
BOM, schematic or overlay.
All op amp packages are oriented in the same direction, reducing
placement errors. In addition, all op amp footprints have three
indications of orientation - a dot at pin one, an angled corner and a
half-round dimple at the end of the package - eliminating ambiguity. Polarized capacitors are
marked with a + and a band at the negative end, visible even when the
component is mounted. All component designations are visible even when
the component is soldered in place simplifying troubleshooting.
Additionally, test points are clearly marked in boxes with pads to which
header pins can be attached, if desired.
Power to the boards is handled differently to the original. A power
PCB sub-assembly is provided with each board set. Depending on which
option you chose the LX521 ASPs can be powered as the original with an
external Mean Well switch mode supply or with a conventional linear
supply using the supplied PCBs. You have the freedom to mount an external power connector where you chose rather than being restricted to the same surface the audio connectors are mounted on.
End placement of regulators makes it easy to bolt them to the case (with insulators in between, of course) to aid in heat dissipation or add separate heat sinks. Do not neglect using some form of heat sink or it will shorten the life of the regulator.
You can also use a power source of your choice utilising the
pass-through board with convenient footprints for Molex KK style
connectors.
Large storage capacitors are fitted to each ASP board and each op amp
package have small decoupling capacitors close to the supply pins as
usual. Power is supplied to the ICs through wide power planes on the
top layer of the PCB. In addition a rail to rail electrolytic capacitor
gives a path for class B currents at each op amp package.
The on-board input jack can be an unbalanced RCA or balanced Neutrik
Combo jack. If both are required a footprint for a Molex KK connector
can be connected to a chassis mounted RCA jack.
Milled plated-through slots for the PCB mounted RCA jacks allow them
to sit closer to the front edge of the board. This in turn allows the
RCA jacks to protrude further through the panel of the enclosure. Two
woofer output jacks are provided, eliminating the need for Y cables.
Two headers are included - one for the 1429-2090 shelving low pass
filter (shunt to engage) and 30 high pass sub-cut (shunt to bypass).
Switches can be fitted as front panel controls if desired that can be
either hard-wired or fitted with Molex KK-style connectors.
