Levinson LNP-2
Update 7/2023: I recently found a schematic of the LNP2 online, and have attached it below. Based on the schematic, I believe this is an earlier version than the one documented below, but mostly the same. Note that it does not include the schematics for the LD2 amp modules or VU307 meter modules.
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This project describes the construction in early 2011 of a new build of a Levinson LNP-2 (or reasonably close), which was originally designed in 1973, as Mark Levinson Audio Systems' first commercial product. I was fortunate to come across a new old stock faceplate and the two main circuit boards that were key to the start of this project. This webpage is organized as follows:
A. Background on the original LNP-2
Levinson marketing materials and Audio magazine review
A look at some of the changes made during production of the original LNP-2.
B. My LNP-2 build
The starting point (original Levinson parts)
Changes from the original design
Power supply
OpAmp modules
Phono section
Chassis
Overall assembly
Comparison to original LNP-2
Note that the information contained here is accurate to the best of my knowledge, but I would encourage any corrections or supplemental material on the LNP-2. My email is at the bottom of this page below.
A. Background
1. Marketing Materials and Review
Above: Levinson LNP-2 sales flyer, front. Click to enlarge.
Above: Levinson LNP-2 sales flyer, rear. Click to enlarge.
Above: Another Levinson LNP-2 sales flyer. Click to enlarge.
Above: Audio magazine review of LNP-2 November 1973, page 1. Click to enlarge.
Above: Audio magazine review of LNP-2 November 1973, page 2. Click to enlarge.
Above: LNP-2 Block Diagram. Click to enlarge.
2. Production Versions
Above: An early version of the LNP-2, showing the bottom of the motherboard and the point to point wiring for all the frontpanel switches. Click to enlarge.
Above: This intermediate production version shows the addition of several smaller circuit boards for the switching, including three on the bottom row of switches (shown here near the top of the photo), as well as two more for the selector and gain switches not readily visible here.
Above: Latest version of the LNP-2, showing one single PCB for all eight of the bottom switches. Note there are still two small PCBs under the selector switch and gain switch near the top of the unit, the same as the previous version of the unit.
Above: Earlier version showing Burwen UM201 plug-in modules. These LNP-2s also included the Burwen VU306 meter modules for the meter circuit. I'd guess the blue dot on the two phono opamps indicates selected for low noise.
Above: Later version showing the LD-2 modules made by Levinson. These units sometimes have the Burwen VU306 meter modules, but often have the Levinson-branded VU307 modules shown above.
B. My LNP-2 build
1. The Starting Point - Original Levinson Parts
First, thanks to fellow Connecticut Audio Society members Steve Marsh and Charlie King, who helped me acquire key parts and provided invaluable assistance in this project. This project started with the faceplate (NOS), the latest switching circuit board (mostly populated, looked new/unused but had a bad switch and needed re-work), and the motherboard (partially populated, but no plug-in opamp modules, also needed a bit of repair work). I also started with a pair of the original Weston 2022 VU meters (one of which was dead and needs work) and bezels.
Above: The starting point of this project. Click to enlarge. Note that one (dead) LD-2 plug-in module is shown on the motherboard.
This photo shows Randy & Jack Weidner, of FJ Weidner in East Haven, CT, holding an LNP-2 faceplate.
The Weidner brothers were extensively involved in designing and manufacturing parts, including the engraved faceplates, for Levinson and Cello. They were able to replicate the original LNP-2 knobs for my project.
2. Changes from the Original Design
I decided to build something as close to an original LNP-2 as reasonable, but there were a number of variances from the stock 1973 design.
I extended the chassis 2" deeper to allow the inclusion of an on-board power supply. This was to simplify the design (no separate out-board power supply chassis required), and to put the regulators as close to the active circuits as possible. The objective of the original separate supply design was to minimize noise, however this unit is dead quiet.
The Opamp modules used on the later LNP-2s were discrete transistor designs, although the earliest LNP-2s appear to have used ICs in the plug-in opamp modules. I used IC op-amps on the plug-in modules, based on much more recent Cello designs. This can easily be changed or upgraded later simply by plugging new modules into the motherboard. More details below.
I simplified the signal path. See the Block Diagram above. The original design called for a selector switch, followed by an input opamp, then the volume control followed by the line opamp (which Levinson called the "output amp". A more traditional design omits the extra active stage of the input opamp, so I bypassed it, although it remains in place and still performs its additional functions of tape output buffer and meter amp.
I omitted the XLR connectors on the rear panel, and used only RCAs. The original LNP-2 had no balanced circuits, and the XLRs were simply wired as XLR to unbalanced adapters for the convenience of anyone using balanced cables. I simply used Vampire gold RCAs for all input/output connections.
The original knobs were custom made for Levinson. I found some very similar knobs at Digikey (P/n 226-2016-ND), made by Kilo that are the same diameter and height, with the same basic profile, but the end is slightly thinner. They are available in both 0.25" shaft diameter (for most of the controls) as well as 6mm shaft diameter (to fit the three pots on this unit). I later had exact matches for the original knobs made by the original manufacturer - FJ Weidner (see above).
I changed the phono section EQ for a flatter response, see below. I also wired the phono input directly to the phono preamp, unlike the original which had two phono inputs wired to the input selector switch first (I don't believe it's a good idea to switch such low level signals).
3. Power Supply
I based this design primarily on the article entitled "Preamp Power Supply" by Gary Gallo in The Audio Amateur magazine, issue 4/90, p.47. In that article, he indicates several key changes from the datasheet recommendations to optimize simple three terminal adjustable regulated power supplies for audio use, all of which I incorporated into this supply. They include:
1. Use of a much higher current transformer than traditional: in this case an Avel dual 18V, 60va transformer (stock LNP-2 is 30va).
2. Use of very large output capacitors (typically data sheet recommendations are much smaller than the input caps). In this case 5,600uf input caps and 4,700uf output caps, both bypassed with small value polypropylene caps.
3. Use of divider resistor values around the regulator IC that are several times the typical values, dramatically reducing output impedance and ripple rejection.
4. The use of Linear Technology LT1085/LT1033 series adjustable regulators instead of the common LM317/337s.
Since I wanted the power supply to be compact I designed a custom PCB using the tools at ExpressPCB.com, highly recommended. Their double sided boards are very nicely made, with plated thru holes.
Above: Power supply PCB, component side, with diagram from ExpressPCB software.
Above: Assembled power supply PCB. I used MUR860 soft recovery diodes for rectification, Panasonic TS and FC caps, bypassed with 0.1uf Vishay MKP1837 caps, and LT1085/33 regulators. The supply delivers +/-25 volts to the regulators, and provides +/-15.0 regulated volts at the output (to the motherboard).
Above: Rear panel with assembled power supply. Click to enlarge. Power switch is at upper right, fuse below that, and IEC below that. Note tight layout with short wire runs for entire supply. The yellow (+15V), green (-15v) and black (ground) wires will connect to the motherboard.
4. OpAmp Modules
The LNP-2 is basically a motherboard, with plug-in modules for each active stage, connected by a nest of wiring to the switching circuitry and input/outputs. When the LNP-2 was originally designed, it used opamp modules designed by Dick Burwen. Designer John Curl (who designed the Levinson JC-2 among many other pieces of high end gear) indicated that these original modules actually contained an IC: a selected Harris HA-911, his comments here. This is confirmed by Dick Burwen's website, which describes the original UM201 modules as follows:
Burwen Laboratories Modules MP202, UM201, and VU306 - 1970s
These epoxy potted modules were designed for use in the Burwen Laboratories Model 1000 Dynamic noise filter and the Model 2000 Noise Eliminator.
Some were incorporated in Mark Levinson's famous LNP-2 Preamplifier. Dick's 20,000-watt sound system still uses more than 250 of these modules.
The MP202 is a microphone preamplifier; UM201 is a Universal Mixing Amplifier; and VU306 is a Peak VU meter circuit. Dick was able to greatly improve
the high frequency performance of their Harris HA-911 op amps via a more complex stabilization network, and they were selected for low noise and DC
offset.
These modules are in a form factor/layout this was widely used in professional audio equipment at the time, and is still apparently used today. It appears that one of the early more popular versions was the API 2520 (which may have been used in some LNP-2s), more info here. Some other current discrete opamp examples are here and here.
The earlier opamp modules were labeled Burwen Universal Mixing Amplifier UM201, as shown in the "Production Versions" section above. At some point, Levinson started manufacturing the opamp modules under their own name, labeling them LD-2 (Line Driver 2). I believe these modules used discrete transistors, unlike the the IC based Burwen modules. This same module was used in all stages (input, output and phono) of the LNP-2. These LD-2 units are what is most often seen in LNP-2 preamps. Note that each LNP-2 also had two VU-306 (Burwen manufactured) or VU307 (Levinson manufactured) peak detector modules for the meter circuit - see 3rd photo below.
Above: LD-2 opamp module (dead in this case), top view.
Above: LD-2 opamp module, bottom view. Note epoxy potting material and exposed trimmer pots.
Above: LD-2 module on left, along with an unpotted VU-307 module, used for the peak meter circuit. The unpotted module would be placed in a plastic box and epoxy poured in, with only trimpots and the gold connector pins exposed. This provided some thermal management, but mostly prevented reverse engineering of the module contents. It also very effectively prevented any possibility of repair of defective modules.
Given the lack of available documentation on the LD-2 module, I used a circuit designed by Charlie King, based on some of the later Cello equipment, that uses a pair of op-amps in a composite configuration as described in Burr-Brown Application Bulletin 007, in PDF format here. We designed a PCB (again using ExpressPCB) for the circuit to match the form factor of the LD-2 modules, and we found sources for the gold connector pins to complete the modules.
Above: My IC based replacement for the LD-2 module, showing bottom view with connector pins, and top view.
Above: Test jig with +/-15 volt power supply to verify operation of replacement opamp modules. Used to test performance at various gain settings before plugging into the LNP-2.
5. Phono Preamp Stage
The phono section in the LNP-2 is a simple circuit, and I decide to stay close to the original. I used the VSPS phono project, a circuit similar to the original LNP-2, but with different and more accurate RIAA EQ. Because of that slightly more complex EQ section, the parts would not fit on the LNP-2 motherboard, so I designed and made two small (0.7" by 1.3") PCBs to hold the EQ parts. I used the simple technique of using dry transfers to mark the traces, and then etching with Radio Shack PCB etching solution.
Above: Phono EQ pcbs, front and back.
Above: Populated phono EQ boards. Resistors were 1% MF Dale RB55s, and the caps are polystyrene selected to be <1% tolerance.
Above: Populated phono EQ PCBs, mounted beneath the motherboard (this view is from the bottom). The original LNP-2 mounted the EQ components in the same location, but since there were fewer parts, they mounted directly to the bottom of the motherboard. The cartridge loading resistor (47K) and cap (100pf) are just visible above the smaller PCBs.
6. Chassis
The original LNP-2 chassis consisted of a single aluminum piece for the sides and back that wrapped around to the front where the controls mounted, and which also secured the faceplate. Simple flat top and bottom plates complete the chassis. Note that although the faceplate is a standard 19" rackmount width, it is a very non-standard 4.1" tall. Standard rackmount panel are in increments of 1.75", so this unit will always be difficult to mount cleanly with other rackmount gear, and I have never seen a photo of an LNP-2 rackmounted. Because of the non-standard height of the chassis, I decide to have one custom made by Par-metal.com. They did a beautiful job, exactly to my specs, black anodized with pressed in threaded inserts, at a very reasonable price.
Above: Chassis as custom built by Par-metal, before any drilling, with faceplate leaning against it.
Next up was drilling the rear panel for cutouts for the IEC connector, fuseholder, and power switch (the stock LNP-2 had those all on the external power supply), as well as the army of holes for the RCA jacks. The front panel had 13 holes for the various switches and controls, but also required cutting out a section for the meters, which I did on a tablesaw using a non-ferrous blade.
Above: Chassis after drilling and cutting, with partial rear panel assembly. Note the front panel has been cut to fit the VU meters.
7. Overall Assembly
Above: Chassis with switch PCB in place, along with selector and gain switches, and showing cross-bars which support the motherboard. Click to enlarge. Note that chassis wiring has begun in this photo - virtually all audio wiring was teflon insulated shielded litz wire, which is by the way fairly time-consuming to terminate. I used Alps mono pots for the input controls on each side of the meters, and an Alps stereo pot for the main volume control.
Above: Motherboard in place, mounted on the crossbars. Click to enlarge. Many of the parts (including all caps) on this board were eventually replaced. The temporary blue painter's tape marks the switches to identify them during wiring and testing.
Above: Faceplate with meters mounted before installation. Note that most of the chassis wiring is completed, and some of the opamp modules are in place for testing here. Click to enlarge.
Above: faceplate mounted. Click to enlarge.
The original LNP-2 had no meter illumination. The Weston meters have a clear top, to allow overhead lighting, but they are mounted just under the top cover in the LNP-2, so there is no room for lights above the meters. After using the preamp in a darkened listening room while testing, I decided to add some illumination. After much experimentation, I settled on using four 3mm yellow LEDs, one on each side of each meter, powered by the unregulated +25 volt section of the power supply (to keep them away from the regulated supply used of audio). Since there is no mounting provision for any lighting, I designed and made an unusually shaped PCB to mount on the back of the meters and hold the LEDS.
Above: New PCB to mount meter illumination LEDs. The dropping resistor mounts on the left side, and the four LEDs are wired in series across the board.
Above: Meter LED PCB mounted. Note the yellow LEDs are visible in front of the PCB, facing into the sides of the meters.
Above: Completed preamp, bottom view. Click to enlarge.
Above: Completed preamp with plexiglas cover.
8. Comparison to original LNP2
Above: Levinson LNP-2 on top, my new build on the bottom.
Above: Side view, original on top, showing extended chassis on my unit to include power supply.
Above: Rear view, original on top. Notice the XLR connectors on the original, and the power switch, fuse and IEC inlet on my unit on the bottom.
Future work
I'm currently working on building a tape head preamp into the two spare opamp sections on the far right of the motherboard. Levinson used these for a variety of custom applications, such as mic preamps. I have also not yet implemented any meter peak reading capability as in the original LNP-2 (although the normal VU function is working fine), and have yet to investigate options there. Listening comparisons between this unit and the original LNP-2 are also on the to do list.