G&L tech resources: Wiring harnesses

 
 

The L-Series and ASAT Basses with preamp and two Magnetic Field Design (MFD) humbuckers are some of the most versatile instruments around. Taking this 1981 L-2000E for instance, with its preamp wrapped in protective foam. The CTS 250kΩ Audio Taper potentiometer for the volume control has a 20pF ceramic treble bleed capacitor, a somewhat unusual value for the L-2000 as discussed below. The PTB tone stack consists of another 250kΩ Audio Taper pot for the treble cut, with a 47,000pF (.047µF) capacitor from the wiper to ground, and a 1MΩ Reverse Audio Taper pot for the bass cut, with a 2,200pF (.0022µF) treble bleed cap from signal to the wiper and a 1,000pF (.001µF) cap from signal straight to ground. The pickup is selected using an ALCO MTA206PA 3-position mini-toggle. The red tip ALCO MTA206N 2-position mini-toggle is the Splitter switch to select “humbucking” (towards bridge) or “single coil” mode with “increase in bass ratio” for the latter, achieved by engaging 100,000pF (.1µF) capacitors, one for each pup, soldered to the switch shorting high frequencies to ground. The Basses by Leo website humorously refers to this bass boost setting as the “OMG” (“Oh My God”) setting. Under the covers, the coils of each humbucker are combined either in series or in parallel, hence this is nowadays referred to as a series/parallel switch. The white tip 3-position switch is another MTA206PA, allowing the player to control the LM4250CN based preamp and select passive mode (toward bridge) with battery disconnected, low impedance active mode (middle) with no real discernible boost in either highs or lows, or low impedance active mode with treble boost (towards the nut). The circuitry has only undergone minimal change over time: change from control panel mounted to rear-loaded starting late-1985, some revisions of the preamp, and replacement of the discontinued MTA206PA with an equivalent. The protective foam of the L2000E preamp has not been peeled away to look at it in detail but to get some idea, check out this original drawing from 1981 or this sketch for the early L-2000/ASAT Bass circuit, both accessible on the aforementioned Basses by Leo site. However, judging from a remark made by Greg Gagliano when discussing this 1989 L-2000, this circuitry for the L-2000E does differ from later versions. Starting in 1992, the preamp revision appears on the epoxy board. Both ASAT Bass Commemorative Editions, #10 and #13 shown below, are from 1993 and have Revision 1.0 of the preamp using the LF441CN Low Power JFET Input op-amp. The block diagrams for this and later preamp revisions, drawn by Paul Gagon himself, can be accessed through the Basses by Leo website (Rev 1.0, Rev 1.1, Rev 1.2, and Rev 1.3). They are also included below for convenience. Note that in the detail picture for #10 below, the value for the volume treble bleed cap is 200pF, which seems to be the more common value since it appears as such on an L-2000 wiring diagram dated 4-5-81. In all there are 13 diagrams, schematics, and mods related to the L-2000/ASAT Bass available on Basses by Leo, providing a rich resource. This 2003 L-2500 has Rev 1.1, using the LM4250CN again. It’s wiring harness, when ignoring the preamp circuit, pretty much agrees with this 1998 drawing by Paul Gagon for an L-Series circuit.

 

L-2000/L-2500/ASAT Bass