SR4 PUPs AND PREAMPS
(Pre-EB & EB)
Pre-EB Pickups (1976 - 1984)
1976 up to Circa Second half of 1977 (First Version).
Pickup from Sting Ray Bass dated Jan/Feb 1977.
Two separate coils
are wired in parallel to cancel hum.
Note that the pole pieces extend below the bottom of the pickup cover and are longer than the latter version Pre-EB pickup (further on). Each pole piece is 1 inch long and 3/8 inch diameter. The resistance of each individual coil is approx 2,400 ohms. As the pickups are wired in parallel, the total output resistance is approx 1,200 ohms.
This resistance is considerably lower than the latter version Pre-EB pickup (introduced circa early 1978) with each individual coil measuring approx 3,900 ohms resulting in a total output resistance of approx 1,950 ohms (in parallel) and fitted with pole pieces measuring a shorter 5/8 inches in length but retaining the same 3/8 inch diameter (see further on).
Note that coil windings varied due to techniques used at the time resulting in slightly different resistance readings between individual Pre-EB pickups.
Pickup cavity routing and Pickup from Sting Ray Bass.
Body date 17 June 1977. Pics courtesy of "calzone".
The main pickup cavity is routed deeper at the bottom to accommodate the extended length of the pole pieces of the two coils.
Pre-EB (and EB period), Sting Ray 4 pickups are passive (not active), the coils are wired in parallel and pole pieces are Alnico. The battery powers the pre-amp
Circa Second half of 1977 to end of Pre-EB period  (Second Version).
Above two pics showing side and bottom views of
the new pickup (from a late 1978 Bass).
Pole pieces are now
shorter (5/8 inch length) and flush with the bottom of the pickup cover. The poles remain at 3/8 inch diameter. Each coil now has a resistance of approx 3,900 ohms. Resistance of the 2 coils in
parallel gives an overall resistance of approx 1,950 Ohms.
1) Even with the introduction of the newer pickup, the older long pole pickup can still be found on some Basses up to circa early 1978.
2) Although the newer pickup has shorter pole pieces, it initially appears to have been used in conjunction with bodies having the deeper cut routing which previously accommodated the older pickup (with its longer pole pieces). Examples exist up to circa early to mid 1978. Thereafter the bodies have a single cut routing for the newer pickup (see below).
The newer short pole pickup used in a pickup cavity routed
for the older long pole pickup. Body date 31 Oct 1977.
Above two pics again showing the newer short pole pickup
used in a pickup cavity routed for the older long
pole pickup. Body date 10 Mar 1978.
The newer single cut pickup
Pic from a late 1978 Bass.
Towards the end of the Pre-EB period (circa 1983), the
pickup routing is re-shaped to the outline ot the
pickup. It is thought that this may have
coincided with the introduction of
A Carey Nordstrand pickup type "MM 4.2"
with alnico pole pieces.
The Nordstrand pickup is designed on the 1977 Pre-EB pickup (second
version) above and will fit all Sting Ray 4 Basses (Pre-EB & EB) from 1976 to present date EXCEPT for the dual pickup Sting Rays introduced in 2005 (with pickup covers similar to the Bongo
Pre-EB PREAMPS (1976 - 1984)
Although the Treble and Bass controls have no centre detent position, the preamps are CUT and BOOST. With respect to the treble control, the cut and boost takes place during normal clockwise/anticlockwise rotation of the control. The flat position is approx. mid way through rotation. On the other hand, the cut position on the bass control appears to be at the extreme anticlockwise position of rotation and begins to boost as the control is advanced clockwise from that point.
The earlier Pre-EB preamps use a 25K audio (log) taper pot for the volume control. Towards the end of the Pre-EB period it changes to a linear taper to make adjustment smoother throughout rotation (see further on). The audio taper tends to bunch the volume adjustment to the upper limit of the pot rotation. A 1Meg reverse audio (log) pot is used for treble control and 100K audio (log) pot is used for the bass control.
All Pre-EB preamps use an "LM4250CN" IC chip. The same chip is also used on all Ernie Ball 2EQ pre-amps to current date. The 3EQ option introduced by Ernie Ball in 1987 uses a "TL062" chip.
1979 pot with code dating on the side.
Pots are code dated
on all preamps during the Pre-EB period. For example "1377626". The "137" component identifies the type of pot (a single pot rather than a stacked pot). The next two numbers identify the year ("76"
indicates 1976 as the year of manufacture). The remaining two numbers identify the week of the year ("26" indicates the 26th week of 1976 which is June). The code example "1377626" therefore
identifies the pot as being manufactured in June 1976. Pot dates do not necessarily identify the date of the preamp. As Music Man purchased pots in large quantities it’s not unusual to find pots that
are made one to two years earlier than the pre-amp itself.
1976 to early 1977 (Black Epoxy).
From 1976 to early 1977 a red/orange coloured outboard capacitor is located on the treble pot rather than being included on the circuit board itself.
Preamps are sealed in black epoxy. The IC chip is soldered direct to the circuit board. The sequence of lead-out wires from the board is completely different to subsequent Pre-EB preamps boards.
Schematic preamp wiring for 1976 and early 1977 Basses.
1977 to 1978 inclusive (Black Epoxy).
There appears to be
three versions of the preamp used during this period.
Pics of type 1.
Type 1 schematic.
Type 2. Preamps are normally attached to the pots, at
each end of the board, with material similar to that
used for the string mute pads. After time the
material can degrade. In the above picture,
the preamp has been re-attached with a
strip of mouse pad.
Type 2 schematic.
Note that the lead-out wires to the bass pot (on right) are now yellow instead of violet and have been reduced from three to two. The bottom lug of this pot is now unsoldered (as opposed to Type 1 above). Note also that the two lead out wires to the volume pot have had their colours reversed as opposed to Type 1. White now goes to the centre lug of the volume pot and black to the bottom lug.
Type 3. Webmasters 1978 preamp.
Note that the lead-out wires to the bass
pot revert back to being violet. This pre-amp appears to be the main one used towards the end of 1978.
Sept 1978. Non-Epoxy Preamps Introduced.
1979 preamp. (Pics courtesy of "freedok"). Note the red
and blue coloured Tantalum capacitors. Green and
maroon Tantalums were often used as well. On
latter preamps, Electrolytic capacitors
From Sept 1978 the
non-epoxy version of the Type 3 preamp began to replace the previous black epoxy Type 3 version. This extended over several months and existing stock of the black epoxy would
still have been used until depleted. It’s not unusual to find the black epoxy version in early 1979 Basses. Putting aside the deletion of the epoxy, the two versions are the same as each
other. Both use the same circuit board which is designated “B3”. Also the wire lead-out orientation and lead-out colours remain the same for each.
The IC chip for the non-epoxy version is now mounted to the board via an IC socket rather than soldered directly to the board itself. However, from 1984 (beginning of the Ernie Ball period) all ICs returned to being soldered directly to the circuit board.
Schematic for non-epoxy preamp wiring from late 1978 to
1984 (end of Pre-EB period). Although the epoxy is now
deleted, note that the colour & sequence of the
lead-out wires is the same as for the Type 3
epoxy preamp used during the
1977-1978 period above.
The same non-epoxy
preamp and colour coding is used by Ernie Ball from 1984. Although the circuit board has changed its shape several times since 1990 the 2EQ circuit still remains the same to current
Late 1979. Left-handed Introduced.
Preamp from a Feb 1980 left-handed Bass.
Courtesy of Gilles (France).
Circa late 1979 or early 1980.
At left is the non-switchable jack first used with Pre-EB
preamps. The jack (right), introduced late
1979 (early 1980), disconnects the battery
when the guitarlead is removed.
Initially, all pre-amps remained permanently turned on. Removal of the guitar lead did not disconnect the battery. Current drain was considered to be low enough for the battery to last its normal shelf life whether left connected or not. A newer jack was introduced late 1979 (or 1980) to disconnect the battery. This is the position to current date.
March 1982. Introduction Of Protection Resistor.
1982 schematic showing where protection
resistor is placed in circuit.
Reproduced with permission.
Protection resistor installed by the factory and covered
with a black plastic sleeve.
The IC chip can be damaged if the guitar lead becomes short-circuited. In 1982 the addition of an out-board 1K ohm protection resistor was recommended to protect the chip.
Circa 2nd half of 1982. Electrolytic Capacitors Replace Tantalums.
The "LM4250CN" chip as used in the preamps (left),
Electrolytic capacitor (centre) and a
Tantalum capacitor (right).
Electrolytic (as opposed to Tantalum) capacitors appear on non-epoxied preamps from circa the 2nd half of 1982 onwards. Audiophiles believe that the electrolytic has a mellower pleasing tone.
1982. Linear Taper
Replaces Audio (Log) Taper On Volume Control.
The previous 25K audio (log) taper pot for the volume control tended to bunch the volume control adjustment to the upper limit of the pot rotation. The linear taper corrects this by allowing a smoother adjustment throughout the whole pot rotation.
1983 Volume pot with linear ("LIN") taper marked on rear.
1983. All updates of the Preamp board completed.
Front and rear pics of Webmasters N.O.S. 1983 preamp.
Music Man covers the protection resistor with
a black plastic sleeve prior to installation .
The Ernie Ball replacement preamp for
all Pre-EB &
EB Sting Rays up to 1990 which use the same circuit
board shape. The protection resistor is included on
the board. See EB preamps from 1984 (below).
Reproduced with permission. A schematic wiring diagram for
the M05400 replacement board directly above.
Note the violet lead-out wire on left hand side as opposed to the normal three yellow lead-outs. However this is the general schematic for all Pre-EB and EB 2 band preamps up to circa 1990. Although lead-out colours may be different, the leadout and hook up wiring sequences are the same.
EB Pickups (From 1984)
Pre-EB pickups (above) varied individually due to winding techniques adopted at that time. Ernie Ball automated the windings to make the pickups more consistent.
As with the Pre-EB Sting Ray pickups, Ernie Ball Sting Ray 4 pickups are passive, the coils are wired in parallel and pole pieces are Alnico. The battery powers the pre-amp only.
Similarly, as with the second version of the Pre-EB pickup from circa second half of 1977 onwards (above), pole pieces measure 5/8 inch in length with a diameter of 3/8 inch. Each coil measures approx 3,900 ohms with a total output of approx 1,950 ohms (in parallel).
Above two pics from a 1989 SR4. Note the
Blue wires. The coils have no outside tape winding.
Pre-EB pickups are Yellow and Green.
From a 1992 SR4 (courtesy "Oliver"). Wire
at right hand
side is now Green. The owner advises this pickup has no
outside tape winding on the coils. The metalic shielding
tape across the pole pieces is an after-market
modification and is not original
from the factory.
Above two pics from a 1994 SR4. Note, for first time, the
inclusion of a winding of Black tape over the coil
windings. It's unknownif this was the
case in 1993.
A more recent SR4 pickup (exact vintage unknown). As
with other pickups the Black lead-out wire is "Ground"
(earth). The White lead-out goes to
the pre-amp (input).
Mid 2003-Current. Rounded Pole Edges.
SR4 Pickup with rounded-edge Alnico pole pieces.
Introduced mid 2003. In all other respects the
pickup remains the same.
2005-Current. Dual Pickups.
Introduced 2005 Sting Ray with dual
(Picture "Steve Dude Barr").
Close-up view of the dual Humbuckers.
The new dual pickup
Sting Ray Basses were introduced at the July 2005 NAMM Show. Pole pieces remain Alnico with rounded edges. However, the pickup covers differ slightly to the single pickup (H) Sting Ray The area
on the side which supports the two height adjustment screws is similar in shape to the pickups featured on the Bongo Bass.
As well as two Humbuckers (HH) above, the Sting Ray was also available with one Humbucker plus a Single coil pickup (HS). The HS option is no longer offered. The HH is offered with 3 band pre-amps only (no 2 band).
EB 2EQ PREAMPS (From 1984)
The Ernie Ball 2 Band EQ preamp (to current date) is the same circuit as the Pre-EB non-epoxy preamp as it was at the end of the Pre-EB period in 1984. Although the IC chip "LM4259CN" remains the same, it now becomes soldered directly to the board and not via an IC socket (as it was during the Pre-EB period). However, some Pre-EB boards are used in very early EB Basses. The out-board protection resistor modification (from 1982) becomes relocated to the board in 1986.
Wiring of the preamp board to the pots, pickup and jack remains the same as the Pre-EB non-epoxy preamp. The sequence and colour of lead-outs from the preamp board also remain the same.
The board shape changed from rectangular to crescent moon in circa 1990 but the circuit remains electrically the same to current date.
1984 to 1986 (2 band).
From a 1985 preamp. The protection resistor is covered
with a black plastic sleeve (on left).
From 1984, the protection resistor has been added as per the 1982 Pre-EB schematic (pictured previously) and is located within the black plastic sleeve to the left.
A 1985 preamp (body date 6 Aug 1985).
The 1985 preamps (above) shows the position of where the protection resistor is to be relocated to the preamp board in 1986.
From c.1985, preamps were dated with a black marker pen on the rear of the control plate.
Circa 1986 to circa 1990 (2 band).
A 1986 preamp. Protection resistor
relocated to the
board (encircled). Neck date 24 Sept 1986. Body
date 8 Jan 1987.
The protection resistor is now relocated on the circuit board in
It was from circa 1988 that the preamps were dated with a round sticker located on the rear of one of the control pots. Preamps are still dated this way today.
Circuit wiring for EB preamps from 1984 to 1990 is the same as the
Pre-EB non-epoxy preamps from late 1978 to 1984.
The Ernie Ball replacement preamp
for all Pre-EB & EB Sting Rays up to 1990 which use
the same board shape. The protection restor is
included on the board (encircled).
Underneath view of the replacement board. The board is
designated at the bottom with "B 3A". Note that the
last of the Pre-EB boards were designated "B 3".
As well as being designated "B 3A", three of the leadout wires on the left are violet, yellow and yellow rather than the normal three yellow wires.
Reproduced with permission. A schematic wiring diagram for
the "M05400" replacement board directly above.
This is the general schematic for all Pre-EB and EB 2 band preamps up to circa 1990. Although lead-out colours may be different, the hook up wiring sequences are the same.
Circa 1990-Sept 2009 (2 band).
Up to this stage, pots have had lugs for point to point wiring (above left). From circa 1990, direct mount pots (above centre) have been used in 2 band preamps due to the circuit board design (see below). As the pot values (and tapers) remain the same, the direct mount pots can be modified for use in the earlier preamps by bending and cutting the pins (above right).
Pots used with preamps.
2 Band preamp with new circuit board design.
From circa 1990, the 2 band pre-amp circuit board changed from rectangular to crescent moon. Note that the lug pots are replaced with direct mount pots that solder to the circuit board with pins. The circuit remains the same as the earlier preamps.
Reproduced with permission. Schematic
wiring for 2 band
preamps from circa 1990 to Sept 2009.
Sept 2009- Current (2 band).
Above two pics of the newer 2EQ preamp
in September 2009. (Pics courtesy of Mike).
The circuit remains the same and continues to use the LM4250CN chip. Although pot resistance values also remain the same, the previous larger pots are replaced by smaller "Noble" pots.
2016- Current. "Old Smoothie" 40th Anniversary SR4.
Black epoxy preamp used in the 2016 "Old Smoothie"
40th Anniversary Sting Ray Bass.
"Old Smoothie" is bassed on Sterling Ball's 1976 Pre-EB Sting Ray (B001026) given to him by Leo Fender. The preamp has the same leadout colours and
wiring hook up as the as the Type 3 Pre-EB black epoxy preamp mention earlier. Pot values are also the same as other 2EQ preamps.
EB 3EQ PREAMPS (From 1987)
Circa 1987 to circa 1990 (3 band) Option.
Pic of a 1988 3 Band EQ Preamp.
Ernie Ball introduced the optional 3 band pre-amp in 1987 and is an option to date. The same preamp was included in the new SR5 latter in 1987. Note that, although the two outer pots are hook-up wiring lug pots, the two inner pots are soldered to the circuit board by pins attached to the pots. Note also that the preamps are dated with a round sticker on the rear of a control pot from 1988 onwards. Prior to this some were dated with a black marker pen on the rear of the control plate. The 3 band uses a "TL062" chip rather than the "LM4250CN" used with the 2 band preamp.
Reproduced with permission. Schematic wiring for 3 band
preamps from circa 1987 up to circa 1990.
Circa 1990-October 2006 (3 band) Option.
Pic of a 1994 3 Band EQ preamp.
Just like the 2 Band preamp, the 3 band preamp circuit board also changed from rectangular to crescent moon shape. Note that the two outer lug pots on the previous 3 Band version (above) are now soldered on the board. The circuit still remains the same as do pot resistance values.
Reproduced with permission. Schematic wiring for 3 Band preamps
from circa 1990 to Oct 2006.
October 2006-Current (3 band) Option.
Pic of an Oct 2006 3 Band EQ preamp.
The circuit remains the same and
continues to use the TL062 chip. Although pot resistance values also remain the same, the previous larger pots are replaced by smaller "Noble" pots.
Back to top of page