SR4H PRE-AMPS AND PUPS
A rough outline subject to amendment.
Pre-EB and EB BASSES
Pre-EB STING RAY (1976 - 1984)
PICKUPS AND ROUTING
1976 up to, and including, circa early 1978 (First Version)
Pickup from Sting Ray Bass dated Jan/Feb 1977.
Two separate coils are wired together in parallel to cancel the hum that would otherwise be present should only a single coil be used for the pickup. Thus the term "Humbucker".
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 all Pre-EB pickups are wired in parallel, the total output resistance is approx 1,200 ohms.
These resistances are considerably less 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 accomodate the extended length of the pole pieces.
Throughout the 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 only.
Circa early 1978 to end of Pre-EB period  (Second Version)
Pickup from a late 1978/79 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 has a resistance of approx 3,900 ohms. Resistance of the 2 coils in parallel gives an overall resistance of approx 1,950 Ohms.
Underneath view of same pickup.
Top view of the pickup and pickup routing.
As the pole pieces are now shorter, the pickup cavity is a single routing.
Towards the end of the Pre-EB period (circa 1983?), the pickup routing
outline took on the shape of the pickup itself. It is thought that this
may have co-incided with the introduction of clear pickguards.
A Carey Nordstrand pickup type "MM 4.2" with alnico pole pieces.
The Nordstrand pickup is designed on the 1978 Pre-EB pickups and will fit all Sting Ray 4 Basses from 1976 to present date EXCEPT for the new optional dual pickup Sting Rays introduced in 2005 (with pickup covers similar to the Bongo Bases). Resistance measurements are the same as for the Pre-EB pickup above with the shorter pole pieces.
Although the Treble and Bass controls have no centre detent position, the pre-amps 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 Pre-EB pre-amps use a 25K audio (log) taper pot for the volume control but it’s taper tends to bunch the volume adjustment to the upper limit of the pot rotation. The remaining controls employ a 1Meg reverse audio (log) pot for treble control and 100K audio (log) pot for the bass control. Although the Ernie Ball 2 Band EQ pre-amps (referred to latter) use the same Pre-EB pre-amp circuit and pot values, the 25K volume pot taper changes from audio (log) to a linear taper to allow for a smoother adjustment throughout the whole pot rotation.
All Pre-EB pre-amps use an "LM4250CN" IC chip. The same chip is also used on all Ernie Ball 2EQ pre-amps to current date. However, the 3EQ option introduced by Ernie Ball in 1987 uses a "TL062" chip.
1979 pot with code dating on the side.
Volume, treble and bass pots are code dated on all pre-amps 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 may, or may not, identify the date of the pre-amp. As Music Man purchased them in large quantities, it's not unusual to find pots that are one to two years older than the pre-amp itself.
1976 to early 1977 (Black Epoxy)
From 1976 to early 1977 a red/orange coloured capacitor is located on the treble pot rather than being included on the circuit board itself.
Pre-amps 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 pre-amps boards.
Schematic pre-amp wiring for 1976 and early 1977 Basses.
1977 to 1978 inclusive (Black Epoxy)
There appears to be three types of pre-amps used during this period.
Pics courtesy of David.
Type 1 schematic.
Normally, pre-amps are attached to the pots (at each end of the board), with
material similar to that used for the string mute pads. In the above picture,
the webmaster has rebuilt the control plate. In order to mount the pre-amp
board, a whole piece of computer mouse pad material has been used.
Type 2 schematic. Note that the leadout 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 leadout 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 schematic. Note that the leadout 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.
1979 onwards (Epoxy Deleted)
1979 pre-amp. (Pics courtesy of "freedok"). Note the red and blue
coloured Tantalum capacitors. Green and maroon Tantalums
were often used aswell. On latter pre-amps, Electrolytic
capacitors become standard.
From 1979 to the end of the Pre-EB period, the epoxy coating was deleted. The IC chip was 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 pre-amp wiring for Basses from 1979 to 1984 (end of Pre-EB period).
Although the epoxy is now deleted, note that the colour coding of the lead-out wires is the same as for the Type 3 pre-amp used during the 1977-1978 period above. Because of this, it's presumed that the 1979 non-epoxy pre-amp is the same. The same colour coding is found on Ernie Ball 2 Band EQ pre-amps from 1984 up to circa 1990. There after, the Ernie Ball 2 Band EQ pre-amp board changed from rectangular to a crescent moon shape but the circuit remains the same.
Circa late 1979 or early 1980
At left is the non-switchable jack first used on Pre-EB preamps.
The jack (right), introduced late 1979 (early 1980),
disconnects the battery when the guitar
lead 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.
Circa late 1981 or early 1982
"LM4250CN" chip (left), Electrolytic capacitor (centre)
and a Tantalum capacitor (right).
Electrolytic (as opposed to Tantalum) capacitors appear on non-epoxied pre-amps from circa late 1981 (or early 1982) onwards. Audiophiles would argue that the electrolytic has a more mellow and pleasing tone to the ear.
A 1983 pre-amp with Electrolytic capacitors.
1982 to end of the Pre-EB period (1984)
1982 schematic reproduced with permission.
The IC chip can be damaged should the guitar lead become short-circuited. In circa 1982, the addition of an out-board 1K ohm protection resistor was recommended to save the IC chip from destruction.
As the Cutlass 1 Sting Ray Bass was introduced in 1983, it features the 1983 pre-amp with electrolytic capacitors (pic above) and the protection resistor modification (schematic directly above).
At the beginning of the Ernie Ball period the resistor remained an out-board addition. From circa 1988, it was included on the circuit board.
An Ernie Ball replacement pre-amp for Pre-EB and Ernie Ball Sting Rays up to
circa 1990 (there-after the board changes to a crescent moon shape).
The protection resistor has been included on the circuit board.
EB STING RAY 4 (1984 - Current)
Pre-EB pickups (above) varied individually due to winding techniques adopted at that time. Ernie Ball automated the windings to make the pickups a more consistent product.
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.
As with the second version of the Pre-EB pickup from early 1978 onwards (above), pole pieces measure 5/8 inch in length with a diameter of 3/8 inch. Likewise, 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 Orange and 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 is unknown
if 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.
SR4 Pickup with rounded-edge Alnico pole pieces. Introduced mid 2003.
In all other respects the pickup remains the same. (Picture "Davtran").
2005 Sting Ray with dual Humbucker pickups (Picture "Steve Dude Barr").
Close-up view of the dual Humbuckers. (Picture "hmagman").
The new dual pickup Sting Ray Basses were introduced at the July 2005 NAMM Show. Pole pieces remain Alnico with rounded edges. However, the black plastic pickup covers differs slightly to that of the standard Sting Ray and is similar to the pickup outline featured on the Bongo Bass.
As well as two Humbuckers (HH) above, the Sting Ray is also available with one Humbucker plus a Single coil pickup (HS). Both are offered with 3 band pre-amps only (no 2 band).
The Ernie Ball 2 Band EQ pre-amps (to current date) are the same circuit as the Pre-EB non-epoxy pre-amp introduced in 1979 (which the author believes to be the same circuit as used for the previous type 3 black epoxy 1978 pre-amp referred to above). However, a Pre-EB out-board protection resistor modification was introduced circa 1982. In 1984, EB included this outboard modification but in circa 1988, the resistor was relocated to the circuit board itself. Although the Pre-EB pre-amps use a 25K audio (log) taper pot for the volume control, this taper tends to bunch the volume control adjustment to the upper limit of the pot rotation. The Ernie Ball 2 Band EQ pre-amps corrects this by using a 25K linear tapered volume pot to allow for a smoother adjustment throughout the pot rotation. The treble and bass pot values (and tapers) remain the same as the Pre-EB preamps (1Meg reverse audio (log) for the treble control and 100K audio (log) for the bass control).
Wiring of the pre-amp board to the pots, pickup and jack remains the same as the Pre-EB non-epoxy pre-amp introduced in 1979. The sequence of lead-outs from the pre-amp board also remains the same.
The board changed from rectangular to crescent moon shape in circa 1990 but the circuit remains electrically the same.
1985 to circa 1988 (2 band)
A 1985 pre-amp. A protection resistor has been added as per the 1982 Pre-EB
schematic (pictured previously) and is located within the plastic sleeving to
the right. Note that, from the beginning of the EB period (1984), the
IC socket is now deleted and the chip is soldered directly
onto the circuit board. Preamps were dated with a black
marker pen on the rear of the control plate.
Circa 1988 to circa 1990 (2 band)
Pre-amp as found from circa 1988 to circa 1990. The protection resistor is
now relocated on the circuit board. 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.
The EB replacement pre-amp for Pre-EB and EB Sting Rays up to circa 1990.
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 pre-amps
up to circa 1990. Although lead-out colours may be different, the
hookup wiring sequences are the same,
To this point, pots have been of the "lug" type (above left). From circa 1990,
direct mount pots (above centre) have been used exclusively for 2 band
pre-amps 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 pre-amps by bending and cutting the
pins (above right).
Circa 1990-Sept 2009 (2 band)
From circa 1990, the 2 band pre-amp circuit board changed from rectangular to
crescent moon shape. 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 pre-amps.
Reproduced with permission. Schematic wiring for 2 band pre-amps from
circa 1990 to Sept 2009.
Sept 2009- Current (2 band)
For comparison. The previous version 2EQ pre-amp as found on the SR4.
Above two pics of the newer 2EQ pre-amp introduced in September 2009.
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.
A protection diode is added to the board to
prevent pre-amp damage should the
battery be connected in reverse.
(Pics courtesy of Mike).
Circa 1987 to circa 1990 (3 band)
Although the 2 band is still available at current date, Ernie Ball introduced the
optional 3 band pre-amp in 1987. (Picture from a 1989 Sting Ray Bass). 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. Also
note that the pre-amps are dated with a round sticker on rear of a control
pot from circa 1988 onwards. From 1987 to early 1988 the preamps
were dated with a black marker pen on the rear of the control plate.
The 3 band uses a TL062 chip rather than the 4250CN used with
the 2 band preamp.
Reproduced with permission. Schematic wiring for 3 band
pre-amps from circa 1987 up to circa 1990.
Circa 1990-October 2006 (3 band)
From circa 1990, the 3 band pre-amp circuit board changed from rectangular to
crescent moon shape. Note that the two outer lug pots are replaced with
direct mount pots to match the two centre pots that solder direct
to the circuit board with pins. The circuit remains the
same as the earlier 3 band pre-amp.
Reproduced with permission. Schematic wiring for 3 band pre-amps
from circa 1990 to Oct 2006.
October 2006-Current (3 band).
For comparison. The previous version 3EQ pre-amp as found on the SR4.
Above two pics of the newer 3EQ pre-amp introduced in Oct 2006.
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.