CIRCUITS FOR SELECTING
BETWEEN SERIES OR PARALLEL OPERATION
OF GUITAR PICKUPS

Guitar Pickup Circuits

Switching circuits for guitar pickups have purposes that are different from those for switching loads. The purposes are:

1. Providing signal to a guitar amplifier.
2. Making sure the line to the amplifier is never open.
3. If a pickup is to be muted, disconnect it or short it out.

Here is a list of the constraints guitar pickups impose on the design:

• Guitar Pickups
  1. The pickup polarity must not be reversed (unless this is desired for an effect).
  2. The ground end of the pickup must not be open when the live end is connected to the amp (causes hum).
  3. The pickup shield and core must have a separate lead. It must not be tied to a pickup lead.
  4. The pickup shield and core must be connected to the ground of the output jack.
  5. The live lead of the amp must never be left open (causes hum).
  6. Shorting switches should be used.
• Volume and Tone Controls
  1. Tone controls are a network of a variable resistor and a capacitor connected in series.
  2. An individual pickup tone network is connected across the pickup itself to load it at high frequencies.
  3. An output tone network is connected across the output volume control input to load it at high frequencies.
  4. An output volume control is inserted just before the output jack in the normal way a volume control is inserted in a circuit.
  5. An individual pickup volume control is inserted backwards, with the pickup connected to the slider and the ground side. See the SP-PIC 2 and SP-PIC 3 diagrams below.
  6. Tone controls are inserted before volume controls.
  7. Shorting switches should be used.

The SEPAR circuit numbers used here have been used by the page author for years to catalog the various circuits.

The SP-STD circuit numbers are new designations by the page author for new circuits.

The following variations are permitted when guitar pickups are used in series-parallel switching circuits.

• The output may be shorted out by some switch positions and during switch movements.

Note that, to conserve website server storage space and bandwidth, some of the following diagrams show light bulbs instead of guitar pickups because they are the same diagrams used on the lightbulb pages. Let the end of the light bulb with the extra arc showing the screw shell be the ground or negative polarity terminal of the pickup.

Examples:

The Original Series-Parallel Switchbox for Two pickups. This has been used for pickups for a very long time. The center OFF position must be eliminated to prevent hum. The negative side of the pickup is denoted by the screw shell mark on the lamp in the image. Remember that guitar pickups are substituted for the lamps shown in the diagrams. KEY TO TABLE ENTRIES ON   - Connected directly to output      (label this switch position      "PARALLEL") DIM   - In series with other pickups      (label this switch position      "SERIES") PAR   - In parallel with other pickups      (label this switch position      "PARALLEL") SER   - In series with other pickups      (label this switch position      "SERIES") B   - Position for the bridge pickup N   - Position for the neck pickup C   - Position for both pickups off   - Pickup not connected to output −   - Switch position unimportant Letters indicate closed switches. No letter for a switch, or an o for a switch, means the switch is open, or is in the unlabeled position. SP-PIC 2 (Seen on some guitars) SWITCH PICKUP S-P B-N B N SER - SER SER PAR B ON off PAR C PAR PAR PAR N off ON This uses the existing pickup switch (bridge, both, neck) and a double-pole switch for series and parallel. Each pickup is either grounded or in series with a grounded pickup. Note that the pickup switch does not do anything in the series position. It can be preset for the next pickup configuration wanted. This example has individual volume and tone controls that work in series or in parallel. SEPAR 303 (Page author, 1963) SWITCH PICKUP A B 1 2 3 o SER SER SER A B PAR PAR PAR Should be built with one double-pole switch to keep the hot side from having two pickups hanging from it (causes hum). Note that the middle pickup is phase reversed in the series position. The page author has seen this circuit on guitars. The unique sound in the series position is caused by the middle pickup being phase-reversed to the neck and bridge pickups for a special effect.

SEPAR 204 SWITCH PICKUP A B C 1 2 o B SER SER o C off ON A B ON off A C PAR PAR The SEPAR 204 Series-Parallel Switching Circuit can use either pickup alone, both in series, or both in parallel. Do not use SEPAR 203 with guitar pickups. A special version of SEPAR 204 must be used with no center-off position on switch B C). The other switch positions are the same. The hot connections on a pickup are removed if the ground side is opened. Note that any switch position with a letter on it is the position indicated by that letter in the table. Remember that guitar pickups are substituted for the lamps shown in the diagrams.

SP-STD 2 (Built by page author in 2013) SWITCH PICKUP A B 1 2 DIM DIM SER SER DIM ON off ON ON DIM ON off ON ON ON ON This circuit provides all possible combinations except all off. This circuit never removes the negative connection from a pickup except when the pickup is in series, or momentarily while a switch is being thrown. Remember that pickups are substituted for the lamps shown in the diagrams. The mark under each "lamp" in the diagram indicates the negative phase terminal of the pickup. Note that no OFF position is available. Do not include the power switch shown in the diagram (it would cause hum). The pickups always maintain the same phase with this setup. The switch should be labeled with PARALLEL for ON, and SERIES for DIM. SP-STD 3 (Two SP-STD 2 circuits cascaded) SWITCH PICKUP A B C D 1 2 3 DIM DIM DIM DIM SER SER SER DIM DIM DIM ON SER off SER DIM DIM ON DIM SER SER off DIM DIM ON ON SER S-PAR S-PAR DIM ON DIM DIM off SER SER DIM ON DIM ON off off ON DIM ON ON DIM off ON off DIM ON ON ON off PAR PAR ON DIM − − ON off off ON ON DIM DIM PAR P-SER P-SER ON ON DIM ON PAR off PAR ON ON ON DIM PAR PAR off ON ON ON ON PAR PAR PAR This is two SP-STD 2 units cascaded. Remember that pickups are substituted for the lamps shown in the diagram. The extra mark indicates the negative phase lead. The switch should be labeled with PARALLEL for ON, and SERIES for DIM. This setup provides all series and all parallel combinations, plus one parallel-series combination and one series-parallel combination.

SP-PIC 3 This is a circuit that places three pickups in series or parallel with one switch. Each pickup has a volume and tone control. These controls are arranged to affect only the pickup they are connected to. A pickup can be totally removed from the output by turning it all the way down. A master volume control adjusts the overall output level. Phase reverse switches are provided for the neck and mid pickups.

LINKS:

1. SELECTING SERIES OR PARALLEL OPERATION (Main Page)
2. LIGHT BULBS, SPECTRA, and HUMAN VISION
3. Computers, Science, and Measurement