Installation guide for the McGrath Tilt EQ preamp (original McGrath Guitars board with three green terminal blocks: P1, P2 and P3). Updated October 2026.
Download the PDF guide (2 pages, includes the wiring diagram).
The board
An active onboard preamp with one panel control: the Tilt knob (bass one way, treble the other, centre is roughly flat), mounted on the board. A Level trimmer on the back of the board is set once during install.
| Terminal (terminal side) | Upper screw | Lower screw |
|---|---|---|
| P1, bottom left | 18V (+) | GND spare |
| P2, right, under the pot | GND spare | INP |
| P3, bottom right | GND → sleeve | OUT |
All GND pins are joined on the board. Run only one ground wire, P3 GND to the jack sleeve. The spare GND screws on P1 and P2 can take the bridge or a jack ground. Never put battery minus on a GND pin.
You'll need
- Tilt EQ board, stereo (TRS) output jack, 9V clip and battery, knob
- Optional: DPDT push-pull pot or toggle for active/passive
- 22–24 AWG hook-up wire (shielded for long signal runs), foam or tape
- 1.5 mm flat-blade screwdriver (Wera 05118003001) for the terminal screws and the Level trimmer
- Soldering iron, strippers, multimeter; a drill if a pot hole is needed (measure the pot bushing)
Power draw
About 4 mA (about 5 mA worst case), mostly the OPA1678 op-amp. Roughly 100–120 hours on a 9V alkaline. It only draws power while a cable is plugged in (and the switch is on active). Figures are from the datasheet, not bench-measured.
Wiring connections
Board seen from the terminal side, Tilt pot at the top. Pad labels (18V, GND, INP, OUT) are printed on the back.
| From | To |
|---|---|
| Pickups and controls (passive signal) | P2 INP |
| P3 OUT | Stereo jack tip (signal out) |
| P3 GND | Stereo jack sleeve (ground): the one ground wire the board needs |
| Pickup and pot grounds | Stereo jack sleeve |
| 9V battery red (+) | P1 18V (+) |
| 9V battery black (–) | Stereo jack ring |
A mono cable joins ring to sleeve when plugged in, which turns the preamp on. Spare GND screws can take bridge or jack grounds.
Step by step
Remove the battery and get access to the control cavity.
- Plan the layout so the board fits behind the Tilt knob position with the terminals reachable.
- Mount the Tilt pot through the panel and tighten the nut. Pad the board with foam or tape so it can't touch metal or rattle.
- Fit a stereo (TRS) output jack in place of a mono one.
- Input: passive signal (volume/blend pot output, or pickup hot) → P2 INP.
- Output: P3 OUT → jack tip (or to the switch, see below).
- Ground: P3 GND → jack sleeve. This is the only ground wire the board needs.
- Other grounds: pickup grounds and pot backs → jack sleeve. Bridge or jack ground → sleeve, or a spare GND screw on P1 or P2.
- Battery + (red) → P1 18V.
- Battery – (black) → jack ring (or the switch). Not to the board.
- Tidy: terminal screws must grip bare wire. Keep input and output wires apart.
18V option: two 9V batteries in series: first + → P1 18V, first – → second +, second – → jack ring. More headroom for hard bass playing. Check that C1 (100 µF tantalum) is rated 25 V or more.
First test and Level setting
- No battery, nothing plugged in: the battery black lead to sleeve should read open. With a mono cable plugged in: about 0 Ω.
- Fit the battery, plug in with the amp low, Tilt at centre.
- Sweep Tilt: one end fattens the lows, the other brightens the highs.
- Start with Level low and raise it until the volume matches passive. Most of the boost is near the end of its travel.
- Dig in on the low strings at full bass. If it distorts, lower Level or use 18V.
Active/passive switch (DPDT)
Pole A picks the signal for the jack tip. Pole B breaks the battery so the preamp is off in passive mode.
| Switch lug | Connects to |
|---|---|
| A common | Jack tip |
| A active | P3 OUT (board output) |
| A passive | Passive signal (same wire as P2 INP) |
| B common | Battery – (black) |
| B active | Jack ring |
| B passive | Nothing |
Ground wiring is unchanged. Check which outer lugs are "active" with a meter first; on a push-pull, the throws swap when the knob is pulled. Switch at low volume.
Troubleshooting
| Symptom | Fix |
|---|---|
| No sound | Stereo jack fitted? Battery – on the ring (or switch B)? |
| Battery dies fast | Battery – must not go to a GND screw. Unplug when done. |
| Hum or buzz | Re-seat P3 GND; make sure all grounds meet at the sleeve. |
| Weak or thin | Raise Level; check the input is on P2 INP. |
| Distorts on low notes | Lower Level, ease off full bass, or run 18V. |
| Crackle moving the knob | Pad the board; tighten the terminal screws. |
Replace the battery when the sound starts to distort or fade.
Questions about your install? Send us a message.