EHX Holy Grail 8-modes mod

Unlock 5 hidden modes on your Electro Harmonix Holy Grail Reverb

May 13, 2020

The EHX Holy Grail, a personal favourite, holds a little secret. The stock version offers you three modes: Spring, Hall and Flerb. However, the chip inside the pedal can give you more ambient goodness, 8 modes in total! Even better, it’s fairly easy to unlock the extra modes.


Let’s check it out: The 8-modes mod!



First of all, this is how it works:

Three of the pins from the chip are responsible for mode selection. Each pin can be high or low. High means you feed it some voltage, something around 5V, low means it’s tied to ground. In the stock pedal, only two of the pins are used for the three modes you get. The third pin is always high.


Now you can easily unlock the extra modes by following these steps:

  • Open up the pedal and remove the guts so you can work on the circuit board.
  • Take a look at the circuit board. The yellow wire connects pin 41 from the chip to the mode selector (through R11), the orange wire does the same for pin 40 (through R12).
  • The blue wire was added later. With this wire you can tie pin 37, which is responsible for the hidden modes, to ground. You can easily add a wire since Electro Harmonix already provided the pcb with a solder pad for some reason.
  • Disconnect the wires from the switch. The brown wire goes to ground, the othe two are the wires to the circuit board.
  • All three pins are high now, which is the stock ‘Hall’ mode. You can pull one, two or three pins low by tying them to ground.
  • Discover all eight modes, like described below (1 is high, 0 is low):


ORANGE

YELLOW

BLUE

Spring

1

0

1

Hall

1

1

1

Flerb

0

1

1

Short Spring

1

0

0

Room

1

1

0

Ghost

0

1

0

Dark Room

0

0

1

Bathroom

0

0

0







I’ll leave it up to you how you implement this in your own stompbox.


If you let me do the mod, I’ll add a 2P4T Rotary switch who works in conjunction with the stock mode selector to give you acces to all eight modes.


There are many ways to do this. You can simply replace the mode selector with three toggle switches if you want to keep it simple. Or if you want to go all the way, you could even add a programmable chip and a little display to scroll through the modes, because why not !?










Have fun modding your pedal!



However, if you’re not confident doing this, there’s always the option to send your pedal in to let Sonic Fields perform the 8-modes mod!







Thanks for reading. If you have any suggestions to improve this blogpost, please let me know.


Erik


CONTACT US

Rerum Novarumlaan 140

2170 Merksem, Belgium

Phone: +32 484 27 43 00

Shipping

Warranty

Terms & Conditions

Contact

FOLLOW US

© Copyright. All Rights Reserved.

www.sonicfields.be - BE 0700.286.352