I got an Electro Harmonix Holy Grail as my first reverb pedal and fell in love… the twangy Spring reverb setting, the huge spacious Hall setting and the weird Flerb (a flange that effects the reverb tails) setting introduced me to a new world of reverb I had never had before. I own several reverb pedals now and is a big part of my playing. But the simple one-knobber had three settings I wanted to play with, and I wished it had presets so I could call up a couple of sounds without having to bend over and change the knobs all of the time. It wasn’t till I came across a post on the diystompboxes forum where a picture of Aron Nelson’s Holy Grail stuck in my mind – a two foot switch, two knobbed Holy Grail with one switch on/off and the other selecting between the two different pot values. This would solve my problem, but I couldn’t buy this exact pedal. Well not until Mr. Nelson revealed how to do it :)

So I set to the pedal with a soldering iron, a switch and a pot and and after awhile had the same Holy Grail as you see pictured. This one is Josh’s from Sydney band Pockets.
After doing a few more, I came up with my own modifications and offer them to you.

cubisteffects have the following modifications for the Electro Harmonix Holy Grail.

TRUE BYPASS (older models) and DC JACK MOD

Some of the older versions of the Holy Grail do not have true bypass. I can mod these versions for TB with a 3PDT switch. Your clean signal passes through the switch alone, not the circuit, preserving your clean tone.

I also can change the 1/8″ DC jack for the industry standard “BOSS style” jack. This makes daisy chaining pedals easier and BOSS style power adaptors are more readily available. This mod can be done with most Electro Harmonix pedals.


The bypass footswitch is relocated to the bottom of the pedal, alongside the secondary Preset Select switch. When selected, the LED will light up indicating the setting for Knob 1. When pressed again, the LED will be off indicating the setting for Knob 2. This is very useful for calling up a small amount of reverb (that can be left on if your amp does not have it) and pressed again for a very wet signal. Two Holy Grails for the price of one!


The secondary footswitch can also be wired to select between the different reverb settings of the Holy Grail: Spring, Hall and Flerb. This mod does not require two knobs. After setting the knob at the desired value, the switch can select between Spring and Hall, Hall and Flerb etc. I found this useful for bringing the Flerb onto the pedal board, while still being able to use the more traditional reverb sounds.

BOOST MOD (older models)

The older versions of the Holy Grail lose a significant amount of volume when close to 100% wet. This makes turning up the reverb not an option, hence limiting the range of the pedal. By retrofitting a small clean boost circuit post-effect, the reverb signal is boosted and can be set to unity or louder. A small knob is placed beside the main knob and can be set at any time. This is not required in the newer versions of the Holy Grail.

Below is a video demo of the cubisteffects modded Electro Harmonix Holy Grail Reverb.
Clip Details: Fender Stratocaster> Devi Ever Soda Meiser Fuzz> cubisteffects modded Holy Grail > Boss RC-50 > Marshall JCM600
Settings: Twin Preset modded Holy Grail swaps between Preset 1 (12 o’clock) and Preset 2 (3 o’clock).
Recording: SM57 > Mbox2 > Reaper


Related Posts with Thumbnails


  1. Danny says:

    can you do holy grail plus mods?

  2. cubisteffects says:

    Probably not. The new XO line have a large PCB so fitting in new switches and pots are unlikely.
    I’ll have to have a look inside to be sure though.

  3. Scott says:

    Noticed your mod of this on your facebook page had an extra knob at the top right. What is it for?

  4. cubisteffects says:

    The extra knob was for an extra boost stage to use the pedal as an overdrive or boost the wet signal past unity gain.

  5. Curtis says:

    Can you mod a holy grail nano to have twin presets?

  6. cubisteffects says:

    Theoretically it is possible, but practically there is no room to fit the required hardware in there.

Leave a Reply