Pimping the EH Holy Grail

Post by **MarcoMike** » 16 Jun 2012, 11:54

as I said... with no schematic I was just relying on my random memory.... sorry for the misleading info

R40 actually meant pin 37, sorry for that. and I wrote PIO in general because I did not remember the pin number we were referring to, which are in fact 37, 40 and 41. pin 35 is PIO3 which stays low.

so, what i actually meant is:
on the board you can find a solder pad (i think marked as "J"... but you know... bad memory...) for pin 37. the PIO is held high by the usual 10k resistor, so with a switch wired to ground it is possible to unlock the short/long thing.
and if you set both pin 40 and 41 low, you'll get ROOM reverb mode.
it's all already there.

Dirk_Hendrik · Post by **Dirk_Hendrik** » 16 Jun 2012, 13:57

Pin J is the "testpoint" for AudioIn and is in fact the hardwired connection for the true bypass. The grailschem lists all connection points in the circuit. There is none for pin 37. And for those who want to know that schem, it cannot be posted due to copyrights. Some think that posting this circuit diagram will cause EHX a lot of damage.

Fortunately there is diystompboxes where this schem is not so heavily guarded.
http://www.aronnelson.com/gallery/main. ... emId=23376
Thank you Aron!

Post by **MarcoMike** » 16 Jun 2012, 18:38

ahah.... really bad memory indeed....
but the solder pad is there, it's where I wired mine!

take a look at this picture:

right above the orange wire. that is connected to 37.

mozz · Post by **mozz** » 26 Jan 2016, 23:20

Just did this mod, works well. Put 3 toggle switches below the jacks. I don't know the name of the presets but will describe below. Some could be known as hall or stairway or large room or ? They don't seems to match up to the evaluation board listings for either the gtr or mxr version of the chip. Maybe someone else who does this mod can correct these.
000 DELAY + CHORUS + REPEATS
001 DELAY + SHORT REPEATS
010 SPRING + CHORUS + SLIGHT FLANGER
011 SPRING + FLANGER +ERRIE GHOST SOUNDS
100 SPRING HALL
101 SPRING SHORT HALL
110 DELAY WITH REPEATS
111 DELAY WITH SHORT REPEAT

Also put the 9v power supply on a scope and you can see the dirty output wave. Added a 100uf and a 0.1uf across the power jack, cleans it up a bit with no voltage change.