Maybe it can help someone fix their broken Holy Grail.
I recently got a used, older big box Holy Grail (pointer knob, Rev A, non true bypass)
Though advertised as 'in good working order', there was very little reverb.
Only with the reverb knob at around 4 o' clock (close to 100% wet) I could hear a faint reverb signal. At that point the dry signal had lost more than 90% of its volume.
Being familiar with the circuit I knew there could be only 3 possible reasons for this behavior:
- dry signal going into the Crystal CS4811 reverb chip is too low
- wet signal coming out of the Crystal CS4811 reverb chip is too low
- wet signal coming out of the Butterworth filter after the Crystal CS4811 reverb chip (going into the blend circuit) is too low
Luckily I had another big box Holy Grail (hockey puck knob, true bypass Rev C).
After comparing the two pedals and taking voltage readings in appropriate places I quickly found the culprit: a faulty capacitor (C8) at the input of the reverb chip:
I didn't remove the old faulty cap (for now) and simply added a new 10µF electrolytic cap in parallel.
End result: perfectly good working Holy Grail!
There are a lot of broken Holy Grails out there.
Most of them have a burnt R1 resistor or some wire that got loose.
Hopefully the fix above can bring the ones back to life that suffer from very low or no reverb levels.
