Author Topic: EHX - Holly Grail - Reverb high cut mod  (Read 436 times)

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ilcaccillo

EHX - Holly Grail - Reverb high cut mod
« on: October 03, 2017, 04:54:50 PM »
Hello,
I have the Electro Harmonix Holly Grail pedal with the Cirrus Logic CS4811 Chip.

I really like the reverb sounds you can achieve with this pedal but sometimes I need to have less high end on the reverb effect.

Could you please advise me on how I could mod the modify the circuit to implement a Pot to reduce the High Frequencies on the reverb, a tone/high cut controlled by a potentiometer that doesn't affect the dry signal.

the schematic of the Holly Grain is available on the music-electronics forum, you can find it on this link:

http://music-electronics-forum.com/attachments/37790d1455470424-ec-0060-holy-grail.pdf

Thank you so much
« Last Edit: October 03, 2017, 04:57:13 PM by ilcaccillo »

Digital Larry

Re: EHX - Holly Grail - Reverb high cut mod
« Reply #1 on: October 03, 2017, 06:55:40 PM »
Increase the caps C25, C26, C28, C30 proportionally.  As designed it says the fc is 12.5 kHz.  If you doubled those cap values it would go to 6.25 kHz.  At least, I think that should work.

Oh sorry you want a pot control.
« Last Edit: October 03, 2017, 07:05:00 PM by Digital Larry »
Digital Larry
Holy City Audio - home of SpinCAD Designer
http://www.holycityaudio.com

ilcaccillo

Re: EHX - Holly Grail - Reverb high cut mod
« Reply #2 on: October 04, 2017, 06:51:04 PM »
Hi Digital Larry, thank you so much for your reply.

Yes I need to have it on a POT so I could easily dial the amount of high frequency cut.
Probably a simple filter would do the trick

Something that could be implemented on the output of U5 (Pin7) has that seems to be the WET Signal's output

 


Digital Larry

Re: EHX - Holly Grail - Reverb high cut mod
« Reply #3 on: October 04, 2017, 08:52:25 PM »
Break the line from the wet side filter op amp output to the blend control pot.

Insert a series resistor, that when connected to a cap shunted to ground, gives you the darkest tone you'd ever want (taken from the junction of the resistor and cap to the freed leg of the blend pot).  You're going to want this new resistor to be quite a bit smaller than the blend pot to minimize the voltage drop, say 2.7k or so.

After you choose the cap (the other side should go to ground for auditioning), then put a pot between the other lead of the cap (that had been grounded) and ground.  Then you're going to need to figure out the value and taper that work best for you.  When the new pot is all the way down you will get max loading effect from the cap.  When it is all the way up you will get minimum loading effect from the cap.  I would try a 25k pot for starters.
Digital Larry
Holy City Audio - home of SpinCAD Designer
http://www.holycityaudio.com

ilcaccillo

Re: EHX - Holly Grail - Reverb high cut mod
« Reply #4 on: October 05, 2017, 09:47:47 AM »
Thank you Larry, gonna try that and let you know

ilcaccillo

Re: EHX - Holly Grail - Reverb high cut mod
« Reply #5 on: October 07, 2017, 11:47:00 PM »
Larry,
I tried doing what you suggested but maybe I didn't understand the way the components were connects.

Do you think you could do a small drawing of it , could be hand drawn and take a picture?

Thank you so much

Digital Larry

Re: EHX - Holly Grail - Reverb high cut mod
« Reply #6 on: October 08, 2017, 12:16:18 PM »
This is what I meant.  And I am really sorry about the ads that pop up on that page.

« Last Edit: October 08, 2017, 01:44:54 PM by Digital Larry »
Digital Larry
Holy City Audio - home of SpinCAD Designer
http://www.holycityaudio.com

Ice-9

Re: EHX - Holly Grail - Reverb high cut mod
« Reply #7 on: October 08, 2017, 03:59:09 PM »
+1 Exactly this.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !
Do me a lemon, that a poor IQ for a glass of water.

ilcaccillo

Re: EHX - Holly Grail - Reverb high cut mod
« Reply #8 on: October 10, 2017, 09:40:29 PM »
Hi,
thank you so much for the work Digital Larry, I will implement that.