Holly Grail Reverb - High Cut Mod

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Whoops

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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

 

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Hi Whoops,      The Blend input is fed from U3 pin 7 (Direct from input) and looks like the output of U5 pin 7 (reverb output) .    The output of U5 pin 7 would be the logical place to roll-off the hi freq in an analog path.  It could be a simple tone control or active EQ.    Try with a simple tone control like whats found on a EMG pickup tone control.  25K with .022uf or .05 uf.  Would be where I would start.
 
fazer said:
Hi Whoops,      The Blend input is fed from U3 pin 7 (Direct from input) and looks like the output of U5 pin 7 (reverb output) .    The output of U5 pin 7 would be the logical place to roll-off the hi freq in an analog path.  It could be a simple tone control or active EQ.    Try with a simple tone control like whats found on a EMG pickup tone control.  25K with .022uf or .05 uf.  Would be where I would start.

Thank you so much Fazer, so the 25K would be a pot?
should I go with a linear or log pot for this porpuse?

Thank you
 
Log would seem to have more granule response but either should work.  If you have a bread board you can play with values  while jumpers go to pedal circuit.  The cap value can then be plugged into circuit bread board to check for were you want rolloff by ear. 
 
fazer said:
Hi Whoops,      The Blend input is fed from U3 pin 7 (Direct from input) and looks like the output of U5 pin 7 (reverb output) .    The output of U5 pin 7 would be the logical place to roll-off the hi freq in an analog path.  It could be a simple tone control or active EQ.    Try with a simple tone control like whats found on a EMG pickup tone control.  25K with .022uf or .05 uf.  Would be where I would start.
The standard arrangement of treble bleed found on guitars wouldn't work here, because the output impedance of U5 is just about zero. You need to increase the impedance somewhat. See attachment .
The problem is that P1 defines the load there as 25k. If you add a 25k pot for treble control, you lose 6dB, which you may not like. I would suggest you use a lower value, such as 10k.
The suggested value of 50nF may be a tad extreme, you need to adjust to your taste.
 

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I was thinking more like an EMG guitar pickup which is active like this.
 

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Abby's method is more like a tone control in an amp.  If your worried about load add a 100 ohm in series with the .022 cap. Also my way requires a parallel circuit so you don't have to lift anything just add wire clips to the blend pot end from u5.  I think in this config there is no drop in level with a 25 k pot except at the turnover frequency set by cap and tone pot.  Again it's an EMG pickup tone volume.  Adjust cap to .01 .02 .05.  See what works best
 
I see what Abby is talking about.  EMG has 10k output impedance due to a buildout resistor on output hidden inside the pickup.  No such resistor on u5.  I would still try the tone circuit with smaller values of the cap to check rolloff being applied could be adequate for application.  If you do Abby's design you need to lift the input from blend pot from circuit to apply new 10k pot in series with blend pot.  Will be more messy to circuit but doable depending on solder/mechanical skills.
 
fazer said:
I see what Abby is talking about.  EMG has 10k output impedance due to a buildout resistor on output hidden inside the pickup.  No such resistor on u5.  I would still try the tone circuit with smaller values of the cap to check rolloff being applied could be adequate for application. 
You may try as much as you want but it won't work. All you may succeed is overloading the output of the opamp and get nasty distortion.
 
Your right Abby .  It's a direct short at high frequency to u5 .  the 10k build out is provided by Abby's method.  Just be careful lifting the blend control input leg from u5 PCB connection to add.  And use 10k not 25k . It also is an easy pot to find.
 
Hi Abbey and Fazer,
I can use an active filter no worries, let's move on from the passive idea, thank you pointing that out.

What would you advise as an active filter for this purpose?

thank you
 
Go to a graphic reverb plugin program and rolloff or dampen the high frequency.  What kind of a curve is that.  Emulate that curve.  My vote is 6db high shelf to start.
That by the way is a passive shelf 1st order.  But can be active .  Opamp cookbook has circuits. You need to disrupt u5 path to blend.  Insert filter..  try the passive circuit Abby posted.  If you like it use it.
 
Hey Whoops have you used Relab VSR verb plugin.  That is the best I've heard.  I know you mix/engineer a lot .  Wondered what you thought about it. Sorry im disrupting the thread.
 
Sorry Abbey, I didn't understand if the circuit you posted is supposed to be a workaround of Fazer first advices or if it's the actual way you would advice to do this.

If you wanted to this on your own pedal, what would you do?

I prefer not to have any gain loss
 
fazer said:
Hey Whoops have you used Relab VSR verb plugin.  That is the best I've heard.  I know you mix/engineer a lot .  Wondered what you thought about it. Sorry im disrupting the thread.

No worries, I never used or tried the Relab VSR.
I have the Relab LX480 and I really like it.
I used to have a Lexicon 480 in the old studio I worked, and I liked it but I can't say I miss it after having the Relab XL480.

Saying this I'm not a big reverb guy, and I don't use or find the need of a lot of reverb. I think I probably use more room mics and short delays than reverb.
I like spring reverbs, cheap SPX90 stuff, and I love EMT 140 and EMT 240 plates.

I was never into the TC system 6000 type reverbs, the Bricasti or even Lexicon. I think they're great it's just that it's not my thing or that it doesn't fit in the type of music I work with.

Plugin wise I like the Altiverb, and that fits most of my needs, I just use the stock IR files and alter to my own taste.
Probably there's some better stuff, but Altiverb just works for me.

The only thing I really miss are the EMT plates I used to have in the studio I worked before I got freelance.

You can check below some mixes I did that I didn't use any reverb during mixing, there might be some reverb used when we recorded on instruments like spring from guitar amp or and FX pedal in a keyboard:

https://www.youtube.com/watch?v=U424AdYxt54

https://www.youtube.com/watch?v=ms5Hfjd-2AI

In this one I used reverbs:

https://www.youtube.com/watch?v=uvYA5-_JAmg


 
That's interesting Whoops I'll listen to those tracks in the morning.  I have a saying "Real Engineers don't need reverb."
So I guess your a real engineer.
I have an emt140 tube setting in a storage building.  It's been a lot of years since it's been hooked up.  This one was ok but never blew me away.  There have been some solid state ones I've had that are lovely .  The ones I like have a single sheet for dampening.  This old tube uses multiple sheets  that make up a  4x8  sheet and they have warped.  If I find room for that some day I plan to fix that.  Anyway back to pedals.

U5 feeds top of 10 k audio pot .  Bottom of pot goes to  .01, .02,or .05 uf cap use and choose cap by ear. Centertap of tone goes to blend control.  That's Abby's circuit .  He needs to tell you his fav eq for this application.  Eq will sound different than dampening and high frequency decay time used as a means to control this.  Your just trying to get rid of hi freq masking in my opinion.  So a tone control can do that.
 
Whoops said:
Sorry Abbey, I didn't understand if the circuit you posted is supposed to be a workaround of Fazer first advices or if it's the actual way you would advice to do this.
It's an answer that takes into account simplicity first.

If you wanted to this on your own pedal, what would you do?
For a pedal, yes, considering the constraints in terms of bulk and current draw.

I prefer not to have any gain loss
With the 10k pot, gain loss is minimal (about 2 dB); with 5k, that would be about 1 dB loss.
 
abbey road d enfer said:
It's an answer that takes into account simplicity first.
For a pedal, yes, considering the constraints in terms of bulk and current draw.
With the 10k pot, gain loss is minimal (about 2 dB); with 5k, that would be about 1 dB loss.

Thank you so much,
Will do that
 
Whoops, like your work. Ive been listening this morning.  Nice and organic but jazzy and laid back.  Brave not going to verb syrup on everything.  Nice.

On the pedal I have one more thought.  If you break the connection into the blend pot from U5 pin7 at the pot it becomes an insert point and could be wired to a TRS jack like on a unbalanced mixer insert.  You could then have TRS normal so if your not plug in T and R would connect and pedal is normal.  If you want passive rolloff you plug jack with 10k pot and cap .  If you want an active EQ you plug a TRS Y cord and plug eq or eq pedal in for tone.    Just a thought.
 

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