Pimping the EH Holy Grail

A forum devoted to mod, tips and suggestions for upgrading and rehousing your VERY CHEAP commercial stompbox to near boutique excellence.
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BJF
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Post by BJF »

Hi,

Rehousing an EH Holy Grail:

This idea came to me as there are a couple of professional guitarists around here that use the EH Holy Grail
and I got one of those guys pedal bord in for service and his Holy Grail had been serviced 5 times for various mechanical faults and the guy said he'd finally given up on it and must find another reverb pedal.

Hm, well the construction has a couple of weak points that one could address:
Potentiometer holds the pcb.
Power is brought with an AC adapter that leaves unregulated voltage and can at start up break a 47R resistor with it removing power from the reverb circuit.
Input- and output- and DC jacks make the contact to ground but none of those have locking washers and metal sides of the case is a bit to thin to hold the jacks firmly without locking washers.

Now measuring the pcb it would fit into a small hammond box with the regulator and crystal facing the top of the case if pot is removed and connected via wires, which then ofcourse removes the weak point of the pot. I choose an Alps RK-09 and mounted that with a locking washer
and found a tooggle switch that would fit next to the pot and have a height over pedal surface the same as the pot with a knob mounted and finally DC jack replaced with a 2,1 mm Marushin chassis mount jack

The 47R resistor was replaced with a 1N4002 diode giving about the same voltage drop but now protecting against false polarity.

To make all fit input and output and DC jacks were placed near the bottom of the case and the pcb folded in neoprane so it can absorb vibrations and then locking washers on all mechanical parts connecting to case makes the finished unit durable and all parts fixed in position.

To address the heat and possible thermal shutdown a new powersupply of stabilized 9V 300mA was included.
It is possible to power the EH Holy Grail from the Voodoo Labs PP2+ using output 5 or 6 as available current is then about 200mA when set for 9V's-using anyother output shuts down the internal regulator.

About a year later neither of the two units rehoused to go on pedal boards have required any service just a nice reverb.

In fact I rehoused one such EH for my personal use the other day and would say I am happy with the sound that gives.

Unfortunately I do not have provisions for taking photoes and posting them but hopefully enough information is supplied in the text for anyone who'd like to try this.

Oh text is always useful just in case one would forget which selctor position is what and since it's an EH might aswell put rehoused EH Holy Grail on the case to save people from asking what it is

Have fun
BJ

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gtrwrks
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Post by gtrwrks »

Sounds like nice work, B. I play thru a mid-60's Bassman and would love some 'verb - and have looked at this pedal, but it seemed so cheaply made I didn't want to mess with it. I might try your modification/rehouse.

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Post by ~arph »

BJF wrote: Unfortunately I do not have provisions for taking photoes and posting them but hopefully enough information is supplied in the text for anyone who'd like to try this.
:( You know what we people are like

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Post by CaptainKirk »

Hi BJF,

I realise this thread is now a good 5 years old, but I hope you'll still see my message. I recently picked up a used and malfunctioning Holy Grail hoping I can fix it. I'd just like to ask, what do you mean by "47R resistor". Which resistor is this? Thank you!

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Post by CaptainKirk »

I'm thinking you might be referring to R1, the large 2W resistor. In my Holy Grail, though, R1 is a 2ohm resistor, which appears to be stock. I live in Japan, though, and my pedal was made specifically for Japanese export. Japan uses 100V power as opposes to 110V in the US or 220 (or is it 240?) in the UK.

Thanks - K

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Post by Dirk_Hendrik »

R1 i a 4.7 ohm in my book. It's the resistor going from the DC input + to the input of the 7805 voltage regulator. It can be a big SMT type or a through hole type. The SMT one is in the earlier grails but tended to desolder itself due to heating up too much.
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Post by BJF »

Hi

5 years later I actually came for a visit ;) Too little time these days I am afraid

Anyway yes that is correct the R1 and I also have one that has an SMD 4R7 resistor.
I believe the ones I reboxed had the through hole resistor and most likely came from same batch since they were all local.

Yes the point is anyway that this resistor may act as a fuse. It felt however safer to use a rectifier diode since many of the guys that use these have complicated pedal boards and sometimes forget which DC wire goes were when they change pedals on their boards.

The Holy Grails in Sweden came with their own adaptor one that left about 17V's unloaded as I recall.

You should be able to read the voltage that comes out of the supplied adaptor, given that one was supplied of course.
That would anyway show something between 12V's and 17V's as a rough guess.

Yes it might be so that for Japan that has 100V, 110V adaptors could have been supplied.

It is fully possible to and much more reliable to run DC from a well filtered 9V supply at 200mA to the Holy Grail.

A further side note:

I put for a touring guitarist one such rehoused HG on his board and connected a One Control Blender so HG could run all wet and balance instead be set via the One Control Blender and that cut residual noise by a couple of dB's and increased overload marginal aswell as reduced distortion to direct path.

When rehousing one can consider this and make an extra pcb for direct path and mixing and make that more low noise and run at higher voltage: 9V for the whole thing would work just fine and I might recommend using an NE5532 for simplicity for an input buffer and a mixer amplifier
or why not a lownoise FET transistor for input buffer and and an even lower noise OP amp mixer
perhaps an AD797 or what have you?
A discrete mixer might take up less room and at 3 transistors could be parallelled to lower noise. Again a low noise fet with some gain to make up for the losses in mixing could also be a great choice at little board space.

Those are just some thoughts I might have.

Anyway have fun
BJ
BJF Electronics
Sweden

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Post by CaptainKirk »

Great! Thanks for all the feedback everyone.

A bit confused: by what you are all telling me and from what I've seen on other discussions, it seems EHX has been using a range of resistors at R1. Mine is very clearly a 2ohm resistor (colour code: red-black-gold), as you can see in the attached pic
DSC07886.JPG
.

Basically the problem is that only sometimes the pedal malfunctions. When turned on, if the "reverb" pot is turned fully counterclockwise (i.e. no reverb in the blend), sound passes through, but as the pot is turned clockwise, the volume decreases and no reverb is applied. It also makes a scratchy sound. At first I thought the problem might be a faulty pot, but from what I've read on a few forums, this might also be due to a voltage leak (?). Other times, the pedal works just fine, even immediately after testing it and havving it malfunction. Ghost in the machine? lol

I like your suggestion, BJF, to change replace R1 with a diode; this might solve the problem.

On a side note, how is EHX charging some $300 for such a flimsy, weakly-constructed pedal? Not only that, the chassis on this particular box was cut unevenly so it does not sit sturdily but rather wobbles on the floor. Unbelieveable.

Any advice or suggestions would be much appreciated. Thank you!

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Post by CaptainKirk »

By the way, I should add that my adaptor is the an EHX adaptor, 100V input (designed for use in Japan) and 9V DC 500mA output. I checked and I am getting about 14V DC coming into the box.

Would truly appreciate any advice or tips on what the problem might be and how I can fix it. It's either a voltage leak issue or a faulty pot, I think. Cheers.

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Post by CaptainKirk »

Dear BJF,

You wrote, "It is fully possible to and much more reliable to run DC from a well filtered 9V supply at 200mA to the Holy Grail".

Could you recommend a well-filtered 9V supply? I.e. brand name/model. Or, please tell me how one determines what is a well-filtered 9V supply.

Do you think voltage leak might be causing the problem (as I described above)? Hard to know without seeing it, I know, but...

Thanks a lot. - CK

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Post by Dirk_Hendrik »

I thought this thread was about pimping!? Let's pimp it for real!
With the slide switch either pin 40 or pin 41 of the CS4811 can be pulled low. In the middle position both stay high. One can measure this state on R11 and R12. One side of these is connected to 5 volts, the other to the forementioned pins and the switch.

- Now locate R13, determine which side goes to +5 volts and which one to the CS4811, pin 37.
- Connect a wire to the side of the resistor that goes to pin 37.
- Connect the other side to ground... and see what happens to the effect.

And after that,
with the 3 wires, the new one and the 2 that went to the switch (not the one from the switch to ground), 8 combinations of grounding or not grounding can be made with 8 different reverb/flange/trem-like algorithms as result. Instead of the only 3 offered on the stock grail.

That's pimping.
Sorry. Plain out of planes.

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Post by Seiche »

CaptainKirk wrote:how is EHX charging some $300 for such a flimsy, weakly-constructed pedal?
wat? :scratch:
they're like a hundred bucks? And it's reverb. Don't see much competition in that sector.

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Post by CaptainKirk »

Nah, you're thinking of the Nano. Pretty sure the regular Holy Grail was listed for something between $200 and $300 new. At least it was in Japan where I live.

Anyway, if anyone has any helpful responses to my questions I'd be grateful. Sorry, perhaps this is not the appropriate thread given that this is about "pimping" the HG rather than straight-up repairing it.

Thanks!

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Post by Seiche »

that's what I found. Maybe it's because of Japan. Many things from the US or UK are really expensive here too.

Anyway, If I could choose, I'd definitely get the nano now after reading this thread :) Seems much sturdier and better made.

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Post by BJF »

CaptainKirk wrote:Dear BJF,

You wrote, "It is fully possible to and much more reliable to run DC from a well filtered 9V supply at 200mA to the Holy Grail".

Could you recommend a well-filtered 9V supply? I.e. brand name/model. Or, please tell me how one determines what is a well-filtered 9V supply.

Do you think voltage leak might be causing the problem (as I described above)? Hard to know without seeing it, I know, but...

Thanks a lot. - CK
Dear Captain Kirk,

I would define a well filtered supply, and specifically for this, one that leaves 9V also unloaded and that has a humlevel less than 10mV.
This could include nearly any supply that has a voltage regulator IC.
Specifally for use with guitar pedals, I would say I have used the Voodoo Labs PP2+ for years, while some 20 years ago I used various Mascot Supplies.
Modtone makes a powersupply at a nice price, likely the lowest I have seen, whereas Decibel 11 today likely makes the one with lowest magnetic field or radiation.
Perhaps you can find a wallwart that has a voltage regulator at one of those stores that sell electronic surplus.

About pimping, one could modify a shoe to have an aquarium and a goldfish, which might be fun or make a heavier sole.

Thank you Dirk Hendrick for pointing out all these possibilities I would not have known, that's really cool if you have use for it!

The Holy Grail actually makes a great reverb sound and is one of the better sounding units one can buy imo, but the mechanics could use some pimping and actually on my personal unit I thought less would be more and so I removed the 'flerb' since I had no use for it.

Speaking of competition in the price range, the Modetone Colisseum is a great sounding reverb aswell.

The Nano does not sound as good as the Holy Grail imo and yes I had really hoped it would. However EH push the development most often and make more and different often under the same name as an allready existing EH model. Oh yes I was very happy to see the Small Clone in reissue my favourite from the 80's however it did not sound the same as the old units.

I think the Holy Grails were such good reverbs that they'd deserve some better mechanics et.c.

I would then also remember the 70's when people would throw away their Big Muff's et.c if they broke down mecahnically and just get a new one.

Have fun
BJ

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Post by CaptainKirk »

Thanks BJF,

I picked up a 1N4003 diode today. I know you recommended the 1N4002, but my tiny local shop didn't have it in stock and I think the 4003 will do the job. Going to replace R1 with this, see if that corrects the problem of my pedal suddenly cutting out due to possible voltage leak.

I'm also going to change the 9V input to accommodate a Boss power supply (100 V [Japan] 200mA). I was hoping the Boss power supply might be one of the ones you would recommened, but no such luck! :( Anyway, I'll try the Boss power supply first and then decide whether it's necessary to upgrade to a better one.

Apologies to anyone in the thread who might find my comments or questions trifling and amateur. Indeed, I am an amateur electronics enthusiast, learning all the while. No pimping for me just yet! lol But hey, I did just rebuild a broken 1980s Roland Bolt-30 tube amp, and after a year or so of learning how to do it on my own, it works beautifully! Thank you all for your patience and helpful advice/suggestions.

Have a great day!

CK

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Post by MarcoMike »

Dirk_Hendrik wrote:I thought this thread was about pimping!? Let's pimp it for real!
With the slide switch either pin 40 or pin 41 of the CS4811 can be pulled low. In the middle position both stay high. One can measure this state on R11 and R12. One side of these is connected to 5 volts, the other to the forementioned pins and the switch.

- Now locate R13, determine which side goes to +5 volts and which one to the CS4811, pin 37.
- Connect a wire to the side of the resistor that goes to pin 37.
- Connect the other side to ground... and see what happens to the effect.

And after that,
with the 3 wires, the new one and the 2 that went to the switch (not the one from the switch to ground), 8 combinations of grounding or not grounding can be made with 8 different reverb/flange/trem-like algorithms as result. Instead of the only 3 offered on the stock grail.

That's pimping.
actually the holy grail already provides the solder pad for R40, iirc, the one allowing for short/long reverb. plus, you can also unlock ROOM mode by pulling the other two PIO low (the ones which already go to the slide switch). on my HG I unlocked these modes just by a DPDT on-off-on switch (missing short mode on room, but no big deal)
more info in case anyone is interested, here I have no reference schematic and I can only give sloppy details.

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Post by CaptainKirk »

BJF, thanks for the repair advice. The diode in place of R1 did the trick and the pedal works fine. I did also replace the power supply jack so that I can use a more standard plug. My Boss 100 V 200mA seems to work fine, too.

Cheers - CK

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Post by CaptainKirk »

MarcoMike, a little confused about terminology. Please explain if you would be so kind:

1. "R40" sounds like you are referring to a resistor, but in fact you are referring to pin 40 of the CS4811, right?
2. What is "PI0"?

Thanks - CK

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Post by Dirk_Hendrik »

There's 4 PIO pins, PIO0 upto PIO3. The 8 different algorithms can be selected by the binary combination of making PIO0 upto PIO2 either high or low.
PIO0: pin 41
PIO1: pin 40
PIO2: Pin 37

I fail to see a resistor R40. I guess marco refers to pin 40. Odd since the unlocking part is based on changing the high or low level of pin 37.

The PIO3 pin is standard low. Making it high does not change anything. The CS4811 datasheet is too limited to be able to determine what it does but the evaluation board schematic utilizes it as a control pin for the output mute.

Cirrus 4811 datasheet and evaluation board documentation is available through google.
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