EHX - Holy Stain [schematic]

[Hides-His-Eyes]

That dangling pot must be a mod, right? It's straight pin rather than right angle.

[Ice-9]

That dangling pot must be a mod, right? It's straight pin rather than right angle.

Not so much a mod as a repair, when the pedal arrived I lifted the knobs from the pots for dissasembly but the knobs are amazingly tight fit to the shaft, the shaft actually came out with the knob on that pot and killed it, so i had to solder in another pot, and that was the only types i have.

[putsia]

From what i remember the fuzz circuit alone is well worth tracing. One of the better bright fuzzes for bass I've heard.

[Ice-9]

From what i remember the fuzz circuit alone is well worth tracing. One of the better bright fuzzes for bass I've heard.

I will see if i can trace out the fuzz circuit soon, at the moment i am working on the switching of the digital fx, (its using a 2 bit binary counter)

[Ice-9]

I am trying to find a datasheet for one of the chips responsible for the effect switching and led indicators. I have the binaray up counter traced out along with the led indicators, but i am having trouble identifying the chip around the momentary contact footswitch.
It's an 8 pin chip that has power to pin 8 whilst pin 4 is gnd, pin 3 is the input from the switch and pin 7 is the output to the Flip flop clock. could it just be a dual op amp ? dual nand gate ?

The chip markings are EF921 with a stmicro logo, but i cant find the datasheet on there website or with a google. Doea anyone have a clue to this chip.

[Ice-9]

I have started to do some tracing and have done the FV-1 section of the circuit plus some of the patch change footswitch circuit, I am going to post this as an ongoing update to the schematics as it is going to take some time to complete the entire schematic. So here is the first draft of the fv-1 section. The input and output to the FV-1 has a buffer built around a dual opamp chip, I will try and do the output next and then try and get the fuzz part of the effect drawn up.

[Ice-9]

As i have now made some gut shot pictures and started some preliminary schematics of different sections of the effect i have started a new thread for the reversing of the pedal here for anyone interested.

https://www.freestompboxes.org/viewtopic.php?f=1&t=11926

[Ice-9]

After initially thinking that EH have had a custom version of the FV-1 made, I removed the FV-1 chip from the Holy Stain and replaced it with a standard FV-1 I have in my spares bin, the effects are the same on both chips.

One thing I noticed is that on the tremolo effect the "amount" pot changes the tremolo speed but i also noticed at maximum it is adding reverb. I never noticed this on the original EH chip but I will look out for it when I put back in the original fV-1 chip.

I have nearly completed all the digital and buffer circuitry around the FV-1 with the patch select circuitry. Pretty much all thats left to do is the fuzz section. I will update the schematic when I get a chance.

[Ice-9]

Here is an updated schematic, the only bits that need adding now are the fuzz effect, the 3pdt wiring and the program scroll switch.

[Ice-9]

.
I do believe there is reverb on when using the trem but only at the higher speeds. At the slowest speed on mine there is no reverb but as I increase the amount knob the reverb increases with the trem speed, which is kind of weird.

The tremolo patch on the FV-1 chip has tremolo and reverb, because the holy stain only has the one pot that adjusts the parameters on the FV-1 EH have decided to have it control two of the FV-1 parameters at the same time which is why that patch i working a bit wierd. ie pot at lowest sets tremolo to slowest speed and reverb to off, but pot at max sets tremolo to high speed and maximum reverb.

A second pot could be aded very easily to allow both these parameters to be set independantly.
The other effects would benefit from this mod as well, for example the two reverb patches. one pot controls both reverb time and a HF filter. So with the second pot mod these can be set independantly as well.

The pitch shift will have no effect as there is only one parameter to control on this one.

[Ice-9]

GOOD MOD ALERT

Ok here is a very cool thing that can be done to add these extra effects to the Holy Stain

Flanger
Chorus
pitch with echo

All that is needed is a SPST toggle switch and a bit of wire.

This is all that is needed to modify this :-
Pin 17 is tied to 3.3v as standard, to access the extra effects pin 17 needs to be able to be switched either 3.3v or gnd

1. This can be done by lifting pin 17 of the FV-1 chip from the pcb, to do this heat up the solder on pin 17 and with tweezers or a stanley blade lift the pin until its floating off the pcb contact.
2. you then need to solder a wire to this pin (thin kynar wire is best) The wire is best glued down to the top og the chip or the pcb as we dont want this wire flexing and breaking the pin from the ic.
3. The final bit ! take your spdt toggle switch and solder a wire to each outer terminal. Now solder one end terminal to ground and the other to 3.3v. The centre terminal from the switch goes to the pin 17 wire that was previously soldered and glued down.

So when the toggle switch is in one position the effect select footswitch selects the 4 effects as normal, when the toggle switch is in its other position the effect select footswich will select the other 4 effects.

I will try and do this mod and take a few pictures.

[Ice-9]

Ok here are two pictures of the mod to access the rest of the effects built into the FV-1 chip

EH in there wisdom have only put one potentiometer in the circuit that controls the DSP but the FV-1 chip has three data inputs for pots. Adding two more pots for parameter control is the next mod and very simple to do as well. The unit suffers from only having the one DSP pot.
Also the DSP in this effect has the ability to use an external eeprom which will also be quite a simple mod to make, this would allow many different effects to be programmed into this unit. ie. an auto wah, different overdrives, high quality reverbs, delays etc.

[Ice-9]

To do this extra patch mod you dont actually have to remove the SMD ic, all you need to do is raise one pin from its solder pad and connect it to a wire which in turn goes to the switch.

If more detailed info is required I am happy to go itno more detail.

[drbob1]

Thanks for the work on this, I'm following, interested in the mod to free up the other modes and other controls.

As to the fuzz, just on cursory inspection it appears to be a 2 silicon transistor fuzz with added diode clipping? It has a harsh edge (more in the spitty, early Tonebender vein) in the drive mode, a bit less in the fuzz mode. It does, however, clean up pretty well with the volume knob. The overall drive has only the 3 presets, no gain knob. The volume knob is active after both effects and so has to be adjusted if you change the drive type. The tone knob is active on the clean setting as well, so it can be used for a clean boost with EQ, as a boost with effects and EQ, as a fuzz with or without effects and EQ. Pretty flexible for a cheap pedal...

[Ice-9]

Thanks for the work on this, I'm following, interested in the mod to free up the other modes and other controls.

The post a bit above is the mod to free up the extra modes. With the switch fitted it allows the 4 other patches to be scrolled through with the footswitch.

The extra effects are
chorus/with reverb
Flanger/with reverb
pitch shift/delay
The fourth patch is just a test patch that is built into the chip.....more like a bypass effect.

I have the pictures and details for the 2 extra control pots and will post them when i get a chance to write up the details of the mods.

I won't be reversing the fuzz part of the circuit as I don't really like it and have put the pedal back to standard to sell it.

[culturejam]

I just snagged a Holy Stain for $60 on ebay. I'll definitely be doing the "extra modes" mod.

[Ice-9]

I just snagged a Holy Stain for $60 on ebay. I'll definitely be doing the "extra modes" mod.

If your going to do the extra program mod , please wait until i get a chance to post the extra control pots mod as well as one of them requires another pin lift and wire soldered to it. The reason I mention waiting is that as its good practice to epoxy or hot glue these wires down to stop any flex breaking the IC pin then it makes the job a lot better if there done at the same time. I am putting some pictures and an explanation of the process together in a couple of days once i have finished my own FV-1 project.

[teej212]

im surprised EHX is using an FV-1, in their newer effects they seem to only use custom chips. i guess you can clone some new ehx stuff

and i agree, i never liked the sound of the fuzz from what ive heard on youtube.

[culturejam]

I am putting some pictures and an explanation of the process together in a couple of days once i have finished my own FV-1 project.

Awesome! Can't wait to see the details of the project.

[Ice-9]

First of all sorry about the delay for the last mod I will be doing on this pedal, I would maybe do an external eeprom mod that you can write your own programs to using the spinsemi program code, but I have sold my Holy Stain and not 100% sure of the trace undeneath the FV-1 chip so can't be sure if it would work correctly.

Anyway here goes the second control mod.

EH in there wisdom wired up one pot to two control parameters, what this means is that on there Tremolo patch as you turn up the speed of the tremolo it also adds in the reverb. At minimum setting of tremolo speed there is no reverb but as you increase the tremolo speed the reverb increases to max. This is a bit pathetic really. Better still though as my first mod added some extra effects like chorus and flanger the use of the second control comes into it's own as you have independant control over the rate of chorus/flange independant of reverb. On the reverb only programs the second pot will adjust the high freq filter of the reverb.

I didn't bother adding the third control pot as in the programs all it does is change the effect output mix, EH added a seperate mix control for this anyway.

Here is the second pot mod. In the first picture i have highlighted the track that need modding in white. This is the centre pin of the pot to the two control pins on the FV-1 chip



First of all we need to remove the resistor R18 circled in red.