EHX - Holy Stain  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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tubehead123
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Post by tubehead123 »

some stuff i've worked out on the analog section:

the input splits and goes in parallel to 2 separate amp stages: a 2 transistor clean boost and a 2 transistor fuzz circuit. The clean amp consists of Q3 and Q4 which are both common emitter stages with an overall gain of about +14dB or 5x roughly. The fuzz is a 2 transistor NPN (Q1,Q2 - BC550) silicon fuzz that has two 'modes' to give the fuzz and drive settings. i haven't fully traced it out but the second switch (bright, dark, warm) switches some stuff in and out to change the EQ of the fuzz, giving the drive mode which looks like the fuzz section with the highs rolled off. the outputs of the two amp stages are then connected to the bright/dark/warm stage via the first rotary switch. that section goes to the volume pot, the BMP tone stack, a buffer opamp and then into the FV-1.

with the signal source i was using the amplitude of the clean section at the first switch output was ~1Vp-p but the fuzz/drive sections were ~3V square waves....i came up with a mod to equalize the amplitudes of all 3 sections so the fuzz isn't super loud when it's kicked in:
HOLYSTAIN-FUZZ-MOD.png
HOLYSTAIN-FUZZ-MOD.png (93.2 KiB) Viewed 6145 times
it uses a trimpot to attenuate the two fuzz stages so they sound equal to the clean section. you could do this with either a fixed resistor if you ear test it first to find the right value or you could break it out with a panel mount pot so it's a knob on the outside that sets the fuzz/drive level. i'm prolly going to work out some more mods for this section, i was thinking of changing the fuzz transistors to germanium ones but they are NPN so there would have to be some power supply trickery to change those...

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Post by eatyourguitar »

Ice-9 wrote:
Hides-His-Eyes wrote: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.
I have seen the factory, they just press the knobs in on a big heavy hand operated press. they don't want those knobs coming off too easy now. breaking stuff is to be expected.

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Green Snake
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Post by Green Snake »

Hi!

Earlier published part: viewtopic.php?f=1&t=11926&start=20#p129199

Here is Holy Stain analog distortion and clean section.
Enjoy
Attachments
HolyStain1.JPG

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Ice-9
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Post by Ice-9 »

Green Snake wrote:Hi!
Here is Holy Stain analog distortion and clean section.
Enjoy
:applause: Nice of you to add this, now the holy stain trace should be complete.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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elicxirmixer
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Post by elicxirmixer »

tubehead123 wrote:i came up with a mod to equalize the amplitudes of all 3 sections so the fuzz isn't super loud when it's kicked in:

it uses a trimpot to attenuate the two fuzz stages so they sound equal to the clean section. you could do this with either a fixed resistor if you ear test it first to find the right value or you could break it out with a panel mount pot so it's a knob on the outside that sets the fuzz/drive level. i'm prolly going to work out some more mods for this section, i was thinking of changing the fuzz transistors to germanium ones but they are NPN so there would have to be some power supply trickery to change those...
Not to keep this thread alive, but I attempted the tubehead123 mod this weekend and it checks out great. I used a 10k pot instead of a 50k because it was all I had lying around, but it still did the job. The clean/fuzz/drive leves are all equal now. I bought this pedal on eBay for about $50 a while back and I've done all of the mods listed on this thread more out of curiosity that anything else. I must admit, for all the options it give me now, it doesn't take up a lot of space on my board.

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Post by Govmnt_Lacky »

Has anyone ever figured out what the mystery chip was? (EF92L...)

My guess is that it is an external memory which is where the EH programs are stored. That is why Ice-9 had the same INTERNAL programs when he swapped chips. :applause:

Has anyone dissected the way this pedal switches between programs? Is it a simple momentary stomp via a switching IC chip?

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Post by Ice-9 »

Govmnt_Lacky wrote:Has anyone ever figured out what the mystery chip was? (EF92L...)

My guess is that it is an external memory which is where the EH programs are stored. That is why Ice-9 had the same INTERNAL programs when he swapped chips. :applause:

Has anyone dissected the way this pedal switches between programs? Is it a simple momentary stomp via a switching IC chip?
I'm afraid there is no external programs, the mystery EF92Lxxx chip is to do with the bypass footswitch and not an eeprom for external programs, the Holy stain uses the FV-1 internal programs only.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by Ice-9 »

Ice-9 wrote:
Govmnt_Lacky wrote:Has anyone ever figured out what the mystery chip was? (EF92L...)

My guess is that it is an external memory which is where the EH programs are stored. That is why Ice-9 had the same INTERNAL programs when he swapped chips. :applause:

Has anyone dissected the way this pedal switches between programs? Is it a simple momentary stomp via a switching IC chip?
I'm afraid there is no external programs, the mystery EF92Lxxx chip is to do with the bypass footswitch and not an eeprom for external programs, the Holy stain uses the FV-1 internal programs only.
No way to edit my last post but Imeant to say the mystery chip is for logic program select of the internal FV-1 programs only, end result is the same there are no external programs.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Ice-9
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Post by Ice-9 »

This pedal could also be improved on by modding it to use an Eeprom for external fx, make the pedal into anything you like. I don't have the pedal anymore but will have a look at the pictures and see if I can draw up a little external eeprom PCB mod.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Ice-9
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Post by Ice-9 »

Here is a quick guide for adding an external Eeprom to the EHX Holy stain so that it can be used to load any program you want, this makes the Holy Stain a very good and cheap Dev board for anyone wanting to have a play with the FV-1 reverb/multiFx chip. If you also have done my previous mods then it will fully open up the possibilities for having some FV-1 fun.

First the PCB and connection picture.

(see post below for corrected drawing)


Connections are as follows.

1. 3.3v and ground = Any 3.3v and ground connection on the PCB
2. Int/Ext switch = Purple wires, to a SPST switch
3. Three Blues wires marked 13,14,15, These go to the FV-1 chip.
Solder the wires from the Eeprom labelled 14 and 15 directly to pins on the FV-1 chip (14 and 15)
13 = pin 13 will need to be lifted from its solder pad on the main pcb so that it is floating freely just as I describe in the other mods and then a wire from the new Eeprom board point 13 soldered directly to the floating pin of the FV-1 (after doing these 3 connections apply some epoxy resin or hot glue around this so that the pin does not snap off. This can be seen in the picures of the other mods)

4. The programming wires on the external Mod PCB, coloured light blue and green, These 3 wires can be used to reprogram the Eeprom and are ground, data and clock. If you would prefer to use a socket for the Eeprom and program it off board then there is no need to connect these 3 wires, Alternatively these 3 wires could be soldered directly to a stereo mini jack socket and mounted to the enclosure making reprogramming possible without even removing the chip or in fact no need to even remove the pedal cover.

As I have quickly typed this up there may be questions you need to ask before modding, so anything you need to know just ask in this thread.

Ohh I almost forgot the Eeprom is a 24lc32a and the resistor is 10k and as its so simple a pcb making it fit on any other type of board would be a 5 minute job.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Ice-9
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Post by Ice-9 »

IMPORTANT INFO ABOUT THE MOD ABOVE

PLEASE forgive me but I have marked the 3.3v and ground the wrong way round and am unable to edit the post so here is the correctly labelled picture.

Image
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by BourbonDevelopment »

Wow, lots of good info in this post. Using the schematic here, it looks like C30 is part of a high pass filter. (Im VERY green when reading a schematic so please correct me if I am wrong.) If I change the value of the cap or the resistor here, can I alter the frequency cut off, and therefor allowing this pedal to be used with a 5 string bass?

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Post by wildschwein »

Great thread. it's got me really interested. I've been using the Stain for years mainly for reverbs in my FX loop but also for a lot of recording work.

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Post by fishcustard »

A small chance to get an answer as the thread is quite old, but still: could anyone help me figure out the mod to add a footswich that will turn off the analog section? I could really use the reverbs in this pedal, but the fact that even the 'clean' mode changes the sound spoils it for me.

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Post by recoveryperiod »

I am also interested as well in a mod that would turn off just the fuzz/overdrive circuit by perhaps adding another footswitch button to the pedal. Anyone done this or know how to do this based on the info and schematics that Iceman posted?

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Post by wildschwein »

I've just done the switch and the pot mod as shown in this thread. Followed it as best I could to the letter. Used a 50k linear pot. I have the extra effects (pitch shifter, flanger and chorus) when the switch is engaged but there is no reverb or echo on them that I can discern -- they're dry. The new pot does change the rate so that seems to be working. In the regular mode it seems that the reverb effects are not as deep as they used to be before the mod and the pitch shift effect there has changed too -- I used to be able to get a unison/slap effect which is no longer there. I'm wondering if I have done something wrong -- maybe there is a solder bridge across one of the chips' pins that is not meant to be there.

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Post by Ice-9 »

wildschwein wrote:I've just done the switch and the pot mod as shown in this thread. Followed it as best I could to the letter. Used a 50k linear pot. I have the extra effects (pitch shifter, flanger and chorus) when the switch is engaged but there is no reverb or echo on them that I can discern -- they're dry. The new pot does change the rate so that seems to be working. In the regular mode it seems that the reverb effects are not as deep as they used to be before the mod and the pitch shift effect there has changed too -- I used to be able to get a unison/slap effect which is no longer there. I'm wondering if I have done something wrong -- maybe there is a solder bridge across one of the chips' pins that is not meant to be there.
I would suggest you have done something not quite right as all the original effect should work exactly as they did before but with the extra pot used to separately control one of the parameters that previously controlled a mixture of two parameters.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by wildschwein »

Ice-9 wrote:
wildschwein wrote:I've just done the switch and the pot mod as shown in this thread. Followed it as best I could to the letter. Used a 50k linear pot. I have the extra effects (pitch shifter, flanger and chorus) when the switch is engaged but there is no reverb or echo on them that I can discern -- they're dry. The new pot does change the rate so that seems to be working. In the regular mode it seems that the reverb effects are not as deep as they used to be before the mod and the pitch shift effect there has changed too -- I used to be able to get a unison/slap effect which is no longer there. I'm wondering if I have done something wrong -- maybe there is a solder bridge across one of the chips' pins that is not meant to be there.
I would suggest you have done something not quite right as all the original effect should work exactly as they did before but with the extra pot used to separately control one of the parameters that previously controlled a mixture of two parameters.
Yeah; I killed it. It's dead. Ended breaking the pins off the chip trying to trouble shoot the problem. I have a glorified fuzz box now. It's always a gamble with smd modding.

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Post by Ice-9 »

wildschwein wrote:
Ice-9 wrote:
wildschwein wrote:I've just done the switch and the pot mod as shown in this thread. Followed it as best I could to the letter. Used a 50k linear pot. I have the extra effects (pitch shifter, flanger and chorus) when the switch is engaged but there is no reverb or echo on them that I can discern -- they're dry. The new pot does change the rate so that seems to be working. In the regular mode it seems that the reverb effects are not as deep as they used to be before the mod and the pitch shift effect there has changed too -- I used to be able to get a unison/slap effect which is no longer there. I'm wondering if I have done something wrong -- maybe there is a solder bridge across one of the chips' pins that is not meant to be there.
I would suggest you have done something not quite right as all the original effect should work exactly as they did before but with the extra pot used to separately control one of the parameters that previously controlled a mixture of two parameters.
Yeah; I killed it. It's dead. Ended breaking the pins off the chip trying to trouble shoot the problem. I have a glorified fuzz box now. It's always a gamble with smd modding.
Have you damaged the PCB, if not it should be an easy repair. I'm in the UK and if you need a repair done.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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