Holy Stain(modded) with expression pedal troubleshooting

[clayton9610]

Hi, I modded my Holy Stain from instructions from this thread
http://www.diystompboxes.com/smfforum/index.php?topic=91016.0 

It is an incredible pedal now but I can't get an m-audio ex-p expression pedal to work with it. 

I wonder if it's because I added the extra pots whereas before the expression pedal was connected to the amount pot.
"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."

I didn't want to bump an old thread so thought I'd ask here for any suggestions.

Thanks kindly.

[slacker]

Did the expression pedal work before you did the mod? If it did see if you can trace where the signal goes from the expression pedal input to find out how and where it connects to the FV-1 pot inputs. It's possible the resistor that gets removed in the mod was to mix or isolate the expression pedal input from the pot, so see if anything else connects around that area.

[Ice-9]

+1 ^  I can't remember if I traced the expression pedal jack traces out. You should easily be able to check if the added pot is now being used for the expression pedal control parameter and if so it should be quite a simple additional mod to allow for use of both the expression pedal or pot control.

I will check back through the original thread to see if I can find the info needed, it sounds like, as Ian said the removal of the resistor may be where the expression pedal has been disconnected to allow the extra pot, in hindsight if I had looked at the expression pedal in the original mod then it may have been an even easier mod than I made it out to be. 

[Ice-9]

From the manual

EXP. PEDAL Jack – This ¼” input accepts an Expression Pedal with TRS connection. The Expression Pedal takes over the AMOUNT knob so that you can modulate the DSP effects with your foot. To obtain the full range of the AMOUNT knob with the Expression Pedal, set AMOUNT to 12 o’clock. To change the range of the Expression Pedal, try different settings for the AMOUNT knob. Some acceptable Expression Pedals incl

The AMOUNT control as standard is connected to both FV-1 parameters (pins 20 and 21) so adjusts both settings at the same time and when the expression pedal is plugged in that takes control of both these parameters. The mod adds an extra pot to control both parameters set individually with their its own separate pot. The way it is done has removed the expression pedal connection.
The expression pedal could be used with some further mods but you would also have to decide which control you want it to alter as they are both individually altered with their own pot now.

I am afraid I no longer have a Holy Stain or the old pictures of close ups from the PCB to try and check out the traces to modify, but I would be looking at just a slightly different wiring mod to do this.

Ie. look at replacing R18 that was removed and then altering how pins 20-21 connect to each pot. This would probably work best by unsoldering and lifting one of those pins from its pad (depending on which one you want the expression pedal and 'amount' pot to control v's which parameter you want the side pot to control).  I Think it would actually be a neater mod this way.

I think this would work.....

1. Undo the 1st added pot mod wiring and replace R18(to pin 20)
2. Lift pin 21 from the pcb pad.
3. wire pin 21 to the centre of the new pot control.

This should now give individual pot control for both parameter and restore the expression pedal control to the 'AMOUNT' parameter.

If anyone spots an obvious error with this please post.

[clayton9610]

You are all so wonderful!  I'll get to tinkering and update.

Cheers.

[Ice-9]

You are all so wonderful!  I'll get to tinkering and update.

Cheers.

Please be aware the tinkering I have outlined is not checked or verified, just an educated questimate from the pictures I can see in the thread.

I would recommend to first remove the 'extra pot' and wiring and revert to the original 'Amount' pot circuit, test the expression pedal is working as it was previously, then start with the alternative mod wiring.

[clayton9610]

I think I'm going to leave as is because the expression pedal controls the added pot1.  I don't want to risk messing up the fv-1 pin connections(i'm prone to breaking what I already have working). 

Also,


pin 7 (write protect) of the ic needs to be wired to pin 4 vss ground(not vcc pin 8 3.3V) or else you can only read the eprom(using a pickit2). 

[Ice-9]

I think I'm going to leave as is because the expression pedal controls the added pot1.  I don't want to risk messing up the fv-1 pin connections(i'm prone to breaking what I already have working). 

Also,


pin 7 (write protect) of the ic needs to be wired to pin 4 vss ground(not vcc pin 8 3.3V) or else you can only read the eprom(using a pickit2).

In that EEPROM addition picture, Pin 7 connects to +3.3 instead of Gnd, this is wrong as it put the EEPROM in write protect so you will not be able to program the EEPROM. Solution.. cut the trace between pins 7 & 8 of the EEPROM and connect pin 7 to Gnd with a wire link. fixed, alternatively redraw the pcb or vero for the correction.