Transferring a DOD delay

[fallingfurther]

Hello, this is my first real pedal project.  I am transferring a DOD FX90 analog delay pedal to a new box, and adding a true bypass switch. I am also changing the old scratchy pots.  What pots should I use?  They say "E.C.I. alpha W100K"  Does anyone know if I should use linear, audio, or reverse audio pots?  I am looking on the small bear website at those little alpha pots, and they don't say if they are 100k or not, does it matter?  Also, has anyone tried transferring a DOD circuit into those Taiwanese BB enclosures?  It seem like it will just fit, hopefully.
Thanks, Louie

[Mark Hammer]

Um, I can understand pot issues, but why are you transferring it?

[fallingfurther]

Just for the fun of it, plus it will look better and will have a much more reliable switch (as the DOD switches always crap out) and true-bypass.  This pedal destroys your tone when its off.  But the delay actually sounds very good, in a dirtier, lo-fi kind of way.

[sfr]

http://geofex.com/Article_Folders/potsecrets/potscret.htm

R.G.'s "Secret Life of Pots" article explains lots of cool info about potentiometers, as well as how to measure an unknown one.

[343 Salty Beans]

I'm thinking of doing the same thing to my FX65 chorus, because those switches are such a pain in the arse 

[Ronsonic]

Hello, this is my first real pedal project.  I am transferring a DOD FX90 analog delay pedal to a new box, and adding a true bypass switch. I am also changing the old scratchy pots.  What pots should I use?  They say "E.C.I. alpha W100K"  Does anyone know if I should use linear, audio, or reverse audio pots?  I am looking on the small bear website at those little alpha pots, and they don't say if they are 100k or not, does it matter?  Also, has anyone tried transferring a DOD circuit into those Taiwanese BB enclosures?  It seem like it will just fit, hopefully.
Thanks, Louie

Dude, at the smallbear stocklist page, click on the pot. It will take you to a page where you can select the value.

You can measure the existing pots to see if they are log, linear, reverse, or you can just use linear and it will surely work. Just might be touchy to set just right.

Ron

[boogietube]

I was just reading in another thread about "W"  taper pots. I think that 's what you have there. There was a link provided by another member.
I hope this is useful:
http://www.gatago.com/sci/electronics/components/2372617.html

[343 Salty Beans]

After reading that article, and looking at a picture of the FX90, it's apparent that there is no level control. I'd probably just use linear for the whole thing.

The general use for audio taper pots is that they have a resistance/rotation curve that is logarithmic...which is the way that human ears perceive volume. Human ears are weird that way...adding anywhere from 6 to 10 decibels is perceived as 'doubled' volume. For instance, you'd hear 12db from 6db and think it was doubled, which makes sense...6 times 2 = 12. However, at 18 or 19 db from 12db, you'd think it was doubled again. Odd, eh? 

Reverse audios are used in a control where you want the the middle area of the rotation to be the most controllable. (I'm pretty sure...more experienced people correct me if I'm wrong here). That's why many people like the sustain pot on a ross comp to be reverse audio...that way, they can dial in a perfect amount of compression without having to make super-tiny tweaks to the pots. The rotation of the wiper across the resistive strip is simply mechanical, which means it's hard to turn it JUST right if you're using a linear taper.

But that's a lot of useless crap. The point is, linear should be fine for all three of those (although reverse audio might be wise for delay time if you need to tweak it JUST RIGHT  ). Smallbear carries 24mm 100K reverse audio pots for $3.95, or 16mm of the same value for $2.75. Good luck rehousing it, and do let us know how it turns out  .

343SB

[fallingfurther]

thanks for all the great info guys.  I think I'll just use linear pots, as that would make the most sense.  I'll post the results when I'm done...if it ever actually gets done!

[fallingfurther]

I have all my parts coming from smallbear right now, but I need one more piece of info. before I can do this.  Can someone describe to me how to hotwire the circuit so its always on?  I understand this needs to be done to remove the FET switching system from the circuit.  Here's the DOD FX90 schematic:

[fallingfurther]

can anyone help me?  i need to wire the circuit so its always on.  thanks

[sfr]

I've rehoused a DOD pedal for a friend of mine, and ended up simply running connections to a Carling-style mechanical footswitch (his preferred switch, not mine)  of the momentary type, connected to where the tactile switch was on the board.   In his general usage, he didn't find any "tone sucking" or other issues that warranted true bypass, but he didn't care for the footswitch of the pedal and wanted a sturdier enclosure.  (I don't particularly think the DOD enclosure was less than sturdy, but I have seen a few DOD pedals have switches fail, althought these where replaced/repaired by the manufacturer)

Regardless, there's an article over at Mark Hammer's site from an old issue of Polyphony that covers the DOD switching setup. 

Link:

http://hammer.ampage.org/?cmd=lt&xid=&fid=&ex=&pg=9

Scroll to the very bottom, it's under the heading "Generalized DOD-style bypass switching".   That should get you started. 

It appears at first glance that the pedal schematic uses the same type of switching, with your signal always going through the first op-amp buffer, and the switching simply cutting out the "wet" signal - although there seems to be something else going on in there I'm not quite understanding (differential amplifier?) looking at all the lines running around.

But basically, all you'd need to do is to get TR7 (the J113 JFET) to always be "on", conducting from source to drain - make sure the voltage on the gate is always negative compared to the source. 

I'll let someone with more experience take it from there - I'd have to do a bit of searching to make sure I actually understood 100% what I was saying so I didn't send you in the wrong direction, but that should be enough to help you find what you need. 

I imagine you might just be able to pull that JFET and add a jumper where the source and drain where?  Anyone want to comment on the feasibility of this?

[Rattlehead]

Little question that have to do with puting Danelectro effects in a new box.

does danelectro use dpdt footswitches for their effects? ( corned beef reverb for example)
is it hard to put a 3pdt instead of the original switch?

tnx a lot =)

[sfr]

The danelectro pedals use CMOS switching, so I believe they use a small momentary switch in conjunction with this. 

More than one person has reboxed these effects; here's the only link I know offhand:

http://beavisaudio.com/Projects/FABRack/

[fallingfurther]

sfr, so when the gate is applied, the source does not make it to drain, and that is how the wet delay signal is removed?  i'm trying to understand which path is source to drain in the schematic.  Would this be right if I jumpered it like this (the green thing on the schematic)?  because i'm guessing the drain will be the path going to the MIX knob.

[sfr]

From that drawing, it looks like you've jumpered the drain and gate.  You'd want to jumper the drain and source.  Again, I'm not sure this is the best solution, but I think it should work.  See here   the little connection in the schematic with the arrow leading into the bar is the gate.

Also - it seems that it may be that the pedal is in "on" mode when that transistor is *not* conducting - I'm not sure what exactly's going on between those two opamps, with that second one being fed at both the inverting and non-inverting inputs, and I'd hate to steer you wrong. (hopefully someone with a little more knowledge than I can pop up and help out here!)  If that is the case, however, you could simply pull that transistor and the pedal should be "always on".

Easy way to find out would be to locate that transistor on the board.  (should be the only J113 on the board, it looks like)  Look up the data sheet online, figure out which pin is what.  Using an audio probe (info at Geofex and in the FAQ linked at the top of the forum) play into the pedal, and see if you've got signal at both the source and drain.  Then switch it to bypass (or out of bypass if you were already there) and see if you get signal at both source and drain.  That should tell you what's going on, as far as whether the transistor needs to be "on" or "off" for the pedal to work. 

[fallingfurther]

thanks sfr, you're right i was jumpering the gate to the drain.  I located the transistor in the circuit, and looked up the data sheet to find out which pin is what.  I'm going to try removing it first.  If that doesn't work, i'll try jumpering the source and drain.  Hopefully one of those will be the solution!  I'll let you you know how it goes.