DOD FX25 envelope filter

[Hepcat]

So I have just come across the board from a DOD fx25.  I want to hook it up to a true bypass 3pdt foot switch. I am still pretty new to  electronics and still learning to read schematics, so  If anyone could help me figure out the wiring it would be much appreciated. There are six places on bottom of board for off-board connections and not sure what is what. Here is a couple pics of the board http://jubaglassbeads.com/josh-effectspics-001.jpg  http://jubaglassbeads.com/josh-effectspics-003.jpg  Thankyou very much !

[Hepcat]

Here is the schematic  down at bottom of page http://topopiccione.atspace.com/PJ11DODfx25.html  Thanks

[Mark Hammer]

There are two major undertakings as part of what you wish to do.  One is to disable and bypass the onboard electronic switching, and the other is to install the mechanical switch.

Quite frankly, there is not a heck of a lot of value to changing from the existing FET-based switching IMHO.  The only real advantage to implementing TB switching here is that the pedal would continue to function in bypass mode if the power suddenly went off. 

Understand that the origins of the TB craze really lie in the use of SPDT switches and poorly-designed input stages in many older pedals.  Because the input was not particularly high impedance and only the pedal's output was being switched, the input of the circuit board was always connected to the input jack.  This loaded down the signal and produced "tone-sucking".  Those unfortunate conditions provided very strong rationale for installing a switch that would disable both the output AND input leads to the circuit board when the effect was bypassed - a "true" bypass.  Thankfully designers have learned all the important lessons since then, and now the overwhelming majority of effects have properly-designed input stages that eliminate tone-sucking.  As such, the sole remaining advantages of mechanical bypass switching include being able to function under power-failure (as noted above), and the sidestepping of any accumulated hiss when large numbers of electronically-switched pedals (say, 8 or 9) are placed in series.  An additional rationale for TB might be that the anticipated input signal is large enough that some distortion in the switching FETs might result.  Of course, if the signal is large enough to do that, it may well be large enough to distort the effect circuit itself.  Not a problem if the effect IS a distortion, but in the case of the FX25, anything large enough amplitude to distort the switching FETs would require majro overhaul of the circuit to permit the effect to actually function properly.

Bottom line?  Stick with the onboard e-switching unless there is some special reason for needing mechanical bypass.

[Hepcat]

Mark thanks for taking the time to reply to my post. I think i understand correctly in that you are saying that there is not much advantage to hooking up to a true bypass?  I wish it was still hooked up to the original FET based switch then i could play it, but basically i have a board  thats not connected to any switch(or anything) . Do you happen to know what the connections are at bottom of the board so i can at least hook it up to any  switch(preferably 3pdt)? Thankyou very much  -Josh-

[Mark Hammer]

Ah, that's a horse of a very different colour.  Using the pictures you posted, you can fairly easily decipher which of the solder pads on the edge of the board are which connections, as they correspond to the schematic.  There are three variants of the original DOD schematic posted at the bottom here: http://topopiccione.atspace.com/PJ11DODfx25.html   One of those will be your board.

For instance, all three designs/schems show the input jack going to a .01uf cap followed by a 10k resistor.  This suggests that the leftmost pad underneath that 100k resistor is the input pad from the input jack.  Similarly, all 3 designs show pin 10 on the CD4007 going to the momentary switch.  The momentary switch simply connects pin 10 and ground.  Given that all 3 designs show a 1uf cap going to a 1k resistor at the output, and a 100k resistor from that 1k part to ground, there is a very high likelihood that the pad with the blue lead, under whereit says DOD, is your output pad to the output jack.

...and so on..

[Hepcat]

So, mark  based on what I have gathered from your posts,  and my very(I mean very!) limited ability to read a schematic this is what I came up with, from left to right , solder side.http://jubaglassbeads.com/josh-effectspics-001.jpg

1-ground
2-power V+
3-ground?
4-LED
5-output
6-input
Does any of that look right?

[Mark Hammer]

Close.  Keep in mind that there are several things off the board that need to be connected to it: the battery/power, the input and output jacks, the LED, the switch.  My guess would be (left to right, using the same pic you did): ground, V+, switch, LED, output, input.  Remember that the switch goes between pin 10 of the 4007 and ground, and the LED goes between the collector of the transistor and ground.

Incidentally, if you look here - http://jubaglassbeads.com/josh-effectspics-003.jpg - that 1meg resistor on the lower right, by the diode and big cap, looks discoloured.  Possible it might be fried.  Best to verify it, or just replace it for insurance.

As a side note, since the momentary switch simply grounds pin 10, you can install a little mini phone jack on the side of the box and route that momentary switch ANYWHERE you like.  That jack could be wired up so that plugging into it defeats the main pedal switch, or it could be wired up to simply parallel that switch elsewhere.  In fact, you could do that with essentially any DOD or Boss pedal, and place all your pedal switching in a small package where you could step on several switches at once if you felt like it.

[Hepcat]

Mark, thanks, this info has helped me out alot, and i have also learned how to better read a schematic, all good stuff. Nice call on the fried resistor it did look a little funky . Now all thats left to do is put it back together and rock out! Once again THANKYOU!   -J-

[xaxxop]

HI, thank you for the pics, the pot sens is the C500K, the pot range?  A, B, C?

Thank you very much for the info!!!!

Leandro