DOD - FX25 Envelope Filter  [schematic]

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Re: DOD FX-25 rev -A gut shots / opinions needed!

Postby czech-one-2 » 23 Dec 2010, 21:33

Sorry you guys,I was side-tracked for a couple weeks. The 3094 ic's are back in,I'm just waiting for some j111 transistors to come in the mail and I'll try swapping those out.
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Re: DOD FX-25 rev -A gut shots / opinions needed!

Postby czech-one-2 » 27 Dec 2010, 18:36

Ok, I replaced the J111 ic's and its passing signal when on and off. But the signal is un-effected. So that leads me to assume its down to the ca3094 ic's,as they are responsible for the envelope.
I feel I'm getting closer, just need to find those ic's now. Is there an equivalent more common ic with a pin for pin match.? If anybody knows could you share that with me?
happy holidays!
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Re: DOD FX-25 rev -A gut shots / opinions needed!

Postby Barcode » 27 Dec 2010, 22:58

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Re: DOD FX-25 rev -A gut shots / opinions needed!

Postby czech-one-2 » 27 Dec 2010, 23:08




Thanks! damn those are pricey IC's! Even on ebay from China they are about the same but at least the shipping is free. Gonna order 2,should be here in a couple weeks :cry:
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Re: DOD FX-25 rev -A gut shots / opinions needed!

Postby MarcoMike » 28 Dec 2010, 12:41

some say you'll probably get some nicely forged chips from china...

EDIT:not me, I love to buy from china, the only problem is that shipping usually takes over a month..
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Re: DOD FX-25 rev -A gut shots / opinions needed!

Postby mictester » 28 Dec 2010, 13:14

MarcoMike wrote:some say you'll probably get some nicely forged chips from china...

EDIT:not me, I love to buy from china, the only problem is that shipping usually takes over a month..


Frequently, they supply forged, poor quality BBD ICs, but everything else I've bought has been fine. I find that shipping to the UK usually takes about a week.
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DOD FX25B, internal pictures

Postby andregarcia57 » 06 Jan 2011, 14:15

DOD FX25B, internal pictures
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Re: DOD FX25B, internal pictures

Postby andregarcia57 » 06 Jan 2011, 14:36

capacitor and transistor
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Re: DOD FX25B, internal pictures

Postby MarcoMike » 06 Jan 2011, 16:02

this is a pedal I really loved... then I made a Meatball, and this had to go... but it was quite effective in its simplicity...

I think the schematic is already floating around... I have a pale memory of it... could be my immagination though....

(demotivational comment: this pedal can be found at something like 30 euro, it's probably not worth RE...)
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Re: DOD - FX25 ( Envelope Filter )

Postby modman » 06 Jan 2011, 16:43

I merged some threads on the DOD Envelope Filters together... great pics.
You should check the version on your pedal and compare with the existing schematics for part changes.
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Re: DOD - FX25 ( Envelope Filter )

Postby MarcoMike » 06 Jan 2011, 17:00

I just googled for fx25b schematic and THIS came out, not sure that is correct, or the right version... but for sure it has a "blend" pot, so it must be a "b" version.
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Re: DOD - FX25 ( Envelope Filter )

Postby Barcode » 07 Jan 2011, 00:12

I'm pretty sure I remember the 25 and the 25b being slightly different, but I don't remember where.
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Re: DOD - FX25 ( Envelope Filter )

Postby MarcoMike » 07 Jan 2011, 12:31

25 has only two knobs, its the one that czeck-2-1 posted. 25b is the modern version of it, it has also a blend knob and uses a 13700 instead of 3080s
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Re: DOD - FX25 ( Envelope Filter )

Postby czech-one-2 » 14 Jan 2011, 21:28

over three weeks and still waiting for 2 ca3094's :cry:
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Re: DOD - FX25 ( Envelope Filter )

Postby czech-one-2 » 20 Jan 2011, 13:09

OK, The CA3094's arrived! Plugged them in and there is no effect when on,just a clean bypassed tone. :(
So up to this point I have replaced all IC's,all transitors, all diodes. gueuss I'll move on to electrolytic caps :(
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Re: DOD - FX25 ( Envelope Filter )

Postby czech-one-2 » 20 Jan 2011, 18:43

Update, all electrolytics replaced,same problem. Any suggestions out there? I'm about ready to use the box to house a tonepad MXR filter at this point. I'd really appreciate any assistance if somebody has time,or I would be willing to ship it to somebody, Analoguru,are you out there? You helped me out by fixing an MXR phase 45 once! 8)
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Re: DOD - FX25 ( Envelope Filter )

Postby Scruffie » 20 Jan 2011, 18:49

So what are your voltages on all the Pins in this? And where are you loosing Signal with an Audio Probe?
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Re: DOD - FX25 ( Envelope Filter )

Postby czech-one-2 » 31 Jan 2011, 23:02

Ok, I finally gave in as a legendary fellow in Austria,far more knowledgable than I, offered to help me out once again. Hopefully it will once again wah , and I will at least be able to post what the problem was on this forum.....
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Re: DOD - FX25 ( Envelope Filter )

Postby bigorangefan79 » 29 Apr 2011, 23:14

Could someone give me some advice on how to make a fx25 with a ca3280 dual OTA? Would I need to change any values? Do I put the .01uF caps to ground after the output pins? Could I make it better or different by incorporating the linearization diodes?

Here is a schem with ca3094's viewtopic.php?f=1&t=978&p=124845&hilit=ca3080+fx25#p124845

Here is the more typical schem with a lm13600 with built in buffers http://topopiccione.atspace.com/pjimage ... 25.sch.gif
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Re: DOD FX-25 rev -A gut shots / opinions needed!

Postby mictester » 30 Apr 2011, 00:25

czech-one-2 wrote: Is there an equivalent more common ic with a pin for pin match.? If anybody knows could you share that with me?


There are a couple of equivalents, but they are obsolete, and incredibly expensive (if you actually manage to find any). You should do exactly what DOD did - they used an LM13600 instead. The 13600 is a dual OTA, where the 4094 is a single one. Both are equipped with optional output Darlington buffers. My FX25 work-alike uses a TL074 quad and a 13600. It sounds exactly like the original, and cost next to nothing to build. It also has the advantage of an output buffer, and "true bypass". I've done another version using CMOS bypass switching too, which uses a more reliable switch (a momentary type) but still sounds the same!
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