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Thursday, July 23, 2015

DOD FX25 Envelope Filter

The FX25 was initially produced by DOD in the early 80s and is an OTA-based envelope filter/auto-wah. It's a fairly tweakable and you can find various mods on other sites, but this is for the stock layout. The original switching circuitry has been removed, so you can use true-bypass. An LM1458 is listed in the layout below, but just about any dual op-amp should work there (TL072, NE5532, JRC4558, etc.), so if you get a little distortion, try a different op-amp.



Update Aug. 10, 2016:

I've fixed the layout as per NapAlpha and Eduardo's comments below. Thanks for catching that guys. Sorry it took me so long to make the fix.

47 comments:

  1. On the PCB there is no connection between C7 and R12-R13. The resistors R12 and R13 are 10K and not by 1K

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  2. Hello layot ​​this work? There I gotta change ?
    Thanks

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  3. i did this layout but no sound at all.. helpless!

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  4. is there someone verified this layout here?

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  5. nap_alfa55 was right. change 2x 1k resistors (COORDINATE H/V C-P/S and D-P/S, up 13600)by 10k and connect C-S to K-J. WORK FINE. VERIFIED!
    any mod or change for bass?

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  6. Replies
    1. Yes, work fine. Remember to connect R12/R13 with C7 and change it with 10k

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  7. Sorry about the error in the original board, guys. Thanks for catching that missing connection. I've corrected it and it's good to go.

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  8. Build this one with 47r ( did not found 51r). Worked for few seconds then burned de 47r twice! Any help? Thanks!

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  9. Could be your power supply. Maybe use a high wattage resistor there?

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    1. Bad 1n4007 diode...short the 47r to ground. Replace it and no more resistor burn. But the effect still don't work as should be. I turn it on and it works well til' 30 to 40 secs of play then it's down. Any help???

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    2. i had this problem but i double check and had a short on my traces check your connections

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  10. Put as VERIFIED! I just finished and it works very good! I made it with a LM13700 and MC1458.

    Greetings from Corrientes, Argentina!

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    1. genial, entonces si lo hago tal cual esta la foto en el layout va a funcionar? es que no se si al decir que lo corrigieron se ven reflejados esos cambios en la imagen

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  11. can i request for a dodo fx25 in a 1590A without the footswitch? thanks and more power..

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  12. Im into audio probing the circuit. From input to pin3 of ic 1458 the audio seems to be ok even for pins 1,2 and 7. For pins 5 and 6 the audio volume drops. I need to max the amps volume to hear the audio output. I tried to test the directly at the output and theres the slightest volume of audio that I can hear with amps volume maxed. The voltage for me are normal for both ic. I will try to get the exact voltage later when im free to get my hands on it again. I use LM13700.
    And can you point out the connectivity of the audio path circuit from input to output?
    Thank you

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    1. Pin 7 is the output of the 2nd half of the opamp, so if the volume is ok out of there I would think it's ok. I'd guess the issue you're having is later in the circuit. Here's the schematic for reference:

      https://images.talkbass.com/attachments/dodfx25_sch-png.2309823/

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    2. This comment has been removed by the author.

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  13. Are the potentiometers log or lin? I've also seen a picture of an original fx25 with one of the pots reading: C500K?

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    1. The B prefix means lin. Those are what were specified in the schematic I believe. Rev. log pots may improve the sweep of the controls. YMMV.

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    2. I tried 100k, 250k, 500k log and lin. It doesnt change that much at least for me ears. Maybe a doberman could tell the difference.
      Thanks for sharing

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  14. This might be a silly question but 4148 is 1n or 2n?

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  15. es mejor el lm13600 o el lm13700?

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  16. hello, has this layout been fixed? then where is the location of R12 & 13 and C7 I only see the value, thank you

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  17. Replies
    1. si, pero no la subieron aca. es esta.
      http://tubehead123.blogspot.com/2015/01/dod-fx-25-envelope-filter-lowpass.html
      la hice con un switch on-on que conmute las salidas y suena muy muy bien

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  18. This comment has been removed by the author.

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  19. Hi! Thanks for your work. What should I do exactly about the pots numbered 2/3?

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    Replies
    1. You just connect those two lugs together and then run a wire to the corresponding pad.

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  20. hi, Can i replace diode 4001 with 4148 too?

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  21. This comment has been removed by the author.

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  22. Hi. Have to hit strings really hard to open filter..can I change something to open it without hitting too hard?

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  23. Hi, i really have issues connecting the potentiometers. It says 2 and 3 connect on one pin? In my count, 1 and 3 are the fixed resistance and 2 is the rotor, so ti variable resistance. So i connect one of the fixed pins and the rotor together to the same pin and the other side of the fixed resistor to the other?
    I assembled it but it does not work at all...

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