DOD - FX25 Envelope Filter  [schematic]

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Barcode
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Post by Barcode »

mictester wrote:
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!
Are you going to post them... ?

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Post by mictester »

Barcode wrote:
mictester wrote:
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!
Are you going to post them... ?
The immediately obvious "equivalent" IC is the BA662. I have a strip of these from about 25 years ago! I can't remember another similar single OTA, but there were several.

There is no point whatsoever in going for "authenticity" in a circuit like this. Just use the 13600 or 13700 and either a quad op-amp or a pair of duals - it will sound just like the original. A useful trick is to put an insert point into the input of the sidechain. This allows you to put unaffected guitar signal in there, and put the filter part after your favourite distortion device. You can then get amazing autowah fuzz sounds!
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Post by bigorangefan79 »

The reason I asked about the ca3280 is because I have a couple and would like to finish up a fx25 perf that I started in hopes of parts I've already got. I've made a perf with the ca3280 pinout in mind, put the .01 caps to ground at the output of each ota since it does not have built in buffers, and ran 9v to both V+'s. It wahs alright but as the signal dies, it distorts and sputters. Any insight on needed component value and/or placement changes, or things to check for would be appreciated.

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Post by mictester »

bigorangefan79 wrote:The reason I asked about the ca3280 is because I have a couple and would like to finish up a fx25 perf that I started in hopes of parts I've already got. I've made a perf with the ca3280 pinout in mind, put the .01 caps to ground at the output of each ota since it does not have built in buffers, and ran 9v to both V+'s. It wahs alright but as the signal dies, it distorts and sputters. Any insight on needed component value and/or placement changes, or things to check for would be appreciated.
It sounds like you're going in the right direction. Can you put your schematic up here? Then we'll be able to suggest improvements.
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Post by bigorangefan79 »

mictester wrote:
bigorangefan79 wrote:The reason I asked about the ca3280 is because I have a couple and would like to finish up a fx25 perf that I started in hopes of parts I've already got. I've made a perf with the ca3280 pinout in mind, put the .01 caps to ground at the output of each ota since it does not have built in buffers, and ran 9v to both V+'s. It wahs alright but as the signal dies, it distorts and sputters. Any insight on needed component value and/or placement changes, or things to check for would be appreciated.
It sounds like you're going in the right direction. Can you put your schematic up here? Then we'll be able to suggest improvements.
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fx25-ca3280
fx25-ca3280

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Post by candletears7 »

I just got one of these in, and its distorting like a bitch? Apparently this is pretty common in thd old 2 knob fx25. Any ideas before I start probing?

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Post by candletears7 »

Fixed!
Dodgy electrolytic :horsey:

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Post by rocklander »

trevize wrote:this one? :D

I heard amazing samples of this auto wah, very "synthy".

http://topopiccione.atspace.com/PJ11DODfx25.html
I've made a layout for 1590a (yet to be etched and verified, so if anyone wants to go over it as a second pair of eyes, I'd really appreciate it). looks right so far, but will check again then build to see how it goes.
did not include the Schem as it's not mine to do so, but available at link posted above.
pdf is for A4 paper. red is 9V, brown is VB
dod-fx25-layout3.02coloured(c).jpg
dod-fx25-pcb3.02.jpg
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dod-fx25-pcb-layout3.02.pdf
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Post by fallingfurther »

Hey guys, I am installing a Deville (Mammoth Electronics) Click-less true bypass in this pedal. I need to have the pedal "always on" so I followed Ice-9's directions on the first page and removed Q1 (the J201 mislabeled as Q2) and removed Q2 (the J113) and jumpered the d and s legs. However, its not working now and just sounds like a high pass filter with no sweep.

Does anyone know how to do this correctly?

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Post by fallingfurther »

Anyone? It would be much appreciated!

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Post by piod »

Here is sound https://dl.dropboxusercontent.com/u/209 ... odfx25.mp3 And my tweaked layout for bass with blend. But I have a one trifle: when we add decay knob, it's work good, but bias voltage on cap is drop down (when we tune this knob). Bias need to be 0,9v on electrolytic cap for a clean first attack. I don't have time for resolve it. (Adding 470-1k attack resistor don't resolve it) Solution is find way to have and hold starting bias voltage on 0,9v then cap will charge to 2,5v. Please comment if you have suggestions.

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Post by Blitz Krieg »

piod wrote:Here is sound https://dl.dropboxusercontent.com/u/209 ... odfx25.mp3 And my tweaked layout for bass with blend. But I have a one trifle: when we add decay knob, it's work good, but bias voltage on cap is drop down (when we tune this knob). Bias need to be 0,9v on electrolytic cap for a clean first attack. I don't have time for resolve it. (Adding 470-1k attack resistor don't resolve it) Solution is find way to have and hold starting bias voltage on 0,9v then cap will charge to 2,5v. Please comment if you have suggestions.

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Post by soupbone »

czech-one-2 wrote:Hi folks, I am placing a call for help! I have an early DOD FX-25. I bought it as a project but am requesting a photo or two of the wiring if anybody has one of these.When I received it it would NOT switch on or off, so I replaced the footswitch and still no luck.Then I replaced the 14007 ic and it is switching fine.However there is no output when on,only when off.The wiring had been re-done when i bought it so I'm feeling there is a good possibility that maybe something is screwy there. The wires and connections are solid,but being that they arent original I suspect there may be a problem there.The circuit protection diodes are fine,and I tried piggybacking the two ca3094 chips with ca3080's and the lm1458 with another lm1458 to no avail,so I dont beleive its the ic's either.I changed the 47uf electrolytic,and installed a blue led as the original was blown, but I'm at a loss for what the problem is.
Any suggestions or photos would be greatly appreciated! Obviously this pedal was damaged early in its life,cause it doesnt have a scratch on it,came in the original box,and had a blown 14007 switching ic.
Thanks in advance! B



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I have a DOD FX25,the model made after this one.I was wondering what the resistor tacked on the back of the PCB was for?

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Post by calosteward »

soupbone wrote:
czech-one-2 wrote:Hi folks, I am placing a call for help! I have an early DOD FX-25. I bought it as a project but am requesting a photo or two of the wiring if anybody has one of these.When I received it it would NOT switch on or off, so I replaced the footswitch and still no luck.Then I replaced the 14007 ic and it is switching fine.However there is no output when on,only when off.The wiring had been re-done when i bought it so I'm feeling there is a good possibility that maybe something is screwy there. The wires and connections are solid,but being that they arent original I suspect there may be a problem there.The circuit protection diodes are fine,and I tried piggybacking the two ca3094 chips with ca3080's and the lm1458 with another lm1458 to no avail,so I dont beleive its the ic's either.I changed the 47uf electrolytic,and installed a blue led as the original was blown, but I'm at a loss for what the problem is.
Any suggestions or photos would be greatly appreciated! Obviously this pedal was damaged early in its life,cause it doesnt have a scratch on it,came in the original box,and had a blown 14007 switching ic.
Thanks in advance! B



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I have a DOD FX25,the model made after this one.I was wondering what the resistor tacked on the back of the PCB was for?
Same problem. Hope someone can give a hand.

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Post by astrobass »

The momentary switches in DOD stomps aren't great, but they're just normal momentary SPST buttons. You can get a bag of 25 for $1 probably on ebay that will be of at least the same quality and get a good five years or more out of one.

Also if you email them with a serial number, they'll give you the factory schematics if they have them. I've received schematics for like four different DOD pedals that way. The factory schematics are quite good too, they're PDFs and are totally legible.

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Post by astrobass »

Ugh. I posted that after reading only the first page and didn't realize how old the comment I was replying to was.

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Post by tubehead123 »

I made a short blog post about doing the filter output mod, to change the output from bandpass to lowpass or make it switchable, take a look at it here:

https://tubehead123.blogspot.com/2015/01 ... wpass.html

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Post by ppluis0 »

piod wrote:Here is sound https://dl.dropboxusercontent.com/u/209 ... odfx25.mp3 And my tweaked layout for bass with blend. But I have a one trifle: when we add decay knob, it's work good, but bias voltage on cap is drop down (when we tune this knob). Bias need to be 0,9v on electrolytic cap for a clean first attack. I don't have time for resolve it. (Adding 470-1k attack resistor don't resolve it) Solution is find way to have and hold starting bias voltage on 0,9v then cap will charge to 2,5v. Please comment if you have suggestions.
Hi Piod,

Try the following solution:

Lift the negative terminal of capacitor C11 from ground.
Make a string with three germanium diodes (or schottky diodes) connected in series, with the first anode soldered to the previously released capacitor terminal, and the last cathode connected to ground.
Connect a resistor, say 100K, from VB to the junction of the negative side of the cap, and the first diode in the series.

This way you have 0.9 Vdc appearing in these three diodes, and have lifted the same amount on the positive side of that electrolytic.

Hope this solve your problem. Please keep us posted about the result of this experiment.

Cheers,
Jose

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Post by ppluis0 »

I forgot to mention that the three diodes must be connected in serial fashion, but pointing to GND... :oops:

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Post by Mbas974 »

Hi all, I'm very happy with my pedal I built some time ago, everything is working well.
One question related to this circuit but O.T.

Will it be possible tweak the circuit in order to not have the envelop ?
Let me explain... this pedal is extremely silent that only when I play sound come out... in other words it is a GREAT GATE pedal.
So I was wondering whether I can mod it to change it in a standard GATE without the envelop.

...hope it is clear.

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