DOD-440 clipping :-/

[mr_doyle]

wondering if anybody could point me in the right direction

i have a DOD-440 envelope filter, and i hear some annoying clipping everytime it's engaged and i'm playing

i tried swapping some IC, from TL022 to OPA2604, but the prob is still there, so i'm wondering where the clipping could be located

thank you for any help!

D.

[loscha]

sounds like a job for a signal tracer.
feed a sinewave or some other tone into the input, then trace the signal forward along it's path until you find where the distortion is induced.
if it's a transistor, check for biasing, supply, if it's an op-amp check the components in the feedback loop, supply voltages.

The 440 is a bit more complex than a fuzz or a booster, though, so, it could be a few things, but, I'm not too familiar with the circuit and how they've done things, so, I can't offer much more advice than these standard things.

best of luck, though!

[mr_doyle]

thanks

i got no oscilloscope or anything, so i think i have to maunally check one component at the time right?

D.

[analogguru]

The problem to give you a good advice is that there doesn´t exist a schematic on the web that you can trust.

There exist pictures of the component side but not from the copper- (track) side...

So if you own a 440 and a camera, maybe you can take some pictures to trace the real schematic, than its more easy to assume what can be wrong with your 440.

analogguru

[bwanasonic]

i have a DOD-440 envelope filter, and i hear some annoying clipping everytime it's engaged and i'm playing

Just to clarify, you are talking about a factory DOD unit, not a DIY version?

Kerry M

[mr_doyle]

Just to clarify, you are talking about a factory DOD unit, not a DIY version?

yep, DOD 440, the red version actually

So if you own a 440 and a camera, maybe you can take some pictures to trace the real schematic, than its more easy to assume what can be wrong with your 440.

sure! i'll take them tonight and post them tomorrow

thank you guys! :-)

D.

[guitarhacknoise]

Mr. Doyle asked:
"i got no oscilloscope or anything, so i think i have to maunally check one component at the time right?"

If you can hear the clipping, You can probably use an audio probe to find it.
I think that's what Loscha was saying. If not than I'll say it.
-matthias

[mr_doyle]

ok, pics can be found here:

http://community.webshots.com/album/303415847nPmHof

sorry for the quality :-/

thanks for your help!

D.

[Dan N]

Thanks for the photos! It's pretty hard to see much difference between the internet schematic and your unit. 4K7 in front of the range pot instead of 10K. Pot wired a tad differently too. 6K8 in front of the LED instead of 22K. That might make a difference in our home brews. 100K to ground at the output. Power goes through 100ohm resistor.

Anyway, that's how it looks to me.

Thanks again!

[mr_doyle]

as far as i know, this version should be the very 1st, with a different input impedance than the later ones.

D.

[analogguru]

So, after my tracing I got independently from Dan the same result as he.

"clipping" may have different meanings, i assume that you mean al little distortion...

As you stated, the problem occurs also after changing the IC.

There is not much else what can cause clipping/distortion so i assume, what you mean is a modulation effect...

The cause can be a bad capacitor...

I would start by changing the yellow 1µF/16V elko - in your picture at the right/down corner.

a second possibility could be the biggest yellow elko - in your picture on the top/left side...value is unknown, can be between 10µF and 47µF...maybe you can tell me, what is written on it.

I assume, that you have a red version produced in 1978.

the oldest hat ceramic in/out capacitors and a "vintage" 6k8 , then changed to film capacitors keeping the "vintage" 6k8, after some time also the "vintage" resistor was gone and replaced by a modern type.

@Dan N
the picture you posted, was it from a red or a green one ?

the blue ones seem to have a complete different schematic, as far as i can tell from a picture i have found 2 years back on ebay.

also the green reissue seems to be different with a higher input-impedance.

funny, that dod claims 100k output impedance only from the fact of the 100k pull-down resistor...they forgot, that the output impedance is in reality much lower - about 1k caused by the chip....

analogguru

[Dan N]

So, after my tracing I got independently from Dan the same result as he.


@Dan N
the picture you posted, was it from a red or a green one ?

Thanks. Nice to have some confirmation about the trace. It gets kind of hard to see what is going on by the Sens (or Level) pot. I still don't know exactly where the 100 ohm res. fits in relation to the 100K on the sens pot.

The board shot from the other thread was from a red unit.

(edit) O.K., I see the battery feeds both the 100K and 100 ohm.

[Dan N]

mr_doyle, if you are still around. I'm no help about the clipping. I have just been using this thread to nail down a proper schematic for the red 440.

If you have time, could you look to see what is written on the vactrol? You may have to kind of peek around to see what is coming from underneath. It would also be lovely to know the pot values and tapers.

I built one and just tonight got to try it a little. I used a pot as a resonance control as per a Mark Hammer thread on the subject (330K res and 300K pot wired as a VR). Cranked too far I got hair raising oscillation. Turning back there was some gurgle in the decay, and some ugliness that may be the "clipping" you hear. Will have to wait for tomorrow to really play with this thing.

Thanks for your help!

[mr_doyle]

back from a few days of holiday

thanks for all replies, here's some info:

- the pedal is the red version

- i actually refer as "clipping" as distortion: now, my idea is that the previous owner had replaced the original IC with a new one, and this causes problems...

btw - i'll track down all values tonight

Thanks again :-)

D.

[analogguru]

To make it more easy for you, here you can find my (preliminary) schematic:

http://forum.musikding.de/attachements/Dod_440_red.gif

analogguru

[Dan N]

mr_doyle, thanks! I don't have a tl022 to try in mine so some of the nonsense may be due to that. Even partial numbers from the vactrol may help.

analogguru, are you sure the sens is neg log? If so, it might be nice to have a note on your schematic that if you switch the wiper around, a regular log pot will work. I mention this just because rev log pots are harder to find and more expensive. Very nice schematic!

Thanks,
Dan

EDIT- Sorry, switching the wiper does not make it right.