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Deltalab Echotron ADM 4096 clock noise -> help!
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Author Deltalab Echotron ADM 4096 clock noise -> help!
monstrinho
OK, I have two ancient Deltalab Echotron digital delays, both of them working _except_ for some really excessive clock noise, especially at longer delay times. I've completely recapped the power supplies in both of them, and this improved the overall signal to noise ratio, but did nothing to improve the clock noise issue. There's very little information about these online, and I'm not able to find a service manual anywhere. I was able to turn up a schematic:



I'm just wondering if the more technically adept of you might be able to take a look at the schematic to see if there might be a modification that could be made to decrease to clock noise? Any assistance you guys could give would really be appreciated. These things sound great at shorter delay settings, but they become almost unusable at longer settings, which is a shame.
monstrinho
Nobody??

Well, OK. Could anyone recommend a good tech who understands older digital gear?
Jarno
Well, noise at longer delay times, so slower clock. Could be a decoupling cap broken. Shouldn't be a layout issue since you have another one which is working properly.
Do you see any differences between the two units?
Can you swap power supplies, or is everything on the same board?
monstrinho
Jarno wrote:
Well, noise at longer delay times, so slower clock. Could be a decoupling cap broken. Shouldn't be a layout issue since you have another one which is working properly.
Do you see any differences between the two units?
Can you swap power supplies, or is everything on the same board?


Everything is on one board, so switching out the power supplies won't work (and I've recapped both supplies, so I'm fairly certain it isn't a power issue). Both of them are working, both have the same clock noise issue, but one is substantially worse. I've read that these units have a "tracking filter" to filter out the clock, but I honestly cannot locate that on the schematic, which is why I asked for help. I was hoping someone could spot which part of the circuit filters the clock, and possibly suggest a mod that would improve the filtering. I don't expect to be able to make it perfect, but when the clock is nearly as loud as the delayed signal, it becomes a serious issue. There are three trimmers on the board, but they deal with the clock frequency (overall delay time) and feedback amount. So, there should be a combination of resistors and capacitors that deal with filtering out the clock noise, but as I said, I honestly cannot spot that in the schematic.
BugBrand
Better schematic here: - http://www.loopers-delight.com/tools/deltalabs/echotron.jpg

On a brief look - I see it uses RAM chips & have had similar(ish) devices where I've had to replace RAM [powertran DDL].
Is the noise 'regular' - if you set to a long delay time, can you hear the noise as individual bursts?
I think the first thing I did was swap around RAM chips pair by pair to ID which had failed and was causing the noises.

edit - RT5 - Noise Tune - ?! Could this be of use to you... what does it do?

edit 2 - I can't spot a tracking filter. Clocking is ICs47-49 and feeds the RAM and Encoder/Decoders. Can't really spot where filtering is occurring other than around the 2nd half of IC1 (the half near the encoder section)
monstrinho
BugBrand wrote:
Better schematic here: - http://www.loopers-delight.com/tools/deltalabs/echotron.jpg

On a brief look - I see it uses RAM chips & have had similar(ish) devices where I've had to replace RAM [powertran DDL].
Is the noise 'regular' - if you set to a long delay time, can you hear the noise as individual bursts?
I think the first thing I did was swap around RAM chips pair by pair to ID which had failed and was causing the noises.

edit - RT5 - Noise Tune - ?! Could this be of use to you... what does it do?

edit 2 - I can't spot a tracking filter. Clocking is ICs47-49 and feeds the RAM and Encoder/Decoders. Can't really spot where filtering is occurring other than around the 2nd half of IC1 (the half near the encoder section)



RT5 is the tone control for the feedback, so it doesn't really affect the clock noise at all. The noise is constant, it doesn't come in bursts. One odd thing is that when you turn the delay time knob for a longer delay, the clock noise changes in volume and frequency, but decreases slightly in volume after a second. It's this strange lag that made me think there must be a capacitor involved somewhere. Swapping the RAM chips around sounds like a possible way forward. The only thing that's a bit of a drag is that all of the ICs are soldered directly to the board. Situations like this make me happy that I invested in a Hakko 808 desoldering gun! Thanks for the help. Hopefully I'll be able to find the source of the problem.
BugBrand
No, RT5 is definitely some form of little offset adjustment - feedback has a simple tone control 'Feedback' (soft to hard - simple RC lopass/hipass crossfade) + trimmer to adjust max amplitude.

Maybe IC 10 and 11 are the tracking filter actually.. PWM style? using 4016 switching.. haven't really got my head around it!
calaveras
Just had to chime in to say I'd never heard of an "Echotron". Only their "Effectron". Which I own a couple of. I've had a problem with reliability of these over the years. But never a noise issue.
Curious about anything you guys can dig up just for kicks.
+ 12, -12 and +5 power supply? Doepfer -ize it.
DIY_geek
That better schematic helps!

I was going to suggest C49, C50 and C51 as part of a 3 pole output filter (doubling each of those and seeing what happens). Bandwidth looks right off hand but I'm not sharp enough to just bang out the math and don't have time to punch it into LT Spice. Course, a tracking filter wasn't on my radar when I looked at it. And there's all that gobbely-guuk in the upper right that might be something clever.
BugBrand
I'd be doubtful those would cause a problem.

Further thoughts
- CMOS chips do go bad (and other chips too, of course). At least things around the enc/dec are easy to source, though removing the chips and putting in sockets would be a chore.
- I see there are polarized/electro caps (C37-39 in particular - C24 too) - those'd be the caps to check first - if there are any tantalums then def. replace them.
DIY_geek
Have you tried messing with RT5 yet?

Looking at it a second time, I concur that U10/11 appear to be a switching filter or a switching something-or-other. I would presume U10 as a diff input is intended to reject the switch noise from the 4016 with RT5 there to adjust the balance (and thus rejection). Anything that would mess with that balance seems like it would create a noise box - part of the 4016 not working, one side of the 4013 not driving, any of those components around there throwing off the symmetry. Can't say I see how but C1 and C2 being leaky?

Just throwing out ideas. Quite a machine thing this is!
monstrinho
Time to place a Mouser order for a boatload of ICs! In the meantime, I'm going to go through and replace all of the electrolytics that didn't get replaced when I did the power supply. No tantalums anywhere, so that's good. I really appreciate the help, and I'll follow up here once I get a little further along with everything.
Peake
I'm a big fan of their DL-2, and was told it is full of tantalum capacitors, which were replaced during a service call...check that. Best luck.
BugBrand
monstrinho wrote:
Time to place a Mouser order for a boatload of ICs! In the meantime, I'm going to go through and replace all of the electrolytics that didn't get replaced when I did the power supply. No tantalums anywhere, so that's good. I really appreciate the help, and I'll follow up here once I get a little further along with everything.


But - still -- what about RT5!!??!! Does tweaking that help?
monstrinho
BugBrand wrote:
monstrinho wrote:
Time to place a Mouser order for a boatload of ICs! In the meantime, I'm going to go through and replace all of the electrolytics that didn't get replaced when I did the power supply. No tantalums anywhere, so that's good. I really appreciate the help, and I'll follow up here once I get a little further along with everything.


But - still -- what about RT5!!??!! Does tweaking that help?


The reason I thought RT5 was a feedback tone control is because that is the effect it seems to have. It doesn't change the clock bleed through at all. If it is supposed to control the degree of clock noise somehow, then the fact that it doesn't is symptomatic of a problem elsewhere. Maybe a blown CMOS chip as you suggested, maybe a capacitor or two. In any case, the clock noise remains constant and RT5 doesn't alleviate it to any degree.
snufkin
resurrecting this thread because my Echotron also has a little too much clock noise, did this ever get resolved monstrinho?

also mine has an issue where the hold function doesn't work in the long delay setting.

Very strange
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