DBA Echo Dream - with reward

[m-Kresol]

Hey guys,

as always, I have a problem with a build. And as with my last view builds, I'll put out a reward for the person that gets me to a working pedal: You get a pcb shipped to your door. The pcb was also included in my BOTY package in the hopes I get it working, so there's that.

So this is my take on the DBA Echo Dream 2. I basically took the schematic that is out there, redrew it in Eagle (it's basically identical) and made a layout. You can find the ,,original" schematic, the redraw and the layout in the zip file linked below. Several people commented on effectslayout and tagboardeffects that they managed to build it on vero, so the schem should be fine and the project doable.

It generally works, all the functions do what they are supposed to except for at long delay times. I get this weird ,,dog farty thing" (© cooder) going on, where the delay chip is motorboating like crazy. It is dependent on the settings of the VCO chip. You can hear the problem in the clip below.

In addition, I got a serious white noise problem, which I didn't notice at first but is very strong at high fuzz and vol settings. (it is possible that it wasn't there in the beginning, but I can't say for sure) could likely be improved by boxing it, but I doubt it would remove it entirely. More likely this is related to the AC ripple I found on the DC supply, which is amplified. More on that in the pdf.

Things I've tried so far:
First, I had fake XR2206 chips, but got decent ones and the oscillator is working (checked via oscilloscope). Also got some original ones from the 70s from a coworker. They are a bit different, but still lots of noise. Overall, I think the chips I've got are decent
I switched out the PT2399 and tried 3 overall, all with similar results
Checked my soldering
Checked component values and schematic on original schem, tagboardeffects and effectslayout.com and compared it to mine. Seems to check out.
Checked my actually soldered components for value and orientation.

Brian suggested to increase R28 (on my schematic) to around 270k. Played around with it, but couldn't eliminate the noise.
He also said that R18 makes more sense to go to pin 13 of the Pt2399 instead of the junction of R16/17. Tried that, didn't make much difference.
Also tried the green LED from pin 7 of IC3 (Pt2399) to GND. Didn't do the trick either.

I populated 2 pcbs overall and both behaved similarly.

The voltages were probed with a DMM and an oscilloscope and can be found in detail in the pdf in the zip file along with the schematics, board layout and pics. In short: the DC input is straight DC, but there is a slight AC overlay after the input resistor, when the VCO chip is inserted. The noises are highly dynamic depending on the settings, but generally are related to depth, rate and delay time settings (amplified by fuzz and vol obviously).

Obviously, I could not find the culprit after about 5-6h of debugging. This is were you come in. I would really appreciate it, if someone finds the time to compare schematics, check the layout for obvious design rule mistakes,  give some tipps on where to search, etc.. I'm busy at work again and hardly motivated for this atm to be honest, but having no idea where to start and always ending without any progress doesn't help either.
Imho, it is likely either a systematic error that I did twice and did not see or a design mistake with the pcb layout. This is my first delay and they are tricky to do right. Especially since DBA is known for their notorious out of spec parts and childlike layouts, this is ok for me. It could just well be that the 8Vpp swing of the VCO is coupling into some other nets or similar stuff. I should have given the VCO it's own seperated ground plane to begin with.

ZIP-FILE thanks for looking!

[DLW]

I'm not sure if this helps, but....
I built the PCB Layouts etched version. I had to swap the 47n above SW2-3 for a 47p and the 220n below SW1-4&5 for a 220p. It sounds good. I even boxed it.

[m-Kresol]

thanks for the input, but I had that already. It was only wrong in the effectslayout layout, but not in the others.

Thanks!

[flanagan0718]

**Necro post**

Hey Felix,
I recently got one of these board and I am going to see if there is anything I can find. Been wanting one for a while and what better way than to trouble shoot this board that was already laid out for me! I will update if / when i find something. PS thanks for the zip file with all your notes!
-Mike-

[Betty Wont]

Not gonna lie. I would totally build a pedal that only made that sound.

[m-Kresol]

thanks Mike, I appreciate your efforts. I have never found the motivation to get back at it again. To be honest, pedal building has decreased drastically for me... I actually picked up my guitar the first time in 3 month after moving just to get a nice text from my neighbor that her 1 year old keeps waking up 

[flanagan0718]

thanks Mike, I appreciate your efforts. I have never found the motivation to get back at it again. To be honest, pedal building has decreased drastically for me... I actually picked up my guitar the first time in 3 month after moving just to get a nice text from my neighbor that her 1 year old keeps waking up 

***another necro post***

I finally got around to building this and it fired right up. The rate and depth don't seem to change much in the effect. Everything else seems to work as it should and I don't get the motor-boating issue. I did make a couple changes (that I can't remember off the top of my head) but they were all recommended by either you or Brian.
I got the XR chip from eBay and they both tested fine, I think, once the board was built up. I also used a TL for the op amp. I'd be happy to take whatever measurements you want me too in order to help. I can also confirm which "Mods" I did once I get back into the shop. I did want to let you know that I got mine, for the most part, up and running. Let me know what you need.
-Mike-


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[m-Kresol]

cool, i appreciate it!
I'll probably start another board from scratch, let me know the mods you made.
rate and depth did change mine a lot - or at least it changed the motorboating. can you measure the output of the XR chip to see if you have indeed oscillation that changes with speed and depth pots? just in the unlikely event your chips are dead after all

[TobaccoBurst]

M-kresol,

Is the zip file in your original post still active?  Seems not to be, but could be an issue on my end.

Cheers,

Jim

[flanagan0718]

I'll check to see if I still have my working one. I still have the old zip file...somewhere and I should be able to figure out what mods I did. Sorry for the delay (haha) on this. Took a break for a while.
-Mike-


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