Apocatastasis (feedback Return for Cheap Digital Delays)

Intro: Apocatastasis (feedback Return for Cheap Digital Delays)

Most expensive analog delay pedals have a feedback knob that lets you drive the output of the delay effect back into the input. My Ibanez DL5 Digital Delay did not have this feature, so I decided to make one and make it cheap. :-)

photo's by Laura Stretz

STEP 1: Parts List

Chassis and knob:
Wanted to use an altoids tin, but my phone jacks wouldn't fit and i didn't want to switch to minis. So I found this Project Enclosure (3x2x1") at my local radioshack for $2.30
absolutely had to use the most obnoxious chickenhead knob I had. Got from mouser for $2.40

Components:
1 x .05uf film cap
1 x 10k resistor
1 x 1k resistor
1 x 10k 12mm log pot
wire (I used 22AWG solid core because it's what I had, use what you want here)
total cost per mouser: $2.47

Jacks, Cable, & Plugs:
I had a cheapo instrument cable that had a short in it somewhere, so I cu the ends off and used the cable for this project. I rang out each piece to make sure it didn't contain the short.
Jacks are Radioshack 1/4" Mono Panel-Mount Audio Jack (2-Pack) $3.99
Plugs are Radioshack Standard Phone Plug (2-pack) $3.99

Grand total cost: $15.10 (The jacks were a little cheaper in the store and everything is cheaper if you get it somewhere that's not RadioShack. It's concievable to get this down to about half the cost without too much effort)

STEP 2: Schematic

The schematic is really simple though it was a little challenging to get the idea working at first. Basically you are splitting the output and building a passive mixer for the input. I started with a 10k resistor on the instrument input but there was too much of the output mixing in, so i switched it to 1k and that solved the issue. I also found that when the feedback was way off in the weeds (pot turned all the way up) there was a really high pitch every delay and that sucked. putting in the cap solved the issue and after using it for a few practice sessions now i'm happy with it.

STEP 3: Assembly

i didn't bother making a PCB for this because there were so few components. Everything is wired point to point matching the schematic.
Tip:
When wiring the mono jack on the one side, the sleeve and ring are reversed from the first side, not parallel. If you touch the jack and it sends a humming sound through the line your shield and tip are the wrong way round.

More tips:
Using a straight edge to draw an X on a side corner to corner is a good way to find the center of plane for drilling.
Hot glue on the inside stops the cables from pulling out of the box.
You could try to put 4 jacks in the box instead of 2 cables, though then you'd have to buy patch cables to use it, and a bigger box, and you might wire it wrong if you're in a hurry.

STEP 4: Enjoy the Sweet Sweet Feedback That Goes on Forever

Here are some samples, first one is just the delay pedal without my feedback box
just the pedal

Next is my feedback box at a reasonable feedback level. Notice the much extended repeats of the delay
some effect
a little more

Here's the fun part, the feedback going off in the weeds. Yeah, it pretty much just does this forever.
there ya go
way out there

Maker's notes:
varying the repeats and the delay time while a lot of the output is fed back in causes some interesting things to happen.
this may work on other pedals like distortions or flange/phasers, though I haven't tried that yet as I have yet to build a flanger or phaser.

Comments

[crrollyson]

Do you have the sound samples hosted somewhere else? Would love to hear it.

[pstretz]

fixed the links, sorry about that. :)

[nnsg]

Awesome thanks so much ;)

[nnsg]

meee toooooooooooo

[pstretz]

fixed the links again. sorry about that.

[nnsg]

Have you got audio sample, would love to hear :)

[synthdust]

This is really cool. I hadn't realized that the cheaper pedals stopped using a feedback knob. And "All of a sudden" I started see a "repeat knob". It has been a while since I have owned a good delay pedal, so I never realized that they actually were not the same thing, I assumed that Repeat and Feedback where different ways manufacturers described the same thing. Now it all makes sense to me: the "change" in the knob names, AND why the newer pedals never sounded as lush as i remember delay/echo pedals sounding. This is a great way to get those sounds i remember out of these newer cheap pedals. GREAT JOB! (I hope that my post wasn't to abstract, and rambling...Rambling...RAmbling...RAMbling...RAMBling...you get the idea!)

[LeoneVuetivavalagi]

Hi I was just wondering if it has to be a film capacitor or whether I could use a ceramic disc?

[pstretz]

shouldn't matter one way or the other as long as the value is the same, I just had a bunch of film ones I had to use up. :)

[synthdust]

why not an electrolyte cap?

[synthdust]

This is really cool. I hadn't realized that the cheaper pedals stopped using a feedback knob, and "all of a sudden" I started see a "repeat knob". It was been a while since I have owned a good delay pedal, so I never realized that they actually the same thing. No it all makes sense to me: the "change" in the knob names AND why the newer pedals never sounded as lush as i remember delay/echo pedals sounding. This is a great way to get those sounds i remember out of these newer cheap pedals. GREAT JOB! (I hope that my post wasn't to abstract, and rambling...Rambling...RAmbling...RAMbling...RAMBling...you get the idea!)

[rathergood]

Thank you for your quick reply. As far as ground goes for a pedal like this, how do I connect them all together? The only circuits that I have ever made I have used a 9V battery, so it was simple to understand where all of the grounds went to. For this, my intuition kinda goes out the window. Thank you for your patience.

[pstretz]

I connected the sleeve terminal of each phone jack and plug to the GND terminal of the potentiometer. If you look at the assembly pic on the next step, you can see the black wires, these are GND. The sleeve on the two phone plug cables are copper, they are also in the bundle.

[rathergood]

I'm a bit new to electronics so I have a few questions. On all the jacks (or jacks/plugs in your case) on your schematic you only have one wire going to it, which I am confused about. Is there some invisible standard that I don't know about, like all the grounds are hooked up to a specific place. I tried figuring it out with the picture, but it isn't quite clear enough to see every connection. Also, just out of curiosity, at a components/conceptual level how/why does this circuit create feedback? Thank you, any help and/or clarification is appreciated

[pstretz]

Oh man, have I so been in your shoes. :) Sorry for not being specific. The sleeve on all the jacks go to ground and they are all mono jacks. This is a pretty standard thing to do. If you look at guitar pedal effects the sleeve on the jack goes to ground about 99% of the time. As far as how it creates feedback, see my reply to A Good Name on the first page, should be right below this reply. It may not be the feedback your thinking of, but this feeds the output from a pedal like an echo or delay back into the input to go through the effect again. Cheap delay pedals seldom have a feedback knob on them anymore. Hope that helps.

[coliusuriah]

i have a LINE 6 ECHO PARK delay with stereo in and out
if i run one output to my amp and the second back through 
into the second input would i get the same thing?
or would i need a some kind of resistance and not just the patch cord?
thanks 

[pstretz]

you might want some resistance to trim off the patch.  If the output just runs into the input, it's just going to feedback into noise.  Which is fine if that's what you're going for, but in most cases, you just want a few more echos. 

I'd just crack open the patch cable in the middle and put in a pot with one pin on the signal wire and another on the ground/shield and the last pin not connected to anything.  If the pedal has two inputs, it should have it's own mixer built in so you're all set.  Try the patch without modification first to make sure the signal gets fed back in before you go cutting up patch cables though.  ;)

Let us know how it works out.  If it works like we're thinking it will, I may have to get a new pedal.  :)

[coliusuriah]

thanks alot for the information! ill try it both ways. hopefully ill have enough time this week.. i will post my results and a link to a video when it happens.
thanks again for the response, you were a lot of help!!!! do you have a site with your own stuff?

[pstretz]

Here's the noise project I'm a part of.  http://www.aphoticdrift.com/  We haven't done anything in a while, but I used the feedback control a lot.  Basically my partner in crime was in charge of the analog parts of the sound and I was the digital part. 

Looking forward to seeing your testing.

[mikebruse]

I'm also new to electronics. After wiring everything together with what I'm pretty sure are the right parts, the pot basically acts as just a volume switch, any ideas?