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)

Comments

[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.

[A good name]

This will sound really lame, but what is feedback exactly? I've heard Tom Morello uses it for quite a few songs, but I'm sort of vague on what it is.

[pstretz]

:) That's not lame at all. Feedback, with respect to delay or echo, is simply sending the output back into the input. Typically with a cheap delay, only the original input signal is repeated and sent to the output. On more expensive echo pedals you had the option to send that output back into the input to be effected again. By sending enough of the output back into the input, you can get a case where the repeating never stops and turns into a huge wall of sound. This is done a lot in dub and electronic music. The feedback that Tom Morello is known for, as far as I'm aware, is more of a feedback loop caused by turning the gain up on an amplifier to the point where the amp output is feeding into the pickups and getting amplified again. You could essentially play forever without ever having to pick a string. In rock music, the lead guitarist will likely finish out a song by letting the guitar ring into feedback. See wikipedia here for more info, http://en.wikipedia.org/wiki/Audio_feedback. The Apocatastasis I designed here will not likely help you with that.

[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.

[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. :)

[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?

[pstretz]

What did you hook it up to? It is not an effect itself, you need to connect it to another effect.

[mikebruse]

I'm not really sure what is going on; I have it hooked up to a fuzz pedal which now only slightly extends the note length. I have the pot turned all the way up too.

[efilho]

Did anyone tried it on a DIST/OD? Any sound clips? Cheers!

[acousmatic]

please be patient with me...long time player but brand new to electronics....it worked really well except the repeats all sounded like they were up two octaves, not natural like your audio examples(quite ear piercing). Could it be the capacitor? the closest i could find to a 0.05 film cap was '0.047uF/47nF Greencap Metallised Polyester Capacitor ', '0.047uF 50V Blue Chip Monolithic Capacitor ' and a '0.047uF 50 Volt Ceramic Capacitor'. (i used the first option). your help is very much appreciated. great project!

[pstretz]

hmmm... any of those should have worked. if you connect the instrument directly into the circuit what do you hear? my delay gets a high pitch if i have this circuit turned up more than 2/3. try setting your pot to 1/4. try switching out the cap for the ceramic one. i have all the patience you need. we'll get it working, have no fear. :) what effect pedal are you hooking it up to?

[acousmatic]

hey! just wired it all together... can you quickly explain the reverse wiring (tip) on the mono jack, not sure i understand. do you mean to say that the 'earth' becomes the 'signal'? but only on one of them? thanks! cant wait to plug it in!

[pstretz]

the first time I wired it up i accidentally reversed the wires on the input. the way i had my jacks mounted, the tip of the output was in line with the ground of the input, but i wired the gnd as tip and spent some time troubleshooting. just pay attention and you should be fine. :)

[thedbc]

sweet, thanks. I am going to build this into the box with a diy digital delay I just got in the mail.

[skincage]

This is a great workaround for pedals that don't come with the ability to self-oscillate. Having a breakout box means you can use it on any effect rather than having a permanent mod in a pedal case that could eventually cause a problem. Thank you for sharing this.