Intentional OD/DS into a basic PT2399 delay.

[Plexi]

Where (and which) will you place an od/distortion in this circuit, to make it sound "LO-FI" and boost with a JFET preamp?
Similar to an Echoplex, to get some tape distortion..

I suggest as example this simple/basic PT2399 delay that clearly shows where end the first buffer ends and where the second one start:

[Plexi]

[Mark Hammer]

When people think "lo-fi" they tend to think older telephone-type bandwidth, which implies bandpass filtering.  That's certainly not what "lo-fi" always means, or the complete solution to achieving it, but it is often an important piece.

The circuit provides the usual lowpass filtering.  All that is needed to get a bandpass-like sound is to restrict the low end.

[ashcat_lt]

I don't see a schematic here, but I'd start by trying to put it after the feedback is mixed in but before it goes into the delay.

[ElectricDruid]

I agree with Mark that a bit of judicious bandwidth limiting will help to give the thing some lo-fi heard-it-on-the-telephone character. I'd put the component values of those filters into the filter tools here and see what you get:

http://sim.okawa-denshi.jp/en/Fkeisan.htm

They look like 3rd order MFB filters, so this would be the page:

http://sim.okawa-denshi.jp/en/MultipleFB3Lowkeisan.htm

If they're fairly full-bandwidth, you might want to cut them down a bit so the top end is lower (but they might be pretty limited already, I dunno). Then go through and change any DC-blocking caps to purposely remove some bass too (C10, C7 for example). Everything below 800Hz say. Experiment. It's a question of taste and objectives.

After that, if you want some actual grit added (beyond what the PT2399 provides itself) I'd patch something in where C23 sits - after the delay output filter, but before the repeats. You want a fairly soft distortion, since it will build up on each echo, so I'd maybe go for a differential transistor pair rather than clipping diodes.

[Plexi]

Thanks everyone for your advices and answers.
In this case, you're right Mark about the therm "lo-fi".
In this case, I'm looking for some grit and dirt over repetitions.

I saw, for example DBA, adds a simple fuzz circuit at the end of all the schematic.
I don't know about MI Audio LoFi Delay, but it have a "Input" knob that adds 'distortion' to the repeats.
Another one is the Caroline Kilobyte Lo-Fidelity Digital Delay w/Analog Overdrive ("We've kept your original, dry signal path analog and pure, then given you a +21db boost/overdrive preamp to smash a low fidelity digital delay chip designed for karaoke machines and kids' toys into smeared, repeated glory").

The main idea is to smash a momentary footswitch, to max feedback and start to oscillates while get distortion.

After that, if you want some actual grit added (beyond what the PT2399 provides itself) I'd patch something in where C23 sits - after the delay output filter, but before the repeats. You want a fairly soft distortion, since it will build up on each echo, so I'd maybe go for a differential transistor pair rather than clipping diodes.

I think the goal could be reached over here...

[Plexi]

ACLARATION: DBA Echo Dream 2 haven't a fuzz circuit at the end.
It just messing the gain of the output stage: 1M pot over R22 as "fuzz" knob.