PT2399 looper? No?

[JimRayden]

One good trick is to take the feedback directly from the OP output and apply the filtering just to the final output. That would be, feedback (for looping purposes) taken from pin 12 back to input low pass (at pin 16, with apropiate resistor). The output to be mixed taken from pin 14.

By a glimpse at the datasheet (the block diagram), I'd send guitar input to 16 (LPF input), then take the signal from 12 and send it into 10 (OP1 input, that seems to enter the circuit after LPF1), therefore ditching the LPF from the feedback loop. Also nip some signal to pin 13 (input of LPF2) and get the output from pin 14.

In delays (and especially on settings of many repeats), all kinds of filters in the feedback loop can turn evil. Better to avoid them...

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Jimbo

[Joep]

Hi Jim,

If you want to create something like the device that is shown in the YouTube movie link you posted the PT2399 will not work for you.

- First of all (and already mentioned) the usable delay time is 300-400ms. You needs at least 5 - 10 seconds, so you need to at least cascade 15 PT2399. How are you controlling delaytime? A 15 ganged pot?

- With PT2399 there is no way of stopping and (re)playing the recording, like is done in the movie.

- Because you need to feedback the output of the delayline (doesn't matter how many) to the input again to create the loop the signal will degrade after every loop (also already mentioned). Filters are used to keep out unwanted high frequency parts introducted by the delay circuit. Leaving the filters out will increate the problem of degraded signals.

Bye,

Joep

[JimRayden]

Thanks for the closer preview of the problems, it cleared stuff out for me a bit.

I'll leave this project for a later time when I'm more vacant.


Meanwhile, visit me at "How Will This Waveform Sound?". (Shameless promotion, I know... )

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Jimbo

[Cliff Schecht]

Honestly, I would never bother to design and build a looper now, the cost wouldn't justify the project. It'd be a great learning experience, but Boss just came out with the RC-2 single Boss pedal sized looper that's a @#$%ing steal for $179 (IMHO). As great of a learning experience it would be to design a looper, it just isn't worth the trouble. Same with something like a pitch shifter or anything else digital, it's just not worth the hassle compared to what's now available. I guess this stems from the fact that I hate programming though.

[JimRayden]

Ahh, still the recorder chips cost nothin compared to the Boss. Plus, I have a principle, or rather an obsession for only playing through self-built pedals (and wierd noise makers from 80's, for that matter ).I'm currently planning on building an amp and also looking into guitar crafting, one day I hope to be playing all self-built gear. DIY to the max!

Besides, I'm not that much into loopers to buy a Loop Station, it's more about if I can handle designing and building one. Don't get me wrong, I will find application for a looper and propably use it extensively once I have one, but I can live without it.

Call me a bozo if you will.

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Jimbo

[Jaicen_solo]

Personally, I think that a looper project would be well within the scope of a DIY project, it's just that people seem to be thinking in a very 'analogue' kind of way.
It is possible to control some 4164 CMOS delay chips such as those used in the Boss DD-2 with just a single micro-controller.Three 4164's will give you 800ms at a clock speed of 1.5MHz in good quality. If you drop it to 1Mhz or less, you get even longer times (i'd guess about 1s at 1MHz), but the quality begins to degrade, not that that's a bad thing actually! Obviously, a looper with these chips would be quite limited, but i'm pretty sure it would be simple to upgrade to larger CMOS RAM.
So, lets say we use the 4164 as an example. The chip can't do play and record at the same time (afaik at least), so if we wanted sound on sound we'd need two sets of ram, so that one can be in playback whilst the other records.
I'm thinking that the RAM could be controlled using a PIC, probably not the 16F84 or whatever, but the larger 40 pin chips perhaps.

[slacker]

I'd go along with that, a more advanced looper is almost certainly a DIY possibility. It's just that I'd guess that a lot of people here, me included have no knowledge of or have no interest in the digital side of things.
I can just about get my head round simple digital switching using invertors and diodes but I wouldn't have a clue what to do with a PIC or micro controller. I'd have to learn an entire new skill set just to know what was or wasn't possible.
Perhaps this is one for the DSP forums?

On a side note my RC2 arrived today, and it's amazing. Not sure how I'll use it with the band but I think it's going to be a very creative tool and it's great fun if nothing else 

[JimRayden]

Although I consider myself an analogue purist (from my fingers to guitar speaker at least), I'm quite intrigued by DSP and PICs. This thread might eventually turn out to be forthe DSP-section, yes. But not yet. As long as I'm merely using a recorder chip. Have you given the chip programming language a look? Although the outcome is nothing but seemingly senseless numbers, it's actually quite fun to put together. Basically you have this big 'house' (the chip) and you start bossing the bits around, as to where to go and what to do. It sure gives a feeling of dictatorship.

I have promised myself to take a month and really concentrate on digital chip programming, this discussion is making me consider pulling it off quite soon.

Perhaps this is one for the DSP forums?

Not yet, slacker, not quite yet.

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DigiJimbo

[Jaicen_solo]

I personally haven't got any knowledge regarding the programming of PIC's, it's something i've just gotten into lately through ucapps.org. So far i've only built a MIDI sync converter for my DR-110 drum machine, but I have more stuff planned.
The thing about PIC's is that they have a host of pins which can all be assigned to perform different tasks depending on the code programmed into them, or from an external input. For example, the PIC i'm working with at the minute takes a MIDI input at one pin and outputs a 12ppqn signal on another pin. Pretty clever really.
I think that a PIC would open up some interesting possiblities for switching if nothing else.

[JimRayden]

Basically you have this big 'house' (the chip) and you start bossing the bits around, as to where to go and what to do. It sure gives a feeling of dictatorship.

Or rather, PICtatorship.

I think that a PIC would open up some interesting possiblities for switching if nothing else.

Ahh, I believe a PIC would also make quite a funky LFO for any circuits. How about a custom wave loop for your tremolo or Neovibe. A shuffle tremolo would be cool for blues. Plus they're synchronizable...

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Jimbo