New Looper Design

[nelson]

full schematic?

[slacker]

full schematic?

thats just what I was going to ask for. Looks like an interesting project.

[Jaicen_solo]

I'm really interested in this. All I think I really want out of a looper is the ability to record and play simple as that. Then what I would do is have an output jack for both the loop and then my guitar. This way if I wanted to add any effects to either one I could do that before recombining the signal and eveyrthing would be solved.

In that case, connect pin 2 of the PLAY pot to the hot pin of an output jack and you're sorted. You could even have the jack be a break socket, so that when nothing is connected, output goes to the internal mixer as per normal. The project will probably be updated to use a buffered effects loop at some point, I just couldn't find space on this particular board for that! (Although that's the whole reason for re-doing the layout in the first place!). Oh, and I put in a space for the LED/LDR control in the top left hand corner. This allows any variable resistance to ground to cause a pitch down effect. Could hook it up to an LFO for a vibrato effect as well.
I've done a couple of updates to the board, mainly moving components to more logical positions to make it more build friendly. Updates soon.
As for the schematic, I'll see if I can find the old digital schematic section. The analogue section is entirely Dean's design which can be found on generalguitargadgets.com. I added some light low pass filtering before the analogue-in pins (0.01uF/100k RC network). I figure since it's not going to record anything above 3kHz, I might get a better signal/noise ratio.

[Jaicen_solo]

Here's the complete digital schematic (I think it's complete at least!).  Whilst drawing it up I noticed a couple of errors on the PCB, so that will definitely need an update!
Voltage regultor is as per my optically variable design, that's on the schematic at the bottom. Using an LM317, voltage can be varied between +4.5v - +6v, should give plenty of pitchshifting action! It would also be possible to just replace the LDR with a 16k resistor for a fixed 6v power point. That said, i'm not sure how that will affect the bias on the TL074, but it seems to work ok in Mathflan's Dirty sam.

[robbiemcm]

Thanks so much for this Jaicen_solo it looks like a really good project. I will build this one when I feel I'll be able to pull it off succesfully, but to do it I'll need the ISD2560. And I'll get that when I go to England in a few weeks as I have no other means of getting here in Australia. I'll just build it as you made it as I would have no idea how to make the modifications you suggested for the ideas I had (I can only follow schematics, lol). Well.. I think I understood the part about using one of those jacks so that when one jack didn't have a lead in it the signal would just combine with the other one before the other jack. Anyway, thanks for the work you're doing.. I'm really excited about this one

[slacker]

cheers for the schematic, I've put this on the to build list, might make a nice project to start the new year

[Jaicen_solo]

Thanks guys, I like to feel i'm giving something back after my many years of learning

Robbiemcm, if you're coming to the UK, search out a Maplins store. Since there's one in my home town, I tend to create projects which use components they stock. I'm leaning toward getting an ISD2532 rather than a 2560 as it's about half the price. It's also half the record time, but I can't see me needing more than 30s anyway. All in, it's possible to get this project together for about £10-15 depending on what caps and things you buy. The board is spaced for mini-electrolytics in the psu filters (+1 ceramic beneath the ISD chip), and Mylar caps in the signal chain. All the resistors are 1/4W, spaced to 0.4 inches. Makes things a whole lot easier when populating if everything can be bent to shape beforehand, and I find mylar caps to be reliable and good sounding.I recommend getting a Header socket for the ISD, which will allow you to add the small ceramic bypass cap beneath the chip itself. If not, it can always be soldered to the traces side. Actually, it might not even be necessary, but I am paranoid about noise in this circuit!
If all goes well, i'm going to get all the components together for my build this week. I'm looking forward to some hardcore looping action by next saturday!   If there are any mod's you'd like to see included then let me know, i'll see if I can work them into the schem. I'm certainly going to try for an FX loop, if I can find room for some in/out buffers.

One final thing to note, is that the LFO section on my variable regulator is taken from Tim Escobedo's site; Circuit Snippets. I think it's a nice neat design, Thanks Tim!

[robbiemcm]

Well, to be honest I really think it would be a great feature to have to two seperate output jacks, and then if one isn't connected they just combine at the other one. Is it as simple as connecting the wires together or do you need weird buffers or 1M resistor across blah blah blah (I have no idea what I'm talkin about now). If you think about it it would be great to have the output going through whatever pedal you desire, for example I expect many people will require a different sound to the backing chords if they want to solo over the top. And if that feature was there then you wouldn't really need that vibrato thing would you? You could just chuck in another pedal.

Also, I think I found the right chip at a place closer to home for a cheaper price than you can get from England.
http://www.futurlec.com/     Then in the search, type ISD2560
Is that the right chip? It seems to fit the right specs and it's also about the same price as the one with less recording time that you speak of. The only confusing thing about that is 60 - 120 seconds? Does that mean it has a minimum recording time? That wouldn't make sense.. either that, or it'd be annoying to be required to record for 60 secs..

[nelson]

Just ordered the IC.


Should be fun messing with this.

[Jaicen_solo]

Robbiecm, that is indeed the correct chip. The record time is quoted as a minimum, as it can be increased by changing the sample rate. Power supply voltages affect the internal clock, hence the pitchshifting. That's also why the play speed decreases.
As for price, I just found the ISD2560 and 2532 at RS components, for £8 and £5 respectively, so i'll probably get a 60 for three squid difference.
I'm going to leave the voltage regulator design in I think, you can just use fixed value resistors if you don't want pitching effects. It will work just as well.
It also occured to me that since you'll need a dpdt play/record switch, I could just dispose of the transistor circuitry and run the indicator LED's directly via the switch. Much easier build that way, and eliminates about 10 components.
I'll work on adding the effects loop this weekend, should hopefully have a final revision on monday. Till then, don't build anything as nothing is verified!

[Jaicen_solo]

Here's something for you guys to be getting on with; a Mobius Lite.
This version of the schem has no effects loops etc, just a straight single sample looper. Record/play LED's are driven from the other half of the Record/Play DPDT stompswitch to save board space, which is down to 2.7" square. I think it would be hard to make it any smaller (The ISD Chip is 1.4" Long!!) The indicator led in the top right pulses at the end/start of each repeat, but can be omitted if not necessary.
The reset pins should be connected to one pole of a 3PDT switch, so that it starts from the beginning of the sample whenever it is engaged. If you want, this can also be omitted so the loop will play continuosly, however this cuts current draw to just 10mA when not in use (as opposed to 30mA when playing). Pin A should be held high by connecting to pin B when the pedal is bypassed.
Other mods that could be added include a tone control, such as a 0.02uF cap from Play pin1 to pin 1&2 of a 100K pot, with pin 3 to ground. This will allow you to dial in some heavy treble cut on the loop, but not the direct signal.
This is intended to be a less daunting build than the other loopers out there, i'm hoping more people will want to build this layout for it's simplicity, especially those new to these things. Everyone should have a looper for practice and songwriting Let me know your thoughts guys, I'm starting work on my Deluxe Mobius now

[nelson]

Great work man.

I am going to wait for the Dlx version, also perhaps you should change the name?

I am going to reiterate a request for a full schematic.

[Jaicen_solo]

Cheers Nelson!
I agree, i'll build the deluxe myself, probably both actually! I just thought it would be nice for a less advanced stompboxer
Below is a layout i've just cobbled together for the deluxe version, which features pitchshifting, effects loop and tone control, in addition to the regular features. Schematic is to follow shortly when i've got it all drawn out neatly. I find them more work than layouts to be honest, though I usually spot any errors when drawing the final schem up. Let me know if you spot any errors. The effects loop i've added is just a buffered loop using a TL072, biased as per the TL074. Mix In & Mix Out should be connected together, though they could be connected to a toggle to send the mix to another output as per RobbieCM's suggestion.


Components:


Traces:

[robbiemcm]

Thankyou so much for the work you've done Jaicen, I hate to think how many hours of work you must have put in to come up with all of this. However, I'm pretty new to this whole thing (although I'm getting there steadily) I might need some assistance in figuring out what to do with the two outputs and everything. The Mobius Lite looks perfect for me, it doesn't have too many extra features like the Deluxe. It'll be far easier to start off with I suspect rather than varying voltages and such.

I must ask this though, is the record button the same as the play button? So it engages as soon as you finish recording? And wouldn't it be good to have a stop switch aswell? What happens when you don't want it playing in the background anymore? Then the reset would become a sort of play/reset.
And also I see the A,B,C parts for the switches, am I right in thinking that that corresponds to one pole of a dual throw switch? B being the input and A and C being the two throws?
With the Lite version, there is just a straight output. Is it possible to divide the guitar and the loop output on that version? If you can show me where to pull the two from I can probably take it from there

Once again, thankyou so much for the work you're doing

[slacker]

I must ask this though, is the record button the same as the play button? So it engages as soon as you finish recording? What happens when you don't want it playing in the background anymore?

If I understand it right you press the record/play switch to start recording then press it again and the pedal plays what you've just recorded. The effect also has a seperate true bypass switch, so if you don't want to hear the loop you bypass it, when you engage the pedal the loop starts playing from the beginning.

This leads me to a couple of questions though. Will the pedal actually work with this switching system? I only ask because the data sheets talk about pulsing the CE Pin low to start/pause the play or record operation, on the schematic above the CE is tied low all the time.
Also I think that if you record for the full duration of the chip it won't loop, and you'll have to start play manually, which may or may not be a problem, just thought I'd mention it.

[Jaicen_solo]

The CE pin only needs to be pulsed if the chip is operating in momentary push button mode. In this design, it's operating on levels, when CE is held low all the time to enable play and record. If CE goes high, everything stops! It is possible to add a pause mode, by taking the CE pin high during record/play. I might add that to the deluxe layout if you guys think it would be useful (can't see it myself though).

The design of the 25xx series now means that there's no longer an OVF or overflow pin. Previously this was used to reset conditions or for cascading multiple chips. With the new chips, if you reach the end of the record time, it will just stop and wait and begin looping as soon as you hit play. If you record a full 60s, it will still loop when it reaches the EOM marker.
If you don't want the pedal to go straight back into play mode when you engage it, just click the bypass switch before you hit the play switch. That will put it into standby mode (thus ending the recording), ready to begin looping when you hit bypass again. If you were really fussy about it, you could just wire up the reset pins to a second latching on/off switch and use that to start and stop things.
Robbiecm, you are correct about the switch wiring. B is the center pole of a SPDT, or one half of a DPDT.
On the deluxe layout, Mix out is the output of the ISD chip, buffered by the effects loop. Effects are wired to the FX send and returns. Mix out needs to be connected either to the MIX IN connection, to use the mixer in the circuit, or it can be wired to a seperate output. In this case, you can omit the fx send/returns. If you don't want to use the FX loop, just connect PLAY pin 2 to the MIX IN on the layout and omit the TL072 and associated components.
On a related note, I found a website somewhere where one of these loopers had been built with a pair of chips, each recording the same thing. They can then be pitchsifted and generally messed with to make some really interesting chorus/flanging and general dischord.  Nice!

[robbiemcm]

Sorry Jaicen, I still don't quite understand what I need to do in order to get the two seperate signals. I tried tracing it backwards referring to one componenet layout, one trace layout and the deluxe layout but that didn't end up doing me any good. And surely it would be best to just use the Lite version? That currently has everything I want except the two seperate outputs. Is it possible to do it with the Lite version, or are they not combined via traces and combined inside a chip making it impossible for me to to it like that.

It seems as though they *could* be from those 100k resistors connected to a cap, then to output, but I wouldn't know. I'd take a guess that saying the lower 100k resistor is the clean guitar signal? Maybe you'd be able to indicate on you schematic where each seperate one is before they are recombined (if it works like that) and then I'm assuming all I'd have to do is chuck a 10uF capactior from those outputs to my jacks? Or would I choose a different value when taking two seperate signals.

Thanks for putting up with me,
Robbie

[Jaicen_solo]

It's actually pretty simple Robbie, once I get a schematic up you'll be kicking yourself

There are basically two paths for the signal, one goes from the input buffer to the input of the ISD, the other takes the output of the ISD, buffers it and feeds it to the mixer stage, which mixes signal from the input buffer, in with the ISD signal.
To Isolate the output of the ISD, wire up the PLAY pot as per normal, but take the wire from the center pin of the pot to wherever you want it to go (ie, seperate out jack) instead of the PLAY2 pad on the PCB. The wiper of the play pot normally connects to the mixer circuit, but if you do this, you'll just get the clean signal from the buffered input at the output of the PCB.
Does that help??
EDIT: How's this?

[Herr Masel]

Am I the only one that gets a blank page when I click the links for the layout?

[Jaicen_solo]

The old layouts have been removed, they had a few errors. The new layouts should all be embedded into this thread.
Don't build anything yet, I've fixed a few errors on them today.