Questions about the Lofi Delay by Renegadrian

[moid]

Hello everyone



I've had this tiny vero layout saved on my PC for years and have always wanted to hear what it sounded like ( I can't find any examples on of it on guitar anywhere; all the links are dead) so I set it up on breadboard today and have only managed to get it to be a weird fuzz effect or very occasionally, a single incredibly distorted slap back echo, or mostly just electronic noise or silence! I was looking at it and I realised there are a few parts of the image that I don't understand and therefore may not have setup correctly on the breadboard. Firstly some strips of the vero are coloured grey (the ones connected to pins 3-5 of the PT2399) Does this signify something? It might be that they all connect to ground maybe? Or that I need to do something to them that I don't understand? I'm also confused by the NC symbol next to pin 5 of the IC. What does that mean? I've googled it and it seems it could mean very different things (normally closed, or not connected) Should I change what pin 5 of the IC does?. I assume the jumper that runs from pin 5 to pin 3 does not also connect to pin 4? I did try splitting it into two jumpers - pins 3-4, then pins 4-5 and I got different squealing noise sounds, but nothing approximating a delay!

Did anyone build the pedal successfully from this layout? I found on Renegadrian's website that he used to sell a PCB of this circuit but it appears to be very different with a lot more components so I wonder if this 'slimmed down' version is one of those designs that only works when it feels like it, or if Saturn is in retrograde and Venus is rising. Thanks for your thoughts!

[RickL]

I'm going to take a guess here, but I think you're right about the grey strips indicating ground. I also think that, in this case, NC means not connected. So lift  pin 5 of the 2399 so it doesn't connect to the strip. I think the jumper under the chip does connect to all three strips, so pins 3 and 4 will be connected to ground and pin 5 is connected to nothing.  That make sense, since most schematics using this chip show pins 3 and 4 connected to ground and pin 5 not connected. This also means that capacitors a, a and b will each have one leg connected to ground and two pins of the 1M pot will be connected to ground.

Any chance you have a link to the schematic? It would be easy to figure out that way.

[ElectricDruid]

+1 what Rick said.

Pin 5 needs to not be connected to ground, and those three grey strips are all connected to ground by the links under the chip.

On a breadboard, you could just use another row *below* the chip and ground the pot and the two caps to there instead of re-using pin 5's row, which is a dodgy space-saving vero trick! 

[moid]

I'm going to take a guess here, but I think you're right about the grey strips indicating ground. I also think that, in this case, NC means not connected. So lift  pin 5 of the 2399 so it doesn't connect to the strip. I think the jumper under the chip does connect to all three strips, so pins 3 and 4 will be connected to ground and pin 5 is connected to nothing.  That make sense, since most schematics using this chip show pins 3 and 4 connected to ground and pin 5 not connected. This also means that capacitors a, a and b will each have one leg connected to ground and two pins of the 1M pot will be connected to ground.

Any chance you have a link to the schematic? It would be easy to figure out that way.

Thanks Rick. I am really sorry for wasting your time but while looking at my phone late in bed last night for more info I actually found Renegadrian had posted a schematic on this site to help someone else out:



Which I think does exactly what you suggested The downside is I've just done this to the breadboard version and now it only motorboats or is silent

+1 what Rick said.

Pin 5 needs to not be connected to ground, and those three grey strips are all connected to ground by the links under the chip.

On a breadboard, you could just use another row *below* the chip and ground the pot and the two caps to there instead of re-using pin 5's row, which is a dodgy space-saving vero trick! 

Thanks Tom, that's exactly what I've done... but the circuit is now silent or just motorboats, no guitar goes through.

I have another question, why does the vero layout show a link under the PT2399 from pins 3 to 5? The schematic doesn't show this, surely it should show a link from pins 3 to 4 only. I also wonder if my chip has locked up. I did try putting a 2k2 resistor from pin 6 to ground but that hasn't helped. I wonder if this is down to the vagaries of breadboard (I rarely have much luck with anything on breadboard actually working) so maybe I should just slap it on vero and try it? I might adjust it a bit and probably (I assume) should add a few components - like a 10K series resistor on the audio in, and a 1M to ground on audio in, and then a 10uF and 100K resistor on the audio out. I think I will re draw it first! And maybe put some sockets on the components around the IC so I can swap different values in to test them,

I might look at how delays use the mix or blend pot, because even if this circuit makes some amazing sounds I almost always want a bit of my original note to mix with the echoes...

[anotherjim]

The chips' Pin 5 leg needs to stick out of bed, or be cut off for stripboard.
This one...

Gives pretty much a perfboard-ready layout.
BUT! input and output need DC blocking caps, don't they?

[ElectricDruid]

Thanks Tom, that's exactly what I've done... but the circuit is now silent or just motorboats, no guitar goes through.

The trouble with "totally minimal" circuits is that they're often not that resilient because they leave out so much stuff that is usually included for safety or security.
PT2399 datasheet suggests *47uF* from pin 2 to pin 3, for example, not just 47p (which does very little).
Similarly, the 10p caps on pins 7 and 8 are almost the same as not using them. That might be the point here, I'm not sure. But until I got it working, I might put 100n's in there as per the datasheet. Once it's running, try 10p's and see what happens.

I have another question, why does the vero layout show a link under the PT2399 from pins 3 to 5? The schematic doesn't show this, surely it should show a link from pins 3 to 4 only.

The vero layout *doesn't* show a link to pin 5. It specifically says that pin 5 is "NC", "Not Connected". Like Jim said, the leg would need to be clipped off or bent out of the way. This is done like that so that the pin 5 vero row can be used as a ground connection.
The schematic shows the pin 3 to pin 4 link, and then shows the 1M Pot and the two caps connected to ground, just like the vero layout.

[moid]

The chips' Pin 5 leg needs to stick out of bed, or be cut off for stripboard.
This one...

Gives pretty much a perfboard-ready layout.
BUT! input and output need DC blocking caps, don't they?

Hi Jim
I'm sure you're right - Renegadrian used to sell a revised version of this circuit which has different caps and a lot more resistors (diff pots as well)
http://getlofi.com/shop/pt2399-lofi-delay-unit/ or this version, which 'almost' shows the whole layout, although other members of this forum couldn't get it working
https://www.diystompboxes.com/smfforum/index.php?topic=97739.0
Maybe I should give up with this one.

I just tested the power going to my breadboard version (running off a slightly old 9V battery) and the power at pin 1 of the PT2399 is 4.8V - would that be too low for the chip to power on?

[moid]

The trouble with "totally minimal" circuits is that they're often not that resilient because they leave out so much stuff that is usually included for safety or security.
PT2399 datasheet suggests *47uF* from pin 2 to pin 3, for example, not just 47p (which does very little).
Similarly, the 10p caps on pins 7 and 8 are almost the same as not using them. That might be the point here, I'm not sure. But until I got it working, I might put 100n's in there as per the datasheet. Once it's running, try 10p's and see what happens.


The vero layout *doesn't* show a link to pin 5. It specifically says that pin 5 is "NC", "Not Connected". Like Jim said, the leg would need to be clipped off or bent out of the way. This is done like that so that the pin 5 vero row can be used as a ground connection.
The schematic shows the pin 3 to pin 4 link, and then shows the 1M Pot and the two caps connected to ground, just like the vero layout.

Thanks Tom for the explanation. Maybe I'll swap a few things around on breadboard, or maybe I'd be better off trying something else?

[duck_arse]

erm - not p, u. if you skwint real hard, you can just make out that the v/2 cap is 47u, and those two caps down low are both 10u, as in microfarads. big difference.

now I'm here, I don't think either of those diagrams could ever be considered a circuit drawing/diagram. mechanical placings only are shown, and people are asking questions about that at that. this is why we always have proper circuit diagrams, schematics if you will, with our projects. information.

[I'd look elsewhere for a simple noise circuit - anchovie comes to mind.] also, don't be shy in showing what you have on the breadboard photographically. we can spot stoff on thum, too.

[moid]

Thankee Duck - My eyesight really isn't great these days, even squinting I can't see what you can see! I put the 47u and 10u caps in place (with the negative side of the cap connected to ground) but sadly there's no audio coming through, only faint hiss. I also found a different version of the circuit which shows a 47u where you said to place one, and 10nFs for the other two caps we were discussing - so in the interests of scientific debate I tried 10nFs instead, but no joy alas.



it's from this thread https://www.diystompboxes.com/smfforum/index.php?topic=97739.0

I did build anchovie's noise ensemble thanks (you helped me add a clean blend / boost circuit to it!) but if you know another interesting delay circuit then I'm all ears. Or fingers and thumbs. Or was it toes? Either way I'll get started on that tremolo and see if I can break that!

PS will take some photos of breadboard tomorow when there's some better light

[moid]

Stared at the above a lot and read through a few comments in the thread and I think I know where most of the traces go:



But I'm not sure about the resistors in the top right (circled in yellow) can't see what they attach to in terms of the trace from lug 3 of the 20K pot that goes under them and then stops which looks odd. Not sure if any of this helps.

[duck_arse]

your dead trace goes up to under the second 10k from top, then cranks left. we haf too asume there izz no other connection, but a circuit diagram would show.

[moid]

Thanks Duck! I'm waiting for parts to arrive before I can finish / fix the small pile of circuits on my desk so I thought I'd draw this out as a schematic in case anyone wants to try it... sadly I am rapidly running out of Summer holiday time so I don't know if it will get to it in time... apologies to anyone who tries it if it doesn't work.

[ElectricDruid]

Is that Repeats pot really wired up like that? That's weird.

[cab42]

I'm having a coffee break, and as I am planning to experiment with pt2399's, I took a quick look.

Isn't there something wrong in your schem near pin 16? (assuming that you are using the layout just above)

On the layout pin 16 is connected to three 10K's and a 10n, but in the schem only 1 10K.

Sorry if I missed something in the discussion. It was a short coffee break.

Edit: I think the 10K from pin 15 should be placed parallel to the 10n between 15 and 16 and then the 10K from repeat pot 3 should be connected to pin 16

I am looking into trying Clari(not) and/or Pitch Pirate

[anotherjim]

That repeats pot scheme is from other popular P2399 delays. It's not the obvious way to do it but seems to be carried over from existing schemes like simplifying the audio filters by leaving out a cap, but leaving in the extra feedback resistor for it.

I can see a few things suspect in the scheme but it's hard to talk about without part numbering.
From pin 15 to the repeats pot, should there be x2 10k in series or should one go back to pin16 across the 10nF cap?

[antonis]

From pin 15 to the repeats pot, should there be x2 10k in series or should one go back to pin16 across the 10nF cap?

Now you make us to dig up ancient data notes, Jim..

[cab42]

From pin 15 to the repeats pot, should there be x2 10k in series or should one go back to pin16 across the 10nF cap?

I think, that was what I tried to formulate above.

[duck_arse]

the 10k on repeats "3" goes hard to pin 16. the 10k currently on pin 15 should go pins 15 and 16. the string to the output is missing something. the 100R on the tip out is deffo wrong. I think the other shown 100R should be 10k instead. the 1k looks suss too, but that might just be me. and you should have a stop resistor of some value in-line with the delay pot.

mostly what cab said.

[moid]

Thanks very much chaps!

Sorry about the slow reply, I've been enjoying my last few days of freedom and have been visiting places, and I've even managed to build my first working chorus pedal* (Seppuku FX Mind Warp) and fixing holes in enclosures and currently spray painting them. Anyways I had a go at what cab42 and duck suggested so I present a new picture for your delight and delectation, plus some questions.

the string to the output is missing something. the 100R on the tip out is deffo wrong. I think the other shown 100R should be 10k instead. the 1k looks suss too, but that might just be me. and you should have a stop resistor of some value in-line with the delay pot.

mostly what cab said.

NOt sure what you mean by the string to the output is missing something... I don't think I missed anything from the image I worked from, or do you mean from a sensible design perspective that there should be something else there? The 100R being wrong - I have copied that from the layout; do you recommend a larger value like 10K or 1M? Presumably because 100R does almost nothing and is therefore pointless?

What's a stop resistor and what line should I stick it on?


*OK it didn't work the first time I built it, but I managed to debug it myself! Don't fall off your chairs! One of the pots was fried (it died and emitted smoke when I plugged the circuit in, that's the first time that's ever happened to me!) and the recommended red 3mm LED had very little effect on the LFO, so I swapped it for a green 5mm LED and the circuit roared into life!