If you’re looking to make money in electronics, there’s no better market than guitar pedals and modular synths. The margins are high, and all the consumers are otakus who will spend outrageous amounts of money chasing the next big thing. The products are just one step above audiophile wank with zero oxygen cables, and if your opamp sounds ‘more transparent’, you’re going to make a fortune, never mind how something can sound
If you want to do something really cool, build a delay, because everyone needs another delay. If you want to build the latest in delay technology, just grab a PT2399 chip. That’s what ElectroSmash did with their Open Source Time Manipulator delay. Everything’s right there, all the parts of the circuits are described, and you too can become an effects pedal engineer.
This pedal is based on the PT2399 chip from Princeton Technology, a digital delay chip that can be used with something that sounds like an old-school bucket brigade chip or something resembling a tape echo. As a digital chip, you’ve also got the clean, clear sounds of a digital delay, with just a few tweaks of the circuit. We’ve taken a look at the PT2399 before, but surprisingly not many people are sharing their secrets.
Landtone Delay Kit. No Idea Where I'm Going Wrong. It Just Isn't Working. First Pedal I've Built, So It's Probably Something Stupid. Help!!
The circuit for the ElectroSmash Time Manipulator is built around the ATMega328, the same chip in the Arduino Uno, with two PT2399s that can be configured to operate in serial or parallel for everything from a slapback echo to a 600ms digital delay. If you set everything right, you can get choruses, reverbs, or some psychobilly flange-ish sounds.
The entire circuit is open, with a board designed in KiCad, the code is right there written in C, and the only hard-to-replicate tech is the PT2399 chip itself, which can be had from the usual vendors for less than a dollar a piece. It’s a great pedal, and be sure to check out the video below.Recently I’ve been working on a four second digital delay with tap tempo and delay trails. There are lots of digital delay projects already, but the vast majority of them are based on the PT2399, which limits both the length of the delay and the sound quality.
This project is based on the dsPIC 33FJ64GP802 chip, with a couple of 23LC1024 1Mbit/128KB serial RAM chips for the storage. The dsPIC includes a 12-bit ADC and a 16-bit DAC on-chip. The initial sampling is done at 12-bit resolution and 32KHz, but after that, all the internal processing is 16-bit, and the final output is actually 16-bit/32KHz. 12-bit/32KHz is a typical specification for a rackmount studio delay processor of the 1980’s. The sound quality is very good, without being super-clean or sterile. It certainly beats the PT2399 hands down, and it doesn’t suffer from worse and worse quality as the delays get longer either.
Amz Fx Guitar Effects Blog » Blog Archive Delay Pedal (prototype)
The worst (only) problem is background hiss. The dsPIC’s on-chip DAC seems to produce about 10mV of noise. Some of this is removed by the post-DAC filtering, but about 5mV remains. This is pretty noisy by modern standards. For guitars-level signals, modifying four resistor values improves the S/N ratio significantly. This is described below.
As you can see in the guts photo at the bottom of the page, all the parts are DIY-friendly through-hole DIP ICs. This isn’t easy to achieve for something like this, since virtually all DACs and RAMs are surface-mount these days. I’ve managed to keep it to six ICs, and apart from the 28-pin dsPIC, they’re all little 8-pin DIPs, so the project is able to fit in a reasonably sized enclosure. The PCB is designed for a Hammond 1590BB or equivalent.
The current firmware has five controls. Three are the standard delay controls: Delay time, Repeats, and Delay level. The other two are high and low shelving tone controls for the delay signal, so you can sculpt the sound of the repeats. You can cut the bass on each pass which makes the repeats sound “lighter” and like they’re floating away. Or you can cut the treble, and have the repeats get darker and darker, somewhat more cave-like and subterranean. Or you can do a bit of both, which gives you a band-limited sound on the repeats like someone on the telephone or a cheap radio. It’s pretty versatile.
Time Between The Notes...
The audio path keeps the dry signal entirely in the analog domain – it is never digitised and comes straight from the input buffer to the output mixer.
I’ve programmed ‘buffered bypass’ rather than add a true bypass footswitch, though this would be possible. The reasoning is that I can do noiseless switching in the firmware by providing a fade-out over a few milliseconds, and I can also offer the option of keeping the delay tails, which is important with so much delay available.
One further addition is the “echo splash” feature, whereby a short press on the bypass footswitch will toggle the effect on or off in the usual way, but a longer press (currently set at “over 0.5 second”) turns the delay on only while the switch is held down, and the delay goes off again when you take your foot off the button. This enables you to add echoes to just a single phrase, and sounds great with the delay trails.
Pt2399 Delay Pedal Assembly Instructions
The firmware also offers tap tempo as an alternative way of setting the delay time – just tap the interval you want on the other footswitch. There’s also an LED which flashes at the current delay rate to give you an idea of what’s going on, and there’s a Sync Output to provide a pulse which can synchronise other pedals to the delay rate.
The analog side is simple stuff. There’s a buffer, from where the dry path goes off to the final mixer. That’s followed by a anti-aliasing filter, and then the delay line. The delay is followed by a differential op-amp since the DAC outputs a differential signal, and then two reconstruction filters. The final mixer mixes the wet signal back into the dry signal.
The final parts are the five control pots, and the two supplies. The ADC/DAC use a separate 3.3V supply from the digital side to help keep noise to a minimum. The ground planes are separated on the PCB too.
This Is The Delay Pedal You Can Build Yourself
I’ve used the “diode in parallel with circuit” style of reverse polarity protection rather than the alternative “diode in series with circuit”. The diode in series gives you a hefty voltage drop that I don’t care for. On the other hand, the diode in parallel will short out any power supply which is plugged in in reverse and might blow up the power supply. I regard it as my job to protect my circuit and the job of power supply designers to protect their power supplies from shorts (I mean, that’s pretty basic, right?). Just so you’re warned!
Here’s a shot of the Rev.2 PCB in my first unit. It makes for a neat build since most of it is on the PCB. Getting the LEDs the right height requires a little forethought, but none of it is hard. I could have used board-mounted jacks too, but I thought it better to leave people the option of having whatever jacks they like best. I’ve put cutouts left and right for the jacks, and added a cutout on the top edge to make more room for a DC socket. I learned a lesson there from the Flangelicious boards where it’s a tight fit to get a DC socket on the top side of the PCB.
The PCB measures 109x70mm. It is designed to fit into a Hammond 1590BB enclosure in landscape format as above. The PCB-mounted pots make the build easier, and the off-board wiring is very simple.
Stewmac Tape Op Delay Pedal Kit
Pop over to the shop and grab the DigiDelay PCB + chipset, which includes the PCB, DIGIDELAY delay processor chip, and the two SRAMs. You might also need a set of pots for the project.
There are two main sources of noise in this circuit; 12-bit quantisation noise, and the DAC noise. There’s nothing I can do to fix either of these. They are what they are. All we can do is try and get the best-possible signal-to-noise ratio from the circuit.
As shown in the schematic, the circuit can handle signals up to 3V peak to peak. To get the best noise performance, you need to use as much of this as you can.
Glitch Delay Is A Diy Module You Can Make
If you’re using the circuit with a guitar with a low level output, changing four resistor values can be helpful. These changes boost the signal at the pre-delay filter, and then reduce it again at the output mixer (along with any noise). This gives an improvement in S/N of around 13dB. The maximum input signal level is reduced to 680mVp-p.
It’s worth pointing out that the hardware presented here is pretty general purpose. You’ve got audio input/output with a dsPIC to process it and 256KB RAM if you need it. The interface consists of five knobs to control parameters in the code, and two footswitches. That’s a good start for a lot of different digital effects. A change of firmware could turn this into something completely different.
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