For the Love of PT2399

A new Eurorack module release by Tremodular presents me with the opportunity to talk about what is, by a long margin, my favourite type of delay effect. We are spoiled in this area of the market - a huge range of delay pedals, Eurorack modules & standalone devices cater to every cavernous desire; everything from true tape-based designs, dark & noisy BBD gems, to pristine and/or weird digital units.

For me, the PT2399 rules, and this is largely due to how it sounds when pushed. BBD lines, which I also own & enjoy, tend to get a little noisy when clocked outside of their comfortable range (read more about BBD's here), which definitely adds a vibe, however, pushing a PT2399 in the same way? That'll get you unhinged sounds.

I won't spend too long on the technical details, (ElectroSmash has a great article here) but the PT2399 hails from 1998 via Princeton Technology. Designed initially as a Karaoke "echo" effect, the chip basically consists of an ADC, DAC & 44KB of RAM as a delay buffer. The "supposed" max delay time of this fairly pristine digital chip is 340ms - but it can, of course be pushed beyond that at the expense of fidelity. It can also be easily interfaced with external components, e.g. modulation sources or filters - mimicking BBD delay or chorus effects to great effect.

"Although this chip was created as a simple solution to add delay/reverb/echo to karaokes and set-up entertainment systems, it became very popular in the guitar pedal community due to its ability to emulate BBD-based delay circuits, good price, through-hole package, 5V power supply and tolerance to modifications. 

This integrated circuit has also demonstrated that with a careful design and good tuning, could be a fantastic sounding solution. Many well-known effects like Belton/Accu-Tronics reverb module, Danelectro FAB-Echo, and the Rebote Delay use this chip as the core of the circuit." - ElectroSmash

Anyhow, enough chatter, let's hear some examples! Here, the cheapest game in town is probably the SubZero Public Transport Delay Pedal. For £24.99(!) you'll be able to add some PT2399 vibe to your songs. This mono pedal offers feedback but no modulation - crucially, the pedal tops out at 400ms so you won't find much lofi vibe here. Still, £24.99!

Getting a lil' spicier, we have the new Tremodular Liminal Space, a €90 mono Eurorack module which features 2 PT2399 delays in series, a modulation input (yay), up to 1 second of delay time, self-oscillation and some unique voicing:

"Each of the cores has different supporting circuitry. This changes what sounds get passed through the delay and how fast they fall off. This results in unique interaction between both of the cores. We have also added Modulation input that lets you modulate both channel speeds in an eerie way that is reminiscent of tape flutter.

Usually delay circuits using PT2399 IC have their delay time limited to around 300ms. This is due to PT2399 producing increasingly more noise the longer delay time you set. We did not want to do that. We wanted for you to be able to choose when it is too noisy for you. Liminal space goes up to 1 second delay time. We have worked on eliminating as much noise as possible without sacrificing too much of the high frequency content. Liminal space has two separate filtering stages. One is at the output of delay cores and second one is at the output of combined delayed signal.

Both delayed signals get mixed and passed into low-pass and then high-pass filters. They are set to relatively light filtering and only slightly filter the signal. Signal further is combined and sent to the feedback circuit and also into another more aggressive lowpass filter that goes to the output."

I like the vibe of this unit, the modulation gives a nice chewed-up-VHS feel, yet it remains classy - it approaches some subtly lo-fi tones and remains musical. The time for restraint is over however, and we're going into depraved territory with the Synthrotek DLY.

The DLY is an unassuming 4HP module, available in kit or built form and offering a single PT2399 delay line. It sounds pretty conventional right? Well, it's the trimmers Synthrotek included (feedback & delay ranges) that truly take this module into the stratosphere. The delay range trimmer is maxed out on mine, by choice, meaning that the module turns into an aliasing, crazy mess once you go past 1.13 seconds. You can hear some of this digital weirdness at around 10:00 in the demo video:

I love mixing these sounds in with the dry signal to add subtle texture, perhaps modulating the delay time with the keyboard CV of the note's I'm playing, wild. Talking of wild, here's the king of PT2399 delays for me, the Befaco Crush Delay. It has up to 2 seconds of (attempted!) delay time, plenty of connectivity and 3 different Crush Modifiers based on circuit bending techniques.

I own the V2 unit, which is quite deep (47mm), plus the delay time knob is probably only clean for 1/3rd of it's travel! The depth & knob scaling is reportedly improved in the V3 version - but I neither issue bothers me, give me the crush!

Anyhow, thanks for delving into the world of the PT2399 with me. Many more units are based upon this IC, please let us know your favourite. See you next time!

Posted by MagicalSynthAdventure an expert in synthesis technology from last Century and Amiga enthusiast.

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