Synthrotek DLY (Delay) - DIY Build

Synthrotek DLY Kit

Delay, echo, reverb and distortion are all common effects for synthesis and in the world of modular synthesis, they make all the difference in the world. Synthrotek have had a long history of effects modules in their lineup and the DLY module is one of their finest.

The DLY is a PT2399 based delay module that can be dialed in to fit the users preferred range of delay due to the independent rate control. 

Another rad feature of the module is that unlike the ECHO module by Synthrotek, the DLY has a true wet/dry mix knob, giving the module its unique character and allowing it to be chained within the effects loop. Since fall was upon us, we decided to take on a couple of the companies legendary effects modules for our latest builds.

The PT2399...

Before we jump into the build video and all that jazz, let’s revisit an old friend of ours.. the PT2399 IC. You might recall a previous build of the Waveform Magazine PT2399 Delay module, where a karaoke module was converted into a delay module.

The Synthrotek DLY utilizes the same chipset. Aforementioned in the Waveform build, the PT2399 is a CMOS echo/delay processor developed by Princeton Technology Corp. It includes an ADC (Analog to Digital converter), 44Kb of RAM to store the samples and a DAC (Digital to Analog converter).

This chip was created as a simple solution to add delay/reverb/echo to karaokes and set-up entertainment systems. What does this all mean? This means that the chip is a perfect candidate for a delay module and the gang at Synthrotek decided to base a module around it.

Onward with the build ...

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For a novice builder, Synthrotek has put together an assembly guide to help build the module which can really help if needed. Intermediate and experienced builders can simply use the supplied BOM that comes with the module to assemble it. We utilized the BOM as well as our Synth DIY toolset and a component tester to assemble the module. Top down soldering and touch ups on the reverse side of the PCB made for a quick build, which we thoroughly enjoy. (hey, we want to spend our time patching instead of building!!)

We started with the diodes, making sure their orientation was correct due to their polarity requirements. Once these were tacked down and legs trimmed, it was time to move onto the resistors. This was the longest time consuming portion of the build.

Synthrotek does a great job lining up the components on the provided tape strip, but we always double check one or two resistors with our tester to ensure we are 100% with the resistor values. Polarity doesn’t matter with resistors, so you can tack these down in whatever direction you wish.

Synthrotek DLY (Delay) - Time Lapse Build

Play Video

IC's and Capacitors

IC’s and capacitors are next. When mounting the IC headers, make sure you use the correct orientation with what lines up on the silkscreen. The little “U” at the top of the header has to line up accordingly. 

Note: Do not place the IC chips at this time, save those for the last thing you do. 

Ceramic capacitors follow the IC headers and like resistors, polarity doesn’t matter. You can mount these any direction you wish. Just make sure you allow space between the PCB and the top of the capacitor. You don’t want any of the coating to be down in the soldering pad. It is best to allow 1-2mm of space when mounting so you can ensure a good connection is made. (this has gotten us in the past). 

Electrolytic Capacitors are next in the build and their polarity does matter. You want to make sure that the white stripe on the cap is facing the correct direction. Make sure that the longer lead goes through the solder pad with the ‘+’ next to it, and that the stripe is pointing away from that side. If these are mounted incorrectly, you can damage the circuit. 

DLY Build Gallery

The Halfway Point…

If you need to take a break, take one. At this point in the build, you are pretty much half way done. Transistors, trimmer pots and the voltage regulator are next up, and they are pretty quick to complete. Watch for small soldering area with the transistors and that their orientation matches the silkscreen.

Trimmer pots will only mount one way and its easy to see with the silk pattern. The voltage regulator is the same as the others in that one just needs to match up with the silkscreen layout. 

Our power header and vactrol are quick and easy components to mount. Just pay attention to their orientation and be aware that you can damage a vactrol by keeping your iron on its legs for too long. When inserting the vactrol into the board, align the dot on the side of it with the dot on the silkscreen. Put the shorter set of legs through the solder pads inside of the circle, so that the body of the vactrol sits in the circle, and the longer legs stretch out to the other two holes. With the header, make sure you align the notch on the header to the notch on the board. 

Before we get to the panel mounting, we have to have a spot to mount it to. This means the jacks and pots are required. After trimming the nubs on your pots (if they are present), place the pots in the board first, turn the board over with the pots in place, and then solder ONLY center pin to the PCB. You will want to do this likewise for the jacks at this point.  

The Completed DLY Module

Wrapping it all up...

The panel can now be lined up and placed against the jacks and pots. Pay attention to the movement of the panel at this time. You can accidentally bend component legs and render the part useless by over handling the board.

Hand tighten the nuts to the jacks and pots, ensuring everything is lined up and there is no bow in your panel. If everything lines up, flip over the module and tack down the rest of the legs of the pots and jacks.  At this point you can tighten down the nuts on the jacks and pots (we use our Synth DIY toolset) and call the module complete. 

Calibration and Testing...

Prior to patching, you need to go through the calibration process which is listed on the assembly guide or can be downloaded here (we made it into a PDF). Time to pat yourself on the back and congratulate yourself… you have completed the Synthrotek DLY module and it is time to patch it up!

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Features and Specifications


  • CV over DLY Rate
  • CV over Feedback
  • True wet/dry Mix
  • Feedback amount trimmer adjust
  • Rate range trimmer adjust
  • Rate/delay range: ~30ms – 1.13 seconds
  • Overclocked PT2399 “glitch” effects from fully turned Rate knob


  • Current draw: -12V = 10.1 mA;  +12V = 56mA


  • Module Height: 3U
  • Module Width: 4HP
  • Depth: 1 13/16 inches (4.6cm)
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Sythrotek DLY - Purchasing Options

Synthrotek has a couple different options when it comes to purchasing the DLY module. We wanted to keep it simple by just placing images of the options and linking out to the direct purchase. The prices are excellent and the quality of this build is way worth it! Head on over to SR and tell them we sent ya!

Our Final Thoughts . . .

The Synthrotek DLY module is a wonderful compliment to any rack or effects rig. It’s wet/dry controls along with its rate control allow the artist to tailor the sound to their liking. The width of the module is only 4HP, which is great if you are struggling for rack space. Along with the easy build, detailed assembly guide and BOM, the DLY module is honestly a no-brainer.

As one of the “legacy” modules from Synthrotek, the PT2399 DLY pairs well with its counterparts, the VERB and the ECHO. Together these three modules can really add some much needed dynamics to your audio compositions. If you decided to head on over to the Synthrotek store to pick one up, tell the gang we said hello!

Comments or Suggestions?

If you have questions about the build process or suggestions/feedback about this article, feel free to let us know by contacting us  We look forward to hearing from you!

Until the next build … 

~ f i N

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