Digital Delay

"Digital delays with analog sound"



The Digital Delay rack delay effect module is a GT design that compares to other digital delays based on the Princeton Technologies PT2399 delay chip, such as the Mad Professor Deep Blue Delay.



The Digital Delay module is uniquely designed.  It includes a modular collection of circuit boards that provides different features and functionality.  This allows you to select the features (and cost) you want in a digital delay.  Additional configurations are under development at the time this was written, so this page will be updated as new configurations and options are made available after testing and final QA. 

The Digital Delay modules are presently designed around a single digital delay chip, the Princeton Technology Corp PT2399.  The PT2399 is one of the more popular digital delay chips which was released as the older analog BBD delay chips went out of production.  It was originally intended for use in karaoke machines and other consumer electronics.  However, its flexibility lead to its quick adoption in delay pedals.  It is not a "hi fi" delay chip.  Most of the hi-end delays chips are proprietary and used only in specific brand products.  These hi-end chips can produce pristine echoes with lots of options, but tend to be found in studio or other more expensive products.  You might consider the PT2399 as a digital emulation of an older BBD chip.  The PT2399 adds some color and noise to the echoes.  It is not a pristine digital delay.  There is a fair amount of control over the tone of the echoes, determined by the circuit components around the PT2399.  Tone, length of the maximum delay time, distortion, and noise in the echoes can all be affected by circuit design and control settings.  It is also true that the performance PT2399 chips vary from one to another, mostly in the level of noise that is introduced.  We toss out any PT2399 chips that are too noisy, but there is still some variation in noise level from one to the next, similar to the level of noise in an old BBD chip delay circuit.

The Digital Delay module is built from a collection of boards in a layered design, with the boards selected based on the features desired in the final configuration.  There are a couple of choices of "character" boards.  These are critical to the base sound of the configurations that we offer.  There is another board that can be selected based on the different tone, loop, and feedback options you might choose.  There is a delay board that accommodates one or two PT2399 delay chips, and a couple of modulation and tap tempo boards.  You don't really need to know these details, other than knowing that it gives you a good deal of flexibility in choosing your configuration, optional features, and cost.

Since we are still developing additional configurations, you'll see additional options and configurations listed below in the future.


Option/Feature Ocean Blue  DD DD Plus DD Deluxe DD Super Deluxe
Compares To Mad Professor Deep Blue Delay other PT2399-based delays other PT2399-based delays other PT2399-based delays other PT2399-based delays
Controls Delay, Repeats, Mix Delay, Repeats, Mix, Tails Delay, Repeats, Mix, Tails, Level In, 1 tone stack with Tone control, Tap Tempo, Rate LED on footswitch, Subdivisions Delay, Repeats, Mix, Tails, Rate, Depth, Modulation LED, Chorus/Vibrato switch, 2 switchable tone stacks - 1 with Tone control Delay, Repeats, Mix, Tails, Rate, Depth, Modulation LED, 2 switchable tone stacks - 2 Tone controls, Level In, Tone Bypass switch, Tap Tempo, Rate LED on footswitch, Tap Multiplier
# Delay Chips 1 1 2 1 2
Options Included none Echo Mode is Dirty by default Echo Mode is Dirty by default, tone stack is Hi Cut by default Echo Mode is Dirty by default, tone stacks are Smooth and Custom by default Echo Mode is Dirty by default, tone stacks are Tape and Custom by default
Buffers none none none none none




  • Input Level - Extra knob to control the level of the signal coming into the module.  This is especially useful for higher output pickups or hot signal chains that may cause clipping in the delay circuit, resulting in distorted echoes.
  • Volume - Extra knob to provide more control over the level of the signal coming out of the module. 
  • Unswitched Tone Control - Some configurations allow you to select a tone stack which controls the tone only of the echoes, but not the original note.  This option lets you select one of the tone stacks that will be "always on".  See "Tone Stack Options" below for descriptions of the choices.
  • Switched Tone Control - Some configurations allow you to select two tone stack configurations which you can switch between.  These tone stacks affect the tone of the echoes, but not the original note.  See "Tone Stack Options" below for descriptions of choices.
  • Tone Bypass Switch - If you select an Unswitched Tone Control or Switched Tone Control, you can also select this option to bypass your tone stacks, giving you another tone option for echoes.
  • Tails Switch - Normally when you turn a delay off, all echoes end immediately.  With this option you can select that functionality or "Tails".  When you select Tails, echoes for notes you've already played will continue until they fade out, but there will be no echoes for new notes you play.
  • Modulation - This provides the usual controls for Rate and Depth of modulation.
  • Modulation LED - If you have modulation, this additional option gives you a flashing LED showing the modulation rate.
  • Chorus/Vibrato Switch - If you have modulation, you can select this option.  It is similar to the Chorus/Vibrato modulation switch on the EHS Deluxe Memory Man
  • Subdivisions - You can select this option if your configuration includes two delay chips.  It gives you an extra "double time" echo, with the ability to control it's volume.
  • Tap Tempo - This option provides you with Tap Tempo capability with a special module-specific footswitch.  In addition to the tap tempo switch, you'll also have a rate indicator LED on the footswitch.  The footswitch is included, but it requires a 1/4" stereo TRS cable, which is not included.
  • Tap Multiplier - If you have tap tempo, this option lets you select timing options to create quarter notes, dotted eighth notes, eighth notes, triplets, and sixteenth notes.
  • Loop - Add an external loop where all repeats will be routed before they go into the feedback loop.  This gives you the ability to process your repeats through other effects.  The dry portion of the signal does not go through Loop.
  • Echo Mode - You can select "Clean" or "Dirty" for this option.  This controls whether or not the first echo will be routed through your (optional) tone stacks.  "Clean" means the first echo will bypass your tone stack.  "Dirty" means the first echo will go through your tone stack.  All echoes after the first echo will go through the tone stack (or tone bypass).  This is not switchable.
  • Change Mix Control - There are two types of Mix Controls.  One we refer to as the 50/50 control.  It allows you to adjust the level of repeats from 0 to 50%.  The other we call the 0/100 control.  It lets you mix the level of repeats from 0 to 100%.  This is not available on all configurations, only those that are digital adaptations of old analog BBD delay designs.


Tone Stack Options

  • Smooth - This tone stack is designed to tame the low end and the very high end (where the noise lives), leaving you with brighter echoes like you would get in a hard-surface room that is acoustically active.
  • Hi Cut - The HiCut tone option is a simple high-cut option like the Tone controls on many pedals.
  • Custom - The Custom stack is architected after a Big Muff Pi tone stack, but allows you to adjust the mids to be flat, scooped, or boosted, whichever you prefer. 
  • Tape - The Tape tone option seeks to mimic the sound of old analog tape delays.  It is similar to the Ibanez DE-7 Tape Mode, but adjustable.


Front Panel

  • Delay - adjust the amount of time between repeats
  • Repeats/Feedback - adjust the number of repeats
  • Mix/Blend - adjust the ratio of wet and dry signal
  • (optional) Input Level - cut the incoming signal level to prevent clipping
  • (optional) Volume - adjust output level
  • (optional) Tone - one or two Tone controls to adjust optional tone stacks
  • (optional) Tone switch - switch between optional tone stacks
  • (optional) Tone Bypass switch - bypass tone stacks
  • (optional) Tails switch
  • (optional) Rate - control modulation speed
  • (optional) Depth - control intensity of modulation
  • (optional) Modulation LED - blinks with modulation rate
  • (optional) Chorus/Vibrato switch - change character of modulation
  • (optional) Subdivisions - control volume of "double speed" note in configurations with two PT2399 chips
  • (optional) Tap Tempo jack - for connection Tap Tempo footswitch
  • (optional) Tap Multiplier - select alternate timings of echoes


Rear Panel

  • Audio In
  • Audio Out
  • On/Off Footswitch
  • On/Off Override
  • DC Power
  • DC Power LED
  • (optional) Loop Send
  • (optional) Loop Return


Module Width

  • 1.5" for simple configurations, 2" or 3" for more complex configurations
  • some configs available as wing modules, check for specific configurations of options
  • configurations with loops are 2", loop configurations are not presently available for left or right wing positions.


Power Consumption (aprox)

Depends on options and configuration.  Typically between 40 - 100mA.


Base Configurations

Part # Description List Price
MOD-DD-OCEANBLUE DD Ocean Blue Delay module $209
MOD-DD-DD DD module $229
MOD-DD-DD+ DD Plus module $289
MOD-DD-DDDLX DD Deluxe module $279
MOD-DD-DDSDLX DD Super Deluxe module $349



Part # Description List Price
MOPT-DD-INPUT Input Level Control $19
MOPT-DD-VOL Volume Control $19
MOPT-DD-TONE Unswitched Tone Stack $0
MOPT-DD-TONESW Switched Tone Stacks $19
MOPT-DD-BYPASS Add Tone Bypass switch $19
MOPT-DD-TAILS Add Tails switch $19
MOPT-DD-MOD Add Modulation controls (Rate, Depth) $39
MOPT-DD-MODLED Add Modulation LED $9
MOPT-DD-CHVIB Add Modulation Chorus/Vibrato Switch $19
MOPT-DD-SUBS Add Subdivisions control $19
MOPT-DD-TT Add Tap Tempo, incl Footswitch but not cable $59
MOPT-DD-TMULT Add Tap Tempo Multiplier control $19
MOPT-DD-MIX Change Mix Control Type $0
MOPT-DD-MODE Select Clean or Dirty first echo $0



Part # Description List Price
MPT-DD-CA Replacement pot, switch, jack, LED cable assembly $19
MPT-DD-LJACKS Replacement loop jacks cable assembly $29
MPT-DD-KNB Replacement control knob $2
MPT-DD-PB Replacement power board $29
MPT-DD-SB Replacement switching board $29