The Reverberatory
Dual Delay, Reverb, and General Ambient Choas Generator
Overview
Every once and a while, an idea presents itself to me that I feel I have to do, even if I'm not sure it's a great idea. The Reverberatory is one such project. I had the idea of a dual delay and reverb that had some features that would allow for the creation of everything from simple delays to ambient washes and sonic mayhem. I had diagrammed it all out and had the schematic almost done when I happened upon the Earthquaker Devices Disaster Transport Sr, which I had not heard of before. This now discontinued pedal is also a dual delay and reverb pedal, but the structure was a little different than the Reverberatory. However, there was one idea that I totally stole, and that was the “series” delay control. With that addition, it brought the number of control pots up to 11, which is a new personal record for me. However, each control does something very useful and specific.
How It Works
The Reverberatory is built on six (6!) PT2399 chips. I've never seen a schematic for the EQD Disaster Transport Sr, but I'm all but certain the reverb is provided by a Belton brick, as is the case with many of their pedals, especially the earlier designs. It's a great solution, but I prefer not to use bricks or FV-1 for cost reasons. That and I have a whole boatload of PT2399 chips on hand. Besides, it's not like I needed to shrink board space with a circuit that has 11 controls.
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Before I jump into the schematic, it's helpful to understand the high level concept of the design. Below is a block diagram of the functional blocks in the pedal. First, we have an input buffer like on all my other delay/reverb projects. After the buffer, there are two delay stages that are both fed by the input. Each delay stage has controls for time, feedback, and mix. The first delay stage also has the ability to have modulated repeats through the use of a simple, single-opamp LFO design. It has controls for speed and depth. The second delay stage has a fun trick of its own that I will discuss shortly.
The delay outputs are then summed with the dry signal using a typical summing amplifier configuration. The output of this summing amplifier goes to the input of the reverb stage. The reverb circuit is a lightly modified version of my T60 Reverberator design, with fixed size and dwell controls. This utilizes 4xPT2399 and roughly a bajillion 100 nF capacitors. The output of the reverb is then sent to a mixing amplifier with the dry delay signal before going to the output. The reverb output also goes to an “Ambience” control that sends some of the reverb out signal into the Delay 2 feedback input, which creates some large ambient wash effects when used in moderation. When cranked up, you can get all kinds of self oscillation and other weird sound effects.
Reverberatory Block Diagram
The input buffer is not my typical buffer. You will note that it is a unity gain, non-inverting opamp buffer, as opposed to the traditional inverting opamp input buffer. The reason for this has to do with the fact that we are combining dry signal with our effects. Because we need to sum the dry signal with the delay and then the dry+delay with the reverb, we need to ensure that we aren't combining any of the effects out of phase. So the first buffer is non-inverting so that after the necessary inversions for the two summing amplifiers, the dry signal will still be in phase with the effects. If we made the input buffer inverting, then we would get the dry signal summed with the effects causing comb filtering, which we don't want.
Reverberatory Input Buffer
Next up is the first delay stage. This is configured as a very standard PT2399 delay stage with the typical multifeedback input and output filters. The most notable differences with this stage are the presence of the LFO signal on the pin 6 output and the added “Series” control that takes the output of stage 1 and feeds it into the input of stage 2. Another thing you will see is the presence of two sets of solder pads. These allow for cutting the input to the delay stages, which allows you to disable delay while still having the trails, or tails, decaying out when switched off. These can be wired either to a single DPDT switch for turning of delay with a single control, or to two SPDT or SPST switches to allow for enabling/disabling each delay individually.
Reverberatory First Delay Stage
The second delay stage is also a fairly typical PT2399 delay stage, with the notable difference being that it takes as an input to the feedback loop the “Ambient” control, which is a portion of the reverb output signal. This will cause a delayed and reverbed signal to get delayed again, which will create a big wall of repeats that are delayed/reverbed/delayed/reverbed/etc.
Reverberatory Second Delay Stage
The two parallel delay stages then have their outputs summed with the dry signal. This is the first of the aforementioned two inverting summing amplifier stages. This is a pretty straightforward buffer/summing amplifier.
Reverberatory Delay Output
The delay output is now fed to the input of the reverb section of the circuit. Because the topology is the same as the T60 Reverberator, we won't go into it in depth here. I refer you to the documentation for that circuit for more info. However, do note that the delayed signal output can be cut using the two supplied solder pads to allow for turning off reverb with trails.
Once the signal has been reverberated, it goes to two separate controls. Reverb controls the mix of the reverb signal with the delay output and dry input. The “Ambient” control determines how much of the reverb signal gets fed back into the delay stage 2 feedback loop. It is a very large value because smaller values can result in bleed where you can't get rid of the reverb signal in delay stage 2 entirely.
Reverberatory Reverb Controls
Now that we have all of our effects generated, we have one final summing amplifier to sum everything together prior to the output. This is another standard inverting opamp summing amplifier.
Reverberatory Output Buffer
The modulation for the first delay stage is accomplished using a simple LFO that I basically stole from the Little Angel chorus and then modified to suit. I was searching for a single opamp LFO due to my desire to minimize the size of components in this already monstrous device.
Reverberatory LFO
The power section for the Reverberatory is really bog standard stuff. The 9V in goes through a reverse polarity protection diode, we create a reference voltage for the opamps, and we regulate a 5V line for the PT2399's. Some filtering caps round out the design. However, the one thing that should be noted is that the 5V regulator MUST be able to provide 1A. A smaller, TO-92 78L05 that provides 100mA max simply won't cut it here with all the PT2399's sucking up power. The 1A rated regulator does not need to be heatsinked, but it will get a little warm to the touch.
Reverberatory Power Section
So yeah, it's a little bit of a monster circuit, but it's a lot of fun. The fact that the reverb is all done with individual PT2399's also allows for more personalization of the reverb effect, if you like. You can find all the things to make your own here.