Very interesting piece on parallel mixing delays.

PARALLEL MIXED DELAYS IN THE MK II BOARD - The delay system inside and outside the Mk II board is very interesting. People always wonder how David gets his smooth delay sounds. David often uses two delays. Stacking one delay after another in your signal chain can degrade your tone because your original signal travels through, and is altered by, two delay circuits before coming out the other end. Also, two delays in line, while useful for some double tap delay effects, means that one delay creates repeats that are then repeated again by a second delay, which can create a messy delay sound. David's setup in the Mk II board is very different.

Inside the board is a two mode delay. The first mode is a Boss DD-2 digital delay, with controls located in the Delay 1 section. Controls are identical to the old Boss DD-2/DD-3 delay. L/M/S (shown in the board diagram above) represent long, medium, and short delay time modes. David has tick marks for only long and short positions. DTM is delay time. F/BK is feedback, or the number of echo repeats. Knob settings shown above correspond to a Boss DD-2 set at approximately 440ms delay with feedback/echo repeats set at 80%. The red knob marked DLY in the Delay Masters section is a mix knob for the DD-2.

The second mode of the delay circuit is the T.E.S. This is meant to simulate the warm, limited bandwidth sound of an old analog tape echo delay by rolling off the high frequencies gradually wth each echo repeat. The on/off switch for the TES circuit switch is labeled B/W on the board, for bandwidth, and the B/W knob in the Delay Master section is to control the amount of roll off the TES applies to the DD-2 echo repeats. The blue MXR knob is a mix knob for the external MXR digital delay.

There are foot switches to turn the delay on (Delay 1), switch to the T.E.S. circuit (B/W), and switch on the external MXR digital delay (MXR). To maintain the best possible signal quality, these delays are mixed parallel with the original signal. This keeps the original dry signal from being altered when running through the delay circuits by splitting off a separate signal to the delays, while the original signal is allowed to run though the other effects on the board, then mixing the delayed signals back with the original dry signal at the end of the signal chain before it hits the amplifier. The signal splits three ways - a dry signal, a DD-2/TES signal set for 100% echo repeats only (meaning no dry signal, only the repeats), and an MXR signal set to 100% echo repeats only. These are then mixed together inside the board with the red and blue mix control knobs you see in the Delay Masters section. By having the two delays in separate signal chains, one delay does not repeat the other. This allows David to get the benefits of two delays, each with different delay times, creating a huge delay sound without very noticeable echo repeats. At times it has the feel of reverb, but without the negative tone altering affect reverb causes. The unique characteristics of each delay remain intact, and are nicely blended together with the pristine dry signal before they hit the amplifier.