The Amdek Delay is a high-quality, mains powered echo unit which can be built in a couple of hours using only a soldering iron, cutters and screwdrivers.

★ Input Volume attenuation
★ Delay time and Repeat controls
★ Variable delay volume
★ Choice of outputs and levels
★ Mains powered
★ Complete PCB with detailed assembly instructions

Bucket brigade echoes are long going to remain popular, unless digital designs take another nosedive in price. They're relatively inexpensive, reliable, easy to use and versatile, and Amdek's mains-powered design emphasises all these desirable features. With delay times from 25 to 300 mS it can produce a wide range of echo, reverb and slapback effects, and because it has a selection of input and output level and mix facilities, it can equally well be used on a single instrument such as guitar or synthesiser (or even vocal) or in conjunction with the effects send of a mixer.

The Kit

The Delay Kit is the most complex Amdek device we've looked at, and comes in a box as opposed to a bubble pack. As usual there's a hexagonal wrench supplied, and the other tools needed are a 15-30W fine tipped soldering iron, wire stripper, cutters and pliers, and a crimping tool for the caps to fit over the mains transformer joints.

Parts identification should be carried out first, the main elements being the built-up PCB, case top, case bottom, metal sub-chassis and foot-switch. In addition to these parts there are various switches, nuts and bolts and pushbuttons to be accounted for.

Step by step assembly commences with preparation of the subchassis by inserting the control pots, mains switch with spacers and PCB support screws. After this is done, connecting wires can be cut to the stated lengths and soldered to the tags of the pots and switches (steps 1-5 and 5-11). After this is done the eyelets at the edges of the PCB are filled with solder (although in practice this was found to have been done); the ready-assembled PCB is temporarily mounted on the sub chassis and the connecting wires are soldered into the eyelets (steps 12-14).

Steps 18-22 involve cutting the LED leads, connecting them to the PCB and soldering wires to the input/output sockets. Steps 24-33 include the connection of the transformer and footswitch, the insertion of the jack sockets and slide switches into the casing and the permanent fixing of the sub-chassis to the casing. Next the mains lead is prepared, and carefully clamped in place: the transformer connections are equally carefully insulated to avoid stray mains voltages. The sub-chassis is earthed, and then the case is screwed together. When this has been done rubber non-slip sheets are stuck to the underside of the casing (steps 34-36). The final step is to push on the four rotary knobs and the mains pushbutton (step 37); the mains lead supplied has a welded 2-pin plug on the end and it may be felt desirable to replace this with a conventional 3-pin 13A design.

Circuitry

The BBD echo design is based on an IC (MN 3005) containing a series of capacitative cells, which charge up when an input is presented. A switching clock pulse (from IC1, MN 3101) causes the charge to move from one cell to the next, giving a variable amount of delay before a sound reappears at the output. The delay time available ranges from 25 to 300mS, representing clock speeds from 6.8 kHz (longest delay) to 82 kHz (shortest delay). Filter circuits are used in the pre and post processing signal path to remove these high frequency clocking signals, and since the BBD is inherently noisy compression and expansion circuitry is used to improve signal to noise ratio. The foot-switch uses a flip-flop controlled FET circuit to operate noiselessly.

Operation

The Amdek Delay should work first time, with careful use of the input peak reading LED and Delay feedback LED to avoid distortion or runaway effects. If there are any problems, Roland operate an 'Amdek Hot Line' for advice on (Contact Details). The Amdek Delay can be used as an instrument processor, in mono or in stereo with two amps connected to the two output sockets, or for sound reinforcement in conjunction with a mixer.

Modifications

Amdek do not recommend that modifications are made to the completed unit. However, if you are adventurous enough you could add a socket which allows voltage control of The Delay time. This means that external control sources such as a low frequency oscillator, sample and hold or sequencer could be connected.

A switched jack socket is used to connect the voltage. Disconnect the wipe from the wiper of The Delay control and wire it to the non-switched side of the socket. Then solder a wire from the Delay control wiper to the switched side of the socket. An earth contact can betaken from one of the other sockets.

The unit will now operate as normal until a jack is inserted and the Delay control switched out. Control voltages should be in the range of 3-15V to cover the 25-300mS delay.

E&MM's Special Offer prize for the Amdek Delay Kit is £108.00 inc. VAT & postage. Please order as Amdek DMK-100 Delay Kit.