Magazine Archive

Home -> Magazines -> Issues -> Articles in this issue -> View

Amdek Phaser Kit

Build this versatile effects pedal

Amdek's PHK-100 is a versatile high quality Phaser kit which can be assembled with the minimum of technical difficulty.

★ Phasing effects with Rate and Depth controls
★ Variable Resonance control
★ LED effect-on and battery check
★ Pre-assembled circuit board
★ Complete kit with detailed instructions

Phasing, that instantly recognisable 'skying' sound, is a useful effect to impose on any instrument signal which otherwise may appear to be flat or static. By mixing the signal with a delayed version of itself, phase cancellations occur which produce a 'comb filter' type frequency response. Controlling the delay with a LFO produces the characteristic moving sound. The Resonance control introduces feedback into the filter circuitry and therefore a more coloured sound.

Three parameters can be modified on The PHK-100. These are: modulation Rate, modulation Depth and Resonance which allow a wide range of effects to be produced.

Complete set of parts ready to be checked off.

The Kit

The Phaser is available in bubble-pack form, complete with parts, spanner and detailed assembly manual. To complete the kit you should have: a 15-30W fine-tipped soldering iron, wire cutter/stripper, pliers and a cross-head screwdriver; not forgetting a PP3 battery - unless you intend to use the Amdek Power Distributor described in the June '83 issue.

After having removed all the parts from the packaging, they can be placed on a clean surface and checked off with the parts list.

Stages 1 to 4 involve cutting 8 lengths of wire, stripping and tinning their ends and then attaching them to the respective control pots. When this is complete the leads from the battery snap, LED and footswitch can be cut to length, then stripped and tinned (Steps 5-7).

Eyelet holes in the PCB should now be prepared by filling them with solder to produce a neat blob!

Pots and LED fitted to the PCB (Steps 2-9).

Footswitch fitted to the case and connected to the PCB (Steps 10-12).

Wires from the pots, LED and battery snap can now be connected to the board using the wiring diagram given in the manual. Having done this the footswitch should be mounted to the top of the case using the two screws, springs and stopper plate supplied. When the LED holder has been clipped into place the top of the case is complete and wires from the footswitch can be soldered to the PCB (Steps 8-12).

To ensure a good seating the detention stud on each pot should be broken off and the pots mounted, with terminals downwards, into the top of the case. They can then be secured using nuts and washers supplied, tightening with the Amdek spanner.

Next, slip the lock ring over the LED and clip the LED into the holder, locking with the ring. The PCB can now be fixed to the case with the two jack sockets and secured, using toothed lock washers, washers and nuts (Steps 13-16).

The insulation sheet is adhered to the back plate to prevent the PCB shorting and an anti-slip pad attached to the base. The plate can now be fixed to the case, using 4 screws and a battery fitted. This is then secured using the rubber cover.

Finally, fit the 3 knobs by rotating the pot shafts fully anti-clockwise and line up the knobs with the left-hand dot (Steps 17-22).

LED and pots fitted into the case (Steps 13-15).

PCB fitted into case and insulation added (Steps 16-18).

The completed Phaser (Steps 19-22).

Figure 1. Circuit diagram of the Phaser.
(Click image for higher resolution version)


As previously discussed, the phasing effect is produced by mixing a phase-shifted signal with the original causing phase cancellations to occur. The phase delay is produced using four FET controlled stages, based around ICs 2 and 3, which, as the resistance of each FET changes, alter the phase shift between input and output from 0-180°. The output from the phase shifting network goes through a FET switch and is then mixed with a buffered version of the input. Feedback is introduced using the Resonance control to increase the phasing effect.

Modulation is produced by the LFO based around IC4. The triangular waveform is first attenuated by the Depth control and then fed to the phase shift FETs.

On/off switching is accomplished using a flip-flop, which comprises of Q4, Q5 and associated components, controlling the FET switch.


When connected up the Phaser worked first time providing a pleasing warm phasing sound. Slow speed settings gave an effective movement to the sound while faster settings led to tremolo type effects.

However, if you have any problems with this or any other Amdek Kit you can contact the Roland 'Hot Line' at the UK factory. Tel: (Contact Details).

Figure 2. Panel description.


Amdek suggest that no attempt should be made to modify the circuitry. However, as suggested in the last few Amdek articles you could disconnect the LFO at connection 7 and insert a jack socket to include external control.

E&MM's special offer price for the Amdek Phaser Kit is £41.00 inc VAT and P&P. Please order as PHK-100.

More with this topic

Browse by Topic:

Electronics / Build

Previous Article in this issue

Electro-Music Engineer

Next article in this issue


Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.


Electronics & Music Maker - Aug 1983


Electronics / Build

Gear in this article:

Guitar FX > Amdek > PHK-100 Phaser

Gear Tags:



Previous article in this issue:

> Electro-Music Engineer

Next article in this issue:

> America

Help Support The Things You Love

mu:zines is the result of thousands of hours of effort, and will require many thousands more going forward to reach our goals of getting all this content online.

If you value this resource, you can support this project - it really helps!

Donations for December 2021
Issues donated this month: 0

New issues that have been donated or scanned for us this month.

Funds donated this month: £4.00

All donations and support are gratefully appreciated - thank you.

Please Contribute to mu:zines by supplying magazines, scanning or donating funds. Thanks!

Monetary donations go towards site running costs, and the occasional coffee for me if there's anything left over!

Small Print

Terms of usePrivacy