CGS dome filter

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CGS45 the CGS dome filter is a 90° phase difference network, as used in frequency shifters. It is not a project in itself, and will be of no use to most people. I designed this board simply because I needed some dome filters for my own experimentation.

The circuit is based on the work of, and Copyright by Bernie Hutchins. It was presented in Electronotes 83, in Nov 1977. The implementation is very similar to that of the JH. FS-1A Frequency Shifter by Jürgen Haible for his frequency shifter. Do not expect either of these people to help you with the construction of this PCB.

While untested, the module should work on +/-12 volts.

Component values are selected using the formula printed on the PCB itself.

I will be giving no more details on this project at this stage, and suggest you purchase Electronotes 83 if you need more information.


Before you start assembly, check the board for etching faults. Look for any shorts between tracks, or open circuits due to over etching. Take this opportunity to sand the edges of the board if needed, removing any splinters or rough edges.

When you are happy with the printed circuit board, construction can proceed as normal, starting with the resistors first, followed by the IC socket if used, then moving onto the taller components.

Take particular care with the orientation of the polarized components such as electrolytics, diodes, transistors and ICs.

When inserting ICs into sockets, take care not to accidentally bend any of the pins under the chip. Also, make sure the notch on the chip is aligned with the notch marked on the PCB overlay.

Two resistors are placed in series in each network, to allow for the creation of the odd value resistors required. Alternately, the resistors can be left out, and a small trim-pot substituted. There are suitable holes on the PCB for one common trim-pot footprint.


There is an error on this board at the output buffer op-amp (TL071). A trace goes to pin 5. This should be cut and jumpered to pin 3.

Parts list

This is a guide only. Parts needed will vary with individual constructor's needs.

Part Quantity
100n 12
1uF (MKS) 3
10uF 2
C1-C12 See text
R1-R24 See text
10k 25
100k 1
TL071 1
TL072 6
Ferrite bead (or 10R resistor) 2
0.156 4 pin connector 1


  • PCB is 6" x 2" with 3mm mounting holes 0.15" in from the edges.


Readers are permitted to construct these circuits for their own personal use only. Ken Stone retains all rights to his work.

See also


Dome Filter for music synthesizers. by Ken Stone, 2001, with permission of the author - archived

External links