Modification of the Mach-Zender Servo-filter

The following settings and modifications were done for the MZ Servo-filter to the original Servo-filter which electronic schematics and bill of material are saved on the wiki.


1-Setting of switches on the front panel:

* The differentiator shall be disabled on the front panel in setting the switch on "OFF".


2-Setting of the 8 straps on the board:

Low-pass filter, Notch filter 1 and notch filter 2 are activated on the board in setting strap on connectors P7, P8 and P9 (3 pins) between pins 1 and 2

* No transmission signal: the strap on connector P4 (3 pins) is set between pin 2 and 3.
* Strap is set on connector P11 (3 pins), between pins 2 and 3, in order to activate the sample-and-hold on the triangular signal, on the locking.
* Strap is set on connector P3 (2 pins) to connect the triangular signal to the output stage.

* Strap is set on connector P2 (3 pins), between pins 1 and 2, for test purpose.
To check low-pass filter, notch 1 and notch 2 filters (in scan mode) between TEST IN and TEST OUT. For this test the differentiator, shall be set on "ON" (not intuitive but important). After this test, the differentiator shall be disabled the front panel in setting the switch on "OFF".

* Strap is removed on connector P1 (2 pins): modification of Offset circuit (see below)


3-Modification of components:

* Integrator 1/f: corner frequency changed to 2.2 kHz
Capacitor CMS 1206: C38 = 33nF

* Integrator 1/f2: corner frequency changed to 220 Hz
Capacitor CMS 1206: C26 = C33 = 330nF

* Low-pass filter: cut-off frequency changed to 2.2 kHz
Capacitor CMS 0805 : C45 = 2.2nF
Resistor CMS 1206 : R59 = 33k

* Notch filter 1: notch frequency changed to 12.9 kHz / quality factor changed to 3.6 (measured)
[Capacitor CMS 0805 1% : C49 ; C50 ; C51 ; C53 = unchanged (560 pF)]
[Resistor CMS 1206 : R65 ; R66 ; R67 ; R68 = 22k
Resistor CMS 1206 : R73 = 2.7k

* Notch filter 2: notch frequency changed to 18.95 kHz / quality factor changed to 0.9 (measured)
[Capacitor CMS 0805 1% : C60 ; C61 ; C62 ; C63 = unchanged (560 pF)]
Resistor CMS 1206 : R79 ; R80 ; R81 ; R82 = 15k
Resistor CMS 1206: R89 = 13k

* Modification offset:
The offset circuit is modified in order to have an offset between -3.5V and 3.1V. It is injected at the input of the servo: pin 2 Op-amp U3

Resistor CMS 1206: R4 = 100
Resistor CMS 1206: R6 = removed
Strap (wire) between pin 2 and 3 of the resistive divider RN1
Strap (wire) between pin 2 and 3 of the resistive divider RN2
Resistor 1k6 added between pin 1 of the J2 connector and the wire (red) going to potentiometer 2k on front panel
Resistor 1k added between pin 2 of the J2 connector and the wire (blue) going to potentiometer 2k on front panel
Strap P1 removed
Wire set between pin 1-P1 and pin 2-U3 (pad of C7 connected to pin 2-U3).

* Gain adjustment (G): Gmin = 0.02 / Gmax = 5 / Gtyp = 0.8
Resistor CMS 1206: R33 = 22k
Resistors CMS 1206: R7 = 10k
Resistors CMS 1206: R5 = 5.1k

* Input impedance: 50 Ohm load removed
R145 and R146 removed