CMRR / SYMMETRY Trimming Jig

A little gadget for CMRR and SYMMETRY trimming  and general characteristic testing  ( such as frequency response) of 500 and any other type of module/gear.  The jig is mainly designed to facilitate the use of unbalanced test equipment in balanced environment. In its basic form it converts unbalanced input of a meter and output of a signal generator to balanced. It also has a simple PHASE switch for checking signal polarity.

The jig consist of a Module Extender and CMRR/SYMMETRY Trimming Card. The module extender has on board test points and allows direct access to all pins of the card edge connector/module using probes.





The CMRR/SYMMETRY Trimming Card is inserted between the edge connector and finger cards to facilitate the trimming procedures.




The jig also allows the testing of non 500 standard equipment through the vertically positioned TRS jacks by means of a balanced signal generator output and balanced measuring meter input.




As well as the main output the signal source for the measuring equipment (meter) can also  be  directed to unbalanced  (edge connector) pins such as 3, 7 and 9  by selecting their respective jumpers. Below picture shows the main output selected.




Typical test set up using a signal generator and an AC/Audio Voltmeter.




A scope is connected to the parallel meter output as the second meter.




The parallel signal generator output is fed to the second channel of the scope to monitor the test signal. This can also be fed to the second channel of the audio voltmeter.




If a computer is to be used it is recommended to use software from True Audio or similar.
http://www.trueaudio.com/rta_abt1.htm - the free version is sufficient to carry out the tests.




User and assembly manual with a good amount of info on CMRR and SYMMETRY. Jig schematic is also included.

http://www.robotica.co.uk/tac/CMRR_TRIMMING_JIG_MANUAL_V3.pdf


And it is available through the  White Market  http://groupdiy.com/index.php?topic=52462.0

Hello,


I have built the jig yesterday.


Supereasy and relaxing build.


The box comes with labeled (!!!) baggies,pcbs are high quality,same as I know from my EQ ONEs and Mic Pre Ones.


The build manual shows tons of examples on how to use it with external gear,great.It´s easy to follow and well explained.
Even pinouts and diagram can be found on the last pages.


Since I´m about to build some more of the eqs and preamps this tool comes in very handy for me because I have lost my test adaptors from the last builds somehow (XLR-plugs with precision resistors).
Now I have it all on one jig by a simple button(s) press,very cool.Buttons have LED indicators.
Can do both CMRR and symmetry measuring as well as a simple phase check,balance/debalance gear,internal routings via jumper setting etc.
Has a bazillion of those nice ring shaped test points to easily clip on your probes on every useful spot,nice!
Lots of possibilities to hook it up to your favorite testing gear,generators or daw.


You can also use it as a standard extender cable by just unplugging the main pcb and the connect the card edge and goldfinger boards,they have testpoints too!


I´m happy,will soon do a "real life condition"-test while building my next gear and post some pics then.


Meanwhile a pic attached of the finished build.


Have fun building,


best regards,


Udo.

So here´s a pic while CMRR-trimming on a MicPre One,I had just Minilyzer & Minirator attached as well as a scope on output,pretty handy to switch between normal and test modes,no need to alter wiring or setup:
(Edited for better pic).

…and another one,have fun,


Udo.