Hello all,
here are some pics from the inside:
Some words about output symmetry and cmrr adjustments.
Symmetry must be done for both the main as well as the monitor output.
This should be done
first,after that the input cmrr.Same as on tape recorders(output head,then rec. and erase heads),some of us might remember those days,hahaha...
The manual describes the procedures pretty well,but some of us might not have a signal generator doing the mentioned 50kHz.
Not necessary,even 1kHz sine at +20dBu can bring pretty close results.
There is a provision to skip these procedures,but I wouldn´t do that.
I tried this on both symmetry and cmrr,I ended up in just a 10th,maybe even a twelveth of a single turn on the trim pots to let the dmm jump off from 0vac readings.
If done with a dmm please confirm that yours is capable to read the 1kHz!
If you have better equipment then use it,if your dmm or attached peakmeter can read 20kHz then do adjustments that way.
Just prepare two adaptors with well matched resistors and you´re good to go.
One word on trimming especially the monitor output (VR3):
This must be done with the boards un-sandwiched but connected of course.
Here some pics how they look like,put some isolating cardboard under the subboard when adjusting:
In this position you can do it in an empty rack in the leftmost slot.A bit tricky but doable.
Best of course is doing it with an extender cable outside the rack.
What´s really nice is that oputput symmetry for main out and cmrr for input can be done with the module fully assembled.
Output trimmer (VR2) is reachable directly and the variable cap (VC1) on the mainboard can be accessed through a nice hole in the subboard-clever!
Look here:
Best,
Udo.