Gilderfluke&Co old MACs 8 bit Digital Audio System - Manual (Page 106)

- Calibration -
The DAS-100 may require an occasional calibration of its analog circuitry. To check the calibration,
take a stereo sample with both volume controls turned fully down (counter clockwise) and no audio
cables attached. Then look at the sample with the dump screen. Both channels should look like fairly flat
lines dead center in the screen with only a touch of jitter on each side.
To adjust the DAS-100, remove the top of the case. Inside you will see six multi-turn trimmers. The
four pots to the left of the case are used to set the offset of the operational amplifiers (TLO71's) located
right below them. With both of the volume controls turned fully down (counter clockwise), no audio
cables attached (these could be a source of electrical noise), and the DAS-100 software running in
monitor mode with a sample and filter rates set to 15 KHz, attach a good quality meter between ground
and pin #2 of each IC and adjust the pot directly above it until the meter reaches exactly 0.000 volts.
Start with the two IC's and pots closest to the left of the case, and then move to the two middle pots and
IC's. Once these four pots are adjusted, it is time to adjust the two pots located above the LM311's. The
right channel is controlled by the pot towards the top of the case. The only remaining pot controls the
left channel. Take a short audio sample (10 blocks or so) and look at it. Adjust the two pots as needed to
bring both traces back into the center line. Repeat the sample and adjust sequence until you are
satisfied with the calibration.
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