Instruction manual

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9. Adjust R65 (between IC21 and IC22) for a right-channel null.

NOTE: The third filter null is at approximately 34.5kHz. Rather than

to match frequency response between channels at this point, the third

filter adjustment is used to help match phase response in the next

procedure.

Crosstalk Trim

If your station Mod-Monitor includes a true “precision” FM-stereo

demod (crosstalk/separation resolution of 70dB or better), it may be

used in lieu of a Spectrum Analyzer for this part of the Calibration

Procedure. If a Mod-Monitor of insufficient precision is used, final

Calibration (and performance!) of the DAVID-II will reflect the

inaccuracy.

1. Connect the COMPOSITE OUTPUT of the DAVID-II to the input of

the Spectrum Analyzer (or directly to the Composite Input of the

Mod-Monitor).

2. Turn the output of the Audio Generator completely off.

3. With the DAVID-II MODE switch in STEREO, and PILOT switch

ON, adjust either the front-panel OUTPUT LEVEL control (or the

Spectrum Analyzer or Mod-Monitor input gain attenuator) for a

19kHz pilot reading of –20dB (10% injection).

4. Adjust R20 (between IC12 and IC17) to null the 38kHz second-

harmonic-distortion component of the stereo pilot. The Spectrum

Analyzer should display the 38kHz component at the noise floor;

the Mod-Monitor should indicate a 38kHz “residual” reading at the

bottom of its most sensitive scale (–70dB or better).

5. Next, re-apply the Audio Generator test signal to the LEFT and

RIGHT PROGRAM LINE INPUT of the DAVID-II as described in Step

3 of the Low-Pass Filter Matching section of this Procedure. The

Audio Generator frequency should be set to 1kHz, and the level set

the same as before. If in doubt about the level, check for 6-volt p-p

signals on the right-hand ends of R22 and R27.

6. Monitor the “sub channel.” This is the 38kHz double-sideband,

suppressed-carrier component on the Spectrum Analyzer (or an

“L–R” Mod-Monitor reading).

7. Carefully adjust the front-panel INPUT GAIN L control for a null in

the sub channel.

8. Adjust R157 (to the left of IC35) to further null the sub channel.

NOTE: Because the effect of the two preceding adjustments will

appear to interact, it will be necessary to repeat Steps 7 and 8 until no

further improvement in the sub-channel null can be achieved.

9. Increase the Audio Generator frequency to 10kHz. Adjust R111

(between IC24 and IC25) for the best null in the sub channel at

10kHz.

10. Repeat Steps 7, 8 (at 1kHz) and 9 (at 10kHz) until the sub-channel

null at both frequencies is at maximum. You may wish to “split the

difference” to balance crosstalk measurements, sacrificing a null at