Section 11 TECHNICAL INFORMATION
206
the A/D converter, depending upon JP1,2.
Motherboard Rev F: Audio Input
The revision F motherboard has some significant improvements made to the Audio
Input section. Audio enters the Zephyr via XLR connectors and is RF filtered. The stage
gain may be set for either microphone or line level by changing feedback resistance
using SW1A, B. The signal is then sent to the new “B audio” plug- in board through JA1.
The input stage consists of a very low frequency “servo” to remove DC offset, and then
to the send limiter. Balanced audio is received at the A/D converter, U16, and the digital
output leaves the “B- audio board” through JA2 to be sent to the motherboard and
audio encoder. U- is used to multiplex the analog audio source data with the AES/EBU
input data based on the front panel setting.
Motherboard Rev A-E: Send Limiter
The Zephyr has an send audio limiter which serves to keep the usual “digital nasties”
from happening when the send program signal grows instantaneously too large. This is
a very fast and very “tight” limiter which does not assert itself during times of normal
audio level.
It is possible to bypass the send limiter. On the motherboard inside the Zephyr, near
U34 and U37 are small jumpers. They can be set as follows:
BYP
AGC
EN
BYP
AGC
EN
Limiter Enabled. Limiter Bypassed.
As this is intended as an “extreme audiophile” mode,
we bypass the send level Voltage
Controlled Amplifier as well, so the front panel send level control does
not have any effect
. Note also that the LIMIT LEDs on the front panel continue
to function and are useful as an indication that the A/D converter may be clipping the
audio.
The limiter section has a dual function: in addition to the limiting, it uses the SSM2120,
U23 as a VCA (Voltage Controlled Amplifier) to implement the system send input gain
control.
Diodes D6,3 and D5,4 are clipping diodes, which prevent the A/D converter from ever
getting a signal which could overload and clip offensively. The op- amp U40 makes plus
and minus voltages of equal amplitude and low- impedance to bias the diodes at the
proper point to protect the A/D without sacrificing any headroom.
Summary of Contents for Zephyr
Page 13: ...Table of Contents 13 SECTION 1 QUICK RESULTS ...
Page 26: ...Section 2 INTRODUCTION 26 This page intentially left blank ...
Page 27: ...Section 2 INTRODUCTION 27 SECTION 2 INTRODUCTION ...
Page 38: ...Section 2 INTRODUCTION 38 This page intentionally left blank ...
Page 39: ...39 SECTION 3 ZEPHYR AT A GLANCE ...
Page 52: ...Section 4 INSTALLATION BASIC OPERATION 52 This page intentionally left blank ...
Page 53: ...Section 4 INSTALLATION BASIC OP 53 SECTION 4 INSTALLATION BASIC OPERATION ...
Page 84: ...Section 4 INSTALLATION BASIC OPERATION 84 ...
Page 85: ...Section 5 ISDN 85 SECTION 5 ISDN ...
Page 105: ...Section 6 NON ISDN NETWORKS 105 SECTION 7 AUDIO CODING ...
Page 118: ...Section 7 AUDIO CODING PRINCIPLES 118 This page intentionally left blank ...
Page 119: ...Section 8 DETAILED MENU REFERENCE 119 SECTION 8 DETAILED MENU REFERENCE ...
Page 157: ...Section 9 REMOTE CONTROL 157 SECTION 9 REMOTE CONTROL ...
Page 176: ...Section 9 REMOTE CONTROL 176 This page intentionally left blank ...
Page 177: ...Section 10 ADVANCED PROBLEM SOLVING 177 SECTION 10 ADVANCED PROBLEM SOLVING ...
Page 196: ...Section 10 ADVANCED PROBLEM SOLVING 196 This page intentionally left blank ...
Page 197: ...Section 11 TECHNICAL INFORMATION 197 SECTION 11 DETAILED TECHNICAL INFORMATION ...
Page 219: ...Section 12 SCHEMATICS 219 SECTION 12 SCHEMATICS ...
Page 221: ...Section 13 MANUFACTURER S DATA SHEETS 221 SECTION 13 MANUFACTURER S DATA SHEETS ...
Page 223: ...Section 14 SPECIFICATIONS WARRANTY 223 SECTION 14 SPECIFICATIONS AND WARRANTY ...
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Page 229: ...Section 15 APPENDICES 229 SECTION 15 APPENDICES ...