The Effect of Transformers on Transmission of Digital Audio Signals Presented at the Audio Engineering Society International Convention, San Francisco, 1998 By Jon D. Paul, Vice President Scientific Conversion, Inc. California, USA
	Index 1. Transformers in Digital Audio Transmission Systems 2. AES/EBU Signal Bandwidth 3. Transformer Equivalent Circuit 4. Frequency Response and Saturation Effects 5. Pulse Aberration 6. Common-Mode Rejection Ratio and Interference Suppression 7. Common-Mode Interference: Induced Jitter Test 8. Common-Mode Interference: Induced Jitter Results 9. Transmission System with Shielded Transformers 10. Typical Digital Audio Transformer Applications 10.0 Balanced 110 W System with Shielded Transformers 10.1 75 W Unbalanced Interface with 2:1 Ratio Transformers 10.2 Bridging Unbalanced Input and Floating Coax Connector 10.3 Phantom Power Remote Digital Device 10.4 Dual output transmitter, 110 W Balanced and 75 W Unbalanced 11. Comparison of Typical Transformers 12. PC Layout Considerations
	Figures Fig. 1 Direct Coupled Transmission System Fig. 2 Transformer Coupled Digital Audio Transmission System Fig. 3 Spectrum of Digital Audio Signal 10kHz/div Fig. 4 Spectrum of Digital Audio Signal 5MHz/div Fig. 5 Equivalent Circuit of Transformer Fig. 6 Frequency Response of Transformer Fig. 7 Frequency Response of Transformer Fig. 8 Effect of Transformer High-Freq. Bandwidth on Pulse Resp. Fig. 9 Effect of Transformer Low-Frequency Bandwidth on Eye Pattern Fig. 10 Effect of Core Saturation on Waveform Fig. 11 Comparison of Pulse Aberration Squarewave Gen. 12.288 MHz, 75 W in/out Fig. 11A Comparison of Aberration Received AES/EBU 31M UTP 96kHz FS, 110 W in/out Fig. 12 Common-Mode Noise Rejection Test Circuit Fig. 13 Common-Mode Noise Rejection Fig. 14 CS8412/48kHz Common-Mode Noise Induced Jitter Setup Fig. 14 HP 5370B Time Interval Counter Fig. 14A 96kHz Common-Mode Noise CS8404A/CS8414/96kHz Jitter Fig. 14A Yokogawa TA320 Time Interval Analyzer Fig. 14B no transformer. RMS jitter 3401ps Fig. 14C type "B" RMS jitter 1540ps Fig. 14D type "V" RMS jitter 906ps Fig. 14E type "H" RMS jitter 396ps Fig. 15 Induced Common-Mode Noise Jitter Comparison Fig. 16 Shielded Transformer in Common-Mode Noise Equivalent Circuit Fig. 17 Balanced Transmission System Using Shielded Transformers Fig. 18 Application of 2:1 Transformers to 75 W Unbalanced System Fig. 19 Hi-Z Bridging Unbalanced Input with Floating Coax Connector Fig. 20 Phantom Power to Remote Digital Device Fig. 21 Dual Output Transmitter, both 110 W Bal and 75 W Unbal Fig. 22 Comparison of Transformers Fig. 23 Suggested PCB Layout for Transformer Input Circuit
	Summary and Conclusions Commercial transformers exhibit tremendous differences in parameters and performance. Digital audio transformers substantially improve common mode noise rejection and EMI emission. Second order effects such as pulse aberration and saturation greatly influence waveform fidelity. AES/EBU receivers exhibit jitter that is a function of the transformer CMRR and capacitance. Professional, broadcast and high resolution applications need maximum CMRR to minimize recovered clock jitter in the presence of noise. High quality transformers offer cost effective improvements in product design. Click here to download a PDF file of this AES paper NOTE: If the papers don't load completely, save the PDF file to your disk; open with Acrobat Reader 7. You can download and upgrade your Acrobat Reader here Copyright © 2008 Scientific Conversion, Inc. All rights reserved. Information in this document is subject to change without notice. THE BEST TRANSFORMERS IN THE INDUSTRY! Last revised: 8 March 2008