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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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In Reply to: CMRR and input transformers vs. transformerless posted by Mike P. on March 19, 2001 at 07:28:20:
This is a real difficult one, Mike. My only real balanced experience is with duplex telephone interconnects and sending digital signals over relatively long distances. The telephones did use transformers for DC isolation and depended on the highest CMRR to get rid of crosstalk, echos and the like. They had rather complex nulling networks to be sure superior balance was achieved. Some networks had servos that continuously balanced the lines for even better performance. The digital signals needed direct coupling and were reconstructed with high-speed comparators at the other end. There we used balanced connections to keep the noise to a minumum so the reconstructed pulse train was close to the original. They also needed the best possible bandwidth for good rise and fall times. So, enough of the tangent for now.I don't believe either technique is inherently superior. Both require a bit of work to realize the highest CMRR. In our applications, it really doesn't make all that much difference. We seldom have our audio cables in very harsh, very noisy environments. Any residual noise, AC or even RF, would be attenuated to very low levels with only a minimum if CMRR, especially compared to single-ended interconnects. I'm more concerned with waveform integrity and we don't need DC isolation. I do like the higher bandwith available with direct coupling. It is easier to use transformers, no doubt. In many pro audio circles, it's considered heresy not to use a transformer. It can certainly simplify a design, due to the DC isolation. If it sounds like I'm rambling, I am. Bottom line, properly designed, neither solution has a serious advantage in our application, IMHO.
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Follow Ups
- Re: CMRR and input transformers vs. transformerless - mark 19:15:37 03/19/01 (1)
- Impostor? - mark 18:49:37 03/20/01 (0)
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