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budjoe
2
Mar 16, 2018
Regarding the benefits of Balanced amplifier design, balanced cables and the related topics. I am a technician more than an engineer, so feel free to further research and dispute my opinions. I will also state that I am more a digital, than an analog person. That said, balanced = differential = common mode noise rejection. In the digital world it is pretty straight forward and easily defined and controlled. You are only looking for 1 of 2 states of a signal, at a very specific frequency. It is relatively straight forward to filter out all unwanted signals. In the analog domain, you are looking for a variable signal over a frequency range of 20Hz to 30kHz. The signal is commonly referred to as sine wave, but in reality it is not. Attack and decay are not symmetrical and vary greatly by instrument, and note, and octave. I used 30kHz as the max that most high end audio equipment tries to attain to capture fast attack, and high harmonics that lend realism to the sound versus a strict 20 - 20kHz for the general audio range. Some high end electronics try to optimize up to 40kHz or better. If the electronics limit their bandwidth to only the general audio range they will tend to sound flat or lifeless. To get rid of common mode noise we have to find the samples that are added to the desired signal. That mean we have to look for anything that is unexpected, which means that we have to oversample the signal to find the unexpected. Easy in the digital world, but the same logic applies. Typical oversampling to remove unwanted samples is typically 4x or better of the desired frequency. In the analog realm, that means I need devices that are capable of slew rates of 120kHz or better (30kHz X 4). Not unheard of, but there are other complications involved. The main goal in audio at all stages is to amplify the desired signal and keep noise or undesired signals to a minimum. Balanced can help this by reducing the undesired signal, but requires care to ensure that it does not remove desired low level signal. Balanced is NOT automatically 2x the power as some here have said. It means a cleaner signal (better SN ratio) at the same power, hence it is easier to raise the power and achieve the same specs. That being said, in the analog world and to some extent, in the digital world, as we increase frequency, a number of other considerations come into effect. Voltage and temperature affect frequency response of all electronics. In addition, The higher frequency any electronics operate at, the more noise they radiate (due to EMI and magnetic radiation). With all of that, as others have said, For low level signals such as microphone and phono, there is a good argument for balanced. For other areas of interconnect, there is not as much, but I will allow that between preamp and main amp it may help due to the large number of different wirings in the area (power, speaker, input and output) all at various frequencies and power levels. With all of that said, call me old school, but to me the best sound generally has the least signal processing, pays a lot of attention to voltage and temperature control, and isolates signal paths as much as possible. Class A amplification and dual mono designs for stereo are the ultimate, but there are many high quality manufacturers that use high quality components and careful consideration of voltage, temperature, and channel cross talk to provide a great musical experience. A final note: regarding balanced for headphone cables. Unless you are dealing with High end planar head phones, I doubt you will find any difference given two amplifiers of the same power output and SN ratio. There is very little that the headphone cable is subjected to unless you are in a high noise environment. That said, some computers and other electronics radiate a lot of EMI, and there are reports of a lot of EMI radiation from some USB 3 devices, so you may find a benefit from balanced headphone cables if that is your main environment.
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