Sorry for the perhaps confusing thread title but it's just as ayt999 said about the intended direction of this thread. Maybe using the term "differential" instead of "balanced" would have been more appropriate and less misleading.
Tim D, those links were excellent, especially the extremely informative rane.com site.
Originally Posted by Dreamslacker
From my computer device knowledge (mainly SCSI because I use it):
A differential device is concerned with the voltage difference between the hot and cold signals. It's not concerned with the voltage difference between hot-ground and cold-ground.
Hence, a twisted pair wire is used to transmit the hot and cold signal. Since any interference is applied to both hot and cold, the voltage difference is the same.
ie. Hot = +2v, Cold = -2v, Difference = 4v.
Interference adds 0.1v to both:
Hot = +2.1v, Cold = -1.9v, Difference is still 4v.
Common mode rejection (CMR).
From rane.com:A common-mode signal drives both inputs with the same polarity. It is the job of a well designed balanced input stage to amplify differential signals, while simultaneously rejecting common-mode signals. Most common-mode signals result from RFI (radio frequency interference) and EMI (electromagnetic interference, e.g., hum and buzz) signals inducing themselves into the connecting cable. Since most cables consist of a tightly twisted pair, the interfering signals are induced equally into each wire. The other big contributors to common-mode signals are power supply and ground related problems between the source and the balanced input stage.
For those interested, Tyll Hertsens from Headroom raises slew rate, shared ground and power in regards to the Blockhead vs. Max: http://www6.head-fi.org/forums/showt...68591#poststop
From what I gathered so far:
1a. half impedance seen by each channel -> double current (I)
1b. Same voltage swings in both channels but out of phase (180 degrees), '+' and '-', instead of '+' and 'ground' for single-ended -> double voltage (U)
1a & 1b -> P(ower) = U x I -> 4-times power (which in reality apparently never happens due to restraints from the power supply to provide the required current at a given voltage, thermal reasons or current restraints from the ICs used in the amp)
2. Slew rate (in audio) = 2 Pi x Fmax x V-peak; Fmax is constant because f=1/T and T is constant for single-ended or differential in a given scenario. V is doubled -> Double slew rate
(I hope this is all correct...)
Other virtues about differential drive amps include: Lower distortion, which is quite a confusing issue and I'll need to read up on this. Apparently, there's a difference between single differential and dual differential, which have different distortion behaviours. Not sure which of these two would apply here.
From an old post by Kevin Gilmore, it says that balanced amps (differential output) have "3db less THD due to matching of slew rates." but also "3db more signal to noise ratio if driven balanced." I think it's 3db because of double everything. Another obvious disadvantage is that you basically need 4 entire amplifiers, 2 per channel, which can be quite expensive...
Anyway, it seems that there's much more to it than just "more power = awesome" (which according to Tyll Hertsens's post in the link above does not make the big difference) or "no shared ground = awesome" (again, Tyll Hertsens post in regards to the PPA). So far the slew rate issue seems to be of most interest but reading through various diy threads here, mostly about the PPA, it appears that there's even more to it than just "double slew rate = awesome". For example, in the shared ground issue it seems that the PPA uses a methology, which avoids the noise floor issue common in "normal" single-ended amps. So it would make sense to me that there's far more out there, which can't be reduced to these concise yet simplifying statements (handy for interested audiophiles like me but not necessarily meaningful). For instance, there are threads on diyaudio mentioning that slew rate is more of an end condition to distortion rather than the cause. Of course, this is completely taken out of context and should only point out the complexity of this issue. Perhaps posting a thread about this topic in diyaudio would lead to some interesting input.
What I have learned from this thread and the following research is that the implementation of a design is more significant than a fundamental discussion on differential vs. single-ended (or maybe not). So due to lack of technical understanding, I'll leave it be. Hopefully, I'll be able to compare two highend SS amps, a balanced
Dynamight to a non-balanced
dual mono Headcode to at a mini-meet in less than two months time. Technical discussions, as attractive as they might be, have only little meaning if a they're thrown of by practical listening tests. But in the end, this is more due to the fact that I don't really understand all this technical verbiage
In any case, don't mind me and keep the ideas coming. This has been a very informative thread so far!