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Originally Posted by jazznap /img/forum/go_quote.gif
Thanks UglyJoe. That helps immensely. It also sounds like there is no reason to upgrade to a balanced amp early and run it SE with the intent to upgrade the source later, since performance may suffer in the interim.
Are there some high-end SS amps that are not balanced (since most seem balanced) or do unbalanced SS amps sort of cap out at some point in terms of performance (say M3, GS-1, etc; in general w/o discussing the merits of each).
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Beta22, active ground build. Amb's active ground beta22 had Ray Samuels saying, "It doesn't sound solid-state, it sounds like music... takes you so close... doesn't get any better than this." As far as performance suffering in the interim running a balanced amp with an unbalanced source... don't read too much into that from what I said. Yes, the L-/R- amps of a balanced amp would amplify ground noise... but on any decent source, this aught to be minimal anyway. I think the better reason to avoid balanced is cost, especially if you don't see yourself changing sources or getting an external phase splitter at some point. As far as capping out, yeah, high-end SS amps really are about as good as you are going to get without going to extremes, at least as long as you remain single-ended. The beta22 is about as extreme as you can get. Designing something single ended that would have the test-specs of a beta22 balanced would be.... well, really difficult and expensive. There is no reason - from a cost perspective - to attempt this when you can simply balance the system and have such an increase in measurables at basically twice the cost, as opposed to 4 or 5 times the cost or more trying to replicate it with a SE amp. If you intend to upgrade to a balanced source later, then by all means go with a balanced amp now. Your performance won't be noticeably hurt, and since most professionally built balanced amps are based off of extremely nice SE amps, then running a balanced amp as though it were a SE amp won't hurt anything, and will cost less in the long run if you go fully balanced.
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Originally Posted by KingStyles
If I understand what I have read, the eddie currant BA and the millet 307a have splitters in them. So does that mean they are fully balanced even if they are fed from a unbalanced dac?
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A lot of tube amps (any that are push-pull) have a phase splitter in them. In most cases this is not "balanced" in the way a balanced SS amp is. Very often the signals are summed before being sent to the headphone. The headphone still "sees" an amp on one side and power supply ground on the other. I've even seem some designs that are called "balanced" that accept a balanced source but basically bypass their own phase splitter and then do the same thing as above, with the ground of the transducer being directly tied to power supply ground. This IS NOT balanced, at least not in the way that we think of when we say a "fully balanced system." I'm 99% sure that the Millet 307A at TTVJ falls into a category like this. After all - it's a single ended triode amplifier; the "balanced" outputs are almost assuredly for show - you could tie the grounds of the headphone transducers together and the amp would behave exactly the same. The amp is transformer coupled... depending on how you look at it the transformers can be seen as "balancing" a single-ended source or as "unbalancing" a balanced source. It's really a different monster all-together, and nothing like a balanced SS amplifier, which won't be transformer coupled.
I looked at it more closely just now. The 307A has transformer coupled outputs and inputs. Remember, transformers block DC, so ground is whatever you want it to be after going from the primary to the secondary of the transformer. If you don't force a point of the circuit to ground intentionally, then the circuit after the transformer is floating and you can call any point you want "ground". The transformer doesn't care. So if you call one side of a transformer coil "ground" then the signal is all on the other side of the coil - i.e.- single ended. If you had a tapping point at the center of the transformers secondary and measured the ends of the coil you would see equal but opposite signals on either coil - i.e.- balanced.
This is how a transformer could be used as a "phase splitter" (terrible word, because that's not what it does... the old nomenclature has stuck around for years, though). A transformer would have have a secondary that was tapped at the middle. This tap would be tied to the ground of the input of the amplifier. Either side of the secondary would then feed the inverted signals to the +/- inputs of the amplifier, and away we go. Each amplifier would then amplify it's signal, and the signals would be sent to either end of the headphone itself.... the headphone never see the "ground" of the amplifiers or the source... it just sees the differential signal and plays the music.