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horseman612
31
Sep 10, 2017
How do you run a fully balanced stereo signal through one 12AU7?
lugnut
103
Sep 10, 2017
horseman612It also does not have balanced inputs ! So this is just for someone with a set of headphones with a xlr cable ? Sorry, another item I call bullsh*t on ! Man these companies are making anything to sell to the uninformed !
rafael.sampaio
19
Sep 10, 2017
horseman612I have the exact same question... I cannot believe the "fully balanced from input to output" and wish someone could explain to me how that would be possible.
Dellwolf
35
Sep 10, 2017
rafael.sampaioMaybe balanced when only using the usb or spdif input?
iatsbohdan
200
Sep 10, 2017
lugnutCorrect me if I'm wrong, but this is a DAC/AMP combo, so you connect it to your PC with a USB cable and send digital data to it. The balanced magic starts when that balanced DAC converts digital data to balanced analog signal, then it goes to the balanced amp, then to your balanced headphone cable, and finally to your ears. Am I missing something? Is there a way to transfer balanced digital data into this device?
rafael.sampaio
19
Sep 10, 2017
DellwolfOnly if the audio never passes that tube.
andyo
55
Sep 10, 2017
horseman612I don't know much about this particular product but based on my circuit knowledge I have some idea about the topology. This preamp/DAC is not fully balanced, since it has RCA inputs. The single-ended signal is passed through a tube and made balanced at output stage.
brainwave
705
Sep 10, 2017
horseman612It definitely can run in fully balanced mode with USB digital input. The 12AU7 tube is a double triode that uses two identical triode circuits one each side. If each side of the tube is used for the amplification of each stereo channel you can get fully balanced headphone output. You even can get balanced output to the phones with a single ended stereo RCA input if xDuoo claims are true and amp uses two fully separate channels layout inside, though in this case it wouldn't be "genuinely" balanced since the analog RCA input signal is not balanced to begin with.
horseman612
31
Sep 10, 2017
brainwaveHow do you get each balanced channel through one triode though? A traditional balanced preamp (I'm assuming the tube is in the pre stage) would require a minimum of 2 matching output devices per channel, one each on the + and - side of the balanced signal - that'd be four triodes (or two 12AU7s) for a balanced stereo signal. Or am I missing something here?
brainwave
705
Sep 10, 2017
horseman612I don't believe this cheap amp uses true balanced differential mode circuit, most likely it is internally balanced only from DAC analog output and tube does not run in true balanced mode, though you can use a single double triode tube to ran stereo signal in impedance balanced mode.
brainwave
705
Sep 10, 2017
iatsbohdanA digital signal can't be balanced or single ended it is just multiple packets of ones and zeros. If a stereo signal is coded into digital domain it is possible to made it balanced at the DAC/amplification stage. Two separate DACs for the left and right channel, or a single DAC chip with the inside topology of two or more independent DACs must process L/R signals independently for each channel. If I'm not mistaken, AK4490 chip is not a balanced DAC. The digital section of xDuoo TA-10 does not have a separate DAC topology and thus the analog stereo output wouldn't be balanced. It seems only headphone stage of this device is fully balanced (if we can trust xDuoo advertising) and the benefit of balanced signal processing starts only from analog stage amplification. xDuooTA-10 is a single end DAC with balanced headphone amplifier section. You can't even use it as a true balanced headphone amplifier since it does not have a balanced input.
horseman612
31
Sep 10, 2017
brainwaveThen it shouldn't be advertised as "fully balanced from input to output"
Baljortar
3
Nov 7, 2017
brainwaveActually, the balance inputs xlr are for other reasons, not for the separation but for more power on the other side and also the cancellation of the noise collected in the cable. Those XLR cables are for pro audio , for distance and power but no for separation. 2 rca cables are balanced enough for a balanced headphone output because they use the same aspect that the grouds are separated one from the other. In other words, a balanced headphone output is just a way to listen the sounds of each side without the combination of the grounds and a balanced input does not works in it at all. But, if the grounds are not separated in the output of the chip itself, it just cannot be a balanced headphone output. So if they claim that they are ballanced from input to output, and the dac itself is balanced, it is trully a full balanced headphone amp. (but it has just one tube so that can be their mistake).
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