[pjchappy]

My SN TubeDac+ SHOULD be on it's way.  

The tube in this is used as a buffer. . .what exactly does this mean? It is not put in the signal, right?  Then, where is the 'tube majic' as a result? What are its benefits?  How are other tubes used in other DACs where it is put in the signal. . .?

Thanks!

p

[WEEZ]

pjchappy,

..good question- looked on the website and the circuit is not explained-at least as far as i could find-but;

If I'm remembering correctly(dangerous at my age) the Ah! player uses tubes that only drive the 0p-amp- and don't directly see the output load. Frank Van Alstine uses similar technology in his T6 and T7 pre-amps and also his TDAC.

Someone far more technical than I might explain the science- but would suspect that you will find that a tube change will change the sound as in a conventional tube output device- but the change may be more subtle.

Let us know how it sounds!

WEEZ

[pjchappy]

Well, I haven't heard back from the person I sent money to. . .SOOOO, hopefully things work out.  

Yes, I am looking for some technical speak, in laymen's terms.  

p

[markC]

I may be wrong here, but will risk embarassment. I think that the term buffer implies that the device does not do the job all on it's own. In a buffered output cdp for example, there is one or more opamps amplifing the minute signal from the transport and decoding chip. This is then passed on to the tube for the final output amplification to say 2v.That's why tube rolling still has such a dramatic effect on the sound.

[vrs]

A friend of mine uses a tube buffer between his satellite receiver and pre amp. It increases the gain.With some inexpensive tube of 12 dollars he can change the tonality.His satellite receiver Globe sat world) does not have a Digital out put.He says it can go between other source components such as DVD player and also between pre and power amp.
His preferred position is between the satellite receiver and Pre amp.I guess it costs about 350$

[JohnR]

A buffer is a circuit with a gain of one, ie the output voltage is the same as the input voltage. It's purpose is (usually) to provide a low output impedance; also, it electrically isolates the previous stage from whatever is being driven by the buffer.

Another way to look at it is that it's an amplifier that doesn't amplify...

Yes, it is 100% in the signal path.

[pjchappy]

OK, then I must have misread when it said the Tube Dac had a tube that wasn't in the signal path.

What are the benefits of using a tube in such a design?

Thanks. . . again!

p

[JohnR]

The benefits... well, it gives you buffering using a tube

According to SN's webpage, the output impedance from the DAC chip is 1.65k -- this would usually be considered on the high side for driving cables. I'm not sure what the output impedance with the tube is... probably a couple hundred ohms. This means that the buffered version cares less about what you are driving; highly capacitive interconnects or lowish input impedance (less than 10k, say) on the preamp might affect the sound. In theory, anyway.

If you mean why use a tube instead of an op-amp to do the buffering? Well, some people just think it sounds better

HTH - ?

[JohnR]

I just noticed on Scott's webpage that the output impedance w/ the tube buffer is 100 ohms. He seems also to now have a version with op-amp buffers.