preamp - what is an active buffer?

[HTWillie]

In search of another preamp, I'm getting a little antsy waiting for the right used one to appear, so I've been looking at the Schiit offerings. The $350 Saga looks pretty cool. It's switchable between a pure passive mode, and an active buffer mode.

Now passive mode, I get. Passive mode is simple attenuation.

Schiit describes the active buffer mode as being useful for driving long cables, and mentions 200V rails yet the specs state the preamp has a gain of 1 (0dB) in either mode.

What does an active buffer do while it's not increasing gain?

 

[whoaru99]

What does an active buffer do while it's not increasing gain?

Usually provides lower output impedance than a passive attenuator, while still maintaining decently high input impedance.

Pass talks about it a bit here -
https://www.passdiy.com/project/preamplifiers/b1-buffer-preamp

 

[Hyfi]

Not sure if this helps, but I asked a similar question elsewhere about my VAC which has Low Gain - High Gain, and Buffered Passive modes.

http://www.audioshark.org/pre-amps-9/buffered-passive-12ax7s-1018.html

 

[HTWillie]

Both of those links were helpful. I remember now reading the Pass write-up a few years ago, but at the time it didn't mean much. I really like the way he writes.

So, in general terms a buffer can add current or voltage to alter the impedance. Now I've got to wrap my head around input and output impedance and what suitable drives what. It'll take me a while but this is a good start for me.

 

[Finjima]

But the Saga also comes with a remote! Bonus right?

 

[E-Stat]

What does an active buffer do while it's not increasing gain?

WRU answered your question, but I'll cite an example. I use a Music Hall 25.3 DAC in the garage system directly driving a Crown XLS1500 amp. Like many SS amps, it's input impedance is exceptionally low. You really need a low impedance to drive that adequately.

The DAC offers both balanced and unbalanced outputs. While balanced is usually desirable all things being equal, the unit has a 4000 ohm output while buffered single ended is 600 ohms. The buffer stage lowers the impedance to better drive the amp.

So, which is better with the Saga? It depends upon the amplifier being driven and the length and quality of your cables. Try it both ways.