[WireNut]

FWIW, going from unbalanced to balanced connections from my Sonic Frontiers SFL-2 preamp to the balanced inputs of my Audio Research amps gave me more dynamics and slam. I like it.

 

[RDavidson]

Seems like an active buffer is not all that simpler than an active line stage. You still need a power supply and a transistor or tube to amplify the signal at unity gain. (In other words, a buffer is really just an active gain stage with a gain of 1.)

Also, I don't believe (anymore) that a source component has enough mojo to drive the typical amp and speaker in the same way that a good preamp does. I mean, it can drive it to a desired volume level, but not with the same peak dynamic range or slam factor that an active pre can. If you have a super high gain tube amp and something like Klipschorns,,, OK, maybe.

I think the OP should keep his power amp and get a killer tube preamp. Can always buy a tube amp down the road.

The way I understand active linestages to work, is that they have an active input stage, a potentiometer of some sort, then another active output stage. There's gain at the input, output, or both. Perhaps this isn't true of all active linestages, but I've read this in a publication somewhere. If I'm wrong, please correct me. I enjoy learning new things. With that said, you see where my thoughts on circuit simplicity reside. Buffered preamps don't have the active input stage, just potentiometer and active buffer.

You've kinda hit the nail on the head, though I think you're overstating the need for ultra high sensitivity speakers and needing A LOT more than unity gain. There are a lot of factors, and I've stated this in another thread ; Amp and speaker matching is important. Matching speaker to room size, listening distance, and loudness (peak) levels is even more important. How much voltage an amp needs to reach full output needs to be noted. Some amps need 2V. Some need 1V or less. I will go out on a limb and say that the majority of modern sources output 2V average. So, for instance, if you have an amp with input sensitivity of 1V to reach full output, then all one should need is something like .25V for average listening levels (assuming amp and speakers are matched to reach desired peak volumes in room). .25V is nothing. Hell, it'd be hard to find any source that outputs 1V or less.

So, keeping all the above in mind, why would one need an active linestage (with gain)? If you tell me you just prefer the sound of an active linestage, even if it is boosting the source signal in a way that may not be ENTIRELY true to the source, but you find it more enjoyable, that's cool! Anything in the chain, including buffered preamps will affect the sound in some way. I just tend to disagree with blanket statements/recommendations of any sort.

The truth is there are just too many factors to consider, and everyones' preferences differ.

We're kind of going way off topic, but this is an interesting discussion.

[vortrex]

Seems like people flip this brand of amps frequently. You sold yours pretty quickly too. What was it that you didn't like about them not to keep them for more than 6 months?

I loved both my amps, no complaints at all.  The only reason why I sold them is because I heard Shindo.  I'm Shindo for life now.
 

[InfernoSTi]

Are you saying that only the single ended Quicksilvers have a unique topology? Or all Quicksilvers? Can you elaborate?

The reason why I ask is because I think that Quicksilver makes a good push pull amp, but a dull and boring SET amp. The one I heard was a real yawner. (Single ended KT 88.) I have heard second hand that Mike doesn't like the single ended topology and the high voltages that are necessary to make it work scare him. I don't blame him. Anyway,  his specialty is push pull.

I always wanted to hear the Quicksilver Horn Mono amp. That seems like the one to get if you have a good preamp and moderately efficient speakers.

The unity coupled are definitely not their single ended amp...thus distinguishing them from SET amps (yet they seem to have that "magic" folks talk about).  I haven't heard the QS Horn Monos so I can't comment.

The unity coupled design is unique (again, referencing the McIntosh MC275).  Here is the patent write up from 1948: http://www.google.com/patents/US2477074 

It is a primary object of the present invention to provide improved push-pull amplifiers having negligible leakage reactance in their output transformers, and hence negligible transient effects during change-over of each tube of the amplifier from conducting to non-conducting condition.

As background, this 1949 article http://www.alinden.mynetcologne.de/mc/mcintosh.pdf discusses the concept in a marvelously straightforward manner.  Basically it overcomes the P-P inductance issue (crossover distorition...the "notch" in the article) through the use of a unique transformer configuration.  Page 1 has easy to see pictures of the "notch" and page 2 has a description of why it works.  So you get Class A sound with Class AB power/efficiency.  A truly clever solution that dealt directly with the critical kind of distortion (not THD via feedback that just makes things worse).

John

[Quiet Earth]

The way I understand active linestages to work, is that they have an active input stage, a potentiometer of some sort, then another active output stage. There's gain at the input, output, or both.

Typically there is the selctor switch, the volume control, and two active gain stages in an active linestage preamp. And it is in that order. The reason why it is that order is so the source component always sees the constant resistance of the volume control (10k, 20k, or 100k attenuator) then the make up gain, and then the impedance handshake. Again, this is typical. My pre-amp has exactly this configuration except that the second gain stage is not capacitor coupled to the amp, it is transformer coupled. So the make up gain is quite huge (big dynamic swings) but the step down transformers bring the impedance down and make the overall gain not so huge.  But this is a costly way to do it and not as common.

So anyway, a buffer is sort of like an active pre, but there is only a single unity gain stage (or impedance buffer) after the volume control. That makes it a little bit simpler, but not all that much different. You are just missing the first make up gain stage.


Regarding the voltage that it takes to drive an amp - I think that it gets complicated. Let's say your Dac has 2 volts out at full scale digital. That means the very loudest peak on the hottest recording that you have will be 2 volts out. Peak. Are all of your recordings this loud? What happens when there are quiet passages? What about the mean volume, or RMS?  Also, what is the output topology of the DAC? Can it drive 2 meters of cable into a variable load (passive pre) with no effect on its freq. response etc., etc.? Would another gain stage help to overcome any losses or impedance difficulties?

Don't get me wrong, I was a passive-pre user for about a decade (TVC and high gain tube amp). I think that passive is a great way to go within a certain budget. My TVC sounded better to me than most preamps that I compared it to within a certain budget. But once I got into a certain price range, there was no denying that the dynamics could be improved along with maintaining the clarity and purity of keeping it simple. So there is really no easy answer here. Try lots of things and keep your mind open. Don't audition anything that you can't afford because once you hear something better in your house then there is no way to un-hear it. Oops.... 

It is a good topic though. 

[Quiet Earth]

I loved both my amps, no complaints at all.  The only reason why I sold them is because I heard Shindo.  I'm Shindo for life now.
 

Ahh yes...... I totally get that. Totally makes sense.
 

[Quiet Earth]

InfernoSTi (John),
Thanks for the link. I'll read it tomorrow when I have more time.

[RDavidson]

....Regarding the voltage that it takes to drive an amp - I think that it gets complicated. Let's say your Dac has 2 volts out at full scale digital. That means the very loudest peak on the hottest recording that you have will be 2 volts out. Peak. Are all of your recordings this loud? What happens when there are quiet passages? What about the mean volume, or RMS?  Also, what is the output topology of the DAC? Can it drive 2 meters of cable into a variable load (passive pre) with no effect on its freq. response etc., etc.? Would another gain stage help to overcome any losses or impedance difficulties?

Don't get me wrong, I was a passive-pre user for about a decade (TVC and high gain tube amp). I think that passive is a great way to go within a certain budget. My TVC sounded better to me than most preamps that I compared it to within a certain budget. But once I got into a certain price range, there was no denying that the dynamics could be improved along with maintaining the clarity and purity of keeping it simple. So there is really no easy answer here. Try lots of things and keep your mind open. Don't audition anything that you can't afford because once you here something better in your house then there is no way to un-hear it. Oops.... 

It is a good topic though. 

Interesting. You're VERY right. There are so many things to consider. Perhaps gain vs no gain really isn't the key takeaway that people (including writers for publications) focus so much on and lead others to focus on, when talking about active vs passive preamps. It's really about impedance matching (which, note, a full passive can't do). At the core, gain or no gain, active preamps are really just impedance matchers. From there, it's all about who has implemented the most ideal (cleanest) circuit. This is not to shun full passives, which can indeed work in the right setup......but, that's the tricky part that many don't understand. I think full passives get written off as sounding dull and lacking dynamics, when it is actually the impedance mismatch causing the problem.

Enough about preamps. The OP has a buffered preamp, which should be fine as long as output voltage from pre and input voltage sensitivity at the amp are considered. Thank you very much for your thoughts. This honestly has made me reconsider the core goal of preamp design/function in general.

[a.wayne]

Here is a link to the preamp:

http://vinylsavor.blogspot.de/2012/06/making-of-6ah4-line-stage-circuit.html

Cool .......

[a.wayne]

FWIW, going from unbalanced to balanced connections from my Sonic Frontiers SFL-2 preamp to the balanced inputs of my Audio Research amps gave me more dynamics and slam. I like it.

6 db more gain, if true balanced ........