Input sensitivity, Gain and Preamp matching

Thank you most kindly, Mofi. I should qualify your statement, though, by saying that at best I'm just an amateur master, while Ralph (Atmasphere) is of course a professional master :-)

Pani, Ralph frequently makes the excellent point he states above that to perform at its sonic best a SET should be operated within just a relatively small fraction of its rated power, such as 25%. Unless, and perhaps even if, your speakers are super-efficient, though, such as being in the 103 db area he mentioned, I personally would nevertheless want to have the flexibility of being able to drive the amp to full power, even if it is only a relatively few recordings having particularly wide dynamic range that might require that.

If you are using the single-ended output of a typical digital source, its maximum output won't usually be much if anything over 2 volts. And it will be less than that for many recordings. So with 0 db of preamp gain (meaning, with the volume control set at max, that preamp voltage out = preamp voltage in) you would not be able to drive the amp to full power. On the other hand I believe that some of the Slagle autoformer-based passive preamps, as in the case of the one-stage tube preamp you are considering, provide up to around 6 or 7 db of voltage gain. That would result in their output being double the voltage they are provided with when the volume control is set at max. That would probably allow you to drive the amp to full power with many and perhaps most recordings, but almost certainly not with some.

Perhaps more significantly, if I'm recalling correctly you use a high quality analog source. Most (although not all) cartridge/phono stage combinations provide significantly lower peak output levels than digital sources, for nearly all recordings (the cannon blasts on the famous and nearly unplayable early edition of the Telarc 1812 Overture perhaps being a rare exception :-)).

So it seems to me that even with 6 db of gain you would at best be introducing a significant marginality into the system, that would probably prove to be unsatisfactory for some recordings. Especially if your speakers are not in the 103 db/1 watt/1 meter area that Ralph referred to, or higher. Personally, my instinct would be to pursue a different path.

IMO. Good luck. Regards,
-- Al

Pani, yes as George indicated it would certainly be relevant to know exactly what your source component(s) is or are.

In the meantime, though, in regard to what I alluded to earlier about the peaks of some recordings leaving margin relative to the maximum volume capability of the medium, my curiosity was sufficiently piqued that I've just made some measurements to shed some quantitative light on that.

What I've done is to use the Sony Sound Forge professional audio editing program I have to examine the waveforms of about a dozen different tracks from about a dozen different CD's, both classical and popular, dating from very recent years all the way back to reissues of 1940's and 1950's material. The Sound Forge program can quickly tell me the level of the highest instantaneous peak on a track.

While several of the tracks essentially reached the maximum possible ("full scale") level of the CD medium, which is identified as 0 db, many others peaked at various points between -1 and -4 db, with one peaking at -6 db and another at -8 db.

A -6 db peak will result for that track in the maximum output of a CD player or other digital source being 1/2 of its rated (maximum) output. So for example a CD player rated to provide 2 volts would never put out more than 1 volt for that track.

As I alluded to earlier, my philosophy is to avoid configuring a system in a manner that might be marginal (or worse) even with just a relatively small number of recordings.

Regards,
-- Al

03-31-15: Georgelofi
But, and a big BUT, when do we do our listening just below full output (clipping) of the poweramp anyway???

We (or at least most of us) of course don't do that on anything approaching a continuous basis. But it should be kept in mind that the main usefulness of the upper part of the power capability of an amp is typically to support the BRIEF dynamic peaks of those recordings which have wide dynamic range (meaning a wide DIFFERENCE in volume between the softest notes and the loudest notes).

For example, listen to this excerpt from Stravinsky's "Firebird", from the 7 minute point to the end at 10:54, as the music descends to near inaudibility and then builds to a concluding note that on some well engineered minimally compressed recordings I have reaches 100 to 105 db at my listening position.

Or consider this very simple arrangement (female singer with piano accompaniment) of the old standard "All The Things You Are". That is one of the tracks I described analyzing in my previous post. Prior to the last 15 seconds of the track the RMS average level is a very low -31.1 db, with the very highest value during those 3 minutes being -13.2 db. Yet in the final few seconds a peak of -4.7 db is reached. As I'm sure you can calculate, that peak will require 437 times as much power as the average level.

My point is that unless the OP's 16 watt amplifier is being used with speakers having an efficiency in the area of the 103 db Ralph referred to, there will be SOME recordings which on brief peaks are likely to require most or all of the amp's power capability to be used. And unless his source components have output levels that are a good deal higher than average he won't be able to turn the volume control up high enough to be able to utilize that power capability, if his preamp provides little or no gain.

Regards,
-- Al

Pani, the Naim Superline has a specified gain of 64 db. That corresponds to a voltage multiplication of 1585. (20 x logarithm 1585 = 64). So the 0.5 mv output of your cartridge under the standard test conditions would be raised by the phono stage to 0.5 mv x 1585 = 0.79 volts. However the maximum levels of some recordings may exceed those standard test conditions several-fold, I believe by something like a factor of 5 in at least a few cases. So there may be SOME recordings on which the max level of the phono stage output might reach 3 or even 4 volts. But as far as I am aware that won't be the case with most recordings.

Also, keep in mind that the difference between 16 watts and 9 watts is just 2.5 db, which subjectively is not all that much of a difference. If you presently cannot listen to 30% of the music at desired volume levels, I would not expect that a 2.5 db increase in power would represent a solution. And even more so considering that on many recordings you may not be able to utilize much or any of that added power if you do go with a low or no gain preamp, because of the amp's low sensitivity (corresponding to a high sensitivity number, as was pointed out).

Re your question about running power amps at full gain, if the amp has a volume control and is used with a preamp having a volume control, yes, chances are that in general it would be preferable to run the power amp's control at max, which in effect takes it (and any adverse sonic effects it might contribute) out of the signal path. On the other hand, though, there may be some cases where that benefit would be outweighed by other considerations. One example perhaps being a need to increase the signal level at the output of the preamp in order to minimize the audibility of groundloop-related noise, and another example perhaps being a need to avoid running the preamp's volume control undesirably close to the bottom of its range.

I believe that your last question relates to what Ralph (Atmasphere) often refers to as power paradigm vs. voltage paradigm amplifiers, which is a separate subject relating to matching amplifiers and speakers in a manner that will result in proper tonal balance.

Good luck, however you decide to proceed. Regards,
-- Al