Input sensitivity, Gain and Preamp matching
Pani hi, before doing anything suggested, what are your source/s, maybe they have the output volts that's needed >2.5v as many do these days, even phono stages Your amp is high at 2.5v, the input impedance at 47kohm is fine, if your source/s have this >2.5v then yes a 10kohm passive will work great. But I would be wary of passive TVC's that have a gain switch, as they can "ring" if the gain part is used, in unity gain they seem ok. Cheers George |
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 |
Hey Al good to hear from you, as you stated, yes a few of the quietest early cd's have low recorded volume and your -6db seems about right for these. So even if Pani has source outputs 2.5v this will be ample for 90% of the rest of recordings to play at full amp clipping, and if he has 4v from his source/s that will also take care of those quite -6db as well to drive the amp to clipping. But, and a big BUT, when do we do our listening just below full output (clipping) of the poweramp anyway??? Unless we like blowing amps up to speakers. All is moot anyway till we find out what source/s Pani has. Cheers George |
03-31-15: GeorgelofiWe (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, My experience is based ONLY on TVC and not other types of passives. But nevertheless, I would like to share. Your amp's sensitivity is actually very low. The way people would look at the sensitivity would be - if it requires less volts for full power, then it is high sensitivity. If it requires more volts for full power, then it is low sensitivity. For a passive to work with an amp, the max sensitivity that you should go for an amp would be 1.5V for full power. The lower the better. My amp is 1V for full power,and I use a TVC. Or else, like Al mentioned, you will not hear the "full potential" of your system. Also Ralph has mentioned about speaker sensitivity - this also plays very important role in a "passive based" system. Ideally your speakers should be 90+db. At this point, it looks like active pre would be the way for you, unless you change some components in your system. |
