A.k.a. 32 dB.
The required amount of gain will obviously depend on required output power and signal level delivered to the power amp. Or seen the other way round, it determines input sensitivity.
As a rule of thumb, the more gain one stage has, the higher its contributions to noise and distortion will be. Many hi-fi amps has as much gain as 45 dB after the volume pot, and they're not easy to get dead quiet.
I've tried shedding a bit of light on that in a little blog entry.
The required amount of gain will obviously depend on required output power and signal level delivered to the power amp. Or seen the other way round, it determines input sensitivity.
As a rule of thumb, the more gain one stage has, the higher its contributions to noise and distortion will be. Many hi-fi amps has as much gain as 45 dB after the volume pot, and they're not easy to get dead quiet.
I've tried shedding a bit of light on that in a little blog entry.
Around 30dB is about right.
It does vary with the input sensitivity and the output required.
Lets take a fairly standard 100W Power Amp.
In order to produce 100W into 8 Ohms it will need to output approx 28VRMS.
If it is to be fed with a CD input (Typically 2VRMS)
It will need a gain of 20xlog(28/2) = 23dB
If it is to be fed with a line source of 100mV RMS
It will need a gain of 20xlog(28/0.1) = 49dB
You have a linear gain of 39 which is equivalent to 20xlog(39) = 32dB
With a CD input, assuming that the amp has the guts to produce it, you will get approximately 50W into 8 Ohms.
It doesn't matter if you have a 2Kw amplifier with a Gain of 32dB, it will still only output 50W with a 2VRMS input signal.
It does vary with the input sensitivity and the output required.
Lets take a fairly standard 100W Power Amp.
In order to produce 100W into 8 Ohms it will need to output approx 28VRMS.
If it is to be fed with a CD input (Typically 2VRMS)
It will need a gain of 20xlog(28/2) = 23dB
If it is to be fed with a line source of 100mV RMS
It will need a gain of 20xlog(28/0.1) = 49dB
You have a linear gain of 39 which is equivalent to 20xlog(39) = 32dB
With a CD input, assuming that the amp has the guts to produce it, you will get approximately 50W into 8 Ohms.
It doesn't matter if you have a 2Kw amplifier with a Gain of 32dB, it will still only output 50W with a 2VRMS input signal.
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As I said. If the amp has the guts to go that high.
If you are talking Pre-Amps then YES you are right.
Power Amps need much more gain in order to achieve their target outputs.
Hopefully my earlier post makes that clear.
For a pre-amp the reasoning is slightly different.
The maximum output voltage is marginally less than +Vcc to -Vcc.
Lets take a standard Op-Amp that is powered by +/- 15V.
Max Vout RMS is 10.6V RMS, probably slightly less.
In which case with a CD (2VRMS) signal the maximum gain before clipping is about 14dB or 5x.
100mV Line Input is 40dB or 100x.
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Hi,
No it doesn't, it contradicts itself, it states :
A) 100Wrms into 8 ohms with 2Vrms input needs a gain of 23dB
B) 2Vrms input with a gain of 32dB can only produce 50Wrms into 8ohms
Clear as mud ......
Power amplifier gain is usually around 1Vrms in for maximum output.
That gives you the "standard" gain of 28 (100W with 1V in 8ohm).
But some are about 3x times higher (10dB), 300mV in for full power.
This allows the use of a passive volume control for line inputs.
B) 32dB, can be considered a case of the above.
rgds, sreten.
I believe there is an industry standard of about 26 dB for audio power amps. It is like a sweet spot which balances output power, effective loop feedback to lower distortion and stability (no oscillation). For example the gain factor for Threshold S/150 is + 26.6 dB (no loop feedback). and for Adcom GFA-535 is +26.8 dB (loop feedback). The plus sign signifies no inversion of the signal phase.
No - it signifies gain, as opposed to attenuation. Try to take the log of a negative number...
As already mentioned above the gain should go with the power of the amp, assuming some sort of standard for input signal and speaker impedance.
So higher power amps need more gain than lower power amps in order to fully utilize the power of the amp.
yes the question is sideways to the real issues
you want to know what is the avaiable input V from your source, or what is the "standard" consumer line V level
then you want to know ranges of source material recording levels and if that implies a need for more system gain
then with amp supply V/power rating you can determine gain - if it sin't already limited by stability concerns (chip amps)
unusual speaker sensitiviy can also change the equation since what you really want is proper "gain structure" to avoid noise, give adequate volume, range of SPL at the listening position
you want to know what is the avaiable input V from your source, or what is the "standard" consumer line V level
then you want to know ranges of source material recording levels and if that implies a need for more system gain
then with amp supply V/power rating you can determine gain - if it sin't already limited by stability concerns (chip amps)
unusual speaker sensitiviy can also change the equation since what you really want is proper "gain structure" to avoid noise, give adequate volume, range of SPL at the listening position
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There are many preamplifiers with +12dB gain.
This is same as x4.
We can say sort of a standard is x4 = +12dB
but of course there can be other gain.
So, x10 is sometimes seen in preamplifiers.
I guess x4 (12dB) is a good value. Preamp gain needs to be low. In most cases it only needs to be around x1 (0dB), which means either no preamp or a genuine buffer to make up for weaknesses in other components. x2 (6dB) is hardly worth bothering with, as it won't sound much louder than x1. So x4 (ish) is the smallest number above x1 which is worth doing. Going higher than x4 is almost always a mistake, as you are merely amplifying a signal in order to attenuate it again - only worth doing if you like your music with unnecessary noise and distortion.
So the sensible choices are:
(a) no preamp
(b) genuine buffer (x1, 0dB, high input impedance, low output impedance, low noise, low distortion).
(c) x4 (12dB) or thereabouts
Curiously, most people who wish to avoid (a) either go for an FX box calling itself a buffer, or far too much gain so have to add attenuators.
So the sensible choices are:
(a) no preamp
(b) genuine buffer (x1, 0dB, high input impedance, low output impedance, low noise, low distortion).
(c) x4 (12dB) or thereabouts
Curiously, most people who wish to avoid (a) either go for an FX box calling itself a buffer, or far too much gain so have to add attenuators.
That looks like Nelsons thoughts with the B1. For those that don't know the B1 it is a unity gain ie gain=1 buffer amp.
Even my mighty Pass Aleph 4 with only 15dB of gain needs only the output of a standard CD player to drive it to its maximum. I could use just a passive pot but I choose to use a B1 to match all the impedances together. And it works an absolute treat.
Even my mighty Pass Aleph 4 with only 15dB of gain needs only the output of a standard CD player to drive it to its maximum. I could use just a passive pot but I choose to use a B1 to match all the impedances together. And it works an absolute treat.
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15db gain is enough for a moderate power amp but for 100W/8R (28V RMS)
for instance it s somewhat short.
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