[Btrmousetrap]

To all,

I again would like your help to understanding amplifier gain ratings. I have researched via the internet and am still a little cloudy regarding amp specs and determining preamp input requirements. If I understand correctly, improper amp preamp mating could result in faster clipping voltages? If my understanding is correct, what do you look for in a preamp to insure a “good” compatibility? I have seen Nuprime amps with gain specs ranging from 21 up to 29. If I was to use a DAC 9 as an example, how would I determine dynamics capabilities with out early clipping potential? Please excuse me if I am too far off base as I am definitely not at a high level of understanding.

Thanks

Btrmousetrap

[avahifi]

Amplifier gain is simply the measurement as to how much an amplifier increases the voltage level of the signal.

For example if an amplifier had a voltage gain of 20, then a 1 volt input signal would provide a 20 volt output signal.  Typical amplifier gain is around 25.

Of course the limit to amplifier gain is also defined by just how much signal increase the amplifier can product before it runs out of room to produce more. Its limits are caused by its power supply voltage output maximum and its ability to generate its gain into a low impedance load (a loudspeaker).

If an amplifier was rated at 25 watts per channel into 8 ohms then at maximum power it would be putting out 20 volts peak.  If that amplifier had a voltage gain of 25, then them most voltage amplification it could provide into an 8 ohm load would be 20 (its max power before clipping) divided by 25 (its voltage gain) which yields 0.8V peak.  Anything more into the amp than 0.8V just causes the amp to clip and badly distort.

If the amplifier was rated at 300 watts per channel into 8 ohms then at maximum power it would be putting out about 70 volts peak.  That means the amplifier with a voltage gain of 25 could put out about 70V peak into the speaker.  70/25 yields 2.8V peak voltage input to make full power.

The voltage into the power amp is determined by the level of the signal into it.  This comes from the signal level of the source recording, the gain of the preamplifier used, and the setting of its volume control.  Your results will vary depending up the specifications of your equipment.

Oh, by the way amp power is determined is by taking maximum peak voltage output before clipping times .707 to convert to RMS voltage, that quantity squared, then divided by the load resistance (usually 8 ohms).  Note that using this formula into a 4 ohm load shows double power into the load although the amplifier has not changed.

So gain determines how much the input signal is increased, power determines how much of the increase is possible before other factors such as power and load ratings take over.

Frank

[Btrmousetrap]

Frank,
Thankyou for explaining amplifier gain. Is there anything I should look for on the preamp side to match with an amplifier? Is the output of a preamp or in the example of the Nuprime DAC 9 a standardized output voltage? I looked and don’t remember seeing an voltage output listed. Is it of no concern?

Btrmousetrap

[rustydoglim]

Generally manufacturers try to design their components within a normal range.  For preamp/source, it is typically 2V.
Amplifier gain beween 20 to 29 are all ok. 

[kevb]

Btrmousetrap....

Feel honored, as Frank has forgotten (or discarded as BS) more about traditional amp design than any one of us has probably ever learned.  Having owned a couple of his designs over the years, his amps are tremendous values as well.  He's a no-nonsense type of guy.

NuPrime amps work better for me because of the "lifestyle" size, where you get tremendous sound and power in a small, unobtrusive package.  But for class A/B amps, you won't find much better value than AVA amps.

Thank you for chiming in, Frank......

[Btrmousetrap]

Thanks to all for the responses.

It is great to have generous people share and help others with a lesser understanding on our common interests.

 

Btrmousetrap

[walkern]

I have an STA 200 amp with 35 db of gain (a pretty high figure), and a Pass Amp Camp Amp with only 14 db of gain (a pretty low figure).  The Nuprime can be easily driven by a good DAC or by using a passive attenuator.  The ACA on the other hand sounds thin and bland or a little dull unless you throw some juice it's way.  It sounds best with a preamp with somewhere between 6 and 12 db of gain.  To some extent the sound of the amp will also be influenced by the efficiency of the speakers you are using.  High sensitivity speakers will allow you to (in general) get away with a lower gain amp.  Last but not least, some speakers LOVE plenty of current to drive them (Maggies are famous for this), and that too will affect how a lower or higher gain amp will interface with them.  As Frank noted, if you stick with an amp in the 20 to 30 db gain range that's usually a safe bet for being easy enough to drive (at the input), and potent enough to drive most loudspeakers.

[RafaPolit]

Frank, that is an incredibly useful and thoughtful post.  Thanks for sharing!

[avahifi]

Remember that amplifier voltage gain has no corrollation with amplifier power.

Voltage gain simply shows how much the amplifier increases the input signal level up to its maximum power potential.  You can have either a high gain or low gain amplifier with either low or high output power, or anything in between.

Power is the maximum voltage level possible into the rated load. A low gain amplifier simply requires a higher input level to reach its rated load limits then a high gain amplifier does.

In general, a high gain amplifier, which requires less input voltage signal, is useful for those wanting to eliminate the preamp gain stage and use either a passive volume control or direct output from a DAC with a built in volume control.  This is even more useful with a high sensitivity loudspeaker.  Of course since thermal and other noise from the source is amplified by the power amplifier as much as the wanted signal input is, and the noise is constant while the source signal varies, a high gain amplifier with efficient speakers will have a poorer signal to noise ratio (more final output hum and buzz and white thermal noise).  Your results may vary.

Frank

[RonN5]

With more and more higher sensitivity loudspeakers being offered, why are there not more amplifiers being offered with some form of gain control?

If, I understand Frank's post correctly, amplifiers with gain controls might result in two benefits for users...first, they might be able to turn their DACs or Preamps up to the 10-2 range (rather than the situation where volume is already too loud before the dial hits 9 o'clock) and second, an opportunity to use a lower gain setting and reduce the overall noise level?

[walkern]

The down side to a gain control is that you are adding another attenuator to the input.  Most good attenuators don't have much 'character' or sound of their own, but they all have the potential to downgrade the incoming signal in some way or another.  The higher the quality of the amp, the more likely it is that you'd not want any additional signal modifying device between your source or preamp and the amp.

[JLM]

The down side to a gain control is that you are adding another attenuator to the input.  Most good attenuators don't have much 'character' or sound of their own, but they all have the potential to downgrade the incoming signal in some way or another.  The higher the quality of the amp, the more likely it is that you'd not want any additional signal modifying device between your source or preamp and the amp.

+1

A second volume control/gain stage would be another opportunity for electronic noise.  If everyone would follow a single ended 2.0 volt standard for maximum pre-amp output and rated amplifier input we wouldn't have a problem. 

A bigger problem exists in the balanced arena.  Professionals use a variety of standards, up to 12.2 volts, while most consumer gear is rated to only 4.0 volts, making for problems when trying to mix and match. 

In 50 years at this and 20 some years of particular interest in high efficiency speakers I haven't noticed an increase in high sensitivity speakers in the marketplace.

[RonN5]

My "increase in higher sensitivity" speakers comments stems from companies like Tekton and Spatial Audio gaining more and more market traction...and themselves offering most/all of their products in the >92db range....but then again, it could just be my own increased awareness of higher sensitivity...

when I owned the Tekton Lores (rated at 98db but probably more like 95 db) I had a heck of a time driving them at a reasonable (meaning under 85db) level and then also getting enough signal for my sub to even turn on (power sound audio s1500)....so, for now I'm using a Halo A23 with gain control which gives me flexibility to balance the voltage....although I probably don't really need the gain controls now for my Salk Veracity STs.

A question then, relative to the balanced outputs on preamps/dacs.....if the balanced output voltage is double the rca output voltage...then would using a balanced to rca adapter reduce the balanced output voltage?  (granted, this may negate the advantage of balanced output)....

[avahifi]

Balanced line operation with XLR jacks has three conductors; plus, minus, and ground.

A passive XLR to RCA converter will use only one of the two active signals from the XLR jack because the plus and minus signals cannot be combined as they are out of phase and will then cancel. Without the balanced connection, the amplifier gain will be cut in half.

Likewise a passive RCA to XLR connector will only feed one audio signal to the XLR connection, thus providing only half of a balanced amplifier with the signal.  You loose most of the power from the balanced amplifier and the advantage of differential operation.

For very efficient speakers you need a preamplifier with the option of setting the preamp gain down substantially or with a front panel low gain setting to provide better use of the volume control.

Frank

Frank

[avahifi]

Balanced line operation with XLR jacks has three conductors; plus, minus, and ground.

A passive XLR to RCA converter will use only one of the two active signals from the XLR jack because the plus and minus signals cannot be combined as they are out of phase and will then cancel. Without the balanced connection, either the plus or the minus signal will be used (but not both) and the system gain will be cut in half.

Likewise a passive RCA to XLR connector will only feed one audio signal to the XLR connection, thus providing only half of a balanced amplifier with the signal.  You loose most of the power from the balanced amplifier and the advantage of differential operation.

For very efficient speakers you need a preamplifier with the option of setting the preamp gain down substantially or with a front panel low gain setting to provide better use of the volume control.

Frank

Frank