My 30 Watt class A is louder than my 100 Watt Class AB?

It has to do with the different input sensitivity (gain) of the two amps!!

@yogiboy 

Thanks!

That was what I thought. Wasn’t until after I had listened for a bit that it dawned on me the impedance difference was the cause.

It’s the gain difference and input sensitivity difference of the two amps!

Thanks. I re read the answers, watched the video, and it’s a bit clearer now! 

Hiraga has a gain of 26db, input sensitivity TBD.

Adcom has a gain of 27db, and an input sensitivity of 1.25V

I’m going to contact the vendor for the Hiraga PC boards I bought, and see if I can find out the input sensitivity.

Amp settings vary with gain.  I recently use the same preamp into two different amps, one of whiich can use 3 tubes for different power levels,  with the following results for the same voume level.

ZMA  40 wpc  -40dB

Techtron 300b 6 wpc   -45dB

Techtron 2A3  2.8 wpc  -48 dB

Techtron 45   1.8 wpc   -50 dB

So the gain produces the same valume at a lower setting but if I were to turn it up on a night when I felt particularly sadistic toward my eardrums, they woulld run out in order of power from low to high.

I thought it was ironic that the lower the power the more gain.

Jerry

The voltage gain of amplifiers is a convention, but not a rule. I think most solid state amps have 23 or 26 dB of voltage gain, but there’s no rule that forces this number. Lower gain may be a good thing given that so many preamps have too much gain already.

Also, there's no correlation between amplifier power and voltage gain.  From 50 to 500 Watts, amps following the convention will be just as loud at the same input.

I had a situation that was opposite of the "too much gain" scenario. I tried to use a Schiit Saga preamp (unity gain) with their Aegir power amp which is on the low side of amp gain. I had to turn the volume up to near max on most recordings to get an average listening level. That meant when I tried to play recordings with lower-than-average volume levels I was unable to reach my desired volume even though the amp had more than adequate power. I solved the problem by selling the Saga and switching to their Lyr 3 which has switchable gain (+3.5 dB or 17.5 dB).

I tried to use a Schiit Saga preamp (unity gain) with their Aegir power amp which is on the low side of amp gain. I had to turn the volume up to near max on most recordings to get an average listening level.

The Sega has no gain, your source has to be high voltage such as a CD player to drive an amp with enough voltage. If you were hooked to a low voltage source like a record player, you would run out of steam. And that is why active pre-amps exist. 

Volume isn’t my problem :)

Using 4ohm 84db speakers, I never go past 11 o’clock on the dial :)

@russ69 -- I know the Saga has no gain (that's what "unity gain" means.) And I was using a DAC with the typical 2 volt output, so nothing amiss there. While most of the time I got the desired playback volume, the problem was when the recording itself was recorded at lower than normal volume. Certainly not a problem with most pop/rock material, but there are some recordings out there where this can be an issue.  Its not an issue limited to certain turntables/phono preamps.

I went from a tube preamp with 3-5 db of gain into a ZMA and always had the preamp up more than half way to get reasonable volume from 96db sensitive speakers. When I got a Backert preamp with 9db of gain now all of the sudden the ZMA is a  power house and never needs the pre up nearly as much to reach very robust listening levels. Gain staging is crucial and of course component synergy.

Watts per channel are only the out put measurement ( horse power). There is so much more (torque) inside the an amp that produces the watts per channel. They did not name the company “First Watt” because it was catchy!

gain and input sensitivity ...man, how about my conrad johnson preamp:

Gain:

Phono stage 47dB

Line Stage 31dB

is is sometimes too loud at 9 o clock. i use inline attenuators on amplifiers that dont have a volume knob. man this thing has a lot of gain.

Heard back from Stanton re: the Hiraga specs

Input sensitivity is .5v

30db of gain - not 26 as I had thought.

That would explain the volume increase!

The Cary SLP-30 I am driving it with has variable gain, so I gave some wiggle room to play w that adjustment.

That would explain the volume increase!

haha... when seemingly weird stuff happens there is ALWAYS an explanation, it is just that sometimes it takes us a while to figure it out!

Very much appreciate the input/information!

This surprise, sent me down a rabbit hole of “research”.

Now, I have more questions than I had prior to this observation :)

mwood:

I'm assuming your preamp has a resistive volume control. If that's the case. the "higher" the volume setting the less resistance. That's preferable for better sound. It's been the case for decades that many home audio preamps have much more gain than they need or is desirable. If your volume settings run only up to, say halfway before maxing out, your preamp has too much gain. Your tube preamp 3-5 db gain was actually better suited to your system than the 9db gain preamp. 

Excess gain preamps that result in volume settings between 1-5 have trained users to expect that. When a preamp with a resistive attenuator is used mostly between 5-9 (on a scale of 10) that's ideal, but seems wrong due to previous experience with excessive gain preamps. The output voltage of the preamp should drive the amplifier to maximum power output at just about the full volume setting. That's when the attenuator is resisting the least and converting as little as possible of the voltage gain to heat.

I’m assuming your preamp has a resistive volume control. If that’s the case. the "higher" the volume setting the less resistance.

"Less resistance" where?

You don’t know where the volume control (VC) is located. Is it the first device in the chain functionally a load for the source, or is there an input buffer then the VC, or is it on the output of the preamp which would be very unusual. In any of those scenarios, the total resistance seen by the previous stage will include whatever is loading the VC, which may be so high compared to the VC that the total resistance is effectively constant.

The output voltage of the preamp should drive the amplifier to maximum power output at just about the full volume setting. That’s when the attenuator is resisting the least and converting as little as possible of the voltage gain to heat.

This assumes the VC is at the output of the preamp. This is extremely unusual. It is also inconsequential if it is. The output impedance of the pre will be much lower than the input impedance of the amp so the load it presents will be effectively constant no matter the volume. The VC will dissipate the same amount of heat (extremely little) whatever the volume so it simply doesn’t matter.

The bottom line is without knowing  the topology of the preamp you simply have no idea how the VC is affecting anything. . In any case, it doesn’t work as you described.

I compared a 100w / Channel Shiit Vidar against a 50W / Crown amp. The Vidar had slightly more low-end punch, but the 45yr old 50W Crown amp left it behind when it came to loudness with no distortion. I am not sure why?  When I got a 30W tube amp running KT 77s it seems louder than both with greater dynamics.  I was amazed, but happy!  I think tubes have higher gain. I am sure some electrical engineer could explain.