Did I buy a broken amp?

I purchased a used amp to mate with a dac / preamp in the same line which I own. The new amp is suppose to be 150 watts into 8ohm.  When I play the amp at 35/100 volume, I barely hear any sound.  I need to get volume  to at least 75/100 or 80/100 to provide adequate listening sound. 75/100 sounds how 50/100 should sound. (And so on)   It does not seem to clip or distort.   Could the amp be broken or does it just not provide enough juice for my speakers? 
Preamplifier / Dac Wadia 321
amplifier:wadia 315 
Apple TV source 
speakers: Kef 201/2
Disconnect the preamp. Connect the TV audio left & right outputs to the amp inputs. Use the remote to control the sound volume. If this results in adequate volume then your amp is ok. The preamp is now suspect! 
What amp were you using with the Kef's before the Wadia?
Does the Wadia amp have input level controls? If so, these may be set too low!

It’s all good the input sens is on the amp 2.4V Balanced 1.2V Unbalanced, and what you’ll find is the volume on the dac will be logarithmic, and after 80 it will go up twice as fast as it did before 80.
All this is good that your up so high on the digital domain volume control, as you run far less risk of "bit strtipping" (detail loss) if your up high rather down low in the count for the same volume.

Cheers George
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Just an unfortunate not enough gain situation.
It’s not unfortunate, if there's enough volume at 80 it’s all fine, having the same volume at 50 is not going to sound one iota better.
Take heed of the last sentence.

Quote from Nelson Pass

Nelson Pass,

"We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.

Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.

Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.

What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.

And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."

  It does not seem to clip or distort.   Could the amp be broken or does it just not provide enough juice for my speakers?
What happens when you turn it up all the way? Can you overload it- does it get loud enough? If yes to both, its fine- that's just how it was designed. You could contact Wadia- there's a good chance they know the answer :)
At 100/100 it is pretty loud for book shelf speakers but usually I expect that kind of loudness at 70/100 with unknown headroom beyond that. Perhaps it was the way it was designed.  I’m just surprised that it seems barely audible at 40/100 volume level.  I can try the speakers with another 150 watt amp later this week to see if there is much of a difference but I guess that probably won’t matter much as it may go to the Wadia design. 
Don't know if you have access to Ground and In tap hole on volume pot to run in series 2 resistors. My  Preamp with goldpoint stepped pots 9:00 was my preferred loud listening level now am at 3:00 to be at preferred listening level by adding 2 resistors. I may tweek resistor value a little. I'm now where you are on volume position level and like it. It's strange to be at 3:00, I'm use to being between 11:00 and 1:00 but as long as I have headroom before distortion I'm okay. My problem was there was to much gain between each step and could not get sweet spot on volume level, now I can. I used the Takman carbon resistors I was told they were warmer than the metal, I also thought they made the amp sound a little better, maybe who knows. 
The following statement appears in the manual for the Wadia 321:

A Volume Setting of 88% on the Wadia 321 will provide optimum performance when it is connected to a Preamplifier (Integrated Amplifier or Receiver).

Also, Stereophile measured the sensitivity of your speakers as being a rather low 85.5 db/2.83 volts/1 meter.

Both of those facts seem consistent with the need to utilize the Wadia's volume control at relatively high settings.

-- Al
YouTube has an in-depth documentary on the importance of the volume control. Its only a few minutes and well worth the time. Search for Spinal Tap ours goes to eleven.
Thanks guys.  I think you are all right in the money. The speakers are very inefficient at 85/86 and it sounds like Wadia did not want to offer much headroom through their design for whatever reason.  At 88 the unit is satisfying enough I suppose.  I think the speakers still need to broken in some as I bought them new old stock recently.  That’s probably another discussion though.