Volume and Scale: Educate Me...

[MadFloyd]

I think this holds true regardless of the genre. I have always felt that way. I hope most of us can agree on that. However, the essence of what Mad Floyd is saying is that to achieve the correct scale, he has to turn up SS gear louder than tube gear. I think before this discussion goes to much further, we need to know the gain of the preamps he is using and what the input sensitivities are for the amplifiers he is using because those differences could account for the differences in scale he is talking about.

Input sensitivity for the Doshi JHor tube amp is .775v rms. The Pass XA160.5 is not known (not in manual or on their website).

As far as preamp gain, doesn't the preamp just attenuate volume and not add gain unless you really turn it up? (I am guessing I am wrong )

 

[mep]

Input sensitivity for the Doshi JHor tube amp is .775v rms. The Pass XA160.5 is not known (not in manual or on their website).

As far as preamp gain, doesn't the preamp just attenuate volume and not add gain unless you really turn it up? (I am guessing I am wrong )

I think you just showed us why you are noticing the differences you are. With an input sensitivity of .775v for your Doshi amp, it's not going to take much gain from your preamp to bring your amps to full output power. .775v is very low and I doubt the Pass Labs amps are close to that in terms of their input sensitivity. I found one article that listed the input sensitivity for your Pass Labs amp as 1.79v. That's a HUGE difference between your Doshi and the Pass Labs amps. You will have to crank the crap out of your preamp volume control when using your Pass Labs amps to get the same level of sound when using your Doshi amp.

As for preamps, they do provide gain unless they are passive devices which means they really aren't preamps in the technical sense. Preamps commonly provide between 6dB-12dB of gain. I think you are confusing that the volume control only throttles that gain back when you say that the volume control doesn't add gain.

 

[microstrip]

I think this holds true regardless of the genre. I have always felt that way. I hope most of us can agree on that. However, the essence of what Mad Floyd is saying is that to achieve the correct scale, he has to turn up SS gear louder than tube gear. I think before this discussion goes too much further, we need to know the gain of the preamps he is using and what the input sensitivities are for the amplifiers he is using because those differences could account for the differences in scale he is talking about.

I think that MadFloyd is addressing perceived loudness levels and not electrical levels.

 

[microstrip]

Input sensitivity for the Doshi JHor tube amp is .775v rms. The Pass XA160.5 is not known (not in manual or on their website).

As far as preamp gain, doesn't the preamp just attenuate volume and not add gain unless you really turn it up? (I am guessing I am wrong )

Input sensitivities are specified for maximum power of the amplifier and unless you want to do the maths are not relevant. What would matter is voltage gain (usually specified in dB or just X ...)

And yes, you are correct, most of the time the preamplifier will attenuate - usually the output of the source is even higher level than the sensitivity of the amplifier. Do not connect them directly, your Alexia's tweeters would not like the clipped distortion! And probably your neighbors would also complain...

 

[mep]

I think that MadFloyd is addressing perceived loudness levels and not electrical levels.

I agree, but that's only because I don't think he understands how the input sensitivities of a power amp can affect the volume level you are used to hearing at a given point on your preamp's volume knob. Mad Floyd was trying to figure out why he had to turn his system up so much louder in order to achieve the same volume of sound when using SS amps. I think I found his answer.

 

[Phelonious Ponk]

I agree, but that's only because I don't think he understands how the input sensitivities of a power amp can affect the volume level you are used to hearing at a given point on your preamp's volume knob. Mad Floyd was trying to figure out why he had to turn his system up so much louder in order to achieve the same volume of sound when using SS amps. I think I found his answer.

I think you found his scale answer as well. Very often, volume = perceived scale. There can be other perceptual drivers, but this is the biggie. Unless Madfloyd was measuring and carefully matching the volumes of his SS and tube listening experiences and, really, unless he was doing that with the ability to switch immediately back and forth between them, he doesn't really know what he may have heard. Any number of things besides tubes vs. SS could be causeing a perceived difference in scale; higher volume is the most likely cause, and you've found a good reason why his tube system would be running hotter than his SS. What's that about the simplest, most obvious answer being the most likely one...?

Tim

 

[MadFloyd]

I am measuring. I always use a sound pressure meter when I listen to police myself. I typically listen around 80-90 db.

At 85 db, the Doshi provides a life size image whereas the Pass does not. I need to go louder with the Pass.

 

[hvbias]

A classical example of scale is the difference between an old Krell pure class A system playing cold and after a few hours warmup. If Mep is reading he will surely enlighten us on this subject. Some people will not agree, but power cables can have also have a significant effect in scale.

My test for scale is usually the finale of Shostakovitch 5th symphony or the 3rd movement of the 8th - the orchestra must fill the whole hall!

This is my experience with all the Pass amps I have owned as well as my Atma-sphere I've got now. I also found that with my last Pass monos (Aleph 2) at the same measured SPL I was getting a wider and deeper soundstage with my M60, that certainly translates to a sense of scale in listening.

 

[Phelonious Ponk]

I am measuring. I always use a sound pressure meter when I listen to police myself. I typically listen around 80-90 db.

At 85 db, the Doshi provides a life size image whereas the Pass does not. I need to go louder with the Pass.

Interesting. Added harmonic content, then?

Tim

 

[mep]

Mark - what is the idle power of the Krell KSA-250?

From the original SP review:

"The Krell's rated output of 250W per channel into 8 ohms implies a standing bias current of 3.95A per channel—square root of 250W/(2 x 8 ohms)—if all this power is to be delivered with the output stage running in class-A. Assessing an amplifier's bias current is not straightforward, however, particularly when, like the Krell, it doesn't have a fuse in series with the rail voltages."

 

[microstrip]

From the original SP review:

"The Krell's rated output of 250W per channel into 8 ohms implies a standing bias current of 3.95A per channel—square root of 250W/(2 x 8 ohms)—if all this power is to be delivered with the output stage running in class-A. Assessing an amplifier's bias current is not straightforward, however, particularly when, like the Krell, it doesn't have a fuse in series with the rail voltages."

I have read it. But I am looking for the specified idle power consumption of the amplifier - but it seems no one has it.