Visit to Henk van der Hoeven -- Apogee Acoustics Re-builder/Restorer

[Ron Resnick]

Hi Ron, I checked second time. Sitting down or standing up should not affect treble. You heard what you heard. I did not find it dark. . . .

Please recall I got the whole "little to no treble due to sitting too low" thing from you. You told me about the better treble response you experienced originally (during your first visit to Henk) standing up rather than sitting in Henk's big chair, so I immediately assumed that the listening height was the source of my treble anomaly.

 

[bonzo75]

Please recall I got the whole "little to no treble due to sitting too low" thing from you. You told me about the better treble response you experienced originally (during your first visit to Henk) standing up rather than sitting in Henk's big chair, so I immediately assumed that the listening height was the source of my treble anomaly.

Yes that was my guess, since I did my listening standing up, but it was a wrong guess.

 

[Ron Resnick]

Fair enough!

That being the case, then, I heard what I heard and -- even though I like a rolled off treble response -- I did feel that the high frequencies were a little more shaved off than even I like. (But Henk has the tweeters on potentiometers and he easily could have boosted the tweeter level if I had asked him to do so.)

 

[spiritofmusic]

I used to run ProAc Futures loudspeakers back in the early 00's
These had ribbon tweeters at 4' high, beaming upwards over ear level due to the tilt backwards of the speaker front baffle
Thus meant that treble was reticent in sitting position leading to veiling, but fully energetic when standing
God, was this frustrating, and despite the overall excellence of the sound, for this reason alone I ended up selling them
From what I can see, the Grands baffle is tilted somewhat backwards (unlike FRs, Divas etc)
If a lot of treble information is being beamed above ear level by this arrangement, maybe this is what lead to Ron's experience?

 

[Ron Resnick]

It is a mystery to me, Marc. With the Grand tweeter ribbon being a tall line source I have no idea why I felt the treble was somewhat Missing In Action.

 

[spiritofmusic]

That ribbon starts, what, 18" off the ground, and then tilts upwards for its whole extent to, what, 90" high?
It's quite natural to assume you were getting only 20" of it's output, not all 80" (with ears 36" off the floor in sitting position)
Just why does Henk stand to listen to music, and why did Ked also?
Maybe the treble truly missed out sitting down
Sounds just a LITTLE crazy to me

 

[bonzo75]

That ribbon starts, what, 12"-18" off the ground, and then tilts upwards for its while extent to, what, 90" high?
It's quite natural to assume you were getting only 20" of it's output, not all 70"
Just why does Henk stand to listen to music, and why did Ked also?
Maybe the treble truly missed out sitting down
Sounds just a LITTLE crazy to me

Henk doesn't, I did. Instead of his chair I walked back - I have done this often, relocated myself. I just felt the soundstage more locked in that way. Plus, it was easier to air conduct while standing.

 

[bonzo75]

Anyone has experience on amps which provide partial class A output, and at some level switch to AB? How does this sound on Apogees, or other speakers, while listening to orchestral, where I assume some passages would play in AB mode?

 

[microstrip]

Anyone has experience on amps which provide partial class A output, and at some level switch to AB? How does this sound on Apogees, or other speakers, while listening to orchestral, where I assume some passages would play in AB mode?

All push-pull AB amplifiers behave this way. Otherwise they are class A or class B! And most class A amplifiers are only class A at 8 ohm loads.

 

[Zero000]

Anyone has experience on amps which provide partial class A output, and at some level switch to AB? How does this sound on Apogees, or other speakers, while listening to orchestral, where I assume some passages would play in AB mode?

From the A21 manual. I keep telling you - it is a very good Apogee driver, given a tube front end.

"The A 21 input and driver stages employ pure Class A while its output stage operates with higher pure Class A power than many amplifiers selling for twice or three
times its price. The result is less fatiguing, more natural sound."

 

[bonzo75]

All AB amplifiers behave this way. Otherwise they are class A or class B! And most class A amplifiers are only class A at 8 ohm loads.

Really? So all these pure Class A amps would drop to B at the 4 ohm load of the apogees, making it moot if it was class A or B?

 

[spiritofmusic]

According to reports, my NAT SE2SEs which are specced to 60W in pure Class A, but then go to another 40W in Class AB, before distorting/clipping. Amazing
Lord only knows how powerful the Transmitters are? Class A to 120W. AB to 150?
Magmas NEW 170W Class A. 200+ AB?

 

[bonzo75]

According to reports, my NAT SE2SEs which are specced to 60W in pure Class A, but then go to another 40W in Class AB, before distorting/clipping. Amazing
Lord only knows how powerful the Transmitters are? Class A to 120W. AB to 150?
Magmas NEW 170W Class A. 200+ AB?

I thought 120 and 170 was max, including the B.

Also on amps which get bridges and the total wattage increases, will the class A percentage remain constant?

 

[microstrip]

Really? So all these pure Class A amps would drop to B at the 4 ohm load of the apogees, making it moot if it was class A or B?

Yes, these push-pul amplifiers will drop to class B much earlier. We had a thread on this subject in WBF http://www.whatsbestforum.com/showthread.php?13781-What-are-the-most-powerful-Pure-Class-A-Amplifiers-ever-made/page3.

As power = resistance x current x current , and maximum class A current is determined by the bias current, the class A power is proportional to the resistance. To make it clear a 100W class A amplifier has 50W class A at 4 ohm and 25W class A at 2ohm.

This happens for true class A. Some designers have sliding bias schemes to increase bias depending on signal prediction, but IMHO they are creating new problems and can not be considered class A anymore.

 

[bonzo75]

Yes, they will drop to class B much earlier. We had a thread on this subject in WBF http://www.whatsbestforum.com/showthread.php?13781-What-are-the-most-powerful-Pure-Class-A-Amplifiers-ever-made/page3.

As power = resistance x current x current , and maximum class A current is determined by the bias current, the class A power is proportional to the resistance. To make it clear a 100W class A amplifier has 50W class A at 4 ohm and 25W class A at 2ohm.

This happens for true class A. Some designers have sliding bias schemes to increase bias depending on signal prediction, but IMHO they are creating new problems and can not be considered class A anymore.

So Bridged Luxman M800 is 240*8 class A. At 4ohms will be 120 class A, even though total power is going to 480

Symphonic Line Kraft is 300 ohm class A. That's 150 at 4ohms, though total power is 600w.

Of course there are other things.

 

[microstrip]

According to reports, my NAT SE2SEs which are specced to 60W in pure Class A, but then go to another 40W in Class AB, before distorting/clipping. Amazing. (...)

Amazing? Why? Please see http://www.whatsbestforum.com/showthread.php?16397-Class-A-power-vs-Class-A-B-power&p=299492&viewfull=1#post299492

 

[bonzo75]

So Bridged Luxman M800 is 240*8 class A. At 4ohms will be 120 class A, even though total power is going to 480

Symphonic Line Kraft is 300 ohm class A. That's 150 at 4ohms, though total power is 600w.

Of course there are other things.

Or is the 4 ohm Class A for bridged Luxman half of 480, instead of half of 120?

 

[microstrip]

So Bridged Luxman M800 is 240*8 class A. At 4ohms will be 120 class A, even though total power is going to 480

Symphonic Line Kraft is 300 ohm class A. That's 150 at 4ohms, though total power is 600w.

Of course there are other things.

Bridged amplifiers increase voltage swing capability, but not bias current. Class A power is the same as that of a single unit!
However you get a better power supply capability to delivered power ratio, and the physical separation of them.

 

[morricab]

Yes, they will drop to class B much earlier. We had a thread on this subject in WBF http://www.whatsbestforum.com/showthread.php?13781-What-are-the-most-powerful-Pure-Class-A-Amplifiers-ever-made/page3.

As power = resistance x current x current , and maximum class A current is determined by the bias current, the class A power is proportional to the resistance. To make it clear a 100W class A amplifier has 50W class A at 4 ohm and 25W class A at 2ohm.

This happens for true class A. Some designers have sliding bias schemes to increase bias depending on signal prediction, but IMHO they are creating new problems and can not be considered class A anymore.

A single ended amplifier will not drop into Class B at all. It cannot as it must trace the whole waveform, unlike a push/pull amp where one tube turns off in Class B. The NAT SE2SE seems to be go into Class A2, where the grid is driven positive (normally not an option for most SETs). When this is done much more power can be generated but with a significant increase in disotortion (but it is not clipping).

Whether or not the Transmitter or Magma can do more depends on the design and whether it leaves Class A1 and go into Class A2 or not.

I seem to remember that the SE 1 MKI never left A1 and made 15 watts...pretty normal for a 211 SET. Also, the bigger SE3 made far less power than the SE2SE was able to do.

 

[Diapason]

From the A21 manual. I keep telling you - it is a very good Apogee driver, given a tube front end.

"The A 21 input and driver stages employ pure Class A while its output stage operates with higher pure Class A power than many amplifiers selling for twice or three
times its price. The result is less fatiguing, more natural sound."

It just so happens there's one going for a very keen price on audio-markt (well, keen by European standards). I've been quite tempted myself.