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Old 30th September 2008, 07:24 PM   #1
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Default Current from PassLabs amps

Last week a friend of mine bought a X1 pre- and X250.5 poweramp. At the same time another friend of mine bought a pair of Levinson ML-6b preamps to accompany his Levinson ML-2's.
I myself operate a pair of ML-2's and a ML-3 on Acoustat fullrange Electrostatics.
Of course we were interested in some comparison with the three amps.
First the 2 x 200 Watts ML-3. It sounded very powerfull effortless reaching high soundpressure levels with no sign of stress at all, not very delicate or having much inner detail a brute force solution nice to have around for feeling Le Sacre du Printemps from Igor Stravinsky. Next the monophonic ML-2's with only 25 Watts Class A. Much more refined very precise crystal clear performance with pinpoint imaging but not a lot of depth and sometimes maybe to clean.
Then what would be in potency in our minds the refinement of the ML'2s with the power of the ML-3: The Passlabs X250.5 2 x 250 Watts.
The sound was very good vocals moved to the front there was depth and musicality at last. But to our astonishment the meter rapidely moved to the right corner when power was asked to deliver especially when a female singer like Kate Bush or Tory Amos were stating to sing loudly. The maximum listening level was not much louder then the pair of ML-2's and a way down compared to the Levinson ML-3.
I noticed this behaviour wit earlier Nelson Pass designs like the Stasis 300 optical bias and the S/1000 series II monoblocks I had. I liked the sound very much but they always seem powershy compared with Krell and Levinson designs of that era.
Especially compared to the Levinson ML-3 amp the X250 doesn't seem to deliver much power (maybe in the lower impedence regions I reckon?). The Acoustat has a lousy 82 dB/W 1 meter response with in the higher frequency region a impedence that is sloping downwards to maybe 1 Ohm. So I now the speaker can be critizised but it's there lik a lot of aothe old planars like the Apogees that are all treasured by there owners.
For the sound only I was considering to sell my ML-2's and ML-3 to buy a X350.5 but after the experiment I got reluctant because I do not think a couple of amps on paper (max 28 instead of the 20 of the X250) will not help a lot.
Can anybody tell my why this behaviour is typacal for Pass products or am I in error?
Thanks for the reactions.

ps Why are the X250 cooling fins designed as dustcollectors?
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Old 1st October 2008, 09:38 PM   #2
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Perhaps you should keep your ML-3's and be happy.

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Old 2nd October 2008, 12:43 AM   #3
KBK is offline KBK  Canada
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Old 2nd October 2008, 12:44 AM   #4
KBK is offline KBK  Canada
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Old 2nd October 2008, 12:56 PM   #5
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Quote:
Perhaps you should keep your ML-3's and be happy.
Don't worry be happy

Just read a Pass X350.5 review from a German Audio publication 'Stereoplay', 3/2005, http://www.stereoplay.de/suche/ergeb...?term=PassLabs) where its Labreport clearifies the matter.
The X350.5 and probably all current designs from PassLabs have a optimized powerstructure for higer impedences. They were not designed to behave like a almost perfect Voltage Source because the measured rating at 2 Ohms was even lower then the 4 Ohm rating where according to Ohm's law a double figure should be expected. (4 Ohm 612 Watts, 2 Ohm 604 Watts).
Another somewhat puzzling figure was the dampingfactor that was at lowfreqs 345 but at highfreqs it sank down to 129. I mention this because in different Pass/Threshold publications a point was made that a good damping behaviour was not a extreme high figure but one that was independent of the frequency and did not slope downwards when the frequency rises.
Maybe there is an explanation/designer choice for the above and is a 1.5 kVA Toroid (as stated by the magazine) for a 2 X 350 Watts @ 8 Ohm's sufficient. A 4 or a 5 kVa toroid as in Krell designs with the same specs at 8 Ohms make those amps a spinetwisting riskfactor when haulong them around of course.
The punchline was they found the reviewed X350.5 the best Stereo amp they ever listened to and that's that.

When no other amps were developed after the ML-3/ML-2's I would be very happy camper not having the knowledge and experience, after listening to the X250.5, that there's something better around. So all you folks be happy with what you have and never look, listen or long for something better, that's the advice here.

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Old 2nd October 2008, 01:02 PM   #6
Zen Mod is offline Zen Mod  Serbia
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well - I'm cleverly proposing that all these gadgets may be shipped to my place, for proper disposal ;

as fee for my troubles , I'll pull few parts (here and there ) out , but nothing more ...

("ooops - ya see - I'm going to pull that fugly xformer from this lousy Papamp , but seems that rest of amp is simply glued to him ....... ! " )


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Old 2nd October 2008, 01:28 PM   #7
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@BrianEno,

whatever the reasons for your dismay of the Pass-amp are, the power capability for sure isn't.

Even in large rooms you will never drive the full 350W into 8R speakers, your neighbours would get deaf instantly.

You would wonder how little power you really demand - by the way you could find out yourself: get a multimeter and measure the voltage at the terminals as an crude estimate (during play). Take care!

Have fun, Hannes

PS: by the way a solid 300W amp is already usable for PA (small concert up to 30 poeple).
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Old 2nd October 2008, 01:42 PM   #8
EUVL is offline EUVL  Europe
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IMHO, the point of having lots of power in the amplifier has little to do with what level of power you actually need to play music, but rather the level of distortion at a certain output level, plus the capability to cope with reactive low and transients.

I, for example, am not ready to give up my 100W monoblocks for its 25W equivalents, although 25W is already plenty.


Patrick
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Old 2nd October 2008, 02:12 PM   #9
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Me neither - I'm myself currently finishing the pcb-artwork of a 100W amp

Why ever not? It's a hobby so I build what pleases me.

My previous post was just to give an hint to the original poster to look somewhereelse for the fault.

That guy throws around fearlessly numbers like 28A output current as if it was peanuts

Have fun, Hannes
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Old 2nd October 2008, 03:13 PM   #10
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Default Re: Current from PassLabs amps

Quote:
ps Why are the X250 cooling fins designed as dustcollectors?

I was just wondering why the top plate of the ML3 was designed as a dustcollector! Imagine that?
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