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Old 28th January 2007, 09:41 AM   #1
ro9397 is offline ro9397  United States
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Default Is 60W enough?

This will eventually get around to being a Pass Labs class A amplifier question. I humbly request your patience.

First, my opinion is that no one can determine if amp "orange" has enough power or not for a given venue, except the listener at a given moment in time. Change any one parameter of literally dozens including the software & time of day, & I realize power requirements could easily double.

I intend to make sure of my requirements before I start an amp project, even if I must borrow a friend's power meter & hook it up to an amp rated well over the required number of watts. Before I get that far, curious of your opinions for the following theoretical system.

Bongiorno-designed Trinaural Processor-based analog 3-ch system (unique; the top-tier Meridian digital synthesized multi-channel is likely the closest in performance). Trinaural appears to benefit when the center speaker quality exceeds the L/R speaker quality.

Center speaker: large hybrid, cones below 270 Hz & a 92 dB planar array above 260 Hz

L/R speakers: largish standmounts, smaller cousins to the above center speaker, estimated 88 dB senstivity (output will be maximized, distortion & power requirements minimized by use of a high-pass 80 Hz XO in the Trinuarual Processor).

Consistent w/ the better center/lesser satellite rule mentioned above, am considering driving the L/R speakers w/ something good but more importantly an amp that wonít clip playing music.

The center speaker has two bass systems below 270 Hz, each system w/ its own 1000W amp/active xo/parametric eq. So that brings us to the center speaker planar mids & true ribbon tweeter (above 270 Hz). Which brings us to one of my two current favorite amps in the world, the absolutely stunning & wonderful Pass Labs "XA" series.

The room is about 3500 cu ft, will be professionally treated (translation, might have a fair amount of OC glass on-board).

1. So, would you predict a Pass Labs XA60 to be adequate driving the 8-Ohm 92 dB planar mid/ribbon tweeter array above 270 Hz? Midrange high-pass is dual-pole staggered first-order, low-pass first-order; treble high-pass is second-order circa 6 kHz.

2. Have members successfully built amps emulating the performance of the XA-series? If yes, can I have your picture to put in my wallet? What is parts cost for something like one A60? How many must I blow up before I build one that works properly?

Yes, I have built several tube & ss amps before. No, canít say Iím anxious to tackle another one...YET! But I am already considering it.

PS: I became smitten by the XA series after hearing them the past two years at the best CES venues. I just canít tell readers how impressed I am by those amps. Also, when you compare the MSRP to other boutique brands, they really start looking like the proverbial bargain.

Someone said an XA60ís heat output would be equal to three 100W lamps. Does that sound right? I would have guessed more.

Can someone Ďsplain for Lucy why their power is fixed regardless of load impedance differences? (Ignore that if it's in the White Paper, which I promise to memorize verbatim soon.)

Sorry to be so nosy on my first visit. I promise more boring posts later.




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Old 28th January 2007, 03:29 PM   #2
lineup is offline lineup  Sweden
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Quote:
First,
my opinion is
that no one can determine if amp "orange" has enough power or not
for a given venue,
except the listener at a given moment in time.

So, by your statement,
you wouldn't have to consider my opinion very much.
But I will try to answer anyway.

92dB SPL is higher than average
60 Watt is medium power - very high for Class A, but normal for AB

By my standards,
60 Watt is 'Too Much' for a 92 dB SPL element.
I would happily settle for some thing like 15-30 Watt.
Or 7-10 Watt True Class A.


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Old 28th January 2007, 07:33 PM   #3
ro9397 is offline ro9397  United States
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Thanks for chiming in.

It occurred to me this morning that it might be appropriate to view the two L/R 88 dB speakers as one 91 dB speaker. The two associated amplifer channels increase the output to at least equal the 92 dB center channel.

Which means the overall sensitivity of the Trinaural System could be viewed as equal to or slighlty greater than a 2-ch system w/ 92 dB speakers. In this analogy, the Trinaural's two L/R speakers are represented by one channel of the 2-ch system, the center speaker is represented by the other channel of the 2-ch system.

If this is correct, the sensitivity of the Trinaural System could be compared to a normal 2-ch system in the same room described above, w/ the following parameters: 92 dB speakers; one channel has limitless power (L/R), second channel (center) has limitless power below 270 Hz (bass through mid-bass), and a Pass XA60 powering above 270 Hz. Is it enough?

I'd guess yes. But because the center speaker contributes more to the overall presentation vs. the L/R, it is absolutely critical to confirm the fitness for use before committing $5k to $7k for an amp.

Hmmmm.....
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Old 30th January 2007, 02:21 PM   #4
lineup is offline lineup  Sweden
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what is the average SPL of speaker systems?

Most of us can agree, when it comes to HIFI drivers,
Scan-Speak is very much used and good.
This kinda sets a standard of the SPL of many speakers used.
At least for good quality audio speakers.

Amplifiers will have to live with what speakers is around at users homes.
So I would say, to sell many amplifiers you would make your amp
be able to drive the average speakers of customers, in a decent way.

This kinda makes most amplifiers have power output
good for driving Scan-Speaks speakers systems.

Looking at SPL of ScanSpeak, and other Audio HIFI, woofers,
we arrive at SPLs like:
87-90 dB sensitivity


Scan-Speak speakers/woofers/drivers info:
http://www.tymphany.com/products_ScanSpeak.html
http://www.audiocomponents.nl/index.html


Also remember, that CROSSOVER, especially higher order, 3rd 4th, 18dB/24dB
will 'steal dB SPL'.
Some filters, even, will lower SPL with 2-3 dB!!
... and as everybody knows
each -3dB
requires Twice, x 2, DOUBLE The POWER
to give same Sound Pressure Level


--------------------------------------------------------
For example:
Putting 50 Watt into a 87 dB speaker
gives same Sound Level as:
Putting 12.5 Watt into a 93 dB speaker
( -6dB is needs 4 times the power = double x double = 2x2 )
--------------------------------------------------------

It is not Too Uncommon, to see Real Hifi speakers
having only like: 86-87 dB SPL per watt into 8 Ohm



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Old 30th January 2007, 10:38 PM   #5
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Default Re: Is 60W enough?

Quote:
Originally posted by ro9397

1. So, would you predict a Pass Labs XA60 to be adequate driving the 8-Ohm 92 dB planar mid/ribbon tweeter array above 270 Hz? Midrange high-pass is dual-pole staggered first-order, low-pass first-order; treble high-pass is second-order circa 6 kHz.

2. Have members successfully built amps emulating the performance of the XA-series? If yes, can I have your picture to put in my wallet? What is parts cost for something like one A60? How many must I blow up before I build one that works properly?

Someone said an XA60ís heat output would be equal to three 100W lamps. Does that sound right? I would have guessed more.

Can someone Ďsplain for Lucy why their power is fixed regardless of load impedance differences?
1) You don't say whether the crossover is active or passive. Passive crossovers suffer from insertion loss, which translates as a loss of power. Active crossovers sidestep this problem and bring several dB more efficiency to the table.
That said, no one can tell you how much power you need just from a description of the speakers and amplifier. It depends on what your program material is. A steady diet of organ recordings and nuclear explosions will chew up 60W and beg for more. On the other hand, 60W will do just fine for chamber music and romantic comedies. It's up to you.

2) I don't know that you'd want my picture in your wallet, but I cobbled together a little circuit I called the Aleph-X. There's a thread or two around here about the circuit.
An A60 is an entirely different circuit. Shooting from the hip, I'd guess you could build one for a few hundred dollars, depending on how much stuff you already have on hand and how much you buy surplus vs. new.
How many you choose to blow up is up to you. I prefer to listen to amps rather than watch them go bang, but we all get our jollies in different ways.(Ahem...)

The heat dissipated by either an Aleph or an Aleph-X/XA type circuit is approximately three times the rated output power. 60W times three is 180W of heat per channel. Two channels would dissipate something on the order of 350W. Three light bulbs? Let's say three and a half.

The power into load thing is difficult to explain without getting technical. The short answer is that a given level of bias will only allow the amp to increase power down to a certain impedance level. In order to keep the heat dissipation reasonable--and class A amps are quite hot already--you face limits as to how much you want to increase the bias.

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