Current vs Watt

[wettou]

I know that we have electrical engineers on this forum and was wondering if you could explain the difference between Current vs Watt

Also how does one find out how much current an amp has?

[theblue]

I = V/r

read this:

http://www.howstuffworks.com/question501.htm

[Srrndhound]

Also how does one find out how much current an amp has?

You want to know how much current a power amplifier can output at its maximum? a) It's very hard to find out, and b) it's not useful information in determining sound quality.

[wettou]

You want to know how much current a power amplifier can output at its maximum? a) It's very hard to find out, and b) it's not useful information in determining sound quality.

So why is it that B&W 800D needs so much current?

[Srrndhound]

So why is it that B&W 800D needs so much current?

How much does it need? Being a loudspeaker--of course it needs current. Are you saying it is unusually tough to drive?

[Alaric]

You want to know how much current a power amplifier can output at its maximum? a) It's very hard to find out, and b) it's not useful information in determining sound quality.

It was my understanding that current is more useful than watts. That's why a 15 watt tube amp can drive speakers to decent SPLs. Current (amperes) is the measurement of how "much " electricity is being used. Watts can be measured as voltage. 100 volts at .5 amperes will give you a nip. 12 volts at 150 amps will light you up like a Christmas tree. How is current not relative to driver control? Just askin'.
Ohm's law and Watt's law will tell you what to measure to figure out the other legs of the equation. An inductive ammeter will give you a fair idea of the current flowing through your speaker cable and can be had pretty cheap at a hardware store.

[wettou]

How much does it need? Being a loudspeaker--of course it needs current. Are you saying it is unusually tough to drive?

Yes B&W says that their speaker are current hungry!!

[wettou]

It was my understanding that current is more useful than watts.

Yes that is what I heard

That's why a 15 watt tube amp can drive speakers to decent SPLs. Current (amperes) is the measurement of how "much " electricity is being used. Watts can be measured as voltage. 100 volts at .5 amperes will give you a nip. 12 volts at 150 amps will light you up like a Christmas tree. How is current not relative to driver control? Just askin'.
Ohm's law and Watt's law will tell you what to measure to figure out the other legs of the equation.

What is the equation

An inductive ammeter will give you a fair idea of the current flowing through your speaker cable and can be had pretty cheap at a hardware store.

What is that

[Srrndhound]

It was my understanding that current is more useful than watts.

It's not.

That's why a 15 watt tube amp can drive speakers to decent SPLs.

You mean louder than a 15W solid state amp? It can't.

How is current not relative to driver control? Just askin'.

Currect is very important to driver control. The discussion was about measuring how much current an amplifier can produce. As long as the output voltage of the amp remains undistorted under all signal conditions, it doesn't matter how much more current the amp can produce beyond that point.

[Srrndhound]

Yes B&W says that their speaker are current hungry!!

Where do they say that, and what do they mean by it?

The 800D specs say sensitivity is 90 dB, and the impedance is 8 ohm nominal, minimum 3.1 ohm. Not all that unusual. Any decent amp will handle it. Yes, it can be driven with a 1000W amp if you like--which is more than many speakers can handle, but that's unnecessary. It will play fine with a 50W amp, too.

[Alaric]

You mean louder than a 15W solid state amp? It can't.

We'll probably have to disagree on that. McIntosh also disagrees. Watts , like voltage , is "pressure". Current (amperes) is quantity. One big guy can put a lot of pressure on a closed door. 20 medium sized guys coming through the doorway will accomplish more.
Yeah , that's WAY over-simplified , but it's a (marginally) useful analogy. I've done some A/B between tube and SS amps , and the higher current tube output stages flat stomp the SS amps in SPL , wpc and quality construction being roughly equal. You should hear what a quad of MFA 250 watt tube monoblocks does to a pair of B & W Matrix 801 speakers. I've also noticed a parallel between current and headroom to a much greater extent than the relationship between just watts and headroom. Seems to be why 150 wpc BPC from the 80s can't touch a 75 watt Mac tube amp. In my experience. I haven't seen/heard it all yet.

[mjb]

We'll probably have to disagree on that.

No need, its a fact. Defined by ohms law, which has been around for a couple of hundred years and not disproved. A volt, an amp, an ohm and a watt are all related by a very simple formula.

A 15 watt amplifier will have the same warming effect irrespective of how those watts are generated - solid state, or tube. 15 watts are 15 watts. If the load resistance is the same, the current will be the same. Its a rule of nature - no discussion.

If a 15 watt amplifier sounds louder on one speaker or the other, its down to the speakers sensitivity, not power, or current, or voltage.

If you've heard anything else, its nothing more than a sales pitch from people who don't understand that mother nature has laid down a few rules.

Disclaimer before the smart guys disagree: we can assume DC; audio is almost DC. I realize that speakers do not have a resistance, they have an impedance, which is resistance at a specific frequency, and with audio, the frequency changes, so the impedance changes. BUT, for all intents and purposes, amplifier power is measured statically into a carbon load resistance at one frequency.

[Srrndhound]

I've done some A/B between tube and SS amps , and the higher current tube output stages flat stomp the SS amps in SPL , wpc and quality construction being roughly equal. You should hear what a quad of MFA 250 watt tube monoblocks does to a pair of B & W Matrix 801 speakers. I've also noticed a parallel between current and headroom to a much greater extent than the relationship between just watts and headroom. Seems to be why 150 wpc BPC from the 80s can't touch a 75 watt Mac tube amp. In my experience. I haven't seen/heard it all yet.

You're confusing your subjective experiences, which are rightly influenced by myriad real-world factors, with a theoretical wattage rating discussion. Tube amps indeed sound different than solid state amps. They interact with speakers differently. They clip differently--so it's a debatable topic how to even decide what the maximum power output of an amplifier is. X dB below clip? 1% distortion? 10% distortion? Other criteria? Resistive or reactive load? Wideband or 1 kHz? All channels driven--or one alone?

I agree it's a much more useful and fun to chat about how different amp technologies sound than max current and superficial wattage ratings. But that was not where this thread seemed to start--although it was rather ambiguous to me, I must admit.

[wildtangent]

It was my understanding that current is more useful than watts. That's why a 15 watt tube amp can drive speakers to decent SPLs. Current (amperes) is the measurement of how "much " electricity is being used. Watts can be measured as voltage. 100 volts at .5 amperes will give you a nip. 12 volts at 150 amps will light you up like a Christmas tree.

You’re missing a key component here, the load impedance or resistance. To use your examples a load that has 100V across it and .5A flowing into it is consuming 100x.5 or 50W. While the other load has 12V across it and 150A flowing into it will be consuming 12 x 150 or 1800W. Big difference, but apples with oranges! Now with 100V and .5A flowing …. 100/.5 = 200 ohms. That same 200 ohm load on the 12V supply will draw 12/200 = .06A. 12Vx.06A = .72w. The 12V 150A battery will not light you up because you have a constant resistance depending on temperature and humidity so very little current can flow. But that same constant resistance with a higher voltage available will cause a larger current to flow and that might very well light you up.



Back to the original question, if B&W says its speakers are current hungry, this is just marketing speak for low impedance. You also have to consider the speakers efficiency or the way it uses that power. There are losses in the translation of the electrical energy to sound energy. One way to gauge this is sensitivity. If one 8 ohm speaker requires 10W to deliver an SPL of 85db, while another 8 ohm speaker requires 15W to deliver the same SPL under the same conditions one is clearly more efficient and doing the work. By the way Watts is a unit of power or work, and not just in the electrical sense.

[Alaric]

Then again , I could be full of $hit...

[wettou]

Where do they say that, and what do they mean by it?

The 800D specs say sensitivity is 90 dB, and the impedance is 8 ohm nominal, minimum 3.1 ohm. Not all that unusual. Any decent amp will handle it. Yes, it can be driven with a 1000W amp if you like--which is more than many speakers can handle, but that's unnecessary. It will play fine with a 50W amp, too.

They say that in order to be their best they need a lot of current again I am not sure what that means!! Will a 200W amp not be as good as a 400W amp?

[wettou]

Back to the original question, if B&W says its speakers are current hungry, this is just marketing speak for low impedance. You also have to consider the speakers efficiency or the way it uses that power. There are losses in the translation of the electrical energy to sound energy. One way to gauge this is sensitivity. If one 8 ohm speaker requires 10W to deliver an SPL of 85db, while another 8 ohm speaker requires 15W to deliver the same SPL under the same conditions one is clearly more efficient and doing the work. By the way Watts is a unit of power or work, and not just in the electrical sense.

So with a sensitivity of 90db a 200W should be sufficient what if I get a 600W will the sound be better?

[Srrndhound]

They say that in order to be their best they need a lot of current again I am not sure what that means!!

Could you cite were they state this? A manual, a web page?

So with a sensitivity of 90db a 200W should be sufficient what if I get a 600W will the sound be better?

Depends on your definition of "better."

[wettou]

Could you cite were they state this? A manual, a web page? Depends on your definition of "better."

When you speak with B&W directly they recommend at least 200W for the 802D but suggest 400W if you want to unleash the beast

Better in audio for me: Well being able to be more transparent hearing all the details and play louder with out fatigue

[Srrndhound]

When you speak with B&W directly they recommend at least 200W for the 802D but suggest 400W if you want to unleash the beast

Better in audio for me: Well being able to be more transparent hearing all the details and play louder with out fatigue

Seems like you ended the conversation with B&W a little too soon.

[wettou]

Seems like you ended the conversation with B&W a little too soon.

Meaning?

[Srrndhound]

Meaning?

Meaning simply that since you were already talking to them, you should have asked B&W directly about:

So why is it that B&W 800D needs so much current?

They say that in order to be their best they need a lot of current again I am not sure what that means!! Will a 200W amp not be as good as a 400W amp?

So with a sensitivity of 90db a 200W should be sufficient what if I get a 600W will the sound be better?

[speakerman19422]

Which is better a Krell Amp and Bose 201 or Sony 100 watt per channel stereo receiver and Wilson Watt puppies It still comes down to the speakers. Watts = amperage x voltage.

[wettou]

Meaning simply that since you were already talking to them, you should have asked B&W directly about:

They say more is better they are promoting Classé since they are both owned by Equity:B

I was trying to get an informed opinion not Marketing

[theblue]

this thread reads like you are refusing to understand the theory and just want a marketing number to compare against a spec sheet somewhere.

[wettou]

this thread reads like you are refusing to understand the theory and just want a marketing number to compare against a spec sheet somewhere.

I am not I just want to know if I should get larger amps and if I will have better sound that is all.

I would rather save my money if the improvement is not there:T

[mb225]

This is a great topic. I’m not sure if any conclusions were made here and I have a similar question. My dealer uses this line all the time, he says "it’s current, not wattage, that drives speakers". So is this just a marketing line or is there something to this?

Sorry to use this example in "Club Classe" but I think it’s relevant. Last year my dealer let me try out a Mcintosh 6300 (Integrated stereo amp at 100 w/c). In my room with my speakers (B&W 803s) the meters on the MC where using about 1 watt! Every once in a while they would jump to about 3 watts at very loud volumes.

I talked to B&W support and asked about driving my 803s with a McIntosh tube amp and he said B&W does not recommend using tube amps with B&W since tubes do not control the speakers as well as solid state and that bass will suffer. He then said if you are going to go the McIntosh route, he would recommend using an MC402 (400 w/c) to drive 803s.

My question is, if I was only using 3 watts on the 6300… Would I hear a difference with a bigger amp? Isn’t 3 watts of McIntosh power going to sound the same if the amp maxes out at 100 watts or 400 watts?

[wettou]

Still no response

I guess experiment is the only way to tell :B

[stuofsci02]

This is a great topic indeed.. Old, but good..

I think it is very confusing that some dealers will state that current is more or less important.

Current is a function of voltage and impedance. That means that at a particular amp output voltage and speaker resistance the current is fixed. One amp cannot supply more current to a speaker then the another (assuming neither amp distorts).

For example if an amp is outputing 40V to the speaker with a 2khz tone, and the speaker impedance is 8 ohms at 2khz then the amp must put out V/R amps. That is 40V/8 ohms = 5 amps. Now if the speaker is 3.1 ohms at 2khz, then the amps must deliver 40V/3.1 ohms = 12.9 amps..

So when someone says that a speaker is current hungry it really can only mean that the impedance is low at some or all of the operational frequency.

In the real world some amps cannot supply high current at high voltage. That does not mean they cannot output the specified watts. They just can't do it into a low impedance speaker. That is why one amp might be rated 100 wpc into 8 ohms and 150 wpc into 4 ohms, while another amp is rated 100 wpc into 8 ohms and 200 wpc into 4 ohms. At 8 ohms both are able to output 100 wpc. But if the speaker dips down into the 4 ohm range, the second amp will be more powerful.

Therefor to combat the problem people recommend bigger more powerful amps, not because they need 400 wpc, but rather they want the amp to be stable at low impedance.

Lastly if your McIntosh is only using 6 watts, that does not mean a 6 watt amplifier will sound just as good. In a class A/B amp the amplifier works in class A on a sliding bias, such that for the first "x" number of watts it runs in class A. The bigger the amp, usually the higher this value "x" is. Since people like the sound of class A more then class A/B this could mean that a bigger Class A/B amp may sound better then a smaller one even at low volumes.

Additionally an amp is usually rated at its power based on when it hits a certain amount of distortion (say 0.1% for and example). If you look at a power curve for an amp, the level of distortion will rise as the power usage goes up and will rise very quickly as it approaches its max output. Therefore a bigger amp may have lower distortion at lower volumes then a smaller amp.

[wettou]

This is a great topic indeed.. Old, but good..I think it is very confusing that some dealers will state that current is more or less important. Current is a function of voltage and impedance. That means that at a particular amp output voltage and speaker resistance the current is fixed. One amp cannot supply more current to a speaker then the another (assuming neither amp distorts).

For example if an amp is outputing 40V to the speaker with a 2khz tone, and the speaker impedance is 8 ohms at 2khz then the amp must put out V/R amps. That is 40V/8 ohms = 5 amps. Now if the speaker is 3.1 ohms at 2khz, then the amps must deliver 40V/3.1 ohms = 12.9 amps..

So when someone says that a speaker is current hungry it really can only mean that the impedance is low at some or all of the operational frequency.

In the real world some amps cannot supply high current at high voltage. That does not mean they cannot output the specified watts. They just can't do it into a low impedance speaker. That is why one amp might be rated 100 wpc into 8 ohms and 150 wpc into 4 ohms, while another speaker is rated 100 wpc into 8 ohms and 200 wpc into 4 ohms. At 8 ohms both are able to output 100 wpc. But if the speaker dips down into the 4 ohm range, the second amp will be more powerful.

Therefor to combat the problem people recommend bigger more powerful amps, not because they need 400 wpc, but rather they want the amp to be stable at low impedance.

Lastly if your McIntosh is only using 6 watts, that does not mean a 6 watt amplifier will sound just as good. In a class A/B amp the amplifier works in class A on a sliding bias, such that for the first "x" number of watts it runs in class A. The bigger the amp, usually the higher this value "x" is. Since people like the sound of class A more then class A/B this could mean that a bigger Class A/B amp may sound better then a smaller one even at low volumes. Additionally an amp is usually rated at its power based on when it hits a certain amount of distortion (say 0.1% for and example). If you look at a power curve for an amp, the level of distortion will rise as the power usage goes up and will rise very quickly as it approaches its max output. Therefore a bigger amp may have lower distortion at lower volumes then a smaller amp.

So Pass Labs that runs all in Class A with 100W should do the trick. Yes?

"Pass Labs X350.5 solid-state stereo power amplifier

Specifications: Power Output: 350 watts x 2, 8Ω
Frequency Response: 1.5 - 100kHz
Gain: 26/30dB
Damping Factor: 150
Slew Rate:50V/µS
Maximum Output Voltage: 76 volts
Maximum Output Current: 28 amps
Input Impedance: 30/20 kΩ
Output Noise: 200 uV
Input CMRR: -60dB @ 1kHz
DC Offset: 0.05 V
Temperature:53° Celcius
Power Consumption: 600 W
Dimensions: 19 W x 11 H x 21.5 D (inch)
Shipping Weight: 150lbs.


MSRP: $11,550



My introduction to Pass Labs dates back to some time in the early 1990’s. Back then, there was plenty of “buzz” in the audiophile circle regarding this small solid-state amplifier that actually sounded like tubes. I eventually got to hear the diminutive monoblock amplifier running a pair of Chartwell LS3/5a’s. The all class A operation Pass Aleph 0 left that indelible impression of how far solid-state amplification had come with respect to overall musicality. Later, Pass Labs signed a local Florida dealer, and once again I felt nothing but admiration and respect for the stereo versions and future iterations of the class A amplifiers Nelson Pass was designing. They simply sounded “right” to me. That said, unfortunately I always had to admire them from afar. While the Aleph line of amplifiers were among the best sounding solid-state amplifiers I had heard, they topped out at about 150 watts per channel. They simply didn’t produce the kind of power that I needed for my electrostatic speakers. You see, I am a ‘stat man, and I have had nothing but electrostatics since the early 1990’s.

Of course, this all changed just before the millennium. The entire world took notice of this massive beast of an amplifier that was introduced called the Pass Labs X1000. An amplifier that was rated at 1000 watts per channel into 8 ohms and nearly 2000 watts into 4 ohms. I never did actually hear one, but all I heard from friends in the industry was that it delivered the sonic goods in true Pass Labs fashion, and that it took 6 beefy guys to lift it! Just as impressive was the introduction of what would become Pass Lab’s signature casework: A big, bold sculpted statement faceplate in machined aluminum that cleverly doubles as a pair of handles for lifting the heavy beast. Since its introduction, Pass Labs has expanded the line of “X”- designated amplifiers with the X150, X250, X350, and X600; each with a power rating mirroring their model designation. Since then, that model line-up has given way to the more refined “.5” versions of each.

The sudden upsurge in power delivery of the Pass amplifiers in the form of the X Series is due to the development and realization of the circuit design dubbed Supersymmetry topology that was patented by Nelson in 1994. This topology has two gain stages: A single-ended Class A input gain stage whose output drives a bank of high power MOSFET devices operated as voltage followers with zero feedback. Distortion and noise are addressed though cancellation by running well-matched MOSFET devices in balanced mode. Distortion and noise identical to both halves of a balanced circuit are claimed to disappear at the output through cancellation, and in a supposedly well-matched symmetric circuit, most of the distortion and noise is identical. The patented Supersymmetry circuit design enhances the effect supposedly by delivering an additional 90% noise reduction effect at the output of the balanced circuit.

The class A input gain stage is supposed to impart the sonic character of the amplifier. Therefore in theory, these huge beefy power amplifiers should display the same sweetness, liquidity, and sound staging that has been the heart of the Nelson Pass pure class A amplifiers sonic signature for years.



Getting Started

The Pass Labs X350.5 arrived in late March. Of course I knew that the amplifier was quite large and heavy, and I was even fore-warned that it had to be shipped to me via common carrier; but even with that knowledge it was quite impressive to see this huge box arrive at the base of my driveway, strapped to a heavy shipping pallet.

The Pass Labs X350.5 amplifier is the largest and most powerful stereo amplifier in the X Series line of amplifiers. It is rated at 350 watts per channel into 8 ohms, and roughly doubles that into 4 ohms. Despite its prodigious size and mass, it was a rather easy and straight-forward task (for two guys) to lift the amplifier out of the shipping box and place it on my tubular steel Billy Bags amplifier stand. Hook-up of this amplifier is also a breeze. The speaker binding posts are large flanged units that can be hand-tightened. Signal hook-up is accomplished via a set of single-ended RCA connections or balanced XLR. For this review, all interconnects utilized were single-ended RCA.

A circuit breaker switch on the rear of the amplifier facilitates getting power to the amplifier’s circuitry in standby mode. A front panel button facilitates activation from standby mode. Once powered up, the Pass Labs X350.5 warms up in about an hour.

I used the superb Aural Symphonics Magic Gem v2t powercord over the full term of the review period, and I configured the rest of the system using Aural Symphonics cables throughout. I have been reviewing the MagicGem v2t power cords, Chrono interconnects, and Purple v3 speaker cables for the past few months and I decided that the performance they bring to the table would be very well-suited for the Pass X350.5. During the course of the review period, I occasionally swapped speaker cables; specifically between the copper-based Purple v3 and silver-ribbon Pure Note Paragon-Enhanced, (more on that in a future review).




Stretching those Muscles

The Pass Labs X350.5 amplifier required a fairly short break-in period to sound its optimal. I ran it in for 7 days, 24 x 7 with my break-in CD for starters. I’m sure that’ll be quite an impact to my home electric bill, between the 1800 watts (maximum draw) of the amplifier and the strain on my central air conditioning unit in order to keep the ambient temperatures in my sound room in check. I guess this would be as good a time as any to point out that the X350.5 dissipates plenty of heat. It is specified to run nominally with the heat sink temperature around 50 degrees centigrade, that’s roughly 120 degrees Fahrenheit. Since my Martin Logan CLS2z’s run nominally at 4 ohms and at 1.5 ohms in the high frequencies, and since I was running them plenty loud, I suspect that the amplifier was dissipating more than the usual 120 degrees. Florida Power and Light will indeed be sending me a one heck of a usage bill! The good news is that the amplifier remained rock stable and ran my full-range electrostatics at relatively high levels straight out of the box without any drama whatsoever.

Sonically, break-in was fairly uneventful. Straight out of the box the amplifier already exhibited sonic characteristics more akin to a tube amplifier than solid-state. A certain midrange liquidity was clearly evident and it showcased itself quite well through the electrostatics. After break-in, image depth and width improved and image specificity came into acute focus. There is generally nothing dramatic to report with respect to break-in. The amp is quite good out of the box and simply improves over time.




The Sound

I sat for my first extended listen on a Sunday afternoon as is customary. I was quite confident that the amplifier had been sufficiently burned in. It is important to note that warm up of the amplifier for optimum performance was a relatively short 1-2 hours. By contrast, my long-standing reference amplifier really needs an overnight warm-up to come into its own which is likely why it has no power switch.

As I played the usual range of female and male vocals from my CD arsenal, I was impressed with the sheer liquidity and lifelike presentation the Pass Labs amplifier exhibited. For instance, on Katie Melua’s, ‘What it Says on the Tin”, from the CD entitled Pictures, the X350.5 presented Katie’s voice with such delicacy and “juiciness”, that you would swear that you were hearing triode monoblocks instead of the huge imposing solid-state beast that had taken the center stage of my sound system. Throughout this particular CD it was noteworthy that the soundstage presented in my system was as wide as any I have heard. The midrange performance on acoustic guitar and vocals was astonishingly lifelike and exuded that glowing presence that you normally experience with vacuum tubes.

After listening to a variety of female vocal works from Katie Melua, Dawn Upshaw, Patti Smith, and Rickie Lee Jones, I switched to male vocals such as Neil Young, Kevin Gilbert, and Peter Gabriel. Noteworthy was the way the Pass X350.5 captured the intended darkness, immediacy and emotion of Peter Gabriel’s performance of Paul Simon’s “Boy in the Bubble”, the compelling interpretation of Lou Reed’s “Power of your Heart”, and Neil Young’s “Philadelphia”, and the driving force of Arcade Fire’s “My Body is a Cage”, from Peter’s decidedly dark and personal new LP, Scratch My Back.

Several fundamental traits consistently emerged from the X350.5. Firstly, this is one very accurate and dead-on neutrally-voiced amplifier. It handily and consistently laid bare the fact that my reference amplifier is “voiced” with a midrange “Gundry dip”, a depression plateau of less than 1 dB centered around 1kHz that is said to impart a more liquid and tube-like presentation. The X350.5’s neutrality and lack of any heavy-handed voicing shone through in the form of its musical presentation. Vocals and acoustic guitars were presented beautifully, and placed at the horizontal plane of the electrostatic panels or slightly forward of them. By contrast, my “voiced” amplifier presents the performance at the horizontal plane of the electrostatic panels and slightly behind which, to my ears, makes it appear slightly veiled at times when directly compared to the Pass Labs X350.5. I point this out as a matter of reference. The X350.5 is astonishingly linear and really showcases the transparency, accuracy, and lifelike qualities of the full-range electrostatics to its full effect without ever sounding forward or gimmicky.

OK. So the amp can clearly sing with the best of them, but can it handle the rigors of long hard-driving, dynamic music, and remain composed doing so, even when driving the sub-2 ohm load of the electrostatics? This is literally what separates the men from the boys when it comes to large, high powered amplifiers.

I must admit that this part of the evaluation proved to be the most fun. Back in my South Florida Audio Society days, we used to do power amp shoot-outs with some frequency, and at the end of the day, the true test of fortitude always meant hauling the amplifiers to my sound room and having them power my electrostatics. The inevitable conclusion 90+% of the time was that the test subjects either misbehaved, overheated and shut down, or otherwise suffered from collapsed soundstages and high frequency stridency that bordered on shrieking. The good news is that the Pass Labs X350.5 just doesn’t follow the playbook of most other large, brutish solid-state amplifiers.

For instance, when playing excerpts from the LP Music and Rhythm, a benefit LP for WOMAD, World Music; Arts and Dance, Stewart Copeland’s explosive percussion work on Peter Gabriel’s “Across the River” is a challenge to just about any system. The X350.5 kept an iron fisted grip of the high energy percussion at all times and produced one of the most life-like and credible performances I have heard through my system, or any system, with respect to this particular song. Similarly, from the same album, XTC’s “It’s Nearly Africa” is in some ways, even more of a challenge, but did not ruffle the Pass X350.5 at all. The textures, nuances, and PRaT, not only remained intact, but I found myself actually hearing more of the low frequency information coming from the electrostatic bass panels than ever before. I confirmed this by switching off the subwoofers entirely and indeed, there was bass; tuneful, fast, clean, bass. Not something you usually hear from a CLS IIz panel in any great abundance, especially when the panel is suspended in mid-air and has no benefit from wall or floor reinforcement.

Encouraged by what I was hearing, I went through a process of re-tuning the subwoofers to the CLS IIz’s and decided to follow-up with a Sheffield Direct to Disc recording, James Newton Howard & friends. I mean the real direct-to-disc recording and not a compressed 2nd or 3rd generation pressing from a master tape that was released afterward or excerpted in the Sheffield Track record. The cut, “Borealis” in particular was handled remarkably by the Pass Labs X350.5. The explosive dynamics of this recording remained intact through the audio chain and was amplified without so much as a hint of strain. In fact, the X350.5 shrugged off anything I would throw at it and I constantly had to remain mindful, that the CLS IIz’s also had their limits of power handling!

Of course, this type of muscular flexing does come at a price. My listening sessions had to include intermissions every hour or so because of the tremendous heat that was generated from the X350.5. To be sure, this is no ordinary amplifier. The X350.5 is extremely quiet, with no perceivable noise floor, has the dynamic agility that in my opinion, is literally in a class by itself. Its bass response is first rate in authority, weight, speed, and tunefulness. Yet, through this high-octane athleticism, emerges the soul of a small triode amplifier. The midrange remains beautifully rendered, subtle nuances and textures remain intact, and images are expansive and remain so, even when the amplifier is pushed hard. Again, not a me-too variety solid-state amplifier, far from it.

In summary, a power amplifier’s job is to take the delicate low-level signal being delivered from the source via a preamplifier (usually) and amplifying it without imparting its own character or coloration in the process. This is exactly what the X350.5 accomplishes. If your needs include big power, really big power, as mine do, I wholehearted suggest a visit to your local Pass Labs dealership for an audition.

Kudos to Nelson Pass, Desmond Harrington, and the rest of the Pass Labs team. This amplifier indeed receives an emphatic recommendation from me."

[beden1]

This is a great topic indeed.. Old, but good..

I think it is very confusing that some dealers will state that current is more or less important.

Current is a function of voltage and impedance. That means that at a particular amp output voltage and speaker resistance the current is fixed. One amp cannot supply more current to a speaker then the another (assuming neither amp distorts).

For example if an amp is outputing 40V to the speaker with a 2khz tone, and the speaker impedance is 8 ohms at 2khz then the amp must put out V/R amps. That is 40V/8 ohms = 5 amps. Now if the speaker is 3.1 ohms at 2khz, then the amps must deliver 40V/3.1 ohms = 12.9 amps..

So when someone says that a speaker is current hungry it really can only mean that the impedance is low at some or all of the operational frequency.

In the real world some amps cannot supply high current at high voltage. That does not mean they cannot output the specified watts. They just can't do it into a low impedance speaker. That is why one amp might be rated 100 wpc into 8 ohms and 150 wpc into 4 ohms, while another speaker is rated 100 wpc into 8 ohms and 200 wpc into 4 ohms. At 8 ohms both are able to output 100 wpc. But if the speaker dips down into the 4 ohm range, the second amp will be more powerful.

Therefor to combat the problem people recommend bigger more powerful amps, not because they need 400 wpc, but rather they want the amp to be stable at low impedance.

Lastly if your McIntosh is only using 6 watts, that does not mean a 6 watt amplifier will sound just as good. In a class A/B amp the amplifier works in class A on a sliding bias, such that for the first "x" number of watts it runs in class A. The bigger the amp, usually the higher this value "x" is. Since people like the sound of class A more then class A/B this could mean that a bigger Class A/B amp may sound better then a smaller one even at low volumes.

Additionally an amp is usually rated at its power based on when it hits a certain amount of distortion (say 0.1% for and example). If you look at a power curve for an amp, the level of distortion will rise as the power usage goes up and will rise very quickly as it approaches its max output. Therefore a bigger amp may have lower distortion at lower volumes then a smaller amp.

That's a very clear explanation. Thank you! :T

[mb225]

stuofsci02,
Thanks for the response! Great stuff!

In a class A/B amp the amplifier works in class A on a sliding bias, such that for the first "x" number of watts it runs in class A. The bigger the amp, usually the higher this value "x" is.

Ahh... that makes sense why B&W would recommend such a monster amp to drive 803s.

Do you know 100% if the amplifiers are class A on a sliding bias? I thought class A/B was a design. This would mean an A/B amp is really some kind of class A, A/B hybrid. Is that right?

Additionally an amp is usually rated at its power based on when it hits a certain amount of distortion (say 0.1% for and example). If you look at a power curve for an amp, the level of distortion will rise as the power usage goes up and will rise very quickly as it approaches its max output. Therefore a bigger amp may have lower distortion at lower volumes then a smaller amp.

That really makes sense. If you can lift 400 lbs. when someone asks you to lift 5 lbs., you can do it with ease.

[stuofsci02]

mb225,

Yes, to my knowledge a class A/B push pull amp will run in class A model so long as the output is low enough. This A to AB switch point will vary between amps. For instance I think the Parasound Halo JC1 will stay in class A up to 25 watts.. For most this would cover almost all levels of listening except for maybe the peak transients.

I think B&W recommends a bigger amp because sometimes even professionals start to feel that bigger is better. They want people to avoid using cheap recievers and amps that may not perform as advertised and therefore make blanket statements. Also an amp driven to distortion could damage the speakers. In general you are safer with more power.

That said a well designed amplifier and more importantly power supply can make all the above irrelevant. On my 804s I run a 130 wpc Chord amp and have never felt the need for more power. In fact I even auditioned the amp on a set of 801D to see if it really had what it took (in case I wanted bigger speakers later).. It had no problem with the 801D.. Did the 400 wpc Chord sound better? Yes a little.... Otherwise I would have nothing to dream of..

[stuofsci02]

That's a very clear explanation. Thank you! :T

No problem.. Have to be good for something every now and again...

[Sharp 1080]

In the third photo, the shot of the rear of the amp are the speaker cables reversed? Shouldn't the cable on the left edge of the photo be the amps right channel and trail off to the amps right side? Looks like it's connected to the left channel? :roll: