Emo XPA-100

[Steve81]

What you seem to be arguing for is that constant current strategy that McIntosh advocates. True? Otherwise, you're going to end up with string output into 8 ohms, but much less as the load declines in impedance.

Hi Irv,

I'm not really arguing for or against anything in particular. If anything, I'm just arguing against poo-poohing an amplifier because it fails to double down into 4 (or 2 ohms). If you've got speakers that spend a substantial amount of time in 3 or 2 ohm territory or worse though, I can see the point of an amplifier that can double down. Still, given the price of entry for those models, it seems like you could potentially pick up one that would have excess capability at higher impedance loads and still come out ahead as PENG alludes to.

 

[Irvrobinson]

Hi Irv,

I'm not really arguing for or against anything in particular. If anything, I'm just arguing against poo-poohing an amplifier because it fails to double down into 4 (or 2 ohms). If you've got speakers that spend a substantial amount of time in 3 or 2 ohm territory or worse though, I can see the point of an amplifier that can double down. Still, given the price of entry for those models, it seems like you could potentially pick up one that would have excess capability at higher impedance loads and still come out ahead as PENG alludes to.

As someone who recently chose an ATI, which doesn't double-down, I think we're on the same page. I'm not really an advocate for amps that double-down with most speakers, it's needless over-engineering, I was just reacting to PENG's called it marketing hype. I don't think it is hype in many cases.

 

[Irvrobinson]

To go slightly further off the rails here. Given that speakers are expecting your amp to be a constant voltage source, wouldn't this impedance matching cause the speakers to not get the power distribution they are expecting? [i.e. less power from an impedance matched amplifier where the speakers impedance curve ditches than on one providing constant voltage]

Not necessarily. The speakers would only be deprived if the current demand at a given frequency exceeded the actually capabilities of the amp, which is called clipping. For most speakers in most rooms with amps that can output at least a hundred watts into 4 ohms clipping might be a corner case. Once you get to 2 ohms, however, a pretty beefy amp is usually the only solution.

 

[Grador]

Not necessarily. The speakers would only be deprived if the current demand at a given frequency exceeded the actually capabilities of the amp, which is called clipping. For most speakers in most rooms with amps that can output at least a hundred watts into 4 ohms clipping might be a corner case. Once you get to 2 ohms, however, a pretty beefy amp is usually the only solution.

That is a very different thing than i was asking. If the speaker has a natural dip to 2ohms, but the transformer evens this out for the amplifier to, lets say 8 ohms, then it would be receiving 1/4 the power it would expect from a constant voltage supply. Is this somehow incorrect?

 

[Grador]

Answered my own question, I was under the impression that it was something that happened automatically, not that there were multiple sets of binding posts.

 

[Irvrobinson]

Answered my own question, I was under the impression that it was something that happened automatically, not that there were multiple sets of binding posts.

Sorry for the confusion, and the matching is just a better approximation. My explanation still holds, that power will be delivered into the load until clipping occurs, but due to the transformer the output stage will see a more benign load.

 

[PENG]

What ATI amp does 800w into 4 ohms? The 3002 is rated at only 450w/ch into 4 ohms. While it may very well put out 500w clean watts into 4 ohms, comparing it to a 1997 design isn't exactly apples to apples.

Harman isn't Madrigal, and the Levinson designs show it. A more viable current competitor is the Krell 302e, that does 300/600/1200 watts into 8/4/2 ohms. Into 2 ohms loads, and many high-end speakers present 2 ohm loads in some octaves, the Krell will have a 3-6db advantage over the ATI. Is that important to a lot of users? I don't know, but you know as well as I do that there's an exponential curve for performance like that. And the 302e is not even above the midpoint of Krell's product line.

"Most users" don't buy contraptions like the 334 or a Krell, or a Pass Labs amp for that matter. These are for people with extraordinary systems and fat wallets who (IMHO) are as enamored with the engineering as they are the realized performance, and pay to have something special, just like with a $10K Swiss watch. I don't think this is hype, it is just a classic case of over-engineering to make some particular people happy. (Guilty as charged, at least occasionally.)

We both know ATI does not make a 500/800w model, sorry it wasn't clear to you that I was using fictitious examples and I should have used a fictitious brand. Again, not arguing your point but are you going to answer my other question, if an amp is specified for 100/200/400w 8/4/2 ohms, why can't it do more than 100 into 8 ohms? You know my follow up question to your potential answer right?

 

[PENG]

There are only two solutions to your quandary about 8 ohm power. Run the power rails at a higher voltage and let the power fall off as impedance declines (at least into 2 ohms), or use output transformers a la McIntosh to better load-match the speakers to the output stage. Frankly, for low impedance loads I like the Madrigal/Krell approach a lot better.

I agree that there's not actually doubling going on with these amps, but if you read the test reports on them you can see that they're actually pretty close.

I thought the Mc scheme delivers the same power not double so not even close, but it is distant memory so I should read up on their website.

 

[Irvrobinson]

I thought the Mc scheme delivers the same power not double so not even close, but it is distant memory so I should read up on their website.

Yes, the McIntosh attempts to deliver the same power into 8, 4, and 2 ohm loads, with different output transformer windings.

I once compared their output transformers to the transverse springs in a Corvette suspension. Both are "legacy architectures" held over more for marketing than technical reasons, but neither is bereft of technical advantages.

 

[Irvrobinson]

if an amp is specified for 100/200/400w 8/4/2 ohms, why can't it do more than 100 into 8 ohms? You know my follow up question to your potential answer right?

Because of the voltage the output stage is regulated to. The Levinson 334/335/336 is quite instructive in this regard, because a 335 is, essentially, a 334 with an output stage regulated to twice the voltage. And, of course, the 335 power supply and output stage are beefed up to handle 3db more power. The 334 and the 335 even have the same input sensitivity and gain, so if you drive a 335 with the same input voltage as a 334 you get only a 334's worth of output, 125w/ch/8 ohms. Drive the 335 with peaks of 2v rather than 1.4v and you get 250w/ch. (On the 336 it takes 2.4v to drive it full output, so don't pair one up with a weakling AVR receiver's pre-amp outputs. ) Drive the 334 with 2.0v and it'll clip. The previously posted graph from Stereophile proves that.

I can't read your mind, but is your question, why not just regulate the 334 to have 250w/ch into 8 ohms, 500w/ch into 4 ohms, and let 2 ohm output fall wherever? The 334 is easily capable of 500w/ch into some load. Most speakers don't present a 2 ohm load. If that is your question, the answer is perhaps that it's a marketing decision with its roots in the days of the Apogee Scintilla, the original Wilson Watt, and the original Legacy Focus, all of which had impedances that fell to 2 ohms or below. Real he-man amps drove those speakers.

Here's a related question: why does McIntosh still have 2 ohm terminals on their latest amps? Are they really necessary?

 

[josko]

Before we go too far dissing output transformers, here is a link to a major manufacturer of sonar power amps: Instruments,INC.
Their amps are typically used (in combination) to output more than a megawatt of audio power while driving loads much more difficult than anything in the consumer audio world. They all have several (transformer) output taps as well as overvoltage and overcurrent warning indicators. When setting them up for peak power to a new load, the trick is to select the tap that just flickers on both overvoltage and overcurrent , and then back off until both simultaneously disappear.
Their veritable L6 and L10 are true classics, found in all sonar labs throughout the country.
My point is that output transformers have very much of a role to play with widely varying input loads. I think the reason they are not used in consumer audio is because speaker input impedances have stabilized at 8 ohms, with an occasional dip down to 4; so manufacturers can in effect preselect the output tap at manufacture time.
(FWIW, I'm a sonar engineer.)

 

[Irvrobinson]

Before we go too far dissing output transformers, here is a link to a major manufacturer of sonar power amps: Instruments,INC.
Their amps are typically used (in combination) to output more than a megawatt of audio power while driving loads much more difficult than anything in the consumer audio world. They all have several (transformer) output taps as well as overvoltage and overcurrent warning indicators. When setting them up for peak power to a new load, the trick is to select the tap that just flickers on both overvoltage and overcurrent , and then back off until both simultaneously disappear.
Their veritable L6 and L10 are true classics, found in all sonar labs throughout the country.
My point is that output transformers have very much of a role to play with widely varying input loads. I think the reason they are not used in consumer audio is because speaker input impedances have stabilized at 8 ohms, with an occasional dip down to 4; so manufacturers can in effect preselect the output tap at manufacture time.
(FWIW, I'm a sonar engineer.)

I'm just of the opinion that for solid state home audio amplifiers output transformers are not necessary or cost-effective. On the other hand, if you can afford McIntosh amplifiers they are quite extraordinary devices. They ooze quality, unlike my ATI that looks like an '80s Adcom amp on steroids. Nonetheless, I've always wondered what McIntosh could do in solid-state amp design if they ditched the autoformers.

 

[josko]

I see now that speaker impedance range is narrowing, thus obviating the need for amplifiers to drive a wide range of impedances or use transformers for impedance matching.
I can only assume that decades ago, speaker impedances varied much more than they do now, and thus there was a need for amplfiers such as the ML 334 and Mac.

 

[Steve81]

I see now that speaker impedance range is narrowing, thus obviating the need for amplifiers to drive a wide range of impedances or use transformers for impedance matching.

Hard to say really. Most manufacturers specify 8 ohm nominal impedance with a few 4 ohm nominal speakers, but few really back it up with the impedance plot. I know Klipsch for example has had some "8 ohm" speakers that dip below the 3 ohm mark (RF-7, RF-83; not sure about the RF-7II). Because of that lack of disclosure, I would tend to err on the side of caution.

Of course on a personal note, while my setup/listening level doesn't seem to demand a meaty separate amplifier, I still wouldn't mind one for the cool factor (both kinds ).

 

[PENG]

Because of the voltage the output stage is regulated to.

Exactly, there are cons as well as pros, i.e. not all good, at least regulated mean limited in a sense however narrow sense it is; and it could probably slow things down too depending on the design.

I can't read your mind, but is your question, why not just regulate the 334 to have 250w/ch into 8 ohms, 500w/ch into 4 ohms, and let 2 ohm output fall wherever?

You really didn't have to read my mind as I posted that questions more than once before, but yes you read my mind correctly as that was my follow up question, one that I asked before. My point is that it is a circular concept, and that's why in my first post I called it a circle game, or marketing hype? Note I did use a question mark about the "hype" part. By the way, by circular, I mean:

If an amp can output 400W 2 ohms, it could theoretically do more than 100W 8 ohms if allowed to have a higher voltage, but then if you allow a higher rail voltage, it wouldn't be able to double down to 4 ohm and quadruple down to 2 ohm. Bottom line is, Adcom, Anthem, ATI, Bryston, Emotiva, Rotel, Parasound chose not to market amps that double down most likely have their reasons, valid reasons from their stand point. McIntosh amps use their autoformer for impedance matching/maximum power transfer but that does not result in doubling down at all. That does not make their amps weaker than those that do.

If that is your question, the answer is perhaps that it's a marketing decision with its roots in the days of the Apogee Scintilla, the original Wilson Watt, and the original Legacy Focus, all of which had impedances that fell to 2 ohms or below. Real he-man amps drove those speakers.

Thank you for finally using the M word, note that I did use a ? on my "hype" word as I knew at the time my choice of word was questionable even by myself. However, I did explain in my follow up post that I was more thinking of those hearsay followers who "hyped" things up once they latched onto something that they thought was so important, due to lack of deeper understanding of the matter and associated theory.

Here's a related question: why does McIntosh still have 2 ohm terminals on their latest amps? Are they really necessary?

Good question, likely it is for the maximum power transfer thing but I would like to read up on their autoformer first.

It seems to me we managed to agree on:

- There isn't doubling going on, unless regulated power supplies are used, then it can get really close, but still not 100% true.
- Few amps employ such regulated power supply, ML being one of them (I am not sure if they still do with the latest models?). Actually I am not sure if you agree to this one but I am guessing you may.

The only thing we seem to disagree on for sure, is my choice of word, namely "hype". I have attempted to explain my point more than once already and even though I did call it hype, I had it followed by a ?, and that I did not mean that on the manufacturer but the hearsay followers. I can even agree it isn't much of a hype but would not agree to your "not at all" either. So I agree to disagree on that one.

For some who might have just parrot (no pun intended) what they heard/learnt about this double down thing, I have a good read for them in the following link.

Audio amplifier power supply design - Part 1: Power supply types & transformer considerations

Without revisiting my EE book collections I am not going to validate everything the author said was in terms of electrical principles/theories, but I think it is a good read none the less, and EE times tend to have some credibility IMHO.

 

[Irvrobinson]

It seems to me we managed to agree on:

- There isn't doubling going on, unless regulated power supplies are used, then it can get really close, but still not 100% true.

Yup.

Few amps employ such regulated power supply, ML being one of them (I am not sure if they still do with the latest models?). Actually I am not sure if you agree to this one but I am guessing you may.

Yup again. ML seems to be moving away from the he-man approach. The new 532, for example, is not rated into 2 ohm loads. Krell still rates their amps down to 1 ohm. Talk about he-man stuff.

only thing we seem to disagree on for sure, is my choice of word, namely "hype". I have attempted to explain my point more than once already and even though I did call it hype, I had it followed by a ?, and that I did not mean that on the manufacturer but the hearsay followers. I can even agree it isn't much of a hype but would not agree to your "not at all" either. So I agree to disagree on that one.

You're correct, and I was also just being difficult, as my wife accuses me of often. I probably need to work on that, but I enjoy it too much.

some who might have just parrot (no pun intended) what they heard/learnt about this double down thing, I have a good read for them in the following link.

Audio amplifier power supply design - Part 1: Power supply types & transformer considerations

Without revisiting my EE book collections I am not going to validate everything the author said was in terms of electrical principles/theories, but I think it is a good read none the less, and EE times tend to have some credibility IMHO.

Most of the contributing authors to EE Times have *a lot* of credibility with me. EE Times does like rumor and sensational quotes a little too much for me sometimes. I like The Register too, when I'm in the mood.

 

[PENG]

Don't know why you suddenly become highly agreeable, hope your wife knows that..

Anyway hope you have time to read that 8 pages long article too but it was really intended for the others who know what double down means but not the pros and cons and how it is achieved. You obviously know what he's talking about already but you may still enjoy reading it.

 

[renjy651]

Very interesting thread.

Only few manufacturers can achive the power to double at 4 Ohms and triple to 2 Ohms. This is achived by building a massive power supply using very high value in capacitance and high voltage. The capacitors must be Electro Lytic screw terminal caps. Very expensive.
Many new manufacturers amps uses lower priced many radial capacitors to achive high capacitance. The reason they are less expensive. These caps have higher ESR and lower Ripple.

Mark Levinson when they made the ML33 used 12 39000uF/100V caps on each amp to get 500kuF in capacitance on each amp. Total capacitance 1 million uF on both amps. This is super expensive you need total of 24 caps for 33 mono blocks. Total cost 7000 dollars for 24 caps. This is the way you you can achive power to double or triple.

Levinson 333/336/332/334/335 all used high capacitance and high voltage to achive high power at 4 Ohms and 2 Ohms.
No manufacturers are going to build amps like these any more. Because it is very expensive to use these monster Electro Lytic screw termnal caps. These caps have super low ESR and high ripple current to drive any speakers also it will give you better bass.

 

[Hobbit]

Also, when I see one that says 100W into 8 ohms, 200W into 4 ohms, I have to wonder, why wouldn't it yield >100W into 8 ohms if current is not the problem, so it the amp limited by voltage now, what a circle game!! Or marketing hypes?

Why would an amp yield >100W at 8 ohms? P=E*I and E=I*R. Ergo, power equals the voltage squared divided by the resistance: P=E^2/R. Or, E = sqrt(R*P). The value in the parenthesis is 800 whether it's 100W@8ohm, 200W@4ohm, or 400W@2ohms. All one needs to do is build an amplifier that can regulate a constant E=28.28V and put out up to 400W continuous. Not that hard to do.

However, the reality of a most consumer amp is there's always compromises which result in output variations (do to voltage regulation). In the easier load, 8 ohm, the regulated voltage will generally go up (30ish volts) as the current draw isn't as high, thus allowing the amp to produce a greater max wattage. This is why you'll see an amp rated at 200W@4ohm and 125W@8ohm for example instead of 100W@8ohm.

 

[PENG]

Why would an amp yield >100W at 8 ohms? P=E*I and E=I*R. Ergo, power equals the voltage squared divided by the resistance: P=E^2/R. Or, E = sqrt(R*P). The value in the parenthesis is 800 whether it's 100W@8ohm, 200W@4ohm, or 400W@2ohms. All one needs to do is build an amplifier that can regulate a constant E=28.28V and put out up to 400W continuous. Not that hard to do.

However, the reality of a most consumer amp is there's always compromises which result in output variations (do to voltage regulation). In the easier load, 8 ohm, the regulated voltage will generally go up (30ish volts) as the current draw isn't as high, thus allowing the amp to produce a greater max wattage. This is why you'll see an amp rated at 200W@4ohm and 125W@8ohm for example instead of 100W@8ohm.

If you read the follow up posts, you may have the answer. Anyway, I was trying to say sometimes (not always) people just play games. You can rate an amp 100W 8ohms, 150W 4 ohms, or 75W 8 ohms, 150W 4 ohms so it "doubles down", still the same amp. Another point I made was, if the amp truly doubles down into 200W 4ohms, that means it is not current limited, so the only reason why it could not be rated for higher than 100W into 8 ohms is that it is voltage limited, but if it is not voltage limited then given that it can do 200W into 4 ohms, it should be able to do 400W into 8 ohms. Now if it can do 400W into 8 ohms, and only 200W into 4 ohms you are going to say, see, it is not high current as not only it won't double down, it actually half down, so you would want it to do 800W into 4 ohms and then the argument would just repeat itself. Hence the reason I called that a circle game, and of course I was being silly.

If I manage to confuse you, well just setup an Excel spreadsheet, plug in your favorite formula you have already cited, V=IR, P=I^2*R, P=V^2/R and have fun. By the way, just for simplicity, I see no need to bring up the cos Ø part of the power formula so I won't challenge your formula.