What to look for in a power amp?

Gregadd · Sep 9, 2010

No where in audio except cables is there more confusion, trickery and deception than in amplifiers. At one point it was so bad the FTC had to step in and set standards.
Given the discussion in the "fear of measurement section" that properly designed amps working within their limits should sound the same, what should we look for.

I ask we try to avoid the tube vs solid state debate unless you have a specific narrow point to make.

To start things off why don't we talk about the load presented. On other threads we have discussed,speaker impedance, efficiency and a purely resistive load vs a reactive load.

JackD201 · Sep 9, 2010

Given I'm limited in what I can spend, I look under the following criteria:

1. Specific system's primary use
2. Headroom requirement for that use taking into account speaker load and room size
3. Complimentary Flavor for that use since there's always going to be a trade off anyway
4. Space/Ventilation Constraints
5. Ease of use, maintenance, access to repair
6. Visual Aesthetics, all things being equal I'll take the good looking one

Gregadd · Sep 9, 2010

Type of music
Room size
Speaker efficiency
Speaker impedance
Convenience and practicality
Affordability
Aesthetics/WAF
Brand name/warranty/product support/ manufacturer longevity
Availability
Review opinions help with resale value
Maybe you worry about tube availability.
Flexibility/ 2channel/multi channel or whole house system/HT
Critical listening or background music

Gregadd · Sep 9, 2010

Objective camp-
you know-
what music you like
what spl you require for that music
whether your room is live or dead and room size
how much wattage you require to produce that spl
your speaker efficiency
your speakers impedance curve
how to convert wattage into spl.
how to calculate dynamic headroom

Subjectivist
TAS said it was the best. All the lesser rags were basically in agreement.
You took your favorite records and listened at the store with your best audiophile buddy. Lo and behold tas was right. You put down your deposit.

advanced audiophile- did all they above

Miracle they all picked the same speaker.

You might have guessed I have already picked our mystery speaker. We will start by saying our audiophile is married. His wife likes pop music. The husband likes jazz and pop. What I plan to do next is to give some room dimensions and specifications for our mystery speaker.

audioguy · Sep 9, 2010

Faceplate thickness
Weight
Dimensions
Cosmetic Appeal

No, I don't think all amps sound alike but couldn't resist expressing some dose of afternoon high end audio cynicism

MylesBAstor · Sep 9, 2010

gregadd said:
objective camp-
you know-
what music you like
what spl you require for that music
whether your room is live or dead and room size
how much wattage you require to produce that spl
your speaker efficiency
your speakers impedance curve
how to convert wattage into spl.
How to calculate dynamic headroom

subjectivist
tas said it was the best. All the lesser rags were basically in agreement.
You took your favorite records and listened at the store with your best audiophile buddy. Lo and behold tas was right. You put down your deposit.

Advanced audiophile- did all they above

miracle they all picked the same speaker.

You might have guessed i have already picked our mystery speaker. We will start by saying our audiophile is married. His wife likes pop music. The husband likes jazz and pop. What i plan to do next is to give some room dimensions and specifications for our mystery speaker.

bose!!!!

Gregadd · Sep 9, 2010

Myles I'll add that name to my list. Did you have a model number in mind?

Gregadd · Sep 9, 2010

audioguy said:
Faceplate thickness
Weight
Dimensions
Cosmetic Appeal

No, I don't think all amps sound alike but couldn't resist expressing some dose of afternoon high end audio cynicism

My current amp has a massive faceplate, is heavy, and is quite handsome.

Gregadd · Sep 9, 2010

Our mystery speaker has been chosen.
Sensitivity 88db
Nominal impedance 6 ohms
Recommended power 50-500 watts
Frequency Response 26-50kz

Gregadd · Sep 10, 2010

I have somewhat of a dilemma. I thought it would be fun to have someone guess what our mystery speaker is. OTOH in selecting our mystery amplifier(s) we do need to know as much about our speaker as possible. BTW I have a picture of our room somewhere on my computer. We are making progress. I think I'll reveal small details until someone guesses.

JackD201 · Sep 10, 2010

Amphyon?

MylesBAstor · Sep 10, 2010

Gregadd said:
I have somewhat of a dilemma. I thought it would be fun to have someone guess what our mystery speaker is. OTOH in selecting our mystery amplifier(s) we do need to know as much about our speaker as possible. BTW I have a picture of our room somewhere on my computer. We are making progress. I think I'll reveal small details until someone guesses.

Well I've eliminated more than I've figured out. So far eliminated: Wilson, ML, Magnepan, Revel and NOLA. Magico remains a possibility though.

DonH50 · Sep 10, 2010

Hey Gregadd, I'm here. What did you want to ask?

I have not followed this thread closely; these kind make my head hurt. I do somewhat disagree with the premise of this statement (disclaimer: I am not saying this is Gregadd's position):

Given the discussion in the "fear of measurement section" that properly designed amps working within their limits should sound the same, what should we look for.

I suppose "within their limits" may cover it, but interaction with the speaker is so intrinsic to any discussion on amplifiers that expecting any two to sound the same is unrealistic. Within reason, within a given price range not terribly wide, I would expect most SS amps to sound the same, and most tube amps to sound the same, but even that will not hold with vastly different amplifier classes. E.g., a class A/B and class D amp with the same power rating and roughly the same price are unlikely to sound the same into a speaker even though they may measure almost the same.

As to what I look for, I tend to look at the specs and price to narrow it down, then try to listen to what I can in my system. Given the state of the industry today, that is an impractical goal. I bought my last (Emotiva) amps "blind" based on specs, price, and the help and a little listening in a friend's system. They sound OK to me, but in truth I do not have a good comparison; probably just as well. If I had $10k to spend I would spend a lot more effort on my choices; for $1k, it was going to be SS and Emotiva was good enough to make the cut. I really hate not having the access to equipment to try out that I had in my youth.

Onwards - Don

Gregadd · Sep 10, 2010

Of course the most important thing in our amplifier is adequate power. We generally think in terms:
What SPL is associated with the type of music we like.
Given that our speaker is fairly inefficient and jazz and pop music is generally very loud we are going to have a very hefty power amp.
With all due respect to our speaker manufacturers. He has left us with a range of 50-500 watts. Not very helpful. I have heard our mystery speaker and it is indeed wide range and produces deep bass.
I thought we could choose two amps. A tube amp for our subjectivist and a solid state amp for our objectivist. I have no scientifc proof but my anecdotal evidence suggests solid state amps need to be twice as powerful as the tube amp. So if our tube amp is 300 watts into 6 ohms our ss state amp should be around 600 watts. I have two amps in mind. I'll start by posting the manufacturers spec. Then we will try to find some reviews. I'll try to.

DonH50 · Sep 10, 2010

Interesting comment on SS vs. tube power... I would have guessed the opposite, with about 2x the power in a tube amp to match the bass tightness of a SS amp. In the midrange and up, I expect power to be a wash, with the tube amp sounding a little "sweeter". I have always felt bass to be one of the weaknesses of tube amps, primarily due to their relatively high output impedance (and low damping factor). BTW, assuming a good amp with stiff rails, the SS amp rated at 600 W should put out 800 W into 6 ohms; the tube will put out 300 W no matter the load as long as the tap is there and it is matched to the speaker's impedance.

88 dB/1 W/1 m, say we want it to reach 120 dB peaks at our listening spot, maybe 3 m away. That means we need an extra (120 - 88) = 32 dB, and another 6 - 12 dB for distance depending upon the room gain (size etc.) Let's say an even 40 dB, or 10,000 W (!) Maybe 110 dB is more reasonable, yielding 1000 W -- closer to your target goal. In fact, 600 W is about 28 dB above 1 W, so the speaker should output 116 dB at 1 m and maybe 110 dB at the 3 m listening spot driven by 600 W with a little help from the room; close enough! Good "guess", Gregadd! Leaves the tube amp lagging a bit, though, as it will be 3 dB into clipping at that power. We probably won't notice as it will only happen on the loudest peaks.

I thought this was about amps; it's a "guess the speaker" game? Alas, I cannot play, as I am unfamiliar with most of the newer speaker brands. 6 ohms rules out Magnepan, however.

Onwards - Don

p.s. I am an "objectivist" who has owned tubes until very recently, and sold out to SS due to cost and other considerations. I always did like falling outside the box...

Gregadd · Sep 11, 2010

It was a guess the speaker game. I'm afraid our friend Myles is just being polite.

Gregadd · Sep 11, 2010

I do want to point out a watt is a watt whether it passes through tubes or a transistor. My point is that two amps with three hundred watt specs may behave quite differently under a real world load (playing music through a speaker). Thus follows my observation that the tube amp will appear more powerful. We can discuss that later.

Gregadd · Sep 11, 2010

I have two amps in mind. The tube amp drops .75 kilowatts watts into 8ohms. The ss amp pumps 1.5 kilowatts into a 6 ohms load. Yes , it doubles down and I extrapolated to find the 6 ohm rating.

DonH50 · Sep 11, 2010

I'll make just one quickie then: tube amps tend to exaggerate the bass region due to their higher output impedance, so they can sound louder.

I am confused as to where this thread is going, I guess. The first post suggested looking at speaker impedance and its effect on amplifiers, but to me the effects are quite different between tube and solid-state, with neither being a winner all the time. I'll stop babbling until I figure out whats going on (the longer the better, likely!)

Gregadd · Sep 11, 2010

Let me try to pin things down. I was suggesting when picking an amp, the amp and speaker really are a system. Why don't I go ahead and say Myles guessed right. The mystery speaker is the Magico Q5! He wins only bragging rights. My cursory audition leads that leads me o beleive it is a difficult load requiring a sturdy amp with lots of power. As Alon put it "400 watts is enough but the more power the better."
I'm the customer and I have put down my deposit and have to pick an amplifier. What factors do I consider?

What to look for in a power amp?

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