What to look for in a power amp?

DonH50 · Sep 11, 2010

Disclaimer: I will have to look at the Magico's as I am unfamiliar with them.

Difficult speaker loads have always sounded best to me using fat, sassy solid-state class-A monoblocks. I have not heard the latest high-power tube amps, however. In a previous life, I never found a tube amp that would do something like B&W 801's or some similar hard-to-drive dynamics justice. With a widely varying load impedance, the tube amps always seemed to struggle in the bass (where the impedance often dipped low) and sometimes the high end, especially with ribbon tweeters since they are usually pretty smooth but very low in impedance. I love the sound of tubes, but driving difficult loads the SS amps always sounded cleaner and offered much better bass. Subjectively, to me.

That said, my preferred (price no object) way to drive a difficult load is with a good tube amp on top and a decent SS amp for the lows. I loved my Maggies bi-amped (actively) with an ARC D-79 for the mid/hi end and Counterpoint SA-220 for the bass panels. The Counterpoint was not the best amp on paper in comparison to the Krell and Levinson I considered, but the hybrid design and MOSFET outputs matched best with the D-79. Since the Maggies roll off slowly, matching amps is important (to me, anyway). I am driving them with a SS amp now and the sound is arguably cleaner but I still recall my "old" sound fondly...

FWIWFM - Don

garylkoh · Sep 11, 2010

First let me state that I am biased - my bias is in my self introduction on this forum.

My requirements for an amplifier are:

1) Load invariant - it should sound the same whether it is playing at 0.1 watt or 10 watts

2) Wide bandwidth - we need more than 20Hz to 20kHz. A set of jangling keys, for instance, has frequency spectra and power all the way up to over 100kHz - see here:
http://www.its.caltech.edu/~boyk/spectra/spectra.htm

3) High current - it needs to be able to sustain current delivery when impedance drops.

With the Magico Q5 (88dB/W/m at 4 ohms) and assuming that you are sitting about 4m from the speaker, you will get 76dB/W - which is about normal listening level. So, most of the time you will need 1W. But.....

1) When playing dynamic music - lots of power is needed to overcome the inertia of the speaker cones (and even the airload in front of the cones). With our usual ways of measuring impedance, we do not show the true picture. I have measured instantaneous impedance drop down to 0.4 ohms in a loudspeaker that is nominally 8 ohms. There is a 1982 AES paper on this:
http://www.aes.org/e-lib/browse.cfm?elib=11870

2) High-power amplifiers are needed for speakers with difficult loads not because the high power is actually needed, but because of the much larger energy reserves available in the high voltage power supplies. Energy store is proportional to voltage squared.

3) Large power supplies are usually slow, small power supplies are usually fast. (Due to capacitor time constant) http://en.wikipedia.org/wiki/RC_time_constant

4) Meeting all the engineering specifications for a "perfect" amplifier does not guarantee musical enjoyment.

Sorry I didn't answer your question which really is - which amplifier for the Q5

Gary

Gregadd · Sep 11, 2010

Gary I have chosen two amps for consideration-Muscal Fdelity Titan and the VTL 750.

MylesBAstor · Sep 11, 2010

Gregadd said:
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?

Damn not even a T-shirt? What kinda of contest is this????

garylkoh · Sep 11, 2010

Gregadd said:
Gary I have chosen two amps for consideration-Muscal Fdelity Titan and the VTL 750.

Two others to consider around your price point - the BAT REX power and Burmester 911.

For my tastes, I find a lack of that intangible "musical involvement" when amplifiers get way too powerful. But then again, I like ribbon loudspeakers. My reference was the FM Acoustics 611X - it had magical low-level microdynamic and microtonal detail for a high-power SS amp. I'm not a reviewer or even read reviews very regularly, so I'm not sure if those are the right terms.

MylesBAstor · Sep 11, 2010

garylkoh said:
Two others to consider around your price point - the BAT REX power and Burmester 911.

For my tastes, I find a lack of that intangible "musical involvement" when amplifiers get way too powerful. But then again, I like ribbon loudspeakers. My reference was the FM Acoustics 611X - it had magical low-level microdynamic and microtonal detail for a high-power SS amp. I'm not a reviewer or even read reviews very regularly, so I'm not sure if those are the right terms.

Gary: I think the days of the lower powered amp being the better of a manufacturers line doesn't hold true anymore. Yes, years ago, the low powered amps sounded purer or say the output transformer design of large tube amps wasn't capable of reproducing the highest frequencies.

Give a listen to the cj ART, VTL 450/750 or ARC 610T

These new amplifiers really combine the ease and lack of congestion of big powered tube amplifiers with the delicacy or midrange purity of a triode amplifier.

Maybe the Technical Brain too

Gregadd · Sep 11, 2010

garylkoh said:
Two others to consider around your price point - the BAT REX power and Burmester 911.

Wow Gary.This is a hypothetical. I wish that was "my' price point.

For my tastes, I find a lack of that intangible "musical involvement" when amplifiers get way too powerful. But then again, I like ribbon loudspeakers. My reference was the FM Acoustics 611X - it had magical low-level microdynamic and microtonal detail for a high-power SS amp. I'm not a reviewer or even read reviews very regularly, so I'm not sure if those are the right terms.

Subjective terminology can get you in trouble around here. It's okay for ss amps.( tongue firmly planted in cheek).

Gregadd · Sep 11, 2010

MylesBAstor said:
Damn not even a T-shirt? What kinda of contest is this????

I'll buy you a beer when I see you at RMAF.

MylesBAstor · Sep 11, 2010

Gregadd said:
I'll buy you a beer when I see you at RMAF.

Deal

amirm · Sep 11, 2010

Gregadd said:
Why don't I go ahead and say Myles guessed right. The mystery speaker is the Magico Q5! He wins only bragging rights.

You don't say. As usual, I cheated last night and googled your specs since it looked like a cut-and-paste

. And I hit on Magico Q5. Was going to post and collect my prize except that you said the impedance was 6 homes whereas the hit I found said 4: http://www.soundstagenetwork.com/la...=49:magico-v2-loudspeakers&catid=37&Itemid=27

Which is right and why doesn't magico have a proper spec sheet for this speaker on their site?

Gregadd · Sep 11, 2010

amirm said:
You don't say. As usual, I cheated last night and googled your specs since it looked like a cut-and-paste . And I hit on Magico Q5. Was going to post and collect my prize except that you said the impedance was 6 homes whereas the hit I found said 4: http://www.soundstagenetwork.com/la...=49:magico-v2-loudspeakers&catid=37&Itemid=27

Which is right and why doesn't magico have a proper spec sheet for this speaker on their site?

Myles has to buy you a beer! Specs are to easy for you Amir. Next time I'll post an FR graph.

Magico was slow to even post a picture of the Q5. Give them credit for touring the country with actual demos. Maybe they wanted you to hear it before you saw the specs.

JackD201 · Sep 12, 2010

The 2050

These made the V3 sing like no other amp I've heard them with. The bigger brother Q5 should be a breeze for these giants.

Gregadd · Sep 12, 2010

Don-Just because you only have a $1000.00 to spend does not not mean you have to go ss. Try this hybrid NYAL Moscode 600. Available used for under a $1k. The 300 ain't bad either. For $60 bucks you'll need Edison Price binding posts.
http://www.youtube.com/watch?v=j5JhcMhfuzo

Gregadd · Sep 12, 2010

I do not like to use any machinery that has to be operated "wide open" on a regular basis. ideally I want to see it work within 60-80% of its range.

I think these amps will have no problem in that area.

For me transient response is at the top of the list for stereo system. The only thing I want to ring is my telephone and my alarm clock.

From the subjectivist camp- I would take some recordings of percussion, bells, whistles drum strikes and deep bass.

Is the bass boomy or is it nice in tight? Can I hear the transient attack and subsequent deca?. I hate time smear.
Maybe Don can help us with the technical side. I would look at slew rates or rise times. Square waves and of course damping factors. For or tube amp I'm also going to examine output impedance.

Gregadd · Sep 12, 2010

JackD201 said:
The 2050

These made the V3 sing like no other amp I've heard them with. The bigger brother Q5 should be a breeze for these giants.

Jack can you elaborate on why you think the Boulder is good match? I did consider the Boulder. I heard them with the Wilson MAXX.

JackD201 · Sep 12, 2010

Alon was playing an orchestral piece from his home brew server and the tympani strikes were very well defined, as you said, from attack to decay. This is something I equate with very good control. Tonally, the system was well balanced. Nothing objectionable at all. Reviews say the 2050 is on the "bare" side, whatever that means. I found nothing of the sort in the 15 minutes or so I listened to that system at CES 08. At the very least, I can say that to my ears and my tastes the synergy was very good. I sell a different brand of amplifiers but even I admit the 2050 bettered my highest powered offering in the driver control department and texturally the differences would be IMO entirely a matter of taste. All in all I came away with respect for Magico.

Of course I haven't heard the Q5 so some buckets of salt are in order. Instinct tells me though that the 2050 would handle the Q5 just as easily as the V3. It may even handle it with more ease given the larger internal volume.

An amp that I would like to hear is Karan's big dog. That looks like another amp that would handle pretty much any loudspeaker with a whole lot of ease. Personally, I put "ease" as a very high priority. I'm very sensitive to distortions caused by stress especially thermal distortion in both amps and drivers. So while I love the sound of single ended zero global feedback topologies be it flea tubes or gorilla solid state, I've come to the conclusion that I need adequate headroom because I listen to a lot of large classical and also love banging doses of electronica when the mood strikes.

Gregadd · Sep 13, 2010

Measurements by Stereophile for VTL can be found at:

http://www.stereophile.com/tubepoweramps/152/index8.html

and for The MF Titan:

http://www.stereophile.com/tubepoweramps/152/index8.html

garylkoh · Sep 13, 2010

MylesBAstor said:
Gary: I think the days of the lower powered amp being the better of a manufacturers line doesn't hold true anymore. Yes, years ago, the low powered amps sounded purer or say the output transformer design of large tube amps wasn't capable of reproducing the highest frequencies.

Give a listen to the cj ART, VTL 450/750 or ARC 610T These new amplifiers really combine the ease and lack of congestion of big powered tube amplifiers with the delicacy or midrange purity of a triode amplifier.

Maybe the Technical Brain too

Good point! I've heard the new big VTL's and they are indeed excellent.

Despite being a "tube head" most of my life, I've moved away from them mostly because once I had kids, I no longer liked the idea of an amplifier idling at 500W consuming earthly resources while I was listening to the first watt. Funny how family life changes the priorities of an audiophile. I also needed loudspeakers with a sweet spot large enough for a love seat (and now a full-sized couch!!).

I do agree that amplifier design has improved to the point where it is not the lower powered design being the better of a manufacturer's line - but that's the good manufacturers. Being a loudspeaker designer, I'm always at the end of the chain, and I've been to too many dealer's demo rooms and cringing because they "had" to have an amplifier with a price commiserate with the price of my speakers.

flez007 · Sep 13, 2010

First thing for me would be system compatibility/synergy with the rest of the system. That includes both ends, preamp and speakers.

DonH50 · Sep 13, 2010

The MF amp's measurements are at http://www.stereophile.com/solidpoweramps/musical_fidelity_titan_power_amplifier/index5.html

I suspect bias leading to double-posting of the tube amp's measurements...

Note differences in performance with a speaker load and dramatically different distortion levels. ALso note that the VTL has prmarily 2nd-order distortion in the time plot, whiile the MF has 3rd-order, one of the major differences between (most) tube and (most) SS amps. How much a factor the distortion is when listening to music I cannot say. The variation in FR with speaker loading is what makes me tend to shy away from tubes with difficult speaker loads.

Based upon specs, the MF is a clear winner. Based on sound, your call. I have had high-end tube and SS gear in my system in the past and while I know the SS amps I used measured better, I often liked the tube sound better, warts and all. As I have said, I loved my tube amps on my Maggies, but did not feel they were a good fit to the Inifinity QLS-II's I owned for a while, nor for the B&W 801's I auditioned.

Of course, there's always the chance the variation with a particular speaker in a particular room will help the tube amp win the overall response contest; one reason I feel treated rooms should be used for reviewing, and a key reason I feel the only valid listening test is the one you do at home.

My current Emotiva's do OK for me. I admit as I've gotten older and more back into the making of music (vs. listening to it) the less critical I tend to be of the equipment. At least over a certain threshold, which of course varies with type of music, time of day, phase of the moon, etc.

FWIWFM - Don

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