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Upgrading from a HK AV-630 (Axiom Speakers)

 

New member
Username: Steaktooth

Springfield, IL - Illinois

Post Number: 1
Registered: Apr-12
Hello, I currently have a Harmon Kardon AV-630 receiver and Axiom home theater speakers.

M60 floor R/L
VP 150 ctr
Qs8 surrounds
HSU Sub STF2

I was thinking of upgrading my receiver to have some of the features new receivers offer but I don't want the sound quality to suffer. Can you recommend any receivers that would be comparable sound quality wise. I would only be using 5.1 as it seems to do the job quite well in the 12x24 room. Any suggestions would be helpful. I have not paid much attention to the audio world since I bought this setup seven years ago or so. Many of the new receivers seem much cheaper and quite a bit lighter. That HK weighs over 40lbs I think! Am i wrong to associate weight with a more powerful power supply and likely better quality?
 

Platinum Member
Username: Glasswolf

Columbia, South Carolina America

Post Number: 14600
Registered: Dec-03
Look at the Onkyo TX-NR series receivers like a (used) NR1009, 3009, etc.. outstanding amplifier sections and every feature you could dream of.

I'm using an NR5009 now myself. If that doesn't cut it, find an AVR with pre-outs, and buy a separate amplifier, like a 5 channel Emotiva or Adcom instead.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17221
Registered: May-04
.

My generic suggestion for which amp to buy is to look at the weight of the amp. Certainly, in decades past that would have been a starting point for how well thought out the amplifier would have been as amplifiers are not much more than modulated power supplies. The amperage limits of the power transformer and the storage capacity of the power supply's capacitors would have told you quite a bit about whether the designer was creating a product better suited to the real world conditions of driving reactive speaker loads or whether the design was meant to perform well on a test bench under conditions suited only to those of the test bench. However, new topologies have made such a simple comparison less likely to result in the best sound quality. Specifically, the amplifiers which employ chip output stages can be either very cheaply made and sound it or they can be very high quality and the power supply weight becomes less an issue due to the lower voltage requirements of the chip output stages. Very little - and I mean very little - heat is created by such outputs so heat sinking is also a minimal contribuor to the overall weight of the amplifier.


If we assume you are looking at a conventional class AB operational amplifier - the sort of solid state, transistor output configuration which exists and has existed for decades in receivers - then I would still tend to go with the axiom; heavier the amp, the better the design of the amp. That then asks the question, what is that weight there to accommodate? High wattage alone is no guarantee of good sound quality and, if judged solely on the number of watts per dollar, would actually lead you to what is probably the lightest amp for the money. Why? Simply because most consumer loudspeakers will be a reactive load on the amplifier rather than the simple resistive load of the test bench. That leads the prospective buyer to the question, what sort of amplifier would best suit my speakers? For that answer you need to know a few things about your speakers. Are they a fairly reactive load with low impedance dips and severe electrical phase angles? Or, are they a mostly benign load which does not place the same the same demands on the amp as a more reactive speaker would? If you are unfamiliar with the terms reactive and resistive when applied to loudspeakers, you might want to read a bit here; http://www.avguide.com/channel/the-perfect-vision

http://www.hometheater.com/

http://widescreenreview.com/





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Platinum Member
Username: Glasswolf

Columbia, South Carolina America

Post Number: 14601
Registered: Dec-03
Weight isn't always the determining factor anymore with the introduction of units like the Pioneer Elite AV receivers using all class D amplification.
 

Gold Member
Username: Magfan

USA

Post Number: 2729
Registered: Oct-07
IF the 'd' amp has a conventional powersupply, some of Jan's remarks are still valid. Hi efficiency of 'd' amps ONLY comes in at the very highest power levels, other than that? At more conventional levels the efficiency drops.
My ASP modules are 83%, at 200 watts (250 max) with the measure from plug to speaker. The works.
But, if you are using a 'd' implementation with a conventional PS, that number won't apply. The modules from B&O sometimes have integrated power supplys...SMPS which are very efficient. A conventional Transformer / Rectifier / Cap PS running at line frequency will still make plenty of heat.
I think Rotel uses the ASP modules, as I describe. So, too, do many other manufacturers. BelCanto? W4S and bunches more.

Also, the ability of an amp to drive a reactive load....capacitive OR inductive, while measurable is usually not done. Resistors give much better results, even though I can think of not a single resistive, full range speaker.

The OTHER myth of HT receivers is that of measured power...no matter how its done, usually. Very few receivers will meet spec with all channels driven. You will see 2-ch ratings, but seldom 7x? or 5x?. I'd derate any spec by at least 25% when thinking all channels driven. The counter arguement is just how much of the time will all channels be required to use that much power? Not often, unless you're into ear damage. At that point, I'd say to get more sensitive speakers.

Watch low impedance loads, too. I don't know of any current HT receiver with 4 ohm ratings. Some have 6 ohm ratings, which I guess is the 'new 4'. A low impedance dip coupled with hi phase angles will result in 'ampagedon' and you'll either cook it or blitz it outright.
 

Platinum Member
Username: Glasswolf

Columbia, South Carolina America

Post Number: 14606
Registered: Dec-03
" even though I can think of not a single resistive, full range speaker. "

KEF Reference 104/2 presents a nearly completely flat resistive load at 4 ohms from 50Hz-20KHz. Lower bottom end if the active EQ is used with them. There are some out there, but not that many, granted, and a lot of the better speakers, like electrostatics are highly reactive and low impedance, which can really stress out an amplifier.
 

Gold Member
Username: Magfan

USA

Post Number: 2732
Registered: Oct-07
My original panels, MG-1s from the late '70s were said to be 'nearly resistive' at 5 ohms. And, as many other Magnepans, the 'curve' is very flat as well. My 1.6s, for example, have a largish peak at the crossover frequency of about 600hz while the phase above / below goes from slightly capacitive to slightly inductive.
ANY reasonable amplifier will do.

I'd love to see the Phase data for the KEF. Any chance of recovering that from somewhere? Only Stereophile takes such data, AFAIK, and the manufacturer like to keep it 'secret'.

One of the points upon which I agree with Jan, without reservation, is that speaker designers and amp designers seldom speak. And when they DO speak, it is frequently in different languages. The question becomes....'Is there any need for such a wacky load that requires an amplifier which says Lincoln Electric, Hobart or Miller on the side?'
 

Platinum Member
Username: Glasswolf

Columbia, South Carolina America

Post Number: 14611
Registered: Dec-03
I have the response curve but not a phase curve, although I do know that the crossovers Raymond Cooke designed for those speakers were extremely complex, had hand matched components to each pair of speakers, and to this day, nobody likes to mess with the crossovers if something fails.. haha I believe he actually did pay particular attention to the phasing as well, but as you noted, he kept a lot of the details closely guarded as the speaker was fairly groundbreaking when it came out in the early 80s, and now it's old enough that it's hard to find anything about them in regards to technical detail. if you shoot me an email address I can send you everything I do have on the speakers. I sort of made it a hobby to find what I could on them over the years, then scan it all in.

The nice thing about these resistive loads is that even at a low impedance (for home audio) like 4 ohms, the speakers usually work just fine even on things like older amps and AV receivers that are only "rated" for 6 or 8 ohm speakers at reasonable volumes.

As much as I love Martin Logan ESL panels, I really don't like hoe demanding electrostatics are on amplifiers.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17237
Registered: May-04
.

I sold the KEF line at the time the "new" 104A's were introduced. Not much was said about phase angle at that time but KEF made a point to all sales staff the new 104A was a very undemanding speaker system capable of being satisfactorily driven with a ten watt amplifier. The crossover had been designed to complement the idea of a "purely resistive load" as the ideal target for the speaker. While the crossover could be considered "complex" it was largely a design effort in which each step in one direction was met by another component which pulled the curve back toward a neutral line. Since each such "correction" would have its own affect on the signal more components were required to correct for the correction. The result, as it was described to the sales staff, was to make numerous smaller steps rather than a few large leaps. KEF's greatest strength here was their ability to design and produce their own drivers to meet their own specs. The new 104A pointed to a new direction in KEF driver design and implementation. The results of which are most readily seen in the current line of "Uni-Q" drivers from KEF. Of course, in the new 104A the two twin humps from the vented cabinet remained as the significant lumps in the speaker's impedance curve. The Brtitish press spent a good deal of time writing about the new 104A. Material from the time might be pulled from the archives of HiFi News (and Record Review). My recollection is the new 104A - not to be confused with a similarly number speaker from KEF which had been discontinued just a few years prior - was introduced in 1985.

Complex crossovers were fairly common back in the late '70's through the early '90's and still exist today in a few lines. As with the previous KEF Reference series and similar to many of the BBC derived designs produced by KEF Reference Series crossovers were trimmed by hand to meet very tight specifications. Whether this is good or bad is up to the individual listener to decide. Certainly, each component added to the circuit has some effect on the ability of the signal to go in and come out looking anywhere near the same. Each added component is a point where the amplifier must work harder and where energy is lost in a transfer to heat. Each solder point is a potential loss of signal. And the total self inductance of most modern circuit boards will seldom be taken into acount in the final system. A speaker company capable of producing their own drivers is in a far better position to achieve good results from their designs when such factors are accounted for. As I said, this has always been one of KEF's strong suites.




" "even though I can think of not a single resistive, full range speaker"



"Single speaker" is the key there. A single driver, full range system will be a purely resistive load in most cases where only the self inductance of the voice coil as it heats will add a slight deviation to the phase angle of the system.



.
 

Platinum Member
Username: Glasswolf

Columbia, South Carolina America

Post Number: 14614
Registered: Dec-03
True. When he said "one speaker" I was thinking one "cabinet," and not "one driver." One driver, sure it won't be a flat resistive load, but I'm not sure that'd be an ideal goal to aim for. You're better off focusing on the BL curve of the individual driver if you're after a more pure, transparent response curve.

While the KEF 104/2 did have a fairly complex crossover network, I'm still amazed at it's sensitivity as well.
Sensitivity: 92dB at 2m on reference axis for a pink noise input of 2.83V (anechoic conditions)

quoted from:
http://www.kef.com/html/gb/explore/about_kef/museum/1980s/reference_series_104_2 /index.html

KEF also had the Kube active equalizers for those Reference series speakers like the 104/2, 105/3, and 107aB, etc.. which some people complained about, and others loved. I believe on the 104/2, the EQ smoothed out a small spike in the response in the midrange, and extended the low end roll off from around 55Hz, down to 20Hz remaining fairly flat. I've spoken a few times with the KEF engineer who designed the Kube EQs, and learned quite a bit about them from him.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17245
Registered: May-04
.

"While the KEF 104/2 did have a fairly complex crossover network, I'm still amazed at it's sensitivity as well.
Sensitivity: 92dB at 2m on reference axis for a pink noise input of 2.83V (anechoic conditions)"


Sensitivity is one of those specs that won't really tell you much. It can be measured with too many weighting curves to make valid comparisons between speakers other than from a single manufacturer. But, yes, the 104's did play with not much power. That, however, is not what I'm chiefly concerned with when I see twenty plus crossover components. But I am a single driver fan so anything with any sort of crossover is, to my ears, "wrong".




.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17246
Registered: May-04
.

Oh, yes, the Kube sucked big time.
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