Revisiting "Psychoacoustics and amps" thread from '02/'03-Ken Kantor, are you there?

[soundminded]

"Jourdain (page 41) states that an orchestra produces 67 watts of acoustic power at full blast. Loudspeakers have efficiencies on the order of 0.5 to 2% converting electrical power to acoustic power. Even at 2% efficiency this implies that well over 3,000 watts of electrical power would be required to duplicate this sound level. "

If a symphony orchestra could somehow be physically crammed into a home listening room say by reducing it in physical size but not in acoustical power and play fff at it does at its loudest in a concert hall, the sound would surely be deafening. You cannot compare the sound power necessary to fill up a 500,000 cubic foot concert hall and achieve 100 db spl at your seat 20 or more feet away and the sound power necessary to achieve 100 db in your 3000 to 4000 cubic foot home listening room. At one meter, in dead acoustics, a speaker with a sensitivity of 86 db/watt will produce 101 db with 32 watts. at 2 meters it would need 128 watts. Given that the acoustics of most listening rooms are on the moderately dead to moderately live side, a 150 wpc amplifier should be sufficient to achieve 100 db in most parts of the room with this much power. Most speakers including the midrange and tweeters of AR speakers can't take even that much for very long. My 60 wpc amplifier will drive my AR9s to extremely loud levels anywhere in my moderately live listening room of 4000 cu feet without audible distortion. The combination seems particularly adept at shaking the walls, floor, ceiling, and windows. I've decided that it is sufficient for those speakers in that room.

[Pete B]

I covered some aspects of your question about baffle step compensation in another thread but did not state it outright:

http://www.classicspeakerpages.net/dc/dcbo..._id=6180&page=4

The center of the baffle step as can be seen in Allison's measurements is about 400 to 500 Hz. A crude form of baffle step EQ could have been obtained by setting the mid and tweeter controls about -3 dB from flat in an early AR-3a with the 1.9 mH inductor. It would be more abrupt, and not the full 6 dB but the full amount is not usually required in any case. What I was showing in that thread without stating it outright was that the newer design with the 2.85 mH inductor seems to have modern baffle step compensation since in post #6200 we see that the woofer is flat into half space as is stated in the figure, probably with the 1.9 mH inductor:

http://www.classicspeakerpages.net/dc/dcbo...id=&page=4#6198

Whereas here in post #6227 we see that the woofer is flat, actually overcompensated since the response slopes slightly down, rather than up, where it is stated as being measured into a 360 degree solid angle or hemisphere. This probably has the 2.85 mH inductor:

http://www.classicspeakerpages.net/dc/dcbo...id=&page=4#6198

The two cases should look like A and B in Allison's AES paper if there was no difference in the speaker system:

http://www.classicspeakerpages.net/dc/dcbo...id=&page=4#6198

In fact the speaker in Allison's paper probably had the 1.9 mH inductor.

I believe that the early systems with the 1.9 mH inductor were designed to be flat into half space and the later systems with the 2.85 mH were designed with baffle step compensation. It would be interesting to hear both types of AR-3a's side by side, they should sound very different.

Pete B.

>BTW, would AR speakers benefit from Baffle Step equalization?

>When would manufacturers have stsrted to design speakers with

>Baffle Steo Equalization built in? I have some well reviewed

>speakers like Paradigms and Celestion DL10 that are much

>bassier than AR's when against a wall for instance. The bass

>on these sounds about the same as my AR's when these (newer!)

>speakers are away from room boundaries.

[Pete B]

I like the Paradigm Studio's very much, they're similar to my commercial reference system and designed for a nearly flat response. I've heard the 100s I think it was but it was some time ago. There are very few speakers that I like more than my commercial reference system which I think is a bit sweeter sounding than the Paradigms. Both of these excellent systems reach into the mid 20's with power and extension, not even the AR-3a does that having an Fc of about 41 Hz. The Paradigms are vented tuned to 25 Hz and my commercial reference is vented tuned to 28 Hz. My reference plays about 9 dB louder just where the bass distortion becomes thick to my ears, as compared to the Advent at the point where they bottom with a crack when playing bass heavy material. The bass character is no more sloppy as many claim for vented than the Advents, in fact they're tighter and positively have more extension. I'm fully aware that Advents are not the best example of acoustic suspension out there, as the system Qtc is just a bit high. I might say the bass is rich or perhaps ripe from the Advents in a good way.

I also have Advents, AR-2ax's and Dyna A-25s and I have to say these don't even come close to the reference, no way what-so-ever. I could tell you a story told to me by an engineer who was there when Kloss was voicing the Advents, but I doubt people here want to hear it since it is negative. People worship Kloss and I do respect his work but he made business decisions that most people probably do not want to know about.

Pete B.

>Yesterday I lined The following up on a shelf on one wall and

>compared them with my LST's on the smame wall. They all had

>similar bass characteristics with the LST's, AR12's,

>DynacoA25XL's,AR4's having deepest to least deep in that order

>of course. Interestingly These speakers bass sounds excellent

>when against a wall (about 2/3 of the way up). The following

>had fat boomy sounding bass until they are brought into the

>middle of the room..

>Paradigm Studio monitors, Paradigm Phantoms, Celestion DL10

>seriesII,

>Technics SB7000A.

>

>Interestingly, all the AR's and the Dynacos had similar

>overall sound with the Dynacos having a bit more upper bass.

>All of these sound very good even when compared with the more

>modern Paradigms which are excellent performers. The

>Celestions and the Technics had their own sound

>characteristic, although very good also, it was markedly

>different from the former group.

>

>I am now satisfied that the LST's are operating correctly and

>sound as designed given that I am using the newer Tonegen

>woofers as opposed to original woofers. I need a new 6 way

>switch for the LST's as one is defective and I have them hard

>wired in the '5' mode which replicates the AR3A sound

>according to the booklet. I don't think I can do them justice

>in the room I have and I believe that they would sound/perform

>much better in a larger room with the listener more than 8'

>away as in my listening room.

>

>The driving equipment ( for the above comparison) is a NAD

>tuner/preamp, NAD CD, Kenwood M2A power amp rated at 200wpc

>into 8ohms and almost 400 into 4. I am not using the McIntosh

>stuff for comparisons because it saves me dealing with the

>impedance taps on the MC2105 power amp.

>

>In line with this thread, I believe I hear differences between

>my Kenwood, McIntosh and Crown power amps but I have not done

>instant switching or double blind tests. The Mc sounds the

>'fattest' and the Crown DC300A the leanest. Very subtle mind

>you. The preamps I have tried have a greater effect on the

>sound (I think). No interconnects or speaker cables from

>cheapest to mid priced exotics make any difference to my

>ear..... all cables are of at least decent quality

>construction....

>

>Phono cartridges have sonic signatues as do speakers.

>Turntables, some but again, subtle.

>

>Thes are my humble opinions and findings based on the above

>simple tests and years of messing with hifi equipment.

[Pete B]

I'm curious as to what people here think of Bryston power amplifiers?

Yes this is a trick question, but please go ahead and comment.

I had a very good opinion based on reviews and comments from several trusted friends, I've probably even heard them somewhere along the way.

Pete B.

[Pete B]

You choose the case that Ludwig himself states is extreme where he's just trying to inform people. I believe that you underestimate the peak level required for realisitic listening. I'm not going to debate you, rather I'll ask have you ever put a scope on the output of your amp while playing those pieces that shake the floor?

I did this experiment when I was a kid in elementary school and found that the system became harsh in the mid/high end, or thick/muddy in the low end when there was visible clipping. Clipping is easy for me to hear and pick out to this day. I heard clipping on the commercial CD recordings that I show on my web page:

http://members.aol.com/basconsultants/spkrs.htm

I consider the recordings to be defective.

Pete B.

[rrcrain]

I agree. I have an M&K recording of the Hungarian Philharmonica playing Pachelbel's Cannon in D major, and its quite a piece. It starts out very softly and if the amplifier is left at the same volumn at the end as it is at the start of the piece, my amplifier's peak power lights are flickering with the peak transients, and thats over 500 WPC. Darn straight its loud, but it is an excellent example of the range a full orchestra can have.

[soundminded]

To be honest, I haven't hooked up my oscilloscope to an amplifier in a very long time. The last time was many years ago when I looked at the output of my AR amplifier driving Bose 901 speakers and didn't see any clipping. I'm not sure how valuable that is anyway. First, if you wanted to see transients, you'd really need a triggered storage scope. Secondly, with the impedence of the speaker varying so much especially at low frequencies, I'm not sure how valuable seeing just the output voltage would be. You'd have to know the frequency to determine what impedence the voltage is driving. A true peak power meter is an entirely different animal requiring measurements of both voltage and current probably by using a metering shunt (would a CT be accurate enough?). It would probably take a couple of data loggers and a computerized analysis to get anything meaningful out of it.

[Wally]

I had a 4B about 10 years or so ago when I bought the Paradigm Studios. I had a Classe preamp which was noisy (hiss) by comparison to the other preamps I had. Anyway I accidently pulled the interconnects from the pre to the Bryston out. I heard a loud crack and that was it. When I reconnected and tried to listen to music there was no bass, The Bryston fused the voice coils on all 4 woofers. Fortunately the dealer and Paradigm were very accomodating and replaced the woofers under warranty. These were no lighytweights... they easily handled the power of the 4b to nose bleed sound levels.

Back to the 4B. It was obviously very clean to any level and had no problem driving the 6ohm Paradigms. Compared to subsequent power amps I used on those speakers the 4B's had a deeper more powerful bass. I know it didn't actually go deeper but the interaction with those speakers was such that it sounded deeper and more powerful and bass was very tight and clean. Amazing amp but use speaker fuses...!!!!

I had a 2B prior to that. It was also excellent but nothing I have had since matched the bass and subjective power of the Bryston. I had a Marantz 510M and it was nice but either Bryston in my opinion sounded more powerful. This is subjective because I did not have the Marantz at the same time as the Brystons.

It was wonderful.... should have kept that sucker.

>I'm curious as to what people here think of Bryston power

>amplifiers?

>Yes this is a trick question, but please go ahead and

>comment.

>

>I had a very good opinion based on reviews and comments from

>several trusted friends, I've probably even heard them

>somewhere along the way.

>

>Pete B.

[Guest Bret]

>There would be a HUGE commercial benefit if it could be shown that amps had much, if any, impact on sound quality.<

Ken -

I just put my money where your mouth is and bought a "refurbished" Crown DC300A for less than a lot of the big 70s receivers sell for.

See? I just like arguing around the edges.

Now. . . are the differences in preamplifiers audible? :-)

Bret

[dynaco_dan]

Hi Bret

Try a Crown IC-150 pre-amp for size.

Good luck.

Vern

>>There would be a HUGE commercial benefit if it could be

>shown that amps had much, if any, impact on sound quality.<

>

>Ken -

>

>I just put my money where your mouth is and bought a

>"refurbished" Crown DC300A for less than a lot of the big 70s

>receivers sell for.

>

>See? I just like arguing around the edges.

>

>Now. . . are the differences in preamplifiers audible? :-)

>

>Bret

[soundminded]

Warning! Warning! Danger Will Robinson!

For some reason, this preamp has a very bad reputation among many audiophiles. They say it has to do with the limitations of the IC chip (I think the op amps). As a result, it should be very inexpensive on the used market. At the very least, like all Crown equipment, it should be reliable. If you try it, I'd like to know what you think. I've been toying with the idea of trying one myself.

[Wally]

I have a couple of IC-150's and an IC-150A and they sound great....

That having been said, I replaced all the electrolytics and tantalums with low esr electros and black gates. I replaced the line section op amps with Burr Brown op amps. Beefed up the power supply electros X 10.

The sound now is comparable ( but not exactly the same)to my Hafler preamps.

Curiously the phono section in the 150A sounds slightly better than the phono in the 150. The 150 is discrete transistors and the 150A is an op amp. According to hi fi rhetoric the discrete one should sound better. The op amps in the phono section of the 150A are original because the Burr Browns tend to motor boat when subbed for the originals. I put the original op amps back in and they sound great through the Burr Brown line level section.Can't explain why the phono section opamps sound ok but the line section op amps definitely were improved by subbing the Burr Browns. The phono and line section IC's were not the same but they had similar slew rate specs??????

I have an un modded IC150 that has a power supply problem. When I have some time I will fix it and compare the unmodded IC150 against the overhauled one. I'm convinced there is an improvement in sound with the changes I made. I definitely can hear a slight difference betwen the 150 and 150A although I can't characterize it. The 150 phono section is slightly more edgy for lack of a better word. The 150A sounds a bit smoother. Granted the differences are subtle.

I will post when I am able to compare the unmodded with the overhauled IC150.

These are used through a couple of DC300A's. These sound identical and I can't hear much/any difference with the 200wpc Kenwood M2A. Interestingly my McIntosh MC2105 and Hafler DH200 sound different than the above 3. The Hafler does sound a bit fatter or bassier. The MC2105 sounds fatter also and smoother overall. Mind these differences are subtle. I thought the DC300A's were thinner in bass when I first got them, compared to some old receivers that I had but I later came to the conclusion that they did not sound as fat but the low bass seeemed somehow more powerful and deeper. This was only apparent on material with very low frequency bass material. The Mac and the Hafler sound fatter but they also have ver good low end response. I assume that thes differences are attributable to the damping factor of the various amps and their interaction with the speakers. The Mac of course has an autotransformer on the output which probably has no effect on (audible) frequency response or distortion (Mac knows how to make great transformers)but again it is a low damping factor compared to the others and the autoformer probably reacts differently with speakers than does a direct output from a transistor pair.

Again these differences are subtle and I would not bet my life that I could identify each amp under double blind testing.

Anyway I just wanted to defend the good old Crowns. They suffer from utilization of poor components.... tantalums and low slew rate ic's.

Upgrading these (and all electolytics just cuz they're old) does wonders for these old veterans and they're one of the best bargains around because they are extremely well built and very versatile preamps.

regards, Wally

[Wally]

ps

There is less difference in sound quality of the power amps than the preamps. I have sevaral more preamps and they all seem to sound a bit different. Granted subtle differences but more obvious than the power amps. The 2 Japanese preamps I have, a Kenwood and a Yamaha sound identical and cleaner/brighter????? than the US and NAD preamps. My C-28 McIntosh is the most laid back and easiest to listen to for long terms. When compared to the Japanese preamps it sounds dark by comparison yet all the music is there and it meets original specs. Again subtle differences but more obvious than the power amp differences.

Wally

[dynaco_dan]

Bret

I stand by my suggestion for an IC-150 pre-amp among my other suggestions of Dynaco products.

They have been around for a while.

My IC-150 with a DC-300A amp and the AR-LST's has been running for years, with no fault found.

Yes, if someone wants to compare, go ahead, I stopped that decades ago and now I just enjoy my system.

I don't have a IC-150A pre-amp to compare it to as well.

Undoubtably, there is better choices, but at significant prices increases.

Goo luck in thre chase for perfection.

Vern

>Warning! Warning! Danger Will Robinson!

>

>For some reason, this preamp has a very bad reputation among

>many audiophiles. They say it has to do with the limitations

>of the IC chip (I think the op amps). As a result, it should

>be very inexpensive on the used market. At the very least,

>like all Crown equipment, it should be reliable. If you try

>it, I'd like to know what you think. I've been toying with

>the idea of trying one myself.

[Guest Bret]

>I have sevaral more preamps and they all seem to sound a bit different.<

I've never heard two that sounded alike. I haven't heard them all, and maybe like amps there is a very cheap point of diminishing returns.

Evidently when you are dealing with much smaller voltages it's harder to get the input and output to look the same. (through all those controls and stuff, I guess, or maybe power supply noise is harder to isolate)

I haven't had much opportunity to A/B preamps (very little) and back when I did we were using the phono section. Since different cartridges like different impedences, maybe that was the major difference.

Bret

[kkantor]

OK, I'm seriously jealous.

If you ever decide to part with the Crown, I want it for my test bench.

[Pete B]

You are making things very complicated Soundminded, I used a basic scope scratch built by my dad when he was in college, this was after he was in the Navy were he was a radio and radar tech. Music is repetitive so it's really not very hard to see. Use slow sweep to see bass issues and faster for mid/high. It's not perfect but it works. You can use a high power dummy load and really overdrive the amp with music to make it obvious to see, then back off to learn how to catch it, it's not very hard at all.

Pete B.

[Pete B]

Just wondering Wally, are your Paradigms the model with the poly cone mid and two 8" woofers? The newer model had a kevlar or fiberglass mid IIRC. The tweeter is from Vifa I believe and very similar to the popular aluminum 1", my reference also has a variation on this Vifa tweeter.

Also, which model is your Hafler pre amp?

Pete B.

[Pete B]

Pre amps are generally easier to design than power amps because the voltage swings are lower and the load impedance is usually not reactive.

I'd say the line level section is easiest, it's very similar to a very low power, power amp and with the volume all the way up can be viewed as a fixed gain flat frequency response gain block.

There are a few complexities for the phono section and again we should look at the history in this matter.

Jung and Marsh in their PAT-5 rebuild article in Audio Amateur 1978/79 compared tube and OP amp based circuits and found that the frequency response matching had to be better than .25 dB for them to sound the same. Their initial conclusion in A/B tests before matching to this tolerance was that there were very slight differences, and no differences after matching to the tighter tolerance as reported in a follow up letter IIRC. This is probably why the industry moved to much tighter conformance to the RIAA standard over the years.

Tomlinson Holman points out the importance of having the 47 K ohm input impedance be nearly resistive over the full frequency response range in his AES article "NEW FACTORS IN PHONOGRAPH PREAMPLIFIER DESIGN" May 1976 V24 #4. The input impedance is also therefore more linear (less miller capacitance modulation). Component caps should then be used to load the cartridge with the required value. He also points out the importance of high pass filtering to remove low frequency record warp content and builds it into his circuit. Slight variations on this circuit were used in the Advent receiver and the Apt Holman Pre Amp. The circuit should be low noise, have good slew rate, and clean overload recovery. Holman used A/B comparisions to test and confirm his theories.

This was all well understood by the mid to late 1970s.

I'm PB2 in this thread:

http://www.diyaudio.com/forums/showthread.php?threadid=48419

---------------------------------------

Holman Patent Post #10

See patents 4,032,855 and 4,117,412

http://patft.uspto.gov/netahtml/search-bool.html

From: http://www.tech-diy.com/patents_amplifiers.htm

Phonograph preamplifier network with infrasonic cutoff response

4,032,855

Holman, II June 28, 1977

A phonograph preamplifier network with infrasonic cutoff response. The preamplifier network is an active filter configuration with a high gain, high input impedance differential amplifier provided with an RIAA equalization feedback filter network coupled between the amplifier output and inverting input. An RC filter network is coupled between the inverting amplifier input and ground potential to provide a single, low frequency real axis pole. In addition, an input filter feedback network is coupled between the preamplifier input terminal and the non-inverting input of the amplifier, and further bootstrapped to the amplifier inverting input. The network provides a pair of low frequency off-axis complex poles. The RC filter and the input filter feedback networks are adapted to control the infrasonic frequency response of the active filter preamplifier network so that the preamplifier network is characterized by an 18 dB per octave roll-off response at frequencies below a predetermined infrasonic frequency, and a relatively flat response at frequencies in a range adjoining and above that infrasonic frequency.

[Pete B]

I forgot to mention that while the woofer looks like it is corrected for the baffle step in the case of the larger inductor, the midrange does not. So it seems that they did not completely solve the problem. I noticed this some time ago and it is why I've been saying that I might try a slight mod, or complex if needed, to revoice them.

Pete B.

[Wally]

My Studios are the original model that was part of the 'Export' series of 'reference' speakers.

They have 2 8" woofers, a 5" black poly or some other plastic midrange and originally a 1" textile dome tweeter. When the next series of Monitors came out they had aluminum dome tweeters. The domes were interchangeable so I got a set and put them in my tweeters.

I think I'll get another set of textile domes and bring the speakers back to original.... not that they sound bad... but it will bring them back to the original design.

My main Hafler preamp is a model 110 but I also have a 101 that I haven't used much. I also have an APT HOLMAN, 2 Crown IC150's 1 Crown IC150A, A yamaha can't remeber the model, a Kenwood from the Basic series, a NAD preamp tuner 1600 I think, and my favorite a McIntosh C-28.

Power amps are Kenwood M2A, Hafler DH200,2 Crown DC-300A's, and a McIntosh MC2105.

Also have a few integrated amps and numerous receivers.

Wally

[soundminded]

"You are making things very complicated Soundminded"

It's not me, it's my damned textbooks. They keep telling me that at any given frequency real power as opposed to reactive power is I*V*cosine theta where theta is the phase angle between the voltage and the current. In a complex waveform like music I'd need to take the integral of d(I*V*cosine theta)/df over the range of f=0 to f=infinity to get the actual power delivered. This is made complex of course because the impedence of the speaker is strongly a function of frequency. The only actual power which counts is the kinetic energy being converted by moving the cone against whatever resistance it works into plus the power dissipated as resistive heating (U). I've got peak reading LEDs on a couple of my amplifiers but of course they are absolutely worthless. They'll swing as far as I want them to with an input signal, a high gain setting, and no load connected at all. The are just voltmeters calibrated into power levels delivered into a theoretical 8 ohm load. A peak sample and hold meter would do just as well...or poorly. Calculating actual power seems far more complicated to me than just looking at a scope to see where the voltage maxes out.

[Pete B]

This is interesting Soundminded, your insistance on measuring actual power delivered to the load shows that you have a very different view of how a power amp works than what is actually going on. Just because an amp is rated for a certain power does not mean that clipping is when we exceed that power, the rated power is just a number. For any reasonable load on an amp, clipping is a voltage effect because a good amp does not go into current limiting, rather it supplies whatever current is needed to provide the correct voltage until the output "hits the rail". Most solid state amps come to within about 1 to 2 volts of the supply rails, depends if the output stage is darlington emitter follower or CFP, but the difference is small. So what you typically see in what we call clipping is flat tops on the voltage wave form. Most high feedback solid state amps produce very ideal very flat clipping, tube amps usually produce rounded tops then sometimes flat and tilted for whatever reason.

An amp with a poorly designed output stage, or poorly designed protection might distort due to current limiting but most do not call this clipping.

Clipping in amplifiers looks very much like the flat tops in the digital waveforms on my web page.

Pete B.

[soundminded]

>This is interesting Soundminded, your insistance on measuring

>actual power delivered to the load shows that you have a very

>different view of how a power amp works than what is actually

>going on. Just because an amp is rated for a certain power

>does not mean that clipping is when we exceed that power, the

>rated power is just a number.

Very interesting. Perhaps I am confused by what a "watt" is.

>For any reasonable load on an

>amp, clipping is a voltage effect because a good amp does not

>go into current limiting, rather it supplies whatever current

>is needed to provide the correct voltage until the output

>"hits the rail".

Hmm, why don't we just increase the voltage, then we'd get more output. But don't most amplifiers use a B+ of 70.7 volts? If that were the case, they'd all have the same output capabilities. I guess that partly explains why they all sound the same.

>So what you typically see in what we call clipping is

>flat tops on the voltage wave form. Most high feedback solid

>state amps produce very ideal very flat clipping, tube amps

>usually produce rounded tops then sometimes flat and tilted

>for whatever reason.

>

>An amp with a poorly designed output stage, or poorly designed

>protection might distort due to current limiting but most do

>not call this clipping.

>

>Clipping in amplifiers looks very much like the flat tops in

>the digital waveforms on my web page.

>

>Pete B.

Maybe I should call up my old school and get my tuition money back. It's been over 35 years. Do you think it's too late? :-)

[rrcrain]

>>Hmm, why don't we just increase the voltage, then we'd get more >>output. But don't most amplifiers use a B+ of 70.7 volts? If that >>were the case, they'd all have the same output capabilities. I >>guess that partly explains why they all sound the same.

Are you implying that they will sound differently if they use a higher or lower voltage?