Does anyone care to ask an amplifier designer a technical question? My door is open.

What a terrific thread!  Thank you Roger!

I hope you can answer a couple questions that have long baffled me about the sound of some amplifiers - in this case, using my own as example.

Earlier in the thread, you mentioned how the impedance interaction with a speaker is a significant factor in how one amp might sound different than another, depending on the design.

I've always understood (or not understood?) this to mean that if the amps performance varies with impedance swings presented by the speaker, you will start to get contoured sound around those impedance swings - e.g. more or less bass here, more or less highs there etc.  Like a tone control.

And if I have that right, and one is using an amp that is very susceptible to altering the signal based on the impedance character of a speaker, then the "tone control" variations ought to vary as you switch between speakers.  So one speaker may sound fairly neutral (if it doesn't present a tough impedance load with said amp), another may sound rolled off, another boosted in the bass, etc.

The thing is, in my subjective experience, the character of an amplifier (at least the ones I own) tends to seem more constant than that. 


So take my Conrad Johnson Premier 12 tube monoblocks - for reference, measurements here:

https://www.stereophile.com/content/conrad-johnson-premier-twelve-monoblock-amplifier-measurements


I have had a ton of speakers of varying designs - Quad 63s, big Thiel speakers, transmission line bass, reflex, sealed, tough impedance curves, easy ones....

And I've tried numerous amps, including some solid state (Harmon Kardon, Bryston 4BST, and others), and the thing is, the "character" I hear when I implement the CJ amps seems to remain constant: a slightly more rounded sound, that classic bit of "golden glow" in the upper mids/high frequencies,  rounded but taught bass, etc.  I just don't seem to hear the tonal variation I should think may happen.

An even worse example is my  Eico HF81 14W integrated.  I'm sure you know this infamous little "classic" amp.  It sure didn't seem to measure well:

https://www.stereophile.com/content/eico-hf-81-integrated-amplifier-measurements

And, if I understand the implications of those measurements at all, it would suggest the amp would be susceptible to sonic variation, as speaker loads vary.

And yet, the little guy just seems to "sound the same" no matter what speaker they drive: from easy to drive monitors I own, all the way to MBL radialstrahler 121 omnis (a brutal load), to even my big Thiel 3.7s.  They always have that same sound - a sort of lush, thickened, sparkly not "dark" sound, with a swollen bottom end that makes any speaker sound "bigger."  (My hunch had always been this was some "low damping factor" in the performance of the amp that gives it this character across speakers, but now you'll slap me upside the head for that).

So my questions are:

1. Why might I be perceiving that the amps have the same essential character even when used across a wide array of varying speaker loads?

2.  Even more confusing to me:  We are often told that the distortion signature of an amp tends to give it a sound.   But for the most part, this arises only when power is under high demand, clipping etc, correct?  If so, why do the amps seem to retain their specific character no matter what volume I play them at? 


I don't tend to listen loud.  Often topping at around 75 dB or so.  As I understand it, at least when I'm not listening to music with dramatic dynamics, most amps should essentially be cruising in terms of distortions.  So if they are not going in to the type of distortion that starts to distinguish amp distortion profiles, why do they still sound different even at lower volume levels? All those "tubey" characteristics seem to be there no matter the volume.


Now, of course a confounding variable here is listener bias.  But, if I'm hearing what I think I hear, I'd appreciate your unraveling my confusion.
Thanks!

Since you listen at such low levels both amps are playing no power at all and thus both have very little distortion.

Are there some yes/no questions I could answer. It hard for me to see exactly what you are getting at.

Thanks for the reply!

I’m still trying to understand:

If my amps are being run at levels that do not bring on distortion, why do they still have that classic "tube-amp" character even at those low listening levels? If it’s not the clipping characteristics that are coming in to play...what is it that produces that classic tube sound as I described it?

You write that the low damping factor will come in to play across various speakers, so it seems that’s at least part of the factor. But does it explain everything? I’ve always associated low damping factor mostly with audible effects in the bass region. But with the tube amps there is also a sort of thickening and slightly softening of the mids and upper frequencies - it seems an across the board effect on the sound, not just in the lower frequencies. What other deviations may be coming in to play to alter the sound, even at low volume levels?

Also, I thought that impedance difference in speakers could cause audible issues in the high end as well - e.g. audibly rolled of highs etc.Which never really seems to occur that I can detect, across a broad range of speakers with very different impedance/sensitivity profiles.

If you can get a low impedance amp then you can hear what the speaker designer intended you to hear.

Ha! You trying to nudge me towards accuracy? How dare you! ;-)I’m more concerned with ending up with the sound I like, not in satisfying whatever the speaker designer may like. Normally when I audition a speaker it’s hooked up to solid state amps and I can get a very good indication as to the general sound and character of the speaker. Then I just nudge it a bit more in the direction I like. I’ve found the CJ amps preserve what I like about a speaker, while adding a bit more of what I like in to the equation.


As mentioned, I’ve used amps like the Bryston 4B ST, which would provide the type of low impedance/damping performance I presume you are alluding to. Every time I’d switch to the Bryston I’d hear that slightly more tight, taught, precise sound and think "well, that does some things differently and strikes me as more ’accurate.’ But I always found over time the whole system still had a sonic signature anyway, and I found the sound overall more organic, easeful and believable with my tube amps.

Such is personal preference.

Thanks again.

Thanks again, Roger.

Cary has had notoriously bad measuring amplifiers for as long as I can remember. They have long been the poster-boy amps when people want to argue the "measures awful, but sounds great" stance. Personally, it’s been far too long since I last heard a Cary amp for me to have an opinion on the sonic performance.

I just read the Stereophile review of your amp. Congratulations, it really does impress upon the reader that you know what you are doing!To see JA actually impressed with the measurements of a tube amp is really something.

As for this comment you made to someone else:

I would like someone to tell me why spend big bucks on cone speakers when there are better technologies.

I’m wondering which "better technologies" you are referring to.

Do I infer correctly from your comment to me about the QUAD 57 vs the Alan Jones monitor, that you are speaking of, for instance, electrostatic speakers?

If so, I can tell you why I prefer cone speakers.

I first fell in love with electrostatics in the 90’s and first owned the Quad ESL 63s. As did another audio pal. The shock of not hearing any box sound, and that amazing transparency and "hearing in to the recording" sensation were at first intoxicating. But after a while I found the sound too disembodied, too ghostly, like peering through a window in to another room where the music was happening, but it wasn’t "moving air" in the room I occupied. When I’d play my little old Thiel 02 monitors there was such a difference in palpability, aliveness and "thereness" that it just re-enforced what I was missing. That was the case even after I added the Gradient dipole subwoofers to the Quads. Still among the best sub/panel matches I’ve heard.


I still love to "visit" electrostatics (the Quad ESL 57s being my favorite), for their unique qualities. But every time I listen to an electrostatic, of any make, I come away happy to have moved on to cone speakers.That includes every hybrid I’ve ever heard: The cones seem to add some body, but only within their frequency range. As the frequencies climb up to where they are handled by the panel, the sound character changes to my ears to that ghostly quality, so I am always aware of this discontinuity.

I’m not sure if this problem is solvable. Though, one brand I find intriguing is the JansZen speakers, using the electrostatic panels in more of a sealed box design. I wonder if those might maintain the palpabiity and body in the sound, but I’ve never heard them.

QUESTION: Roger (or Ralph?)...

Question about the effects of different impedance settings and phono cartridges.

I’m a newbie with high end turntables (just replaced my old turntable with a much better one). My phono stage is convenient in that it allows easy access to changing the impedance levels from the front panel. I actually enjoy playing with the impedance settings to alter the sound to taste depending on what I want.

Mine is an MC cartridge and I find an impedance setting of 100 Ohm to be just about right in terms of sounding tonally accurate (like my digital source).

I won’t be telling anyone here what they don’t know when I mention that as I set it to higher impedances, the sound gets brighter and more taught (to more "pinched" and less relaxed/natural sounding towards the high end of the impedance settings). And the sound becomes darker (more rolled off in the highs), richer, more spacious and the bass seems to bloom a bit more in size and lose some tightness. I actually often enjoy just dipping down the impedance from the 100 Ohm setting to the 33 Ohm setting, to enjoy the slightly richer sound sometimes.

So my question is: What exactly is happening to cause the type of sonic changes on hears when changing impedance settings for a cartridge?

My know-nothing layman’s hunch is that it’s similar to how speaker impedance interacts with certain tube amps, where some combinations contour the frequency response...and (sorry for the word) damping factor? (The changes in the bass in lower impedances do give me that "lower damping factor in the bass" vibe).

Thanks..

Ralph,
Thanks.
I didn't totally follow all that, but that's due to my level of ignorance. 

Roger, thank you for the reply about cartridge impedance.

Actually, the talk of switchers raises another question I'd like to direct to Robert:

I have more than one amp I like to use for my system.  It's a minor pain to switch the cables, but it sure would be nice to have a switcher where I could switch between amplifiers to the main stereo speakers.  (So interconnects would lead from one output of my preamp to my main amplifiers, and out the other output to a second amp.  Depending on which amp I wanted to use I'd just flip a switch.


At one point I did a bit of research and saw some candidates, but for the most part they looked awfully cheap, which left me hesitant.

Would you say a fully transparent switcher of the type I'm describing could be built?

Thanks for the note, Al!

@ramtubes

You’re gonna hate me: My amps are Conrad Johnson Premier 12 monoblocks and an old Eico HF81.

BTW, since you asked about hearing "the other side" for power cords:

I was cured of power-cord-fever early on. I had been given a selection of Shunyata power cords to try, from their least expensive to very expensive. I didn’t think I heard any difference between the less expensive Shunyata cables and my 15 dollar power cable (On CD players, etc). But I thought the most expensive cable seemed to obviously change the sound. (Darker, smoother, more lush). To double-check I had a pal help me do a blind test between that cable and the 15 dollar cable. Once I didn’t know which cable was being used, all the "obvious" sonic differences I thought I was hearing vanished and I couldn’t tell them apart. Saved a bunch of money there! I haven’t worried about pricey cables since. (I’ve gone on to blind test other components, sometime identifying differences, sometimes not).

@ramtubes

First, the concept of your building the type of switch box I mentioned is very intriguing.  I'm not sure the idea still fits well with my system, which has become more complex (I'm introducing subwoofers, crossover etc).But I will certainly cogitate on the idea.

Also, love your idea for building switch boxes to text cables etc!  If the timing were right financially for me, I'd likely take you up on that (just out of my own interest.  I'm far from sold on the worth of high end cables, but I do have access to a bunch and it would be fun to test under more ergonomic circumstances, fast switching, etc).

@ramtubes

For those who will likely disagree: If burn in exists in these devices why did we not know about it until recently. I find no references to burn in in the 50s 60s 70s.. when did it start?

And if burn in occurs in cabling, why don’t we see people producing these measurable results between a new and burned in cable? The suspicious thing is that when most cable manufacturers are hyping either the technical reasons why their cables produce better sound, or telling you the cables need burn in, they are always appealing to some objective, technical phenomena whose existence is known because it was measurable. "Here’s a technical problem with cables you need to know about, that we have solved via our manufacturing process!"

But when they tout that they have "solved" one or more objective technical problems in cable design, they typically don’t demonstrate they’ve solved the problem in any measurable way. Instead, the results go straight to hype, marketing and the subjective impressions of audiophiles and reviewers. Same with burn in. Funny that.

As I’ve mentioned before in such discussions, audiophiles think everything changes substantially with "burn in," fuses, resistors, cables. And yet companies like Vishay and others - responsible for selling cabling, resistors etc to professional industries - industrial, computer, and incredibly spec-sensitive applications in avionics, military and aerospace design - don’t go on about "burn in." If the specs actually changed that much over time of a cable or resistor or fuse from when it was delivered new to in-use, this is something customers employing them in sensitive applications would need to know (and it would obviously be very problematic if those industries could not rely on a product actually meeting the stated specs, out of the gate).

And, again, you see (as far as I know) none of this "please burn our product in for 100 hours before application, as the specs will change" when the rubber hits the road, when you sell these things to engineers who can identify B.S. from marketing.

@ramtubes

I could really use some help betting a better grasp of amplifier/speaker interaction. Specifically, in what sense a speaker is "easy to drive" for an amplifier.

This seems to generally relate to two parameters:

1. Speaker sensitivity
2. Speaker impedance (and phase angles etc).

I’ve seen speakers with higher sensitivity but lower or wilder impedance termed "easy to drive" and speakers with lowish sensitivity but higher and smoother impedance being "easy to drive." So I’m trying to get a grasp on what it means...in practical and possibly sonic terms...when a speaker is "easy to drive"for an amplifier and what you get when trading off sensitivity vs smooth impedance.

To turn it in to a practical example:

I owned the Thiel 3.7 speakers. Here are the Stereophile measurements:

https://www.stereophile.com/content/thiel-cs37-loudspeaker-measurements

Note the 90.7dB sensitivity, but with it seems a fairly challenging impedance.

Then take the Joseph Audio Perspective speakers (a speaker I’m considering):

https://www.stereophile.com/content/joseph-audio-perspective-loudspeaker-measurements

JA measured a low 84dB sensitivity but with a higher/smoother impedance he deemed them "a very easy load for the partnering amplifier to drive."

So I’m trying to understand the practical/sonic consequences - higher sensitivity, vs lower sensitivity but an easier impedance load. What does this mean for the power requirements, or type of power for each?

I have Conrad Johnson 140Wside tube monoblocks


https://www.stereophile.com/content/conrad-johnson-premier-twelve-monoblock-amplifier-measurements


And I’m wondering which of those speakers would be "easier to drive" with the CJ amps, why, and in what sense.

(FWIW: the CJ amps seemed to drive my Thiel 3.7s great: tight, non-flabby base, etc).

Thanks for any wisdom you can impart!

Thanks atmosphere. 


(I'm still interested in ramtube's view as well).

My room is on the smaller side: 15' x 13' wide and I listen at modest volume - typically 70 db to maybe 75, probably 90 at the most if I crank it more to listen from down the hall.

I also wonder how the introduction of a subwoofer alters the load to an amplifier.  So say if you have a powered sub and you crossover to the sub from the mains at maybe 80 or 60 Hz.  Once one has off-loaded much of the low frequencies to the sub, I wonder how much the main amp "sees" and if that, in effect, is like adding a more powerful amp in to the equation. 

Mr. Gabriel Claimed:
 
“As stated in #1 the local current and electromagnetic effects directly affect the sonic performance of the component.”




Then you’d the no it would be a cinch for Gabriel to supply measured results showing the output of an audio device is changed when using his cables.

Funny how that is conspicuously missing.

Teo wrote: 

—-“Prof uses the measurement canard which is as old as it gets and is well proven to be ineffective when it comes to human hearing at it's limits - which is the subject at hand.”

Ah that’s right.  Human hearing is more sensitive than our measuring instruments.
Wait...what did we need those instruments for again?  Oh yes, to extend our detection capabilities beyond the limitations of our senses.   Heard any 26k sounds recently Teo?  That’s ok - instruments can easily detect things you can’t hear. 

Of course instruments can’t detect things you imagine.  They really suck at that, admittedly.

— “Interestingly enough, his entire job rides on doing things that are either unmeasurable or so close to being unmeasurable that it is not worth bothering to try. “

Wha??  I work in film post production sound.  What I’m doing is being measured all day long.  I want to reduce a sound or boost it, or eq, it’s all measurable and measured!   

—“Hoisted by his own petard. (modern translation: he blew himself up)”

You have no idea what you are talking about.  I suggest stepping away from the bong before posting :-)

ramtubes 

thanks for the info on tube amps/ speakers!!

Question:

What type of sonic issues occur as tubes get old? 


I had a tube in my CJ power amp fail, and the local shop said it was getting time to replace all the tubes.  But what is likely to happen if they are just left and keep on running?  Is it eventual failure?  Or does the sound start to alter in any way? Frequency response?  Dynamics, whatever?

I have the same question for my CJ preamp.  I know one aspect of tubes getting old: it now has a raised background "hiss" that it didn't have years ago when I bought it (so I've just bought replacement tubes).  But other than possible tube noise floor raising...is the actual sound likely to alter in any way as tubes age?

Thanks.

Thanks atmosphere!!
I'm being a bit lazy in getting around to changing the tubes in my CJ pre, but I'll see if I can note any difference other than (hopefully) lowering of noise floor.