John Curl's Blowtorch preamplifier part III

[benb]

I would love to see some rigor applied to that number. It is of course multi-dimensional, what about the "5%" that prefer one phase or the other of 2nd harmonic distortion. I find it ironic for the Pass Labs approach to be mentioned recently when only a few weeks ago Dick sort of damned it with faint praise.

I was just reading the Linkwitz page mentioned here and quoted in an earlier post:

...
I quoted Linkwitz comments about IMD in speakers resulting in a a sort of hash around quiet sounds, particularly when playing complex music.

... and it looks like he damned second harmonic distortion with no praise at all!

I cannot emphasize enough, that anytime when a device introduces harmonic distortion, it will generate intermodulation distortion, when more than one tone is involved. Some seem to think that a little bit of 2nd harmonic distortion, as often generated by tube equipment, has a pleasing effect, because it enriches the natural even harmonics of acoustic instruments. It will also generate non-harmonic intermodulation, and has little to do with accurate sound reproduction or even generating the illusion of a real sound. Instead it imparts a euphonic sameness to all sounds.

Frontiers

 

[Chris Hornbeck]

Loudspeaker IM distortion actually differs from amplifier IM distortion. The axial movement of the radiating piston causes time modulation of all other signals on that piston. This is even true for an ideally linear translation from electricity to movement. For some cases the FM dominates the IM distortion.

All good fortune,
Chris

AR XA (~ 1961)
I think the designer was Edgar Villchur

I had also believed this until recently, but lately have been reading otherwise. These folks must surely be gone now, so I guess it doesn't matter to them.

I still use parts from my father's XA in my "DIY" turntable. George Merrill pressed in a new fancy spindle bearing to match his polymer subchassis, and I run his 3 Watt (as opposed to the 1.5 Watt original*) clock motor and his lead platter mat. Rega arm. But it's still my father's turntable. Like the story of my grandfather's ax - "the head's been replaced twice and the handle three times, but it's still my grandfather's ax."

*The very first AR's had two motors; one just to get it started!

Always the best fortune,
Chris

 

[rayma]

I had also believed this until recently, but lately have been reading otherwise.

A Glorious Time: AR's Edgar Villchur and Roy Allison Villchur Part 2 | Stereophile.com

Lander: Tell us about the genesis of the legendary AR turntable, which Roy told me was your baby.

Villchur: I wanted to make a complete system, and I thought the next thing should be a turntable, because our forte was mechanical rather than electronic. I hired a consultant for the job, but about a year and a half and maybe $25,000 later, what he had was useless. So I had to do it, and I did almost all of it in my lab in Woodstock in the late '50s and early '60s, just after the AR-3. We thought we could bring it out at $58, but that was an error. Not too long afterward, we had to raise it to $78—complete, with everything but a cartridge. By that time, we had a reputation. When we announced we were bringing out a turntable, we had orders for thousands.

 

[31697B]

Got Bass ?

Fried Hockey Boogie. by Canned Heat.

Boogie with Canned Heat. BenchMark DAC-3 vol at about 5pm position.

Crown -5000's set at -4.5dB

JBL M2' pair set at KILL.

...... and don't forget to Boogie.

-RNM

 

[Max Headroom]

I can see how what I said could result in Mark's reverb tails not being as clearly defined as if there was no hash caused by IMD I quoted Linkwitz comments about IMD in speakers resulting in a a sort of hash around quiet sounds, particularly when playing complex music. I find the lifting of this hash occurs when better playback electronics are employed - lower IMD?

Better electronics, also better load, ie flat impedance cable/speaker load will give better black and better reverb tails. Any junk in the source recording will excite noise behaviours in less than optimal systems, this means from digital interface/decoder/dac and on through to the speakers. Applying electric/magnetic shielding/absorption/loading to the complete board as in the DAC-3 mod will show up as modified dynamic noise floor which may be picked up as subjectively different sound.

There are all kinds of modifiers otherwise known as 'voicing'. For vinyl sound signature out of digital audio just sacrifice a vinyl record and shape it to cover pcb and packages as per the DAC-3 mod.....different vinyls will cause different sounds. Ever notice that a stack of records on a preamp on top the turntable or amp/preamp or speakers changes the sound....sure you did but it's not just the mass/damping at play, there are electrical/magnetic properties involved also......a bit like a standard house brick and a VPI Brick weigh about the same but they don't sound the same.

Dan.

 

[johnego]

Physics has been developed along with assumptions. Often, ime, the difference between those who understand Physics better and those who understand less well is in the understanding of these assumptions. But for sure, those who don't understand Physics (or ignore it) will not understand.

 

[gpapag]

I had also believed this until recently, but lately have been reading otherwise. These folks must surely be gone now, so I guess it doesn't matter to them.

Unless he was lying
YouTube

a bit like a standard house brick and a VPI Brick weigh about the same but they don't sound the same.

Dan, have you tried comparing it to placing a 5 lbs. 6 oz sandbag (OK, sample different seashores )?
VPI Magic Brick (Set of 2)-Elusive Disc

George

 

[Max Headroom]

Dan, have you tried comparing it to placing a 5 lbs. 6 oz sandbag (OK, sample different seashores )?
VPI Magic Brick (Set of 2)-Elusive Disc

Not directly but according to prior exp I am certain of outcome according to some sand types, there is an infinite choice available.
Go ahead and try some fun new sounds.


Dan.

 

[mmerrill99]

Loudspeaker IM distortion actually differs from amplifier IM distortion. The axial movement of the radiating piston causes time modulation of all other signals on that piston. This is even true for an ideally linear translation from electricity to movement. For some cases the FM dominates the IM distortion.


All good fortune,
Chris

Thanks Chris - are you referring to the Doppler effect where "a loudspeaker diaphragm vibrating at two frequencies, for example at 32 and 1000 Hz, would give rise to FM distortion."?

I was just reading the Linkwitz page mentioned here and quoted in an earlier post:

... and it looks like he damned second harmonic distortion with no praise at all!

Frontiers

Indeed he does state that but then if you read Rod Elliott here you come across another complicating factor - that symmetrical & asymmetrical waveforms behave differently with regard to IMD
"that sum and difference frequencies are not created when symmetrical distortion is applied to a complex (but symmetrical) waveform."

"just how I came across this intriguing phenomenon, it was while I was testing the hypothesis that even-order distortion sounds 'nicer' than odd-order distortion. In the process, I was listening to two tones and heard the difference frequency disappear when I switched from asymmetrical to symmetrical clipping. "That's interesting" I thought, "

 

[gpauk]

Hi,

There are a few things that I wish to say before I finally go off elsewhere.

I left the other day not because I was “bullied into submission”, I left due to feeling disgusted by my own debasement after realising that by trying to help, I had in fact become part of the problem. My detractors are right, other than my own idiosyncratic perspective, I have really nothing much to offer here.

Irony is that a lot of members actually like reading my posts. So much so, that two members are going out of their way to help me - so good to feel wanted and appreciated. But sadly, not here.

The only reason this thread exists without overt moderation is to keep the rest of the forum from becoming contaminated. So yes I agree, it was definitely time to move on. I am not indispensable - you can go ahead and sort yourselves out perfectly well without the likes of me around.

Whether you hear it or not, the world is always full of music.

Good luck ToS

Get a grip ToS, and please hang around. Post as and when you want. You add some interest and fun when you do. There's really no need to leave forever...

Its probably going to happen, and soon. The catch is that the dac isn't really $300. Its a $200 dac and $4,000 computer feeding it to make it work. The real price is closer to $4,200, but the good news is that the computer can be used for other tasks too.

Or more likely and just as good, a $50 computer (eg Pi 4) driving a $200 dac.

 

[scottjoplin]

Indeed he does state that but then if you read Rod Elliott here you come across another complicating factor - that symmetrical & asymmetrical waveforms behave differently with regard to IMD
"that sum and difference frequencies are not created when symmetrical distortion is applied to a complex (but symmetrical) waveform."

"just how I came across this intriguing phenomenon, it was while I was testing the hypothesis that even-order distortion sounds 'nicer' than odd-order distortion. In the process, I was listening to two tones and heard the difference frequency disappear when I switched from asymmetrical to symmetrical clipping. "That's interesting" I thought, "

Interesting. Not an issue in an accurate amp though.

 

[gpauk]

It's worth restating that if you haven't read this article, you should, very interesting.

PURIFI Audio and the Audiophile Style reader's Q&A with Lars Risbo & Bruno Putzeys - Bits and Bytes - Audiophile Style

Be interesting to hear JN's comments on the magnetics, too.

And - it'll be really interesting to see how good their speakers are, when they arrive...

And, lastly, re driver distortions, tri amp solutions are surely better than passive crossovers.... I may even get mine finished one day!

 

[Max Headroom]

Or more likely and just as good, a $50 computer (eg Pi 4) driving a $200 dac.

Free Win 7 laptop, ASIO and $40.00 DAC works for me.
Netbook is good if not better because no fan noise.


Dan.

 

[DF96]

Rod Elliot quoted by mmerrill99:

"that sum and difference frequencies are not created when symmetrical distortion is applied to a complex (but symmetrical) waveform."

"just how I came across this intriguing phenomenon, it was while I was testing the hypothesis that even-order distortion sounds 'nicer' than odd-order distortion. In the process, I was listening to two tones and heard the difference frequency disappear when I switched from asymmetrical to symmetrical clipping. "That's interesting" I thought, "

I am surprised that Rod did not know this. Sum and difference frequencies come from even-order distortion, which is asymmetric. Odd-order distortion (symmetric) causes bandwidth expansion (e.g. 10 and 11kHz inputs causes 9 and 12kHz IM to appear in the output).

A symmetric waveform has only odd-order harmonics and IM. An asymmetric waveform has even-order components, and may or may not have odd-order components too.

 

[mmerrill99]

Interesting. Not an issue in an accurate amp though.

OK, that's a wide, all encompassing statement - do you define an "accurate amp" that is natural sounding like the Purifi (& shows very low IMD) or do you define it as one that shows a higher level of IMD than the Purifi or AHB2? What type of test signals are used for these IMD plots - where does symmetrical Vs asymmetrical test signals fit into the IMD products in the plots?

It's worth reading that Rod Elliott article

With a symmetrical input waveform, symmetrical distortion does not create the sum and difference frequencies. At least, it doesn't generate a significant level at either the sum or difference frequency, and as noted below, each can be 75dB below the level that's created by an equivalent amount of asymmetrical distortion. For reasons that are very unclear to me, I can find no reference to this phenomenon in any text that I've seen so far other than the one described above. Almost every discussion you see that discusses distortion, intermodulation, and sum and difference frequencies implies (though very rarely stated) that the distortion mechanism and waveform is inconsequential. It's not, and in fact makes a big difference to the behaviour.

 

[scottjoplin]

I define an accurate amp as one that doesn't distort the signal. Feedback, for instance, reduces IMD.

 

[mmerrill99]

I define an accurate amp as one that doesn't distort the signal.

All amps distort the signal - I guess you must be talking about some mythical not-yet-created amp?

Feedback, for instance, reduces IMD.

Yep.

 

[scottjoplin]

If you want to pedantic, of course

 

[mmerrill99]

If you want to pedantic, of course

It's not just pedantry - there's a serious point here.

All amps distort to varying degrees in varying ways. What you mean to say is that the distortions produced by your "accurate amp" are considered below the threshold of audibility which is a far different definition to just "accurate"

So now you have to evaluate what is the audibility threshold for various distortion types, with what complex signals do we measure such thresholds, etc

Unfortunately it does come back to auditory perception & psychoacoustics, no matter how much people want to avoid this elephant in the room.

That's why I quoted Bruno & his post on ASR which indicated that a great deal of the natural & relaxed sound from Purifi amp was due to the very low IMD distortions - much lower than would be considered the audible threshold for such distortion.

So my question was about this factor - if indeed, IMD is the determining factor, do we need to re-examine audible thresholds for IMD or do we need a different way of measuring such distortions - or do we need to do both?

You sequed into the old amp Vs speaker distortion debate/argument & I was hoping we could get beyond that

Seeing as my every word is rejected on here let me requote Bruno

He also has this definition about amp accuracy which is based on listening

The output signal should be indistinguishable, by ear, from the input signal. I’m stressing the “by ear” thing here because we as audio nerds, and that includes all interviewers here, are often conflicted about what it means to measure and what it means to listen. For me, measurements are lab tools. Measurements tell you technically what your circuit is doing. Before you heat up your soldering iron to, say, change a resistor, you need to have something numerical to point to the right resistance value. Ears don’t help there. Your ear should be used instead to figure out what to measure so as to make those measurements meaningful for sound quality.

What I also need to get off my chest here is the confusion between accuracy and clinical “analytical” sound. What’s implied there is that you have to choose between accuracy and joy. That runs completely counter to my experience. When something sounds “clinical” or “analytical” it always turns out to be totally inaccurate. Overhyped highs and thin mids have nothing to do with accuracy. An accurate system will sound warm, lush and emotionally engaging provided that these characteristics are actually in the recording. Low distortion sound can be incredibly moving.

In vindication of that POV we've now seen more than one enthousiastic "subjective" reviews of the 1ET400A go up expressing delight that we have both great measurements and great sound (as if that were a contradiction). I'd like to state here that in our company, as listeners we are fanatic about sound and as engineers we are fanatic about measured results. The trick is to pick a set of measurements that have a modicum of relevance to psychoacoustics (in the case of amplifiers, accepting that hearing goes south beyond 20kHz and that music is more than sinewaves).

If you test a magnetic core with a sinewave the distortion looks a little like soft clipping, perfectly benign. But what came out of tests on iron parts in loudspeakers was that hysteresis has a long term memory so you can get intermodulation between things that happen now and things that happened 10 minutes ago. With music this distortion sounds like half correlated noise.

And here's his partner, Lars Risbo (just for the people who only listen to authority figures - he's a doctor in Engineering & founder of Tocatto Tech - 30 US patents to his name),going out on a limb (something I do all the time)

Lars: I’m going out on a limb here but maybe there is a wider class of “memory” distortion effects that are completely ignored when you do sine wave tests. Why shouldn’t similar effects occur in capacitors? And thermal effects in class AB amplifiers are also notable for being very audible without showing up on a THD plot.

 

[DF96]

Rod Elliot:

With a symmetrical input waveform, symmetrical distortion does not create the sum and difference frequencies. At least, it doesn't generate a significant level at either the sum or difference frequency, and as noted below, each can be 75dB below the level that's created by an equivalent amount of asymmetrical distortion. For reasons that are very unclear to me, I can find no reference to this phenomenon in any text that I've seen so far other than the one described above.

I find this really surprising. I guess it just shows that everyone has blind spots. I assume the reason he hasn't found it explicitly in textbooks is that the authors think this is so obvious that it doesn't need to be said. Elementary algebra tells us that even-order functions are symmetric and so produce asymmetry when combined with the original waveform.