What an OTL is, and why you should care

[Phantom-Audio]

Part of this is speed and part of this is what kind of distortion is being generated. The trick with distortion is to do everything you can to make sure the circuit is linear. What we've done for decades on now in our amps that is a bit unusual (other than the fact that the amps are OTLs) in that they are fully differential and balanced from input to output. This causes the even ordered harmonics to cancel at each stage of gain throughout the amp. Because this is the case distortion isn't compounded to the degree that it is in a single-ended circuit.

Because distortion isn't compounded as much, as the order of the distortion harmonic is increased, its amplitude falls off at a faster rate than in a single-ended circuit. In addition the 3rd harmonic is the primary distortion component. It is treated by the ear the same as the 2nd (IOW its innocuous and contributes to 'bloom' and 'warmth') and is present at a much lower level than the 2nd is in a single-ended circuit. Because it is significantly higher than the succeeding orders though, it masks them from the ear. So the amp sounds smooth on that account, and because the distortion is inherently lower, also more neutral.

The output section is exceedingly fast- it has linearity to well past 20MHz. We've actually experimented using versions of the circuit as linear RF amplifiers! The bandwidth is intentionally limited by the driver circuit. In a nutshell the amp is very fast in terms of risetime; that in combination with field coil drivers makes for very high speed reproduction (field coil drivers can have speeds similar to ESLs and for the same reason- the motive field does not sag when the driver is asked to do work) that is low distortion as well.

Because the amp runs zero feedback, to have low phase shift it is essential that it be wide bandwidth. So it has unmeasurable squarewave tilt at 20Hz (IOW no phase shift at 20Hz which can rob an amplifier of impact, owing to 2Hz full power response) and less than 1degree of phase shift at 20KHz as well. This is important in two ways- the ear can percieve phase shift of a group of frequencies (although it cannot if only a single frequency) because it uses phase information to help ascertain the soundstage. The other way the ear perceives phase shift is as a tonality; a rolloff close to 20KHz can cause the amp to sound dark. Filter theory tells us why; the phase shift components when dealing with this kind of rolloff can be detected to 1/10th the cutoff frequency or 10x the cutoff frequency depending on which end of the spectrum we're talking about.

Ralph,

why does the volume aspect always feel strange, It never feels loud enough even though the room is hitting 100db ++ i

 

[tima]

Maybe my memory is slipping .... I thought John Wolff's company out of Michigan was Classic Audio Reproductions (CAR). Apparently that changed - recently? And his Web site is no longer active, having taken it to face book? Please correct me if my info is incorrect.

 

[Phantom-Audio]

Maybe my memory is slipping .... I thought John Wolff's company out of Michigan was Classic Audio Reproductions (CAR). Apparently that changed - recently? And his Web site is no longer active, having taken it to face book? Please correct me if my info is incorrect.

http://classicaudioloudspeakers.com/

Its still Active.

 

[tima]

http://classicaudioloudspeakers.com/

Its still Active.

Thanks I am aware of that url. Using my normal Firefox browser the link is redirected, however, all I see is a square blue box with no information. Okay - I tried it with Internet Explorer and see the site. Someone should tell John his Web designer is not doing him good service.

 

[Phantom-Audio]

Told him already, he also needs to get his products done by a professional photographer. his Photos look terrible and nothing like the real thing.

 

[DonH50]

Lack of distortion will allow a system to play much louder than you expect. Without the amplifier clipping and speakers distorting to provide aural cues it is easy to attain ear-damaging levels without realizing it. One of my favorite demos over the years was to raise the volume to the 80+ dB average level (100~110 dB peaks) and watch while new listeners listened wide-eyed, only realizing how loud it was when they tried to tell me how good it sounded and couldn't hear themselves.

Tube amplifiers have softer saturation (lower distortion knee) as you approach clipping so tend to sound "louder" than a similar-powered SS amplifier. This is partly due to their intrinsic properties (factorial, rather than exponential, distortion series so distortion rises slower for tubes compared to bipolar transistors) and tendency to use lower feedback (resulting in softer rise in distortion with power level rather than the sharp upward step often seen with SS designs).

IME/IMO - Don

 

[DonH50]

Don Classic makes an annual appearance AT CAF. Driven by atma sphere it might your mind about tube amp colorations.

Missed this, sorry Greg, 14+ hour workdays make for random and missed posts...

Tube and SS components have their pros and cons. I loved my tube/hybrid amps (ARC D79/Counterpoint 220) on my old Maggies and feel that was a good match. The D79 on my Infinity Q2's helped take some of the edge off the EMIT's but did not provide as solid deep bass, and I did not think it handled the load of the old B&W 801s (forget what flavor) as well as a SS amp. The 801's were not mine, rather at the store I worked, so I had less time auditioning them.

I would love to hear an Atma-Sphere amp. Probably not in the cards, but I have for many years wanted to attend RMAF; maybe the stars will align someday when Ralph and I are both there. I wonder how it would drive my current speakers (Revel Salon2).

 

[Gregadd]

,,, I ,
Don I was not suggesting you don't like tube amps. My point how much atma-spher differs from classic tube amps. You might also try VAC.
i don't know if Ralph makes the show circuit. His amp was part of the Classic room.
Just as an aside don't you live in Colorado? Assuming you have the time it's not far compared to the east coast. Maybe you can take one of your classes and call it a business expense.

 

[DonH50]

,,, I ,
Don I was not suggesting you don't like tube amps. My point how much atma-spher differs from classic tube amps. You might also try VAC.
Classic room don't know if Ralph makes the show circuit. His Amp was part of the Classic room.
Just as an aside don't you live in Colorado? Assuming you have the timeit's not far compared to the east coast. Maybe you can take one of your classes and call it a business expense.

Got it. Given they are fully differential and OTL I completely agree!

Don't think my company would pay for a class and we are still on travel restrictions. It's a thought though, if I can wrangle a way there. Between Life and Work stuff have not taught one recently, either... Maybe when I retire; a couple of local professors have said they'd like to have me back to lecture now and then, and I used to give the odd lecture across the country.

 

[Atmasphere]

But that can also be true of measurements; since test equipment can resolve better than we can hear, then choosing an amp with 0.001% THD over one with 0.01% at rated power, assuming rated power is the same, is arguably an exercise in "subjective preference".

The trick is to know how the distortion signature is laid out. In a nutshell its essential that the lower orders mask the higher orders, regardless of the actual THD. This bit is poorly understood which is why the super low THD values may not result in a pleasant sounding amp.

why does the volume aspect always feel strange, It never feels loud enough even though the room is hitting 100db ++ i

See the post below:

Lack of distortion will allow a system to play much louder than you expect. Without the amplifier clipping and speakers distorting to provide aural cues it is easy to attain ear-damaging levels without realizing it. One of my favorite demos over the years was to raise the volume to the 80+ dB average level (100~110 dB peaks) and watch while new listeners listened wide-eyed, only realizing how loud it was when they tried to tell me how good it sounded and couldn't hear themselves.

Tube amplifiers have softer saturation (lower distortion knee) as you approach clipping so tend to sound "louder" than a similar-powered SS amplifier. This is partly due to their intrinsic properties (factorial, rather than exponential, distortion series so distortion rises slower for tubes compared to bipolar transistors) and tendency to use lower feedback (resulting in softer rise in distortion with power level rather than the sharp upward step often seen with SS designs).

IME/IMO - Don

+1 To which I might add- the lack of higher ordered harmonics and IMD.

We're never going to agree but let me simply answer by asking a few questions.

- As a data point of preference, how many audiophiles in WBF own Classic Audio Loudspeakers and how many own the brands I stated earlier? And since many of these audiophile could own either why aren't they choosing Classic Audio Loudspeakers?

- What modern SS amps are you referring that "sound bright and harsh," because I can name dozens that don't and have exemplary low frequency control.

- Last but not least: What your not asking is - what is the detriment to speakers with 4 ohms impedance if they were designed to be 16 ohms? And if the benefit were so simple, why isn't everyone doing it?

Its probably because most audiophiles haven't heard the CALs (although there are a good number of other speakers that are higher impedance). You know as well as I do that many people buy through brand recognition rather than how things actually sound- or perform. Somehow your question (meant as a bit of a proof by my surmise) sounds a bit like a Bandwagon fallacy. So while we may not agree, I hope on this bit we can agree that simply because many people have them doesn't make them 'right'. It simply means that many people have them.

Its not good politics to state the flaws of other manufacturers - the area I make an exception regards when there is a a balanced line product that doesn't support AES48 and there altogether far too many of those in high end audio.

Again, the 4 ohm speakers by themselves are not bad, the problem is every amplifier made has higher distortion driving them. In high end audio its usually all about getting away from distortion. I find this a bit ironic- its common to get push-back from people that own solid state gear on this load impedance topic, yet one of the reasons those people go with solid state is the claim that its lower distortion and thus more neutral. Yet all amps respond to the load impedance with higher distortion so those people aren't getting the best performance out of their equipment- their amplifier investment dollar isn't being fully realized.

To be clear on one thing- I'm not anti-solid state; we are working on a class D amp of our own design (we were awarded a patent in the field about a year and a half ago). One thing about the measurements- everything I've mentioned about how amps can sound harsh and bright can be seen in the measurements if you can get your hands on the right information. Just look at the nice figures at 100Hz, and then see if they maintain them at 1KHz and 10KHz. If they do then there's a good chance that the amp won't be harsh. If the distortion rises (which will be the case if the Gain Bandwidth Product is insufficient, a common problem) then harshness is likely. I don't regard harshness as neutrality BTW- its just as serious a coloration as the 'too warm syrupy' sound for which some tube amps are known, although oddly I've yet to experience that latter bit.

 

[Mrmb]

I would love to hear an Atma-Sphere amp. Probably not in the cards, but I have for many years wanted to attend RMAF; maybe the stars will align someday when Ralph and I are both there.

Unfortunately, RMAF is no more!! RMAF's website advises the following:
"RMAF is closing its doors." "We have made the difficult decision to cancel RMAF 2021 and all future show."

My son and I made it to Denver for the show from Indiana in 2012. We enjoyed ourselves and had a good time in the Classic/Atma-sphere room. We accomplised our intent, which was to hear all of the speakers at the show, before replacing my SoundLab M1 speakers with newer model M1PX's. What we heard (or I should say didn't hear), caused me to buy the SoundLab M1PX's. I now own SoundLab 845's. Once a line source with the coherence, finesse and electrostatic bass of a full-range stat (being driven by Atma-sphere amps) is heard, moving elsewhere is all but impossible!

Sad to see RMAF close.

 

[DetroitVinylRob]

I will say this about the CAR and the Atma-Sphere OTL combination, I first sat in front of them more than three decades ago (T3 TAD 8? and M60 Mk1(?) with an MP-1)and could not shake the compliment of musically satisfying attributes. I went to a lot of industry shows, have experienced hundreds of peoples personal audio rooms, and tried many different kit combinations and never was completely satisfied. John and I live about an hour apart and I have owned Ralph’s MA-1 amps now for about fifteen years. But finally acquiring a pair of T3 field-coil 16? loudspeakers from John has left me not looking forward to go to shows or dealers with any curiosity or real interest anymore. Perhaps the greatest praise one could bestow on an associated pair of product designs and builds. Love to listen with friends, have a drink or lunch, you name it. Just have no interest in gear shopping really. Just repeatedly enjoy going down to my listening room, firing it up and putting another record on!