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Old 16th August 2012, 03:22 AM   #7781
Salas is offline Salas  Greece
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Originally Posted by Lynn Olson View Post
If the amp looks good at more than 200 kHz at full power, remains unconditionally stable with output load gizmos removed, and has a deep Class A region (at least several watts) chances are that the Ariels and the new speaker will like it.
Try an SSA or TSAA amp at a point, its Andrej's in our SS forum.
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Old 16th August 2012, 04:45 AM   #7782
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I find it unremarkable that amps and speakers you have designed yourself sound better than everything else.
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Old 16th August 2012, 08:05 AM   #7783
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I find it unremarkable that amps and speakers you have designed yourself sound better than everything else.
Really? Have I claimed that my amps and speakers "sound better than anything else"? That's a clever rhetorical tactic, but it's not what I said, in these or any other postings.

What I actually said is that I design my equipment for my own tastes. Not the tastes of an employer, my neighbor, a forum, or a magazine reviewer. If it sounds good to me, I consider it good. I have no way of knowing what other people hear; for that matter, I've only met a few audiophiles whose sonic and musical tastes are similar to my own.

I would imagine nearly everyone here on DIYaudio does pretty much the same thing, since we don't have to answer to a manager or a marketing department. That is one of the great luxuries of DIY; not to save money, but build what is not on the market. What's the point of copying commercial designs, which are almost always compromised to reach a price point, or aimed at a certain narrow demographic?

The majority of high-end products, in the USA at least, are designed for the tastes of a small circle of reviewers who write for the Big Two magazines. These magazines, even today, have the power to make or break a manufacturer. This is not a fairy tale; I've met the people whose businesses were destroyed by a bored reviewer, or an editorial rewrite. (The tell-tale signs of a clumsy editorial rewrite is when the review suddenly changes tone in the last three paragraphs, or when the final conclusion in the review contradicts the middle part of the review. That's a quick-n-dirty rewrite by an editor in a hurry.)

The DIY community is free of these commercial pressures, or the need to satisfy a reviewer. We can design products as weird as we like. They don't need to be manufacturable, or aimed at the tastes of the Big Two magazines.

It is only ethical to warn people who are curious about building the Ariel, Amity, or Karna that they do not sound like the majority of equipment at a high-end show; if they expect to replicate what they hear at hifi shows, they will be disappointed.

Last edited by Lynn Olson; 16th August 2012 at 08:23 AM.
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Old 16th August 2012, 08:11 AM   #7784
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A more exotic version would use a 1:2 Input Transformer -> PP 45, 2A3 -> 1:2 IT Transformer -> PP MOSFET followers -> Output Transformer. This driver would have (much) lower distortion and more dynamic drive characteristics. The B+ would be raised to the 200~250V range for the best possible dynamic range and slew rate from the balanced pair of direct-heated triodes.
<snip>
That's a complete hybrid amplifier; anyone interested?
You here that noise? It's me tearing up the current set of plans and starting all over again. Moving the 2A3s back to the driver stage....
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Old 16th August 2012, 08:45 AM   #7785
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Modern single-plate 2A3's have substantially lower upper-harmonic distortion than the historic bi-plate 2A3's, and really behave more like a souped-up 45.

When you ignore the 2nd-harmonic distortion (which is nearly inaudible), there are quite substantial differences between tubes. Gary Pimm and I look at the 5th-and-higher harmonics; you'll see differences of 10~20 dB in these high-order harmonics, depending on type and vendor.

Changing the quiescent current by 50% will only shift the upper harmonics by 3 dB or so, but swapping tubes can result in a 20 dB difference. Within vendors, distortion is tightly grouped, so the differences are clearly the result of proprietary manufacturing processes.

This is the area where the best DHT's pull ahead of the indirectly-heated driver tubes, and not by a small margin. For example, as good as the 5687/7119/ECC99 family is, the 45 DHT has 5th-and-higher-order harmonics that are 20 dB lower. Gary and I looked at the -130 dB noise floor of the instrumentation, and we could not see any evidence of 5th or higher at all. These things are clean - and to me at least, they sound the way they measure. The modern Chinese meshplate 2A3's are very good as well, and will cheerfully operate at substantially higher currents than a classical 45.

Be careful about microphonics. DHTs are pretty sensitive to vibration thanks to very large grid structures, which are not as rigid as conventional pentodes or indirect-heated triodes. PP operation does not cancel vibration all that well, thanks to the large spacing required by the physically large envelopes (and an additional inch or so for adequate ventilation). In more technical terms, there's a phase difference between the vibration experienced by each grid, and that results in loss of PP cancellation.

I am not familiar with the spectral signature of MOSFET followers, particularly what happens with 5th-and-higher order harmonics. If the upper-harmonic levels are moderate to high, there's no point in chasing after DHT's and their microphonic requirements, as well as hassles with good-sounding DC heating. The whole point of DHTs is their very low upper-harmonic content; if that is masked by the upper-harmonic distortion of the MOSFET followers, a triode-connected EL84, 6L6, or EL34 might be a better choice as a driver. Build it and see for yourself.

Last edited by Lynn Olson; 16th August 2012 at 09:08 AM.
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Old 16th August 2012, 12:46 PM   #7786
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With the output transformer wired in 4:1 mode, the output power into a 4 ohm load is only 27 fast Watts. Damping factor is 29. That's the mode I was thinking mated well with this new speaker.
Oops. Above I specified a damping factor of 29 for the OPT wired 4:1 stepdown. Actually, the damping factor in this mode is 16 for the load of the Beyond the Ariel speaker. (Output Z is 0.25 ohms.)

In case it matters....
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Old 16th August 2012, 01:02 PM   #7787
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I am not familiar with the spectral signature of MOSFET followers, particularly what happens with 5th-and-higher order harmonics.
If you poke around Susan's www.audiophonics.com website, you will find actual fft measurements. Look at the 4:1 modes, which we'd be using for this speaker.

I also look at harmonics 5 and higher. I would not have built the amp if the spectral signature were not favorable. As I recall, distortion was low and concentrated at 3rd harmonic (transformer-dominated distortion).

Noise is in the range of -150db. Yeah.
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Old 16th August 2012, 09:32 PM   #7788
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I would imagine nearly everyone here on DIYaudio does pretty much the same thing, since we don't have to answer to a manager or a marketing department. That is one of the great luxuries of DIY; not to save money, but build what is not on the market. What's the point of copying commercial designs, which are almost always compromised to reach a price point, or aimed at a certain narrow demographic?
True of the boutique transformer designers you can find on diy Audio too. Tribute, Intact Audio, O-Netics, Lundahl and now Susan have all moved beyond the typical simple model hobbled recipe. Each of these designers provide extremely good sounding transformers. Each of them emphasize quite different characteristics, in how much of what, they allow the transformer to actually transform.

The range available is quite wide and deals with internal gradient structures in tone and transients and overall timing issues more than it does with low distortion or tonal purity, those being a given. I am sure there are plenty of other manufacturers that denizens here will be eager to list, I will also point out that I know these few to be at the top of that heap. How high you rate one of them over another will be determined by those characteristics Lynn points to.

I would suggest that the output transformer will have an even greater impact upon the amplifiers eventual sonic character and how you respond to it than any other component. A world renowned designer of tube amplifiers I know says that the output transformer is 90% of what is wrong with a given amp and 70% of what is right. Of course, he designs guitar amps, but nearly all of the professional musicians we love to listen to own his amps, along with a huge number of just normal folks who haven't got the god light shinning on them.

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Old 17th August 2012, 04:03 AM   #7789
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Originally Posted by charliemb View Post
If you poke around Susan's www.audiophonics.com website, you will find actual fft measurements. Look at the 4:1 modes, which we'd be using for this speaker.

I also look at harmonics 5 and higher. I would not have built the amp if the spectral signature were not favorable. As I recall, distortion was low and concentrated at 3rd harmonic (transformer-dominated distortion).

Noise is in the range of -150db. Yeah.
Good website. Interesting that Susan was working on the Zeus at the same time I was working on the Amity amplifier, and had access to the same test gear (my Tektronix pals have superb HP and Tek instrumentation). Back when I was using the Amity amplifier, the transformer-coupled solid-state Rowland linestage was one of the very few preamps that could pass a direct-bypass test; most of the solid-state preamps added a layer of grit-n-grain and a metallic-spunding brightness, and the many (but not all) of the tube preamps were mushy and dull-sounding.
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Old 17th August 2012, 01:42 PM   #7790
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Default Complementary AB Mosfet common source

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Thanks Lynn. Well, Nelson's Class A MOSFET amps take the output from the drains. Per Susan, drains are a bad place from which to take output because 1) gain is involved and transistor gain colors sound, and 2) the drain capacitance is large (amplified by Miller) and non-linear if the voltage swings are large (which adds a kind of "jitter" so to speak).
As part of my studies in the eighties I was looking at MOSFET complementary common source amplifiers - in class AB - to improve the efficiency of the amplifiers by dropping the rail voltage by the 12V of gate voltage.

Suffice to say that it was a very pointed lesson in the limitations of feedback, small signal linear models and even the Spice models we had then (30 years ago). The non-linear capacitances around turn off made a mess of any attempt at stability.
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