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Old 31st January 2018, 09:20 PM   #21
MarcelvdG is offline MarcelvdG  Netherlands
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I slowly start to realize that our difference of opinion may be largely semantic. To me a spec is not just a parameter indicating some aspect of the performance, but a constraint on such a parameter set by a customer, marketer or system designer. If you don't meet it, in the best case you have to ask the system designer to redistribute error budgets and in the worst case your company gets sued by a dissatisfied customer.

Anyway, maybe you get more replies when you (have a moderator) change the title of the thread. When I first saw the title, I thought it was either something about subwoofers or an off-topic thread about limbo dancing.
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Old 1st February 2018, 12:38 AM   #22
nauta is offline nauta  Canada
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Hi Guys
MrMagic: I do not like numbers that begin with a decimal or zero, so choose to use perfectly good and functional prefixes that already exist. To me ppb (parts-per-billion0 sounds a lot better than fractional-ppm. It's also impossible to lose the decimal when copying.

I don't think there are many insensitive ES head phones. Head phones in general have very high sensitivty and the reference level is 1mW. This is about the effective power for the ESL at 100Vrms across the stators.

I know lots of designs that aim for highest output, using +/-400V and higher. When I investigated my project and looked at the capabilities of the head phones themselves, they can output 130dB ! That is totally ridiculous. The problem is that to gain another 10dB of effective output requires about a third more drive signal than the previous step. IXYS has 4kV mosfets and these can certainly be used for the drive you have, although I prefer a true complementary circuit.

Most of the very high output ES drivers are single-ended inasmuch as there is active pull-down by an "n" device (tube, mosfet, BJT) and passive pull-up using a resistor. Since the drive is balanced, there is a mix of passive/active drive going on throughout the signal cycle, but like yourself, I prefer active pull-up/down.

The first time you get six zeroes for THD20 in LTspice you are then ruined forever. Seeing anything else is a bit of a let down - haha. So, I aim for all-zeroes for the signal range I expect to use and will settle for <ppm or single-ppm for much higher levels.

For example, Using the same front-end as for my ES driver, I expanded the design as a PA for dynamic speakers. With 100V rails and 90Vpk output, it is 6ppm at 2R at 20kHz, and about 4ppm at 8R. At 1kHz, THD is about half. Reducing output to 30Vpk, THD20 is about 1ppm at 2R and a feww-hundred ppb at 8R; THD1 is about 100ppb at 2R and <10ppb at 8R. Going down to 3Vpk out, everything is six-zeroes (<10ppb). This is a big amp with eight pairs of output devices in one form and sixteen pairs in another. A made a hybrid class-G version with three rails and its performance is a little bit worse at highest output and lowest z-load.

For the big amp, I figured the goal would be to bridge them as a super-amp, so low-z performance is important. It was more of a design exercise than something to build since 1kW+ is way ridiculous. In my living space with 90dB/1W/1m speakers, I cannot stay in the room at anywhere close to 90dB SPL. I've measured the power I need and it is <1W or so for normal use, split between two subs and two sats. It is easy to get good performance at these levels, which is good for me, since I'm not that smart... haha
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Old 1st February 2018, 03:43 PM   #23
MrMagic is offline MrMagic  Greece
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Quote:
Originally Posted by MarcelvdG View Post
I slowly start to realize that our difference of opinion may be largely semantic. To me a spec is not just a parameter indicating some aspect of the performance, but a constraint on such a parameter set by a customer, marketer or system designer. If you don't meet it, in the best case you have to ask the system designer to redistribute error budgets and in the worst case your company gets sued by a dissatisfied customer.
Try to see specs as challenges instead. A company might decide to design a high performance product, because they consider it a worthwhile challenge, they like creating products that come closer to perfection, and they are proud of them. Those companies who aim profit by any means, like by cheating the customer, are second-class companies with "hit-and-run" marketing policies, who will only invest in the minimum research and development possible.

That said, the hype nowadays is that high-performance is not needed, therefore impressive numbers are not needed, numbers do not represent performance, so research and development is not needed either, and that suits all companies that get away with mediocre products, using poetic descriptions to attract the customers instead, who coincidentally lack the paying capabilities of the past.

Speaking of challenges, personally I'm motivated by two challenges: novelties, and optimization. Both can be extremely fun. Specs in the general notion as features and behaviors, might satisfy the former, and specs as numbers, the later, and usually that's the sequence in development too: first you achieve the main features, then you optimize to perfection -although several revising cycles might be needed until the design takes the final form, which is what "development" actually means.

In the end, an extraordinary design can only be expressed precisely with extraordinary specs -not colorful, emotional expressions. So, in that case, specs is the proof that something extraordinary has been achieved, the celebration of a successful development expressed with victorious features and numbers.

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Originally Posted by nauta View Post
I do not like numbers that begin with a decimal or zero
. . . . .

The first time you get six zeroes for THD20 in LTspice you are then ruined forever.
Seeing anything else is a bit of a let down - haha.
You contradict yourself, but I know exactly the feeling of beeing ruined by the number of zeroes

Imagine 4 zeroes at 1300V and 1300 gain -orders of magnitude higher voltage and gain, (that's where things get exponentially difficult)
After that, I can only accept sub-ppm THD @20Khz to keep those 4 zeroes intact
I personally prefer zeroes, because one can visually and intuitively see the big difference with the best highly expensive amps in the *market. It is also an intuitive challenge during development, to push numbers as far as possible to the right until they ...vanish into a sea of zeroes, while competition struggles to count them

*I haven't found a single loudspeaker power amplifier with less than 0.001% distortion at up to 20Khz (and that is the Elektra HD2 7 Channel Power Amplifier), if anyone knows of a loudspeaker amplifier with less distortion at 20Khz, please let me know!

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Originally Posted by nauta View Post
IXYS has 4kV mosfets and these can certainly be used for the drive you have, although I prefer a true complementary circuit.
Nope, they certainly can NOT be used for the same purpose. They can only be used in pulsed applications by design. If you look closer to their graphs and calculate the demands, you'll find out.

There are no semiconductors for complementary topologies at such voltages and cascoded topologies are too complex for my taste. I'd accept them only for very high voltages in order to drive ESLs directly (as there is no SS alternative).

Quote:
Originally Posted by nauta View Post
Most of the very high output ES drivers are single-ended inasmuch as there is active pull-down by an "n" device (tube, mosfet, BJT) and passive pull-up using a resistor. Since the drive is balanced, there is a mix of passive/active drive going on throughout the signal cycle, but like yourself, I prefer active pull-up/down.
Single ended with a pull-up resistor, are highly asymmetrical causing too much distortion at high frequencies, and thus cannot be used when aiming low THD for the full audio band.

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Originally Posted by nauta View Post
I don't think there are many insensitive ES head phones.
If there are no insensitive headphones, then there are insensitive ears that justify those HV amps in production

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Originally Posted by nauta View Post
they can output 130dB ! That is totally ridiculous.
Agreed, and that is why I'll trade ridiculous high output for better low frequency response in my next custom-designed ES headphones.

Quote:
Originally Posted by MarcelvdG View Post
Anyway, maybe you get more replies when you (have a moderator) change the title of the thread. When I first saw the title, I thought it was either something about subwoofers or an off-topic thread about limbo dancing
Initially I wanted to provoke a competitive spirit for new designs, or great forgotten designs, but apparently there is no interest whatsoever, nor to simply collect most projects in one thread.
More than 200 different members have seen the thread, so I bet that those who would be interested to include their project, have already seen it but they are not interested. I have started to realize that direct-comparison is terrifying to most people.

So, if philosophical spec-tology has become the thread's main subject, then so be it.
And it would be ironic to call it "Amplifier Project Database" after so much blah-blah anyway. Administrators won't let us change the name twice!

That said, bold members proud for their projects, are still welcome.
We are open and we are waiting for you!


.

Last edited by MrMagic; 1st February 2018 at 03:55 PM.
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Old 1st February 2018, 03:56 PM   #24
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by MrMagic View Post
I haven't found a single loudspeaker power amplifier with less than 0.001% distortion at up to 20Khz (and that is the Elektra HD2 7 Channel Power Amplifier), if anyone knows of a loudspeaker amplifier with less distortion at 20Khz, please let me know!
For a moment there I was word blind to "amplifier" and got excited, oh well
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Old 1st February 2018, 04:17 PM   #25
Mark Johnson is offline Mark Johnson  United States
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How low can you go?
I don't think it would upset Nelson Pass, if a super enthusiastic and motivated person dug the measurement results out of his First Watt website, and included them in a table here. There are more than a dozen different amplifiers on that site, built and measured! Here's an example of the measurement data he has published.

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Last edited by Mark Johnson; 1st February 2018 at 04:22 PM.
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Old 1st February 2018, 09:58 PM   #26
tomchr is offline tomchr  Canada
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It was suggested to me that I throw my name in the hat here. I am measuring the following on my Modulus-686 prototype.

Gain: +20 dB
THD+N: 0.00026 % (140 W @ 8 Ω)
THD+N: 0.00029 % (260 W @ 4 Ω)
Onset of clipping: 0.0005 % THD+N @ 220 W (8 Ω)
Onset of clipping: 0.070 % THD+N @ 380 W (4 Ω)
Noise: 15 uV RMS (A-weighted, 20Hz-20kHz)

Build cost: $300/channel + power supply, connectors, heat sinks, etc.

I've attached the THD+N plots. I'll start a separate thread for it in the Vendor's Bazaar over the weekend, so if you have questions, please keep an eye out for it there.

You can find the numbers for my Modulus-86 here: Modulus-86 Rev. 2.2: Composite amplifier achieving 65 W (4 Ω) at 0.00006 % THD.
A brief summary:
0.000061 % THD (1 W, 8 Ω, 1 kHz).
0.000067 % THD (40 W, 8 Ω, 1 kHz).
0.00038 % THD+N (40 W, 8 Ω, 1 kHz).

Tom
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Last edited by tomchr; 1st February 2018 at 10:03 PM.
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Old 2nd February 2018, 06:39 PM   #27
MrMagic is offline MrMagic  Greece
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Awesome work Tom, congrats!
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5 projects so far on this thread and counting.
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Old 3rd February 2018, 05:26 PM   #28
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by MrMagic View Post
Try to see specs as challenges instead.
If you would try to see specs as constraints on performance figures set by customers or marketers, you might understand why I consider them neither necessary nor useful for hobby projects. You can optimize whatever parameters you like to optimize using all your ingenuity and all your common sense without having some external person forcing a set of constraints on them.

It's a bit similar to art. Artists often make their best works when they don't have to worry about whether a customer will like it.
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Old 3rd February 2018, 07:37 PM   #29
MrMagic is offline MrMagic  Greece
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Well, I have no "external persons" dictating specs to me, and I imagine that is the case with all DIYers, so that doesn't apply to us.

And if I had my own hardware company, no one else would dictate the products' specs than myself, and there are many companies like that.

What is required to make art, is inspiration, and the ability to use it in a creation, or part of it, nothing else.
Even if the specs were "dictated" to the designer, if the designer had an inspiration on how to overcome the problems and achieve the tough specs because he likes his job and considers tough specs a challenge, it would still be an inspired product, that would contribute with its inspired novelties (a case where inspiration and art are triggered by tough specs or constraints, as in many other cases).

And that is the real question, the actual quality of the specific product and its contribution to technology, not whether the boss worried about the consumers and the course of his company, or whether the specs were "dictated".
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Old 3rd February 2018, 09:37 PM   #30
MarcelvdG is offline MarcelvdG  Netherlands
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Well, I have no "external persons" dictating specs to me, and I imagine that is the case with all DIYers, so that doesn't apply to us.
Precisely, so according to the meaning of the word "spec" that I'm used to, you have no specs. You have ideas about what kind of performance you would like, but you can change them whenever that makes sense.

Hence my claim that worrying about specs sounds more like work than like hobby to me, which started the whole discussion between you and me. And hence my later remark that we largely disagree about semantics.
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