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post #61 of 83 Old 10-21-2013, 01:56 PM - Thread Starter
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Quote:
Originally Posted by Wayne Highwood View Post

It may be counterintuitive, but bigger bass drivers don't bring "uncontrolled bass", at least not necessearily. If anything, they have a better chance of providing tight, low distortion bass, as they move considerably less than smaller drivers do for the same spl.
So you presumably support my recommendation for something on the larger side, yes?
I've used processors for room correction followed by tube amplification. Why wouldn't the OP be able to do the same, should he desire to? I think the miniDSP would be something he should take a close look at, as it can do a better job than the automagic types (I'm NOT a fan of older iterations of Audyssey, although XT32 seems less obtrusive to me), and is small and can be tucked away so his audiophile friends won't realize he's using fancy modern processing.
Hi Wayne! I've considered some kind of room correction and it seems that the miniDSP is the best solution as far I know. The thing that I don't like about the miniDSP is the resolution, I would like higher, and that its software is for Windows, so I'm gonna need to borrow a computer or buy a cheap one just for that. Maybe you Wayne know a room correction processor that works in higher resolution.
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post #62 of 83 Old 10-21-2013, 02:51 PM
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I've used one of the Behringers listed upthread. They're 24 bit/96 kHz. The miniDSP 2x4 is 24/48. They're both higher res than redbook, if that really matters. I'm not convinced that it does. I do raise my eyebrow at the maximum 0.9V output, though. That wouldn't even push my amps to full output.
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post #63 of 83 Old 10-22-2013, 02:35 AM - Thread Starter
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Quote:
Originally Posted by Wayne Highwood View Post

I've used one of the Behringers listed upthread. They're 24 bit/96 kHz. The miniDSP 2x4 is 24/48. They're both higher res than redbook, if that really matters. I'm not convinced that it does. I do raise my eyebrow at the maximum 0.9V output, though. That wouldn't even push my amps to full output.
Hi Wayne! The resolution matters to me cos I'm gonna use a Wadia 121 DAC that performs an up-sampling technology to 32 bits and it would be pointless up-sample to down-sample later.
I've been thinking about the setup and I'm considering to put a nanoDIGI 2x8 B (it runs 24/192) for "room correction" between my computer and the Wadia 121.
It seems the only one of their "in a Box" solutions that is intended for being used with "high end" DACs. I will use the processor with a bypass preset while using headphones and another with the filters applied for use with the speakers. I will let the subs perform the crossover job. I would like to know your opinion about it Wayne, also if you know a better solution for room correction.
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post #64 of 83 Old 10-22-2013, 05:45 AM
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Quote:
Originally Posted by Fermelom View Post

! The resolution matters to me cos I'm gonna use a Wadia 121 DAC that performs an up-sampling technology to 32 bits and it would be pointless up-sample to down-sample later.

Up sampling is always pointless because if it worked, we would have a violation of information theory. The laws of physics are not to be trifled with! ;-)
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I've been thinking about the setup and I'm considering to put a nanoDIGI 2x8 B (it runs 24/192) for "room correction" between my computer and the Wadia 121.

Are you watching the action very closely? The nanodigi is a MiniDSP!

The data format of the MiniDSP is set by the plug-in you are running, and according to this table:

http://www.minidsp.com/products/plugins

and according to this reference, only one of the crossover plug ins (4 x 10) runs faster than 24/48 and it is limited to 24/96.

The preferred room correction plugin is limited to 24/48 which is not a practical limitation.

I'm interested in hearing were you found a MiniDSP-based room correction solution that runs at 24/192.
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post #65 of 83 Old 10-22-2013, 07:52 AM
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Ferm, keep in mind that my experience with similar gear (the Behr) concerned an active three way speaker, so it may not directly translate. That's where my own wide-band single driver path took me, back to the active approach. I was using the DCX to tune the speaker primarily. The parametric eq was then used to address the modal response in-room, below 250 hz or so. Didn't need to do anything up higher. As I said before, I prefer manual calibration, although that is a bit tedious, and the newest Audyssey is pretty good.

And I have to let you know that I'm with Arny regarding the "high end DACs" and upsampling. Honestly, I think you would be better off selling that stuff and using the funds for an AVR/pre-pro with good DACs, bass management, and the latest version of Audyssey XT32 on board. If you went the AVR route, you would have the bonus of clean, linear amps as an option to use when the valve syrup seems too sweet.
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post #66 of 83 Old 10-22-2013, 02:09 PM
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Hi Fermelom,
Quote:
Originally Posted by Fermelom View Post

. . . a Wadia 121 DAC that performs an up-sampling technology to 32 bits . . .
Snake-oil alert !

Although there are some good reasons to up-convert the sample-rate, up-sampling the bit-depth adds absolutely nothing. Especially in a DAC, where the point is to output an analog signal that can't possibly maintain that resolution. The specs state "All inputs accept up to 24-bit/192kHz input data rates", and if you start with only 24-bits, there is no algorithm that can later determine what those lower eight bits should be.

Here is some perspective: 24-bit resolution gives you one part in 16 million per bit, which translates to .12 microvolts per bit. The noise-floor of the analog audio will be more than that, so those extra bits, even if they could exist, wouldn't even make it to the miniDSP. Going to 32-bit resolution would produce .47 nanovolts per bit (one part in 4 billion), a value so low that we are hard pressed to even measure it, let alone hear it.

Although you can make a case for 32-bit resolution at the front-end of the audio signal-chain (although not a very strong case), I have never heard anyone even try to make a case for 32-bits at the tail-end.

Note: Having looked over the specifications, I cannot see them make any claim that 32-bits offers an advantage, so it would not be fair to refer to it as snake-oil. It does look like a very nice DAC.


EDIT:
For anyone wishing to check my math, the above numbers are based on an analog audio signal with a +/- 1 volt peak-to-peak maximum amplitude.
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post #67 of 83 Old 10-22-2013, 03:57 PM
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Quote:
Originally Posted by MarkHotchkiss View Post

.... Going to 32-bit resolution would produce .47 nanovolts per bit (one part in 4 billion), a value so low that we are hard pressed to even measure it, let alone hear it.

....
Oops, you gave an out to the 'golden ears' just because you cannot measure it they can still hear it. wink.gifbiggrin.gif
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post #68 of 83 Old 10-22-2013, 05:38 PM
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Quote:
Originally Posted by Fermelom View Post
 
Quote:
Originally Posted by Wayne Highwood View Post

I've used one of the Behringers listed upthread. They're 24 bit/96 kHz. The miniDSP 2x4 is 24/48. They're both higher res than redbook, if that really matters. I'm not convinced that it does. I do raise my eyebrow at the maximum 0.9V output, though. That wouldn't even push my amps to full output.
Hi Wayne! The resolution matters to me cos I'm gonna use a Wadia 121 DAC that performs an up-sampling technology to 32 bits and it would be pointless up-sample to down-sample later.

 

When upsampling works perfectly, the sound is perfectly identical to the original. When it doesn't work perfectly, the sound is degraded. In other words, it can't, even in theory, do anything useful.

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post #69 of 83 Old 10-22-2013, 07:00 PM
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Re: Typical 'tube amp guy' and interposing sand devices in tube circuits.

1) I don't give a damn what a typical 'tube amp guy' is. That is always changing. At one point (the 1990s) it was people rehashing 1950s designs in sleek back aluminum. They're still out there, but that's not the state of the art these days; not by a long shot.

2) Triodes at line level benefit hugely from putting a solid-state constant current source as their anode load (way, way high apparent resistance without the kilovolts dropped by say a high value resistor). You get an essentially flat loadline, which means very, very low distortion. You can send the signal output from the triode's anode to a MOSFET source follower, and then it can drive all sorts of gnarly loads. Solid state devices make excellent supporting circuits for vacuum tube voltage amplifiers. And, since the ss devices are so capable at handling current concerns, they can leave the tubes to do only what they're really good at (voltage amplification). That seems like a win-win to me.

That used to be sneered at as 'hybrid' and not true 'tube circuitry.' Whatever.
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post #70 of 83 Old 10-22-2013, 07:20 PM
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English is my second language, so what do you mean by "awfully nice"?

Sorry, it just means "really nice" or "very nice."


Re: Zu speakers:
Quote:
Measurements I've seen also show they're nowhere near as sensitive as they purport to be.

Also, Klipsch and Audio Note have been playing this game. The woofer used in those Zu speakers is closely related to an Eminence 10" that has a really nice midrange response (for a 10" at any rate). That driver's rated sensitivity is 92dB/1W/1m.

Quote:
Subs don't have anything in the way of 'transient response' because of the low BW in which they operate.

"Transient response" -- when speaking in regards to a woofer -- is related to how quickly the driver can start when signal is applied, and very importantly, how quickly it will stop when signal is stopped. Cheaper woofers will 'ring' a bit, not stop after signal has stopped. They may also take a relatively long time to start vibrating once signal is applied, making attacks sound 'slow.' This means poor transient response. If I understand the problem correctly, it is independent of bandwidth.

--

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post #71 of 83 Old 10-22-2013, 08:28 PM
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For an old guy like me who knows no better.....
A simple no DSP formula that works for me.....

Analog Mastered Vinyl
+
Analog Turntable
+
Analog Tube Preamplifier
+
Analog Tube Amplifier
+
90+ dB Speakers
+
Single Malt

= Bliss
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post #72 of 83 Old 10-22-2013, 08:34 PM
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^^ That's a bit like saying you like performance cars, but because you can't be bothered to educate yourself on the newer gear, you'll stick with carbs and points instead of an EMU.

Lots of great music has been recorded completely in digital too.
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post #73 of 83 Old 10-23-2013, 01:00 AM - Thread Starter
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Quote:
Originally Posted by MarkHotchkiss View Post

Hi Fermelom,
Snake-oil alert !

Although there are some good reasons to up-convert the sample-rate, up-sampling the bit-depth adds absolutely nothing. Especially in a DAC, where the point is to output an analog signal that can't possibly maintain that resolution. The specs state "All inputs accept up to 24-bit/192kHz input data rates", and if you start with only 24-bits, there is no algorithm that can later determine what those lower eight bits should be.

Although you can make a case for 32-bit resolution at the front-end of the audio signal-chain (although not a very strong case), I have never heard anyone even try to make a case for 32-bits at the tail-end.

Note: Having looked over the specifications, I cannot see them make any claim that 32-bits offers an advantage, so it would not be fair to refer to it as snake-oil. It does look like a very nice DAC.

Quote:
Originally Posted by Hamilcar Barca View Post

When upsampling works perfectly, the sound is perfectly identical to the original. When it doesn't work perfectly, the sound is degraded. In other words, it can't, even in theory, do anything useful.
You're right guys! I was misundersandig the issue, but I found this in the review of Stereophile of the Wadia 121:

According to Wadia, the 121 has no volume-control bypass and no need for one. Digital inputs are upsampled to 32-bit/1.4MHz, then processed with Wadia's proprietary DigiMaster interpolation filtering algorithm, which, they claim, maintains resolution at all volume settings. Sure enough, I could hear no difference between using the 121 as a preamp or through another preamp, at any volume level. In the latter case, I'd just max out the volume and go. Source; http://www.stereophile.com/content/wadia-121decoding-computer-da-processor

So the upsampling is an internal process to provide accuracy to the digital volume.

After some research and reading carefully your advices I think that in my case the acoustic is not so critical (single drivers in a small room) but I'm still interested in the advantages of the room correction, that's why I've decided to postpone the purchase of any processor for room correction, even though later I will like something like a DEQX mate, they seem more complete in features like perform a "speaker correction" before the "room correction", anyway I started the project of change my desktop setup with a $500 budget in mind but that was left behind several purchases ago.
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post #74 of 83 Old 10-23-2013, 01:59 AM
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Hi Fermelom,

32-bit internal processing and output is a very simple way to achieve an accurate volume control without having to truncate low-order bits at low volume levels. There are other ways to do it, but going with 32-bits would probably be the most reliable approach, introducing the least amount of distortion, although it would be more expensive. In light of that I would have to retract my "Snake-oil Alert" comment.

But I'm still not sure it's worth the price they are asking. wink.gif
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post #75 of 83 Old 10-23-2013, 03:38 AM
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Quote:
Originally Posted by rongon View Post


2) Triodes at line level benefit hugely from putting a solid-state constant current source as their anode load (way, way high apparent resistance without the kilovolts dropped by say a high value resistor). You get an essentially flat loadline, which means very, very low distortion.

Sounds like double talk to me. Please provide a practical example of this, including frequency response and distortion measurements with loudspeaker or simulated loudspeaker loads.

Quote:
You can send the signal output from the triode's anode to a MOSFET source follower, and then it can drive all sorts of gnarly loads.

Why not just build the amp with solid state devices?
Quote:
Solid state devices make excellent supporting circuits for vacuum tube voltage amplifiers.

Tubes have been obsoleted in audio for all but niche boutique equipment.

If tubes had some kind of special advantage for low distortion, why do tubed amps generally have more distortion than many SS amps?

If tubes had some kind of special advantage for low distortion, why is all modern distortion analysis equipment, which justifies having very low distortion based on solely solid state devices?

I ROTFL at tubed equipment designers who use all-SS gear as their reference - as their distortion analysis equipment.
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post #76 of 83 Old 10-23-2013, 05:26 PM
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Quote:
Originally Posted by arnyk View Post

Sounds like double talk to me. Please provide a practical example of this, including frequency response and distortion measurements with loudspeaker or simulated loudspeaker loads.
No Arny, it's really basic EE. Take a read through Gary Pimm's presentation on it. Garry is an engineer at Tektronix.
http://www.pimmlabs.com/web/Active_loads_and_signal_current_control.html

John Broskie has had any number of articles on using CCS in tube stages at Tubecad, and Morgan Jones (BBC engineer) wrote about it at some length, including measurements in his book Valve Amplifiers.

For line stages, it's relatively easy to make a tube stage that whilst it may measure less than an LM4562, do not do so in an audibly distinguishable manner. About a decade ago I built a line stage consisting of a trioded D3a with a cascode Pimm CCS, cascaded into a trioded EL34 with a cascode DN2540. Avol was about 1450, and Avcl 6. Distortion was very low with the only harmonic being seen H2 and at lower than -100dB up to about 20Vrms. Noise was also very low and Zout about 9R. It would happily drive any line stage and probably most headphones, though the Zout would affect the lower Z headphone's FR some.

For a power amp, using this linestage as front end (with 6SN7/ECC99/6H30 replacing the EL84), with feedback loop in place, then 6H30 diff stage feeding same EL84 CCS as before and some KT88's in parallel would easily give 100W, most of it in class A. Lots of other details could be added such as cathode feedback on the outputs, good low noise regulation, controlled start up / shut down via ucontroller etc to extend tube life. I almost built an amp similar to this before I mainly stopped messing with tube designs, but I went full active and 10 channels of this was a little much. These days I'm more interested in the outstanding NatSemi LME49830 with FET output stages as they are smaller, cheaper and more efficient.
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post #77 of 83 Old 10-27-2013, 01:24 PM
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Wow, talk about a thread bird walk! Want a speaker that sounds good with tubes? Get one with a compression driver. Yeah, I know, compression drivers will have a more distortion that a regular driver but they can sound awesome with a tube amp. For example, I heard some large Altecs with tubes and with dynamic classical music, they were impressive, just real powerful.If you want something real cheap, then look for an old (they'll be around 22 years old) pair of Infinity SM speakers I had a pair of the big ones (SM 150) and they had an efficiency rating of 102 db per 1watt). Sound wise, I thought the polycell tweeter did a good job, but the reflex enclosure design wasn't tuned for the deep bass that you'd expect. Plus, the enclosure and crossover were pretty chintzy
i am now running the most accurate speaker type (ESL's) but if I could, I'd have a pair of large cp speakers next to them to use when desired (like the wife would let me, haha!)
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post #78 of 83 Old 10-27-2013, 03:13 PM
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Quote:
Originally Posted by A9X-308 View Post

Quote:
Originally Posted by arnyk View Post

Sounds like double talk to me. Please provide a practical example of this, including frequency response and distortion measurements with loudspeaker or simulated loudspeaker loads.
No Arny, it's really basic EE. Take a read through Gary Pimm's presentation on it. Garry is an engineer at Tektronix.
http://www.pimmlabs.com/web/Active_loads_and_signal_current_control.html

No, Gary Primm is proprietor of Primm labs, a business that builds and sells tubed audio gear. The paper in question was not approved by anybody at Tektronix or it would say so. It is not a technical paper, it is advertising fluff. And it does not contain any of the information that I requested. Please try to provide a relevant response next time.
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post #79 of 83 Old 10-27-2013, 03:33 PM
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Quote:
Originally Posted by arnyk View Post

No, Gary Primm is proprietor of Primm labs, a business that builds and sells tubed audio gear.
Then, he used to be an engineer at Tek. I don't follow everyone's current employment.
Quote:
Originally Posted by arnyk View Post

The paper in question was not approved by anybody at Tektronix or it would say so.
I never said it was. I didn't know he had left Tek.
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Originally Posted by arnyk View Post

And it does not contain any of the information that I requested. Please try to provide a relevant response next time.
You asked for FR and distortion. The latter is at least included in Jones' book and Broskie's site. Feel free to search for yourself.

It is however, still basic EE.
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post #80 of 83 Old 10-28-2013, 05:02 AM
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Quote:
Originally Posted by A9X-308 View Post

Quote:
Originally Posted by arnyk View Post

No, Gary Primm is proprietor of Primm labs, a business that builds and sells tubed audio gear.
Then, he used to be an engineer at Tek. I don't follow everyone's current employment.
Quote:
Originally Posted by arnyk View Post

The paper in question was not approved by anybody at Tektronix or it would say so.
I never said it was. I didn't know he had left Tek.
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Originally Posted by arnyk View Post

And it does not contain any of the information that I requested. Please try to provide a relevant response next time.
You asked for FR and distortion.

And you remain a no-show vis-a-vis your claims. Everybody with a brain knows that if you want low measured distortion forget tubes. All the current sources in the world can't fix their problems in that area which is one reason why all SOTA audio distortion analyzers have been SS since the 70s at the latest.
Quote:
The latter is at least included in Jones' book and Broskie's site. Feel free to search for yourself.

I see no legitimate references. I do see what looks like smoke.
Quote:
It is however, still basic EE.

No it isn't. I don't play "Let me make a wild claim and then you do my research for me". To me that's game playing, not sincere intellectual discussion.

The joke on the tube bigots because that most sold state amps have long had current sources as basic parts of their circuity. Since I believe in showing basic respect I'll give you two good references in this area and where to look in them that you won't have to search them out for yourself:

http://www.amazon.com/Audio-Power-Amplifier-Design-Handbook/dp/0240521625

Audio Power Amplifier Design Handbook [Paperback] by Douglas Self

Chapters 4, 6, 9 and 12

and:

http://www.amazon.com/Designing-Audio-Power-Amplifiers-Cordell/dp/007164024X/ref=pd_sim_b_1

Designing Audio Power Amplifiers by Bob Cordell

Chapters 2,3, 5, 7 and 10
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post #81 of 83 Old 11-23-2013, 07:36 PM
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Quote:
Originally Posted by arnyk View Post

Sounds like double talk to me. Please provide a practical example of this, including frequency response and distortion measurements with loudspeaker or simulated loudspeaker loads.
Why not just build the amp with solid state devices?
Tubes have been obsoleted in audio for all but niche boutique equipment.

Whoa there! I don't know how much you studied about choosing operating conditions for triodes way back when. I thought what I was talking about was really elementary stuff. Load lines and all that. I mean, I'm no EE or anything. But I'm honestly trying to be intelligent about this stuff.

A *triode* can be very linear when you put a gigantic (theoretically infinite) load in its anode (or "plate", which is analogous to the drain in an FET). You'd also need to buffer its high impedance output to drive any solid state stages downstream, but that's not a problem if driving a vacuum tube (high impedance) circuit in the next stage.

Have you ever looked at a triode's characteristic curves? Notice how different they are from a BJT's, or an FET's? They are a different kind of device. If you draw a load line for a triode with the B+ in the lower right going to the max anode current in the upper left, you'll notice that the lower the value of the anode load resistor, the steeper the load line. (Look for Norman Crowhurst on load lines, an article from way back when). The steeper the load line, the higher the distortion (the exact same is true for transistors too). The less steep (more 'flat'), the less distortion (within the linear window of operation, of course).

Now, if you could put an infinite value anode load resistor in there, you could get a flat loadline, which should result in very, very low distortion. You can do that with a cascoded pair of high voltage, depletion mode MOSFETs as a constant current source (or CCS). (That's the same kind of thing you'll see as a constant current sink in the shared sources of an FET differential pair, or as the source load of a source follower/buffer circuit). This CCS acts like a resistor with a value of something like 3M ohms, which gives the nearly flat load line we want, but only has to drop like 50V or so across it (although can drop much more if you use the proper devices). This was not possible without contemporary high voltage-capable depletion-mode MOSFETs, because if you tried to use a 3 megohm resistor as an anode load with only 5mA going across it, it would drop 3,000,000 x .005 = 15kV !!!! OK, that's not possible in the real world. But it can be done with a transistorized CCS as the anode load.

Look at the figure on page 16 of this article about tube load lines: http://valvewizard1.webs.com/Common_Gain_Stage.pdf

See how flat the 220k load line is compared to how steep the 47k load line is? Now imagine a 5kV B+ (horizontal axis) with a 3M resistor and the load line that would make.

Does that make any sense to you?
Quote:
Originally Posted by arnyk View Post

If tubes had some kind of special advantage for low distortion, why do tubed amps generally have more distortion than many SS amps?

If tubes had some kind of special advantage for low distortion, why is all modern distortion analysis equipment, which justifies having very low distortion based on solely solid state devices?

I ROTFL at tubed equipment designers who use all-SS gear as their reference - as their distortion analysis equipment.

OK, first -- Vacuum tubes as triodes have really low self-noise compared to transistors, so are good with very low-level stuff. Note that I do not mean pentodes! They can (note I wrote "can") have quite low distortion if used correctly. So you can have a really low noise, low distortion amplifier stage with no negative feedback loop around it. Transistors just about always require a negative feedback loop around them to be acceptably linear input-to-output. There's nothing wrong with NFB *when applied carefully and correctly*. But that ain't easy, and isn't always done right. So that is one advantage of a simple vacuum tube gain stage. It *can* be super-simple, linear and all without negative feedback to make things complicated. Not that there's anything wrong with NFB, mind you... But it is also true that many people just like the sound of a clean, simple triode gain stage that's done right. It's a nice thing, that's all.

Second, push-pull power amplifiers are NOT where tubes are at their best. The typical guitar amp tubes used in even the most expensive power amps are pretty bad. That includes all the popular types -- 6L6GC, EL34, KT88, 6550A, etc. even as triodes. All of those have pretty high 3rd order distortion, which does not cancel out with push-pull operation. They are high impedance devices, so need to be used with output transformers (OPT's) to match to 4 or 8 ohm impedance loudspeakers, which are really *expensive* to make right. You want a big OPT for high power, and it should have high primary inductance for good bass response *open loop* (before negative feedback is applied). But if you make the OPT really big and with high inductance primaries, you get bitten by the increased capacitance between windings, which degrades high frequency response all the way down to the point where it usually affects the high audio frequencies. It's a lose-lose situation there, yes it is. So yes, a 35W per channel tube power amp made with EL34's is going to perform very poorly compared to a very competently designed solid state power amp of similar power. Start looking at 100W per ch amps and there's simply no comparison any more. I won't argue that point with you, because that's the way it is.

But a phono preamp, or an output stage for a DAC? OK, I can argue that you can make a line level output stage from a triode that has (worst case) only about 0.5% second harmonic distortion and much lower 3rd HD, and only one-tenth of that in 5th HD, *without any negative feedback loop applied*. That's pretty darn linear. And it can even sound really good. I know it's silly, but I find the "sound" I get from a simple circuit with no negative feedback (NFB) loop around it to sound "relaxed" and "musically involving." If that can be made linear (low distortion) then I see no problem with doing that, if that's what some people like.

Also, there are so many bad sounding solid state audio circuits out there. For instance, I have a Panasonic SA-XR75 receiver which has what I think are fabulous sounding DAC's and power amp stages, but its analog line level inputs are ghastly sounding (and its FM tuner is miserable). It's obvious where Panasonic spent their money making this receiver, and for the asking price I think they made fine choices. But, its analog line level inputs still sound wretched. One *can* make bad sounding solid state audio circuits, even now.

Finally, yes, a typical tube power amp is a hobbyist's exercise, especially now that many relatively inexpensive HTR's (AVR?) can sound so good. If you're not building your own amps, I'd say it's best for rational people to buy as good an HTR as they can afford and put the big money into speakers. Or for a small stereo, there's gotta be a good, cheap integrated amp out there somewhere.

Have a look at Morgan Jones "Valve Amplifiers" 3rd edition and/or 4th edition for a nice introductory discussion of this stuff from a contemporary angle. It's very sensible and reasonable, and has lots of great [objective, measured] info on the current thinking in tube amp design (lots of transistorized support circuitry involved, and not just in the DC rectification circuits). It is NOT one of those silly 'audiophile boutique hobbyist' books with lots of arm-waving about the superiority of 12" fullrange speakers with alnico magnets! Really.
https://www.google.com/search?q=morgan+jones+valve+amplifiers

I'm trying to show that there isn't a black-white divide here. Tubes are not all awful for everything. Solid state is not 100% superior in every way there is (at least when it comes to low frequency amplification, aka "audio"). But to make a good audio power amp to drive real world loudspeakers for little money? Heck yeah, transistors rule for that. No doubt about it. So OK? Can we be friends?

- Ron

PS - What was the OP anyway? Oh yeah -- Tube friendly speakers? And this is for a push-pull 6L6 amp, with a paraphase inverter and a high impedance power supply, right? The amp's damping factor will be very low. It's output stage will have relatively high 3rd order harmonic distortion, and the paraphase inverter will probably have high 2nd harmonic distortion (but that could still sound "good"). Look for a nice sounding speaker that has a reasonably flat frequency response, reasonably wide frequency response, high sensitivity (at least 90dB/1W/1m) and a flat impedance curve (preferable at 8 ohms, not 4 ohms). If you find such a speaker at a somewhat reasonable price, PLEASE TELL ME ABOUT IT, because I don't know of one.

--

Hopelessly addicted to this stuff, but on a strict budget.
Snell Type C speakers
Homebrew DC-coupled, push-pull, 2A3 amp, Intact Audio volume control
RIAA preamp (similar to Arthur Loesch design) - Technics SL1200mk2- Denon DL160
Pioneer Elite PD-D6-J (CD, SACD)
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post #82 of 83 Old 11-24-2013, 12:37 AM
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Quote:
Originally Posted by rongon View Post

Quote:
Originally Posted by arnyk View Post

Sounds like double talk to me. Please provide a practical example of this, including frequency response and distortion measurements with loudspeaker or simulated loudspeaker loads.
Why not just build the amp with solid state devices?
Tubes have been obsoleted in audio for all but niche boutique equipment.

Whoa there! I don't know how much you studied about choosing operating conditions for triodes way back when. I thought what I was talking about was really elementary stuff. Load lines and all that. I mean, I'm no EE or anything. But I'm honestly trying to be intelligent about this stuff.

A *triode* can be very linear when you put a gigantic (theoretically infinite) load in its anode (or "plate", which is analogous to the drain in an FET). You'd also need to buffer its high impedance output to drive any solid state stages downstream, but that's not a problem if driving a vacuum tube (high impedance) circuit in the next stage.

Have you ever looked at a triode's characteristic curves? Notice how different they are from a BJT's, or an FET's? They are a different kind of device. If you draw a load line for a triode with the B+ in the lower right going to the max anode current in the upper left, you'll notice that the lower the value of the anode load resistor, the steeper the load line. (Look for Norman Crowhurst on load lines, an article from way back when). The steeper the load line, the higher the distortion (the exact same is true for transistors too). The less steep (more 'flat'), the less distortion (within the linear window of operation, of course).

Now, if you could put an infinite value anode load resistor in there, you could get a flat loadline, which should result in very, very low distortion. You can do that with a cascoded pair of high voltage, depletion mode MOSFETs as a constant current source (or CCS). (That's the same kind of thing you'll see as a constant current sink in the shared sources of an FET differential pair, or as the source load of a source follower/buffer circuit). This CCS acts like a resistor with a value of something like 3M ohms, which gives the nearly flat load line we want, but only has to drop like 50V or so across it (although can drop much more if you use the proper devices). This was not possible without contemporary high voltage-capable depletion-mode MOSFETs, because if you tried to use a 3 megohm resistor as an anode load with only 5mA going across it, it would drop 3,000,000 x .005 = 15kV !!!! OK, that's not possible in the real world. But it can be done with a transistorized CCS as the anode load.

Look at the figure on page 16 of this article about tube load lines: http://valvewizard1.webs.com/Common_Gain_Stage.pdf

See how flat the 220k load line is compared to how steep the 47k load line is? Now imagine a 5kV B+ (horizontal axis) with a 3M resistor and the load line that would make.

Does that make any sense to you?

What makes sense to me is that I asked for one thing, and that you provided another. That's known in the trade as "Double Talk". ;-)

Quote:
Originally Posted by arnyk View Post

If tubes had some kind of special advantage for low distortion, why do tubed amps generally have more distortion than many SS amps?

If tubes had some kind of special advantage for low distortion, why is all modern distortion analysis equipment, which justifies having very low distortion based on solely solid state devices?

I ROTFL at tubed equipment designers who use all-SS gear as their reference - as their distortion analysis equipment.

OK, first -- Vacuum tubes as triodes have really low self-noise compared to transistors, so are good with very low-level stuff.
[/quote]

Except they don't.

Back in the day one of the first things that was migrated from tubes to SS was phono preamps. They were already triodes all along.
Quote:
Note that I do not mean pentodes! They can (note I wrote "can") have quite low distortion if used correctly. So you can have a really low noise, low distortion amplifier stage with no negative feedback loop around it.

What's wrong with feedback?

The only thing that is wrong with feedback is that it takes some serious technical background to understand it, and that makes it hard for rule of thumb amateurs.
Quote:
Transistors just about always require a negative feedback loop around them to be acceptably linear input-to-output.

Wrong. Transistors are plenty linear without loop feedback if you use local feedback, and/or are willing to put up with the sort of nonlinearity that tubes force down your throat.
Quote:
There's nothing wrong with NFB *when applied carefully and correctly*. But that ain't easy, and isn't always done right. So that is one advantage of a simple vacuum tube gain stage. It *can* be super-simple, linear and all without negative feedback to make things complicated. Not that there's anything wrong with NFB, mind you... But it is also true that many people just like the sound of a clean, simple triode gain stage that's done right. It's a nice thing, that's all.

Actually almost nobody wants triodes, which is why only second and third world countries produce them any more.
Quote:
Second, push-pull power amplifiers are NOT where tubes are at their best. The typical guitar amp tubes used in even the most expensive power amps are pretty bad. That includes all the popular types -- 6L6GC, EL34, KT88, 6550A, etc. even as triodes. All of those have pretty high 3rd order distortion, which does not cancel out with push-pull operation. They are high impedance devices, so need to be used with output transformers (OPT's) to match to 4 or 8 ohm impedance loudspeakers, which are really *expensive* to make right. You want a big OPT for high power, and it should have high primary inductance for good bass response *open loop* (before negative feedback is applied). But if you make the OPT really big and with high inductance primaries, you get bitten by the increased capacitance between windings, which degrades high frequency response all the way down to the point where it usually affects the high audio frequencies. It's a lose-lose situation there, yes it is. So yes, a 35W per channel tube power amp made with EL34's is going to perform very poorly compared to a very competently designed solid state power amp of similar power. Start looking at 100W per ch amps and there's simply no comparison any more. I won't argue that point with you, because that's the way it is.

But a phono preamp, or an output stage for a DAC? OK, I can argue that you can make a line level output stage from a triode that has (worst case) only about 0.5% second harmonic distortion and much lower 3rd HD, and only one-tenth of that in 5th HD, *without any negative feedback loop applied*. That's pretty darn linear. And it can even sound really good. I know it's silly, but I find the "sound" I get from a simple circuit with no negative feedback (NFB) loop around it to sound "relaxed" and "musically involving." If that can be made linear (low distortion) then I see no problem with doing that, if that's what some people like.

Also, there are so many bad sounding solid state audio circuits out there. For instance, I have a Panasonic SA-XR75 receiver which has what I think are fabulous sounding DAC's and power amp stages, but its analog line level inputs are ghastly sounding (and its FM tuner is miserable). It's obvious where Panasonic spent their money making this receiver, and for the asking price I think they made fine choices. But, its analog line level inputs still sound wretched. One *can* make bad sounding solid state audio circuits, even now.

Finally, yes, a typical tube power amp is a hobbyist's exercise, especially now that many relatively inexpensive HTR's (AVR?) can sound so good. If you're not building your own amps, I'd say it's best for rational people to buy as good an HTR as they can afford and put the big money into speakers. Or for a small stereo, there's gotta be a good, cheap integrated amp out there somewhere.

Have a look at Morgan Jones "Valve Amplifiers" 3rd edition and/or 4th edition for a nice introductory discussion of this stuff from a contemporary angle. It's very sensible and reasonable, and has lots of great [objective, measured] info on the current thinking in tube amp design (lots of transistorized support circuitry involved, and not just in the DC rectification circuits). It is NOT one of those silly 'audiophile boutique hobbyist' books with lots of arm-waving about the superiority of 12" fullrange speakers with alnico magnets! Really.
https://www.google.com/search?q=morgan+jones+valve+amplifiers

I'm trying to show that there isn't a black-white divide here. Tubes are not all awful for everything. Solid state is not 100% superior in every way there is (at least when it comes to low frequency amplification, aka "audio"). But to make a good audio power amp to drive real world loudspeakers for little money? Heck yeah, transistors rule for that. No doubt about it. So OK? Can we be friends?

Again the question I asked wan't answered. I expected no better. ;-)

You talk about amps with 0.5% distortion, and modern SS amps routinely beat that by a factor of about 100. There is one reason for tubed audio gear which is sentimentality, Nothing wrong with that, but I say call a spade a spade!
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post #83 of 83 Old 11-24-2013, 06:05 AM
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Arny, you know what? You're 100% right. End of story. Bye.

--

Hopelessly addicted to this stuff, but on a strict budget.
Snell Type C speakers
Homebrew DC-coupled, push-pull, 2A3 amp, Intact Audio volume control
RIAA preamp (similar to Arthur Loesch design) - Technics SL1200mk2- Denon DL160
Pioneer Elite PD-D6-J (CD, SACD)
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