Obviously not valves with a top hat anode connection at 750 Volts then.
No. I also do not particularly like the higher voltages, you know, when the wires have to be a certain distance apart or they would arc over. I have seen insulated top connectors, those would reduce the chance of getting zapped.
"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.
Depending on the tube and the circuit design, in some cases a small current can flow between the cathode and heater, introducing hum. Of course this is only noticeable in something like a phono preamp where the input signal is a couple of mV. After all, pretty much all tubes were used with AC powered heater. Only battery operated devices had DC heaters (and most tubes designed for battery operation were directly heated) back in the day when tubes were common.
It was common for small 6.3V transformers to be called "filament transformers". Guess why. Younger players may rarely if ever come across that term.
People building high-gain (high distortion) guitar amplifiers have reported that power the heater of the first tube with DC can cut down on hum that is otherwise inductively coupled through the heater wiring. It shouldn't do much in linear amplifiers. Apparently noisy DC on heaters can result in signal noise as well, surprisingly enough.
The usual heater construction is a folded wire inserted inside the cathode sleeve. In tubes specifically designed for low level audio preamp applications, a twisted/coiled heater wire was used to help cancel out the electromagnetic field that could couple into the cathode circuit and result in hum. An example is the 7025, which is a 12AX7 with a coiled heater, specifically designed for audio applications.
Another trick was to use the input stage heaters as cathode resistors for the push-pull output stage. In this way, they were operated on DC current, without the expense of additional transformer windings/rectifiers/filter caps.
A grid is a physical thing, conductive circular mesh surface placed between the cathode and anode of a tube. Grid drive is a voltage (AC + any required DC bias value) that will effect/control the current conduction between the anode and cathode terminals.
Let me rephrase: Grid Voltage and Grid Drive Voltage. It's specific to the tube tester.
Edit: Salas' tube tester.
Its not my tester, I just have a TV7 mutual conductance military tester, when the Klausmobile is a Russian curve tracer project that I don't think it ever went commercial
http://www.klausmobile.narod.ru/projects/pr_02_kmtt_e.htmA famous digital one was the Italian Audiomatica Sofia (great-expensive-obsolete) from the same guys that make the Clio electro-acoustic measurement system
The most accessible tracer today maybe is the µTracer 3+ kit
http://www.dos4ever.com/uTracer3/uTracer3_pag0.html
The grid is positive wrt the cathode!?
It's running in enhancement mode (to borrow a mosfet term). The data sheet gives data for depletion mode. I suppose that's a consequence of running the plate voltage so low. It's not a mode that's characterized on the data sheet. What do the curves look like for this mode? A spice model probably couldn't be trusted to give the correct result for this region of operation.
Look here http://klausmobile.narod.ru/testerfiles/6j9pe.htm
What's the difference in meaning of "Grid" and "Grid Drive" in the voltmeter section? Is this the voltage across a grid current sense resistor?
A modern tube tester. Cool!
Could be a sense voltage yes. Grid drive is overdriving a valve by pushing it to grid current leaking territory with near zero and above zero voltage swing, but there is also capacitor blocking possibility when AC coupled. i.e. to peg on big transients until discharged. Nasty distortion effect. It takes a DC coupled buffer driver stage either valve or Mosfet to really push it. Especially for power tubes where it makes sense. In this one its just a starved tube drive necessity to go down there because of little anode voltage available. The guys who made this headphone gadget amp wanted to have tubes for show off or to just spice it up too, but it looks they knew how to work with valves even in weird modes nonetheless.
Personally I prefer exact sound reproduction, not distorted, hence I use high end DAC coupled with monitor grade IEM.
What do you consider exact sound reproduction?
IMHO, there's absolutely nothing like the live sound of instruments (that are NOT electronically amplified in any way). How could a speaker, of which the membrane that must reproduce the sound is of a different shape than any instrument, ever come close to reproducing the sound faithfully? Oh, it does a good job at trying, but it doesn't come close to the real thing.
I have a good hifi system that even audiophiles wouldn't frown upon, and I am satisfied with it, but there's nothing like a live acoustic instrument. Perhaps that's one of the reasons why I recently took up learning to play the guitar (but it's also got something to do with doing it yourself).
Finally posting two questions...
One: the output stage has one amplifier driving another unity buffer, then paralleling the outputs. Does this not introduce distortion or other issues due to the propagation delay of the NE5532? I know it has a global feedback, but seems like it would still have issues. A better solution would seem to parallel both amplifiers? Maybe I'm wrong - not an expert on audio buffers, but want to become one.
Two: I have read numerous times never to use SMT ceramic capacitors in audio paths since they 'microphone' and distort the signal. Is this the case or no?
Bonus rant... I HATE HATE HATE blue LEDs under tubes. Looks lame and doesn't let the pretty 'natural' glow out. If anything put an amber one in. Blah!
In high quality audio gear, ceramic caps (not just SMT ones) are generally frowned upon as coupling capacitors because they exhibit a change in capacitance with applied voltage due to the piezoelectric effect. Some are worse than others, however.
Two: I have read numerous times never to use SMT ceramic capacitors in audio paths since they 'microphone' and distort the signal. Is this the case or no?
It depends. Class 1 (NPO, C0G, U2J,etc.) are pretty good.
Class 2 (X7R, Y5R, Z5U, etc.) can be pretty bad especially higher values in smaller packages. If the signal has frequencies for which the capacitive reactance is much smaller than the impedance of the rest of the circuit, it's not too bad. This would be the case for interstage coupling. Otherwise the lower frequencies cause intermodulation distortion. This would be likely be the case for filters and equalizers.
"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.
I've heard that is you hook up the filament backward the audiophiles can hear Paul McCartney whispering to them.
One: the output stage has one amplifier driving another unity buffer, then paralleling the outputs. Does this not introduce distortion or other issues due to the propagation delay of the NE5532?
Probably insignificant for audio frequencies. Anyway, the bias of the tube (12V anode-cathode voltage, 2.5 mA cathode current) is so atrocious that the distortion of that "buffer" will dominate everything (which is of course by design). It's not unlike operating a BJT in it's saturation area which is ridiculous for a linear amplifier.
Tubes have a reputation of having high distortion which is not true if the circuit is designed properly.
If anyone is interested, here is an article on designing a tube audio buffer without any snakeoil and audiophoolery by Stuart Yaniger:
http://syclotron.com/?page_id=2380
No true "audiophile" would buy a 50 dollar headphone amp, so this is not "audiophile quality".
In china, 50 dollars are like 500 dollars
Tell the same people that it has SMPSs in there, and it'll fall off it's pedestal in the blink of an eye.
That's the reason of rubbing off the ICs : people not recognizing that this is a SMPS would not be able to search the ICs
Two: I have read numerous times never to use SMT ceramic capacitors in audio paths since they 'microphone' and distort the signal. Is this the case or no?
It depends. Class 1 (NPO, C0G, U2J,etc.) are pretty good.
Class 2 (X7R, Y5R, Z5U, etc.) can be pretty bad especially higher values in smaller packages. If the signal has frequencies for which the capacitive reactance is much smaller than the impedance of the rest of the circuit, it's not too bad. This would be the case for interstage coupling. Otherwise the lower frequencies cause intermodulation distortion. This would be likely be the case for filters and equalizers.
I'll bet literal bottom dollar that they are Y5V. Maybe X5R, but larger than 0.1uF C0G are virtually non-existent and very expensive (have used a 0.1uF C0G before).
This will all be moot soon. Apple is dropping the 3.5mm analog output jack completely.
If you don't want to use wireless (Bluetooth) headphones, there will be digital headphones that plug into the Lightning connector.
No word on how you will plug in BOTH you headphones AND your charger, sync cable, etc.
Not letting the audio loose in the analog domain means they can enforce DRM right to your eardrums.
This will all be moot soon. Apple is dropping the 3.5mm analog output jack completely.
If you don't want to use wireless (Bluetooth) headphones, there will be digital headphones that plug into the Lightning connector.
No word on how you will plug in BOTH you headphones AND your charger, sync cable, etc.
Not letting the audio loose in the analog domain means they can enforce DRM right to your eardrums.
Wow is that for real? So in the near future the Apple user can't pipe his/her music to a typical analog audio amp/speaker system via a analog jack unless it's an approved and compatible amplifier?
Don't own anything Apple, so no problem here.
"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.
I've heard that is you hook up the filament backward the audiophiles can hear Paul McCartney whispering to them.
Who are you kidding, everyone knows Paul's dead, they told us that many many moons ago.
Or maybe his ghost lives amongst the vacuum in the valves.
The usual heater construction is a folded wire inserted inside the cathode sleeve. In tubes specifically designed for low level audio preamp applications, a twisted/coiled heater wire was used to help cancel out the electromagnetic field that could couple into the cathode circuit and result in hum. An example is the 7025, which is a 12AX7 with a coiled heater, specifically designed for audio applications.
Another trick was to use the input stage heaters as cathode resistors for the push-pull output stage. In this way, they were operated on DC current, without the expense of additional transformer windings/rectifiers/filter caps.
This is always a cute trick. I have a Fisher TA-600 that uses this system. One of the phono tubes developed a heater-cathode short, and that particular cathode was grounded. It did some unhappy things to the bias on the output stage.
There are certainly some interesting bits of economy used on electronics at times. One of the oddest I've seen on a tube amp was the original bias supply in my big Bogen PA amps. It used a 0.47 uf cap off the 300 VAC winding to feed through a diode to get the negative DC supply. That now has a small 6vac transformer fed backwards to run the bias supply.
Tube amps have long been a contentious thing in the electronics world. Audio guys tell you they sound better. Measurement devices tell you they are shite on a stick. Personally I say they are both true. Tube amps measure badly but are pleasing to listen to. Its the difference between steam power and internal combustion engines. By every measurable way the IC engine wins, but we still like steam trains.
I discovered a long time ago it makes no difference which way the little packets of energy go, it all works out just fine.
Also just too many parts to keep track of
24v K-A and a cathode follower arrangement? Whats the point? It would give lower output impedance, but feeding into an op-amp its not like that would be required. Not enough voltage to make any useful gain anyway. Wonder how far out of the linear operating range it is.
In my opinion there is no point, That is not a good tube for a cathode follower, the designer is not taking advantage of the high input impedance a vacuum tube offers, and as you pointed out the plate voltage (B+) is too low.
The designer isn't even trying to prove something.
Why not?
build a 30W headphone amplifier using all tubes, no output transformer, using an output differential amplifier with cathode output. (to keep the voltage and impedance low)? Run it on say............125V regulated(+/- 65.5V).
That would be a concept amplifier worth building, if for no other reason than to prove the idea.
Why 30 watts, not many headphones can accept even peaks at that level? About the only thing that might differentiate a 'headphone amp' form other audio amps is that it might be designed to only work at the higher output impedance of most headsets.
Not many headphones can accept 30W RMS, but 30W peaks? Sure.
I do not suspect that your ears would though. It takes such a tiny amount of power to run a set of cans that even a watt of power would give you ample dynamic range for anything you want to listen to, even at levels that would make your ears bleed. There are a few designs out there for straight cathode drive can amps with low tube count. A 6AS7 works nicely for OTL headphone amp duty.
I have a headphone amp with a white cathode follower made from ECC88s (voltage gain stage is another ECC88). Works quite well, even with 32ohm headphones. Though I currently use 300ohm headphones (did not specifically search for the high impedance).
As for why I need a headphone amp - not all devices I have provide a headphone output and I did not want to use a speaker amp for the headphones all the time (too easy to accidentally turn on the speakers in the middle of the night).
"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.
I've heard that is you hook up the filament backward the audiophiles can hear Paul McCartney whispering to them.
I thought he was dead... we're supposed to be stuck with Faul now...
Just because they're removing the 3.5mm jack, doesn't mean it won't still output analog audio. They could very well push the analog audio over a couple of pins on the Lightning connector. The older 30-pin connectors did that. You would then use a simple Lightning to 3.5mm adapter.
If they don't do analog transport over the Lightning port, they'd be to just stick a DAC in the adapter.
Or they won't remove it from the phone at all. 99% of Apple rumors are wrong, so perhaps it's best not to spread FUD just yet. Also, Apple patents *a ton* of stuff. Of that, a small number makes it into production.
Either way, you'll still be able to use headphones, I guarantee that. It's sort of a basic requirement.
Just because they're removing the 3.5mm jack, doesn't mean it won't still output analog audio. They could very well push the analog audio over a couple of pins on the Lightning connector. The older 30-pin connectors did that. You would then use a simple Lightning to 3.5mm adapter.
If they don't do analog transport over the Lightning port, they'd be to just stick a DAC in the adapter.
Or they won't remove it from the phone at all. 99% of Apple rumors are wrong, so perhaps it's best not to spread FUD just yet. Also, Apple patents *a ton* of stuff. Of that, a small number makes it into production.
Either way, you'll still be able to use headphones, I guarantee that. It's sort of a basic requirement.
There is a trend to remove the analogue link to the outside world, the copyright people want to make it hard to plug that phone (or whatever) into a recording device. They think we are all criminals and want to share our music with the world.