Tube can work in low volt~~fix your knowledge

[soro]

As we know tube are work in high volt.
but in this circuit tube are work in low volt.
and work in linear.

[lineup]

Yes, it can work at lower voltages.
But distortion is of course much much higher.
By using an EMITTER Resistor on the tube, you can try lower current.
The lower the current, the less distortion.

Higher EMITTER resistance - lower current - lower distortion.

What is good with your circuit is the use of OP-Amp as load.
Tubes want very light loads. And have difficulty with heavier loads.
Op-Amp, especially with JFET input (like OPA2134) is practically no load at all.
So, that's perfect

[DF96]

That circuit is likely to have significant grid current, so needs feeding from a low impedance source. The op-amp may offer practically no load, but there is still an anode resistor so not perfect. It is not necessarily true that the lower the current, the less distortion.

This circuit neatly combines two issues: a poorly biassed valve, and an op-amp with high levels of feedback. So you get lots of low-order distortion from the first and (allegedly) lots of high-order distortion from the second. And almost no headroom!

My knowledge tells me that most valves work best at higher voltages. I don't intend to "fix" my knowledge, as it is isn't broken.

[teemuk]

I think the main point in using tubes today is to have them introduce distortion. If circuits with them sound ordinary and clean people would likely just think the tubes are broken or in there just for show. You know, you've got to hear that tube sound, right...?

If the intention is clean sound reproduction you might as well just use an OpAmp that introduces less than 1% of THD.

So, I figure that for modern applications of tubes the starved plate voltage is a actually a pretty good solution.

[DF96]

THD isn't the whole story, as many on here will point out, although it is part of the story.

There are many today who use valves because they introduce distortion. There are some who use valves because they avoid some of the solid-state problems, and do sound nice. Unfortunately these two groups often claim to be one group, and end up denying reality. Then they wonder why sand people sometimes laugh at them.

My rule of thumb is that anyone who puts the valves prominently on display (or, even worse, lights them up with LEDs) is using them mainly because they look nice, rather than sound nice. Better to hide them away and let them get on with their job in a well-designed circuit, then you get good sound.

What does seem perverse is to use valves and sand together in a way which combines their weaknesses!

[soro]

in this circuit tube is a typical common cathode amplifier.OP is a buffer.
If it has the less distortion we can use an oscillosc to test it.
but I do not see any distortion in it. ( maybe it is very low )
I do not use LED to lights them up. only a blue LED for power on.
If it does not work in linear that sound will be terrible.

[lineup]

Originally Posted by teemuk

I think the main point in using tubes today is to have them introduce distortion. If circuits with them sound ordinary and clean people would likely just think the tubes are broken or in there just for show. You know, you've got to hear that tube sound, right...?

If the intention is clean sound reproduction you might as well just use an OpAmp that introduces less than 1% of THD.

So, I figure that for modern applications of tubes the starved plate voltage is a actually a pretty good solution.

I think you have very good points there.
I am The Sandman.
Now my simulator has got some tube models.
For now I have played some with 6DJ8 and 6H30P.
As have dealt with transistors and tried to minimize THD
the old habbit is there when I sim with TUBES.
I do everything to get rid of that dist.

I think you are right.
Maybe I must change my way of thinking, when dealing with valves.
While transistor distortion can be terrible to get into music
probably some little level of Tube-dist wont hurt my listening experience.


Loooking at the circuit at hand,
we have Tube, which will induce some distortion. No doubt.
The Op-Amp we can say will produce zero dist. No distortion.
As a follower there is practically no THD at all.

SUM: We will hear the TUBE.
If there is any contribution, alteration to the input signal
it is coming from the TUBE.

[DF96]

If you see no distortion with an oscilloscope all it means is that distortion is less than a few %, not necessarily low. I was not saying that you light it up with LEDS, but some people do.

Unless you like listening to distortion you would probably do better to remove the valve and just use the op-amp to get the gain you need. If you want to use a valve then do it properly with a higher supply voltage.

Valve distortion usually doesn't sound as bad as transistor distortion, but it is still distortion not accuracy.

[teemuk]

Originally Posted by DF96

I was not saying that you light it up with LEDS, but some people do.

Those LEDs are actually quite a good example of the modern ways to perceive tube-based technology. People need to see those tubes really glowing, and if that glow doesn't match their expectations (like could easily happen in cases where the filament just happens to be mostly hidden due to mechanical design of the tube's interior) people again think the tubes are either broken or that they are being fooled and that the tubes are there just for show - instead of " working hot at their melting point" (which of course none of decently made tube designs did to begin with).

So, manufacturers put LEDs to their products to make them glow more "authentically", because many people actually care more about that than about the actual performance. Few years ago someone discovered such LEDs in a Behringer mic preamp and it resulted into a big scene where people were jumping in to claim that the tubes were not even in the circuit. Like, how could they be because Behringer had to use LEDs to illuminate them - obvously they were fooling people. No one even bothered to test if the claim was true or not (of course it wasn't, the tubes were in the circuit). So, after that LED exposure, people were suddenly not hearing the "tube tone" in what essentially and really was "tube tone". Another ironic part was that Behringer marketed those preamp units with a marketing phrase that tubes introduced "warmth and transparency" to the signal.

So, do not underestimate the importance of seemingly stupid things like illuminating LEDs and mere presence of tubes. The mere imago of something can have quite big psychoacoustical influences - but those influences are not neccessarily consistent and can be rather subjective.

Recently someone even patented a circuit that features heater elements to heat the internal components excessively because people also expect that their equipment should run very hot - because common perception seems to be that running hot is better and makes things sound greater.

The unfortunate thing is, I'm not even kidding. We've come a long way from the 1950's - 1960's when tubes were top-notch HiFi and designers took pride in making tube circuits with excellent performance data concerning things like distortion and bandwidth. Nowadays it's pretty much the opposite and I guess that's the main reason that even kept tube designs floating. Just look where the are mostly used now: Guitar amps with excessive amounts of distortion. Far, far away from HiFi.

[DF96]

There are still some designers who try to get the best out of valves, recognising their advantages and limitations. Valves are more tolerant than transistors: a bad solid-state design is likely to sound nasty or fail, but a poor valve design might still sound not too bad and may soldier on. A good valve design will sound excellent, even though it will not have as many zeroes after the decimal point in its THD.

Sprinkling the odd valve between transistors/chips is generally either cynical or ignorant, depending on whether the designer is deliberately taking money off the innocent or genuinely believes in "tube warmth".