[tomb]

 

  I recently jumped in on a drop for the Aune T1 MK2 headphone amp, and as I was reading more about it I ran across the following post on reddit (there is a very good chance that this guy posts in here too, I'm sure):
 
quote:
 
Dude, this is not a tube amp. This is a solid state amp with a decorative tube.
If there is no high voltage power supply, then it is not a tube amp.
Here, have a look at the 6922 datasheet. As you can see, it is designed to run at 100V-200V. This amp does NOT supply 100V-200V to the 6922.
Tubes have a filament, so they need a second voltage supply in addition to the the main one. But filaments only need 6V or 12V (generally, some have different requirements). The 6922 needs only 6V. So the amp provides 6V to make it light up and then solid state does all of the amplification.
It's like sticking a vacuum tube on the hood of your car, supplying 6V to make it light up, and then claiming that your car is powered by a vacuum tube. Which is just as much ******** as these phony "hybrid" amps are. Don't be a sucker. Don't buy it.
 
/quote
 
I'm a noob when it comes to what is physically happening inside of an amplifier; can anyone enlighten me as to what he means here?  Is any inexpensive 'tube amp' essentially a ripoff?

The person who wrote this is clueless. The tube you place in the T1 has a significant impact on the sound you get from the DAC portion of the T1. As was stated earlier, the amp inside the T1 is solid state. The tube in the T1 is a buffer for the DAC and basically determines the characteristics of the sound you get from the DAC. Essentially, the "better" the tube, the "better" the sound. I put better in quotes because better is subjective and depends on your tastes.
 
Tube amplifiers are different in design and serve a different purpose (because...they are amps). But the tubes in tube amplifiers serve the same overall purpose as a tube in a DAC like the T1. In a tube amp, the tube(s) define the characteristics that the amplifier imparts on the sound.

 
Let's try to deconstruct some of these comments.

If there is no high voltage power supply, then it is not a tube amp.
Here, have a look at the 6922 datasheet. As you can see, it is designed to run at 100V-200V. This amp does NOT supply 100V-200V to the 6922.

Not true.  There are tubes that are designed to run with only 12-24VDC on their plates.  One famous tube that has almost disappeared from the market because of it's extensive use  - the 6GM8. The max voltage rating on the plates is 30V.  The MiniMAX uses tubes that are rated for 30V maximum on the plates (12AE6, 12FM6, 12FK6).
 
Then there's the whole scenario where tubes are purposely run at lower voltages.  This is often done in hybrid amps so that the same voltage source can be used for the solid-state output buffer.  It doesn't mean that the signal stage is not truly running the tube as a signal gain device.  Still, run a tube at reduced voltage on its plates (compared to it's normal rating) and its sound will not be as linear.  There will be noticeable effects in frequency response and perhaps increases in distortion as well.  Still, it doesn't mean the tube is not operating as a tube.
 

Tubes have a filament, so they need a second voltage supply in addition to the the main one. But filaments only need 6V or 12V (generally, some have different requirements). The 6922 needs only 6V. So the amp provides 6V to make it light up and then solid state does all of the amplification. 

 
What's said there about filaments (or tube heaters) is true enough, but that doesn't mean it's not operating as a tube - just with reduced voltage.  6V is pretty easy to achieve, even in a solid-state amp.  Chances are, the voltage is much higher in the solid state section.  Unless the design is running off of USB power or batteries, most likely the solid state has a higher voltage.  As for the tube, there's nothing that says it can't operate at the lower voltage.  As long as the heater is lit, it can move electrons from the cathode to the plate.
 

It's like sticking a vacuum tube on the hood of your car, supplying 6V to make it light up, and then claiming that your car is powered by a vacuum tube. Which is just as much ******** as these phony "hybrid" amps are. Don't be a sucker. Don't buy it. 

 
If this person had qualified this statement some by stating a preference for a "true" tube amp (no solid state in the signal path, in extreme cases, a tube rectifier, output transformers, etc.), he might have a case and we could cut him some slack.  Hybrid amps are valid.  Strictly speaking, they may not be "true" tube amps, but it doesn't mean that the tube is not operating.  It's not a light bulb (although Nelson Pass has used those for actively setting current bias in an amp).
 

Tube amplifiers are different in design and serve a different purpose (because...they are amps). But the tubes in tube amplifiers serve the same overall purpose as a tube in a DAC like the T1. In a tube amp, the tube(s) define the characteristics that the amplifier imparts on the sound. 

 
I'm not really sure about this one (different author).  Regardless of the extreme argument offered by the first guy, he has a little bit of a point.  That is to say, there is no logical reason to employ a tube in a DAC other than to offer "color."  It will be operating at reduced voltage, most likely, and as such will have left any presumption of operating in a linear, low-noise, low-distortion regime.  Further, it is clearly stated that the tube in the Aune is used in the buffer output.  Well, buffers are typically there to supply current, not voltage.  Voltage is typically the same as it was in the previous stage, in this case the output from the DAC.  That's not going to be very high.  Unfortunately, tubes do not supply current very well at all.  They are essentially voltage amplification devices.  This is contrary to the idea of an output buffer.  One might conclude from this that the tube is indeed there for nothing but "coloration."
 
Tubes in a tube amplifier, on the other hand - even ones at reduced voltage as with a tube hybrid amplifier - serve a specific purpose: they amplify and provide gain in the signal stage.  This is what most tubes are designed to do, not provide "coloration."

 

[jnorris]

In my opinion, a tube amp should be a tube amp from input to output. These "hybrid" amps are only inserting a tube stage to add euphonic colorations to the sound. A "Tube DAC"? Yeah, no, I don't think so. Just because the output of a DAC chip is sent to a tube amp or buffer doesn't make it a tube DAC - it merely means that the solid-state audio from the DAC chip is softened or otherwise obfuscated by the tube stage.

 

[Kununa]

In my opinion, a tube amp should be a tube amp from input to output. These "hybrid" amps are only inserting a tube stage to add euphonic colorations to the sound. A "Tube DAC"? Yeah, no, I don't think so. Just because the output of a DAC chip is sent to a tube amp or buffer doesn't make it a tube DAC - it merely means that the solid-state audio from the DAC chip is softened or otherwise obfuscated by the tube stage.

But you get the "tube sound". It doesn't matter if it's technicaly superior or not. A lot of people like this kind of sound even if it's colored.

 

[jnorris]

But you get the "tube sound". It doesn't matter if it's technicaly superior or not. A lot of people like this kind of sound even if it's colored.

 


I get that - it's a "Whatever-floats-your-boat" thing. To each his own. It just brings up memories of Bob Carver tailoring the sound of his amps to match some of the higher-end amps of the period. You're either committed to accuracy or not.

 

[joeq70]

In my opinion, a tube amp should be a tube amp from input to output. These "hybrid" amps are only inserting a tube stage to add euphonic colorations to the sound. A "Tube DAC"? Yeah, no, I don't think so. Just because the output of a DAC chip is sent to a tube amp or buffer doesn't make it a tube DAC - it merely means that the solid-state audio from the DAC chip is softened or otherwise obfuscated by the tube stage.

Arbitrary line-drawing.

 

[tomb]

In my opinion, a tube amp should be a tube amp from input to output. These "hybrid" amps are only inserting a tube stage to add euphonic colorations to the sound. A "Tube DAC"? Yeah, no, I don't think so. Just because the output of a DAC chip is sent to a tube amp or buffer doesn't make it a tube DAC - it merely means that the solid-state audio from the DAC chip is softened or otherwise obfuscated by the tube stage.

Sorry, but a hybrid tube amp is using the tube for amplification.  That's hardly just "euphonic coloration."  A tube hybrid uses the solid-state as an output buffer (no gain).  This is done because a tube likes to drive very high-impedance loads (as in 1000's of ohms).  The input to most transistors is near this level.  Certainly buffers with a FET input can be on the order of 100K ohms.  It's why early tube stuff used ceramic drivers in headphones and they had impedances in the 1000's.  That way, the tubes could drive them directly.  Of course, the use of output transformers takes care of this, too.  For instance, the Edcors used in the amps I sell have a 10K input (what the tube sees), but then the outputs are selectable for 32 and 300 ohms headphone loads.
 
Solid-state is quite happy driving low impedances directly.  It's a good method to use signal tubes and still be able to drive headphones without output transformers.  Whether you want to call one a true tube amp is a valid issue, but the tubes are not sitting in a hybrid amp to look pretty.
 
I agree with you about a DAC.  There's no way tubes can be used in the primary circuit of a DAC.  First of all, these days they're all chips.  Even if one was to make a rudimentary DAC circuit using tubes, the noise level of the tubes would be way too high to do any good.  You can hardly use tubes in phono pre-amps, either, but it's done if the tubes are of a high enough S/N ratio.  At any rate, the explanation in the 1st paragraph above gives some indication for why tubes are no good for output buffers, either.  So maybe they are there "to add euphonic coloration" for a DAC.