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Tube Rolling: Does it Make a Difference?

amirm

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I recently reviewed the Mhdt Pagoda tube DAC. Owner was kind enough to send me three other tubes to test with it. Here are the set of tubes I received:

DAC Audio Stereo Tube Rolling Measurement Review.jpg


Let's start again with the tube supplied with the unit (GE 5670)

MHDT Pagoda Measurements 5670 Tube Stereo DAC.png


Now let's switch to Tesla 6CC42 (GA):

MHDT Pagoda Measurements 6CC42GA Tube Stereo DAC.png


Other than slightly more mains hum at 60 Hz, I see no other difference. Gain is reduced negligible amount.

Next up is the Western Electric JW2C51:

MHDT Pagoda Measurements Western Electric JW2C51 Tube Stereo DAC.png


Distortion is 0.7 dB lower. So nothing significant there.

Finally I tested the Western Electric 396A tube which produced a surprising result:

MHDT Pagoda Measurements Western Electric 396A Tube Stereo DAC.png


Channel 1 is the same but channel 2 has 6 dB lower distortion. Is half the tube better or is there some asymmetry in the design?

That's all I have for you. :)

Conclusions
It is clear that by far the source of distortion is the design and not choice of tube. In three cases the difference is negligible and inaudible. In the forth example, the WE 396A, there is reduction of distortion in one channel. In the larger picture, there is so much distortion here that reducing it with this tube is not going to make a difference one way or the other.

Notice the level of instrumentation it takes to see the impact of the tube. You need to measure to see if there is a difference and not just assume there is.

Personally even if I signed up for a tube product, I would not waste time "rolling tubes." You are likely to suffer more from "rolling placebo" by your brain than any variation in such tubes.

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As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

richard12511

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I recently reviewed the Mhdt Pagoda tube DAC. Owner was kind enough to send me three other tubes to test with it. Here are the set of tubes I received:

View attachment 168967

Let's start again with the tube supplied with the unit (GE 5670)

View attachment 168968

Now let's switch to Tesla 6CC42 (GA):

View attachment 168969

Other than slightly more mains hum at 60 Hz, I see no other difference. Gain is reduced negligible amount.

Next up is the Western Electric JW2C51:

View attachment 168970

Distortion is 0.7 dB lower. So nothing significant there.

Finally I tested the Western Electric 396A tube which produced a surprising result:

View attachment 168971

Channel 1 is the same but channel 2 has 6 dB lower distortion. Is half the tube better or is there some asymmetry in the design?

That's all I have for you. :)

Conclusions
It is clear that by far the source of distortion is the design and not choice of tube. In three cases the difference is negligible and inaudible. In the forth example, the WE 396A, there is reduction of distortion in one channel. In the larger picture, there is so much distortion here that reducing it with this tube is not going to make a difference one way or the other.

Notice the level of instrumentation it takes to see the impact of the tube. You need to measure to see if there is a difference and not just assume there is.

Personally even if I signed up for a tube product, I would not waste time "rolling tubes." You are likely to suffer more from "rolling placebo" by your brain than any variation in such tubes.

----------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
Thanks for measuring this. Something I've always been a bit skeptical of.

Also interesting to see that this tube amp has loudspeaker like distortion numbers :oops:.
 

Pirx

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There must be something wrong with topology of tube stage.
PCM1704 is really great DAC, and simple tube stage shouldn't be so bad.
I wonder what is going on there, anyone has a schematic?
 

xaviescacs

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It's possible that we can't see the effect of different tubes in this case because it gets masked? Or all tubes perform really the same? Perhaps in a better design different tubes make bigger difference.
 

Doodski

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O JoY! Here is a blurb on Mhdt.

"The gang of four founded Mhdt Lab in 2002 and are known as: ‘Music Heaven Development Team’.
They had decided to begin designing DACs to bring the feeling and fun back to digital. Motivated by the shortcomings of most DACs to faithfully convey, with spirit, varying styles of music, they have successfully created affordable great sounding and flexible little gems."
 

xaviescacs

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People would be better experimenting with putting different electric guitar pedals into their system if they like all their music to sound like it's being played by Edge from U2
I friend of mine used to do this with his guitar pedals, it's quite fun actually.
 

solderdude

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There must be something wrong with topology of tube stage.
PCM1704 is really great DAC, and simple tube stage shouldn't be so bad.
I wonder what is going on there, anyone has a schematic?

Looks like the circuit isn't a simple cathode follower. The measurements would be a lot better this way and thus less 'tube goodness'.
So it looks like the tube stage amplifies the signal and that's why measurements are poor and 'tube sound' is maximized.

Would have been interesting to see distortion profile at say -10 and - 20dB
 

Drengur

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I love tubes. I've had a system that would only work with tubes. My Proacs, for instance, refused to sound good with (almost) anything other than an ancient Pioneer SM-83 tube amp. By good, I mean pleasant, like barely picking up an overseas station on long wave radio that happens to be playing a song you like. That was a fun system that taught me a lot about myself. I am not a patient man, nor am I particularly keen on pseudo-science.

The next (il-)logical step would have been to pair it with an old vinyl player, but I was old enough when my father bought his first CD player (a JVC we still have around, it is the most un-dynamic piece of gear ever) to be impressed by the upgrade from vinyl, but young enough to not hold on to nostalgia.

This two year period of having a tube amp with many, many watts (tens of of them allegedly), as a daily driver gave me so much. I've had various tube buffers / CD players etc. and better tube amps throughout the years, but I have never had a system that is only listenable with the help of distortion before or since. I now understand the feeling of having such a flaky setup that connecting worse and worse gear is like multiplying two negative numbers.

If only my current boring desktop system was as temperamental. I miss the days of spending 3-4 hours of twiddling and tweaking and listening for minutes before a cloud of despair rolls over me and I give up. My days now mostly comprise of sitting down, turning on the DAC/HP amp and listening to music for hours on end. Is this all there is to life?

Will I ever buy tube-gear again? No. Do I like tube disortion? Sometimes, maybe. Was there a point to this story? Probably not.
 

Paolo

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Does swapping tubes has an effect on the FR or is just noise?
 

Pirx

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Looks like the circuit isn't a simple cathode follower. The measurements would be a lot better this way and thus less 'tube goodness'.
So it looks like the tube stage amplifies the signal and that's why measurements are poor and 'tube sound' is maximized.

Would have been interesting to see distortion profile at say -10 and - 20dB
Indeed, CF would be better, but they are proud of producing even 3 V at the output of this DAC - so probably tube amplifies signal.
I cannot understand why and how they decided "this is it, let's sell it" ?
I have made many tube amplifiers for myself, some were really bad, but I would never think of them "that is great" - just mistake.
Simply integrated sound-card from PC would tell them that there is something wrong with this device.
Did they deny to make any measurements? Magic brand.
 

maty

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If there are differences between valves, which I suppose, to detect them the harmonics would need to be lower, I say. H2 at -73 dB and H3 about 10 or more dB below.

H2 at -40 dB will match tube sound.

If you want harmonics, better idea with PKHarmonics VST plugin.
 

DSJR

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I love tubes. I've had a system that would only work with tubes. My Proacs, for instance, refused to sound good with (almost) anything other than an ancient Pioneer SM-83 tube amp. By good, I mean pleasant, like barely picking up an overseas station on long wave radio that happens to be playing a song you like. That was a fun system that taught me a lot about myself. I am not a patient man, nor am I particularly keen on pseudo-science.


Will I ever buy tube-gear again? No. Do I like tube disortion? Sometimes, maybe. Was there a point to this story? Probably not.

I'm reliably told that Pro-Acs were designed and set up using ARC amplification. The now deceased designer was well able to configure odd driver combinations to do what he wanted (usually a kind of 'V' or 'saddle-back' shaped response.
 
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SIY

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Looks like the circuit isn't a simple cathode follower. The measurements would be a lot better this way and thus less 'tube goodness'.
That depends. I've seen a LOT of incompetent high distortion cathode follower circuits. Two common mistakes: assuming low output impedance means low loads are driveable (so yeah, let's use a 12AX7!), and biasing (with the grid at 0V, just take the signal off the 1k cathode resistor!).
 
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