If "Tube Sound" Is a Myth, Why Tubes?

[andreasmaaan]

Definitely high enough to audibly affect the amplitude response.

 

[MattHooper]

Hi Matt, I hope you can do some DBT amp testing some day as I would love to hear your comments.... the equipment needed is not extensive or expensive. Regarding the "coloration" of tube amps, I believe you can get 90% of it just by putting a 1 Ohm 10 watt resistor in line with the speakers of a SS amp. This simulates the internal resistance of the output transformers and will give you a FR and damping factor very similar to a tube amp. I am skeptical about hearing distortion differences between amps but FR differences due to internal resistance can add up to multiple dB differences at some frequencies. I saw a chart of a Klipsch Horns somewhere where there was a 10 dB difference at some frequency in FR between SS and tube amps due just to internal resistance differences.... I think I could even hear that.

Yeah, I only bother with blind testing once in a blue moon when I need to or get fired up.

If I had the equipment right now I'd do the blind test. I may ask my local hi-fi service shop if they have any form of switcher that they could lend me that would work. (I doubt it).

I've heard subtle "am I hearing this?" differences that disappeared once I blind tested. But I would be very impressed if I couldn't tell a difference between the CJ and Bryston, given the sonic difference really seems distinct.

 

[SIY]

I've heard subtle "am I hearing this?" differences that disappeared once I blind tested. But I would be very impressed if I couldn't tell a difference between the CJ and Bryston, given the sonic difference really seems distinct.

Interestingly, Stereophile's writeup suggests that the basic control experiment (can the CJ and the solid state amp be distinguished before all the fiddling around?) wasn't done at the beginning.

 

[MattHooper]

Yes, good point SIY!

 

[dfuller]

Even 0.5 Ω is pretty high (compared to solid state amps that easily do 0.05 Ω).

This is true. Tubes are inherently high impedance devices even through an impedance matching transformer compared to solid state.

Definitely high enough to audibly affect the amplitude response.

Eh, not really. 0.7R into an 8R nominal load is still fulfilling that 10:1 load:source ratio for impedance bridging.

 

[andreasmaaan]

Eh, not really. 0.7R into an 8R nominal load is still fulfilling that 10:1 load:source ratio for impedance bridging.

Yes, but this rule-of-thumb ratio is insufficient if the criterion is that amplitude response deviations should not rise above audibility thresholds (unless of the course the loudspeaker in question has an extremely - implausibly - flat impedance response).

 

[tuga]

Disclosure: my university education was in applied physics and signal processing, and I currently work in the software industry, so my knowledge of electrical engineering is not zero, but I'm no EE. So apologies in advance for any technical errors.

This thread is inspired in part by comments I've seen from @SIY , and others, that there is no such thing as "tube sound", per se, and that properly designed tube amps should be neutral.

Which then raises a number of questions, in my mind:

--If tube based amps can be made to avoid "tubey sound", why bother with tubes instead of solid state?

--If a tube based amp is designed to avoid "tubey sound", what impact does that have on tube rolling?

--If a tube based amp is designed to avoid "tubey sound", does it have any impact on the output impedance, current, or other factors that differentiate tubes from solid state?

--Does it matter at all if there are tube rectifiers in the circuit?

--Is there a reason to prefer transformers to boost converters?

--Between driver, power, and rectifier tubes, which are have the most impact on the sound, assuming a "non tubey" design goal?

--If tubes don't have a sound, what's the point of hybrid tube amps?

You may find this an interesting read.
It's about the creative use of tube and transformer and tape distortion in the production of recorded music.
Used at home, such colouration is a bit like producing your own remaster...without much control over the result.

Analogue Warmth
The Sound Of Tubes, Tape & Transformers

https://www.soundonsound.com/techniques/analogue-warmth

 

[levimax]

If it means anything, the output impedance of the ST-70 II is well under an ohm from both 4 and 8 ohm outputs (~0.7R or lower on 8 ohm, 0.5R or lower on 4). I'm not sure that you can simplify it to "it's just higher output impedance". More likely the sound is related to the fact that tube amps are both higher distortion and roll off quite a bit of top end (referencing the ST-70 II again, it's 2dB+ down at 20KHz).

Dynaco ST-70 is only down .5 dB @ 20 Khz per Amir https://www.audiosciencereview.com/...review-and-measurements-of-dynaco-st-70.7224/ . Looking at some of the impedance curves Amir has been posting in his speaker tests even 0.7 ohms would react with them quite a bit compared to the vanishing low output impedance of most SS amps.

 

[MattHooper]

Hmm, I was starting to hope I might pull off a blind shoot out of the Bryston and CJ amps, but my hopes are dimmed about setting up a switcher.
Reading this:

http://audio-room.net/connecting-2-...eakers-making-an-ampspeakers-selector-switch/

And some other commentary on line suggests that it's a dicey proposition to switch between a tube amp and a solid state amp, especially leaving the tube amp with no load. Also the only appropriate commercial switcher seems to be over $250.

https://www.amazon.ca/TC-7220-Ampli...show_all_btm?ie=UTF8&reviewerType=all_reviews

Too bad.

In playing around with the amps the differences I mentioned seem distinct. One that fascinated me was a record of an italian soundtrack, a slow piece, in which someone begins to lightly whistle the tune accompanying the instruments. It was really weird on the Bryston were everything sounded "harder" and the whistling took on a hardened tone that made it sound more like an electronic signal, like a theramin, rather than a human whistling. That's a bit of exaggeration to make the point as I could still tell it was someone whistling...but it just took on a more electronic character.

With the tube amp back in, it went back to the softer sound that seemed more human-breath like, very easy to believe I'm hearing "real" whistling.
I don't think of course that the tube amp is "more detailed" but the slight character change has interesting (to me) consequences for my perception of the sound.

I really would like to see how things hold up in a blind test.

 

[watchnerd]

You may find this an interesting read.
It's about the creative use of tube and transformer and tape distortion in the production of recorded music.
Used at home, such colouration is a bit like producing your own remaster...without much control over the result.

Analogue Warmth
The Sound Of Tubes, Tape & Transformers

https://www.soundonsound.com/techniques/analogue-warmth

Very familiar with this.

See the reel in my avatar?

 

[levimax]

Hmm, I was starting to hope I might pull off a blind shoot out of the Bryston and CJ amps, but my hopes are dimmed about setting up a switcher.
Reading this:

http://audio-room.net/connecting-2-...eakers-making-an-ampspeakers-selector-switch/

And some other commentary on line suggests that it's a dicey proposition to switch between a tube amp and a solid state amp, especially leaving the tube amp with no load. Also the only appropriate commercial switcher seems to be over $250.

https://www.amazon.ca/TC-7220-Ampli...show_all_btm?ie=UTF8&reviewerType=all_reviews

Too bad.

In playing around with the amps the differences I mentioned seem distinct. One that fascinated me was a record of an italian soundtrack, a slow piece, in which someone begins to lightly whistle the tune accompanying the instruments. It was really weird on the Bryston were everything sounded "harder" and the whistling took on a hardened tone that made it sound more like an electronic signal, like a theramin, rather than a human whistling. That's a bit of exaggeration to make the point as I could still tell it was someone whistling...but it just took on a more electronic character.

With the tube amp back in, it went back to the softer sound that seemed more human-breath like, very easy to believe I'm hearing "real" whistling.
I don't think of course that the tube amp is "more detailed" but the slight character change has interesting (to me) consequences for my perception of the sound.

I really would like to see how things hold up in a blind test.

Hello @SIY.... I have a "switcher" that does as Matt mentions i.e. when amp switched out it goes "open". I know tube amps theoretically don't like "open" but that it is not 100% cut and dry that it will cause damage (I know I have run mine into "open" accidently with no issues). Is there a higher load like 50 or 100 or even 500 ohms that I could wire into my switcher that would protect the tube amp but not have to dissipate as much power as an 8 ohm load?

 

[Blumlein 88]

Hmm, I was starting to hope I might pull off a blind shoot out of the Bryston and CJ amps, but my hopes are dimmed about setting up a switcher.
Reading this:

http://audio-room.net/connecting-2-...eakers-making-an-ampspeakers-selector-switch/

And some other commentary on line suggests that it's a dicey proposition to switch between a tube amp and a solid state amp, especially leaving the tube amp with no load. Also the only appropriate commercial switcher seems to be over $250.

https://www.amazon.ca/TC-7220-Ampli...show_all_btm?ie=UTF8&reviewerType=all_reviews

Too bad.

In playing around with the amps the differences I mentioned seem distinct. One that fascinated me was a record of an italian soundtrack, a slow piece, in which someone begins to lightly whistle the tune accompanying the instruments. It was really weird on the Bryston were everything sounded "harder" and the whistling took on a hardened tone that made it sound more like an electronic signal, like a theramin, rather than a human whistling. That's a bit of exaggeration to make the point as I could still tell it was someone whistling...but it just took on a more electronic character.

With the tube amp back in, it went back to the softer sound that seemed more human-breath like, very easy to believe I'm hearing "real" whistling.
I don't think of course that the tube amp is "more detailed" but the slight character change has interesting (to me) consequences for my perception of the sound.

I really would like to see how things hold up in a blind test.

You don't need much of a load to make the tube amp safe. A 220 ohm 5 watt resistor left across the amp leads for 16 ohms and common should do it just fine. This is assuming you are also stopping the input signal to it. I might want a lower resistance if you continue applying an input signal.

 

[SIY]

Hello @SIY.... I have a "switcher" that does as Matt mentions i.e. when amp switched out it goes "open". I know tube amps theoretically don't like "open" but that it is not 100% cut and dry that it will cause damage (I know I have run mine into "open" accidently with no issues). Is there a higher load like 50 or 100 or even 500 ohms that I could wire into my switcher that would protect the tube amp but not have to dissipate as much power as an 8 ohm load?

What @Blumlein 88 said. A safety resistor is all you need.

Pay some attention to his earlier comments as well- bass is where you can hear differences as power demands go up. Of course, with a speaker having significant impedance dips, if you can spot the difference in a DBT, it may be fun to follow that up with EQed comparisons.

 

[MattHooper]

What @Blumlein 88 said. A safety resistor is all you need.

Pay some attention to his earlier comments as well- bass is where you can hear differences as power demands go up. Of course, with a speaker having significant impedance dips, if you can spot the difference in a DBT, it may be fun to follow that up with EQed comparisons.

Thanks!

Would this resistor have any possible sonic consequences for the tube amp? It wouldn't change the way it interacts with the speaker impedance, would it? Or audibly lower the output of the tube amp so it would be a bit quieter than the SS amp?

Would you expect both amps to output the same sound level? Or would a voltmeter be required to match them?

 

[SIY]

Thanks!

Would this resistor have any possible sonic consequences for the tube amp? It wouldn't change the way it interacts with the speaker impedance, would it? Or audibly lower the output of the tube amp so it would be a bit quieter than the SS amp?

Would you expect both amps to output the same sound level? Or would a voltmeter be required to match them?

Yes, you absolutely need a voltmeter to match levels. One amp or the other will have to be attenuated.

The resistor is so large compared to the speaker impedance that it won't affect anything when the amp is running.

You're asking all the right questions!

 

[MattHooper]

Yes, you absolutely need a voltmeter to match levels. One amp or the other will have to be attenuated.

The resistor is so large compared to the speaker impedance that it won't affect anything when the amp is running.

You're asking all the right questions!

Ok thanks. My CJ pre-amp has discrete volume steps - I forget by how much. Hopefully the sound level could be matched.
I don't know that I'll actually do the test, but this information certainly helps.

 

[Blumlein 88]

Ok thanks. My CJ pre-amp has discrete volume steps - I forget by how much. Hopefully the sound level could be matched.
I don't know that I'll actually do the test, but this information certainly helps.

Another option is a series test. You'd load your CJ with maybe some 8 ohm power resistors. Tap those in parallel with some higher value resistors that drop the voltage equal to the gain of your amp (maybe 26 db for the CJ). Then make yourself a box to switch between plain interconnects pre-amp to SS amp or switch in the CJ amp between pre-amp and SS amp. The main drawback is 8 ohm resistors won't interact with the output impedance of the tube amp to alter frequency response. I found this test to show up differences much better. As did the Swedish AES. Your comparing your amp with straight wire to see if you hear a difference. With care you can match the gain perfectly. A 10 turn trim pot and a fixed resistor are one easy way to do that.

Schematic here:
https://www.audiosciencereview.com/...rs-can-you-hear-a-diffrence.12583/post-386164

The Swedish AES built this nice box to make it easy. They found the most revealing signal for this testing was the recording of a mechanical metronome of all things.

 

[levimax]

Yes, you absolutely need a voltmeter to match levels. One amp or the other will have to be attenuated.

The resistor is so large compared to the speaker impedance that it won't affect anything when the amp is running.

You're asking all the right questions!

Hi SIY, I am thinking of doing a test as well. Is it better to level match with a multimeter and a dummy load or with REW and Pink Noise? My tube amp and SS amp have a 6 dB difference in gain so I need to do a lot of matching.

 

[SIY]

Hi SIY, I am thinking of doing a test as well. Is it better to level match with a multimeter and a dummy load or with REW and Pink Noise? My tube amp and SS amp have a 6 dB difference in gain so I need to do a lot of matching.

You don’t need a dummy load, just use the speakers and keep the test voltage low, like 0.5v or so. Yes, multimeter, so have the test voltage at a moderately low frequency, like 500 Hz or so.

 

[MattHooper]

Another option is a series test. You'd load your CJ with maybe some 8 ohm power resistors. Tap those in parallel with some higher value resistors that drop the voltage equal to the gain of your amp (maybe 26 db for the CJ). Then make yourself a box to switch between plain interconnects pre-amp to SS amp or switch in the CJ amp between pre-amp and SS amp. The main drawback is 8 ohm resistors won't interact with the output impedance of the tube amp to alter frequency response. I found this test to show up differences much better. As did the Swedish AES. Your comparing your amp with straight wire to see if you hear a difference. With care you can match the gain perfectly. A 10 turn trim pot and a fixed resistor are one easy way to do that.

Schematic here:
https://www.audiosciencereview.com/...rs-can-you-hear-a-diffrence.12583/post-386164

The Swedish AES built this nice box to make it easy. They found the most revealing signal for this testing was the recording of a mechanical metronome of all things.
View attachment 88511

Thanks Blumlein 88. That's a generous bunch of information.

However, I'm the furthest from a DIY guy you will find. If it's not essentially easy for me to do the test it won't happen, and the above is getting too far down a rabbit hole for my comfort level. I may even have sprung for the switchbox I linked to earlier, but with my industry hit hard by COVID money is tight.