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

[levimax]

Okay, is the variable resistor connected to a series resistor or is that a variable output 20 k ohm pot? I can't tell from the picture.

If it is a variable output pot it should be fine. Max output impedance would be 5 k ohm at -6 db. And you'll be using it at a lower setting with an even lower output impedance.

It is a variable output 20k pot so that is what i will use... Simpler than pre- amp and dont have to worry about touching volume knob after level matching... Thank you!

 

[egellings]

Tubes are fun, and due to their simple circuits as compared to S.S. ones, can be built DIY with a reasonable expectation of success. It the amp-speaker combination is synergistic sonically, they can sound good, a subjective call for sure, even if it sounds euphonic and not highly accurate.

 

[egellings]

And then there's the pet "my little Fi-Fi" aspect to tube amps. you get to fuss with the bias settings and do tube rolling, and in general, see them as pets that don't soil the carpet. It's kind of like a classic car that can't compete with a middling modern day one.

 

[levimax]

I have my Tube vs Solid State ABX test system set up in my listening room. I am using the follow equipment:

Tube amp: Dynaco ST-70 which is the same unit that was tested by Amir https://www.audiosciencereview.com/...review-and-measurements-of-dynaco-st-70.7224/ I used the “good channel” which I think is safe to say based on Amir’s measurements is about all you can expect from a stock Dynaco St-70 i.e. SINAD of 63.

SS amp: Neurchrome Modulus-86 https://neurochrome.com/products/modulus-86 which you can see tests more or less SOTA for a SS amp with similar power to ST-70

Speaker: Sonus Faber Concerto https://www.technologyfactory.com/reviews/SonusFaber/concerto_stereophile.pdf

Switch box: Niles DPS-1 https://www.nilesaudio.com/product/amplifierspeaker-b-selector-FG00003 wired so when Dynaco ST-70 amp is switched out it goes to a “dummy load” to protect it. This means only one speaker and two amps can be switched.

DAC: SMSL M-8 https://www.audiosciencereview.com/.../review-and-measurements-of-smsl-m8-dac.2457/

Source: Windows PC with Foobar 2000. DSP “downmix to mono”

Level Matching: 20 K Ohm pot at input to ST-70 (which has more gain than the Neurochrome) voltage measured at speaker terminals at 500 Hz checked with Fluke 115 multi-meter.

Measuring Set up: REW with UMIK-1. Speaker on stand, Mic 27” from speaker at tweeter height on tripod.

I decided to do FR measurements before blind ABX as it is easier and I have done it before. I also wanted to test my 1-ohm resistor theory (That you can match FR of Tube and SS with a 1-ohm resistor in speaker out to simulate greater output impedance of Tube amp).

I ran the test sweeps in REW and have attached the results. The Brown trace is the Neuchrome and the Blue trace is the ST-70. I tried to make the dB scale as detailed as possible and used 1/21 octave gating. As you can see there is not much difference but there is some. I tried the test multiple times and the results were very repeatable. Interestingly the ST-70 had a little more energy below 100 Hz and a little less above 4 Khz but in general very little difference. I have attached .mdat file in case anyone wants to see it.

Next up is the “blind” ABX test …. Based on “sighted” switching I feel pretty much doomed as they sound very similar. I am hoping to also have a 16-year-old with young ears take the ABX test as well.

 

[DonH56]

I have measured some tube amps (do not recall which off hand, were older ARC models) at nearly 5 ohms output impedance. Some are closer to 1 ohm or even less. When I did the original speaker cable simulations (don't see them here, may still be at WBF) I repeated with 4-ohm Zout because someone said that was what he had measured on his particular (tube) amp. And of course some of the SET guys are up in the 10-15 ohm range or more. Like everything else, it varies.

 

[levimax]

I have measured some tube amps (do not recall which off hand, were older ARC models) at nearly 5 ohms output impedance. Some are closer to 1 ohm or even less. When I did the original speaker cable simulations (don't see them here, may still be at WBF) I repeated with 4-ohm Zout because someone said that was what he had measured on his particular (tube) amp. And of course some of the SET guys are up in the 10-15 ohm range or more. Like everything else, it varies.

How do you measure output impedance?

 

[MattHooper]

Sounds fascinating levimax. I admire your effort - it's more than I'd be tempted to put in.

Looking forward to the test results.

In my subjective comparisons, last night I preferred the solid state amp for Rachmaninoff's Symphonic Dances - tube amp sweeter and more lush, but a sense of laid back presentation/dynamics. Solid state amp seemed to wake the musicians up, more solidity, energy of string section etc seemed better.

 

[levimax]

Sounds fascinating levimax. I admire your effort - it's more than I'd be tempted to put in.

Looking forward to the test results.

In my subjective comparisons, last night I preferred the solid state amp for Rachmaninoff's Symphonic Dances - tube amp sweeter and more lush, but a sense of laid back presentation/dynamics. Solid state amp seemed to wake the musicians up, more solidity, energy of string section etc seemed better.

I did measure -0.5 dB @ 6 Khz and up for the tube amp.... I don't have a lot of experience relating small measurement differences to what I hear but maybe you do from your work ? ..... could 0.5 dB "wake up" musicians and "smooth" out horns?

 

[MattHooper]

Apropos of what I had written before about the sound of real instruments: I just came back from getting lunch and passed by another street band - Tenor Sax, Trombone, Upright Bass, all un-amplified.

Stood there listening from my eyes closed - from far, from med distance, close, off axis etc - and it was constant with every other time I do this.
The sound of each instrument as Big, Rich, Full, Warm, Clear, Relaxed. Just massive sound compared to reproduced. Trombone blattiness, the leading edge itself, was "big and round" and yet "relaxed" by which I mean the leading edge transients that give it "bite" are so clean of any added electronic distortion, and free of any pinching of the frequency range, and so harmonically rich, that listening does not induce in me the "wanting to close down my ears" effect of hearing horns reproduced as squeezed down, extra-sharpened acoustic objects. Sax...warm, reedy, relaxed without any electronic "edge." The timbre of the sax sounded bang-on to what I'm used to hearing from my little Spendors driven by my CJ amps. Mostly just a bigger, clearer version.

As I said, these types of inspections of live sound are what inform and drive my own preferences for choosing a sound system.
(I'm also constantly aware of the sound of the "real world" - what does it sound like walking down a city street? In a small crowd? In a park? etc - because I'm trying to re-create it many days in my work. So the live-vs-reproduced thing is sort of built in to my habits).

 

[DonH56]

How do you measure output impedance?

Either doing a quasi-load-pull test where I measure the voltage and current from the amp as I vary the load impedance (usually just a resistor for this, checking at several frequencies since it varies with frequency), or using a VNA (vector network analyzer). The no-load (open) condition is nice to have but be sure the amplifier is stable with the output open (most are, especially SS amps, but some tube amps do not like the no-load condition).

HTH - Don

 

[MattHooper]

I did measure -0.5 dB @ 6 Khz and up for the tube amp.... I don't have a lot of experience relating small measurement differences to what I hear but maybe you do from your work ? ..... could 0.5 dB "wake up" musicians and "smooth" out horns?

I think a tiny bit. But that is pretty subtle (though a wide Q). I usually bump a sound at least 1dB to make a difference, and usually more like 2 - 3 dB (in the subtle but audible range. Though if it's right on a high frequency peak the less dB shifting it takes to make an impression). And of course I use things like compression sometimes and other effects, to add punch. Also: I'm used to working not with music but with sound effects (some of which includes voices) for my job.

I never bothered with EQ in my system and got rid of my digital EQ a while back. I'm not sure if a frequency response deviation (if anything) is the cause of what I hear in terms of the energy of the string sections in my system with the SS amp. Is it purely a frequency response difference? Dunno. However I notice a similar effect of apparent density and energy when I switch the impedance for my turntable cartridge from 22-47-68 ohms, the higher producing that similar effect.

 

[Blumlein 88]

I did measure -0.5 dB @ 6 Khz and up for the tube amp.... I don't have a lot of experience relating small measurement differences to what I hear but maybe you do from your work ? ..... could 0.5 dB "wake up" musicians and "smooth" out horns?

Yes. A broad tilt like that is rather audible as slightly different brightness or calmness or differing tonality.

 

[Blumlein 88]

http://www.sengpielaudio.com/calculator-InputOutputImpedance.htm

Variation on what Don said. On tube amps I've loaded them with 220 ohms for the no load condition, and you'll get close enough to have an idea even though not 100% accurate. If you bother to use the Thevenin formula including the 220 ohms you can get an accurate reading this way.

 

[levimax]

http://www.sengpielaudio.com/calculator-InputOutputImpedance.htm

Variation on what Don said. On tube amps I've loaded them with 220 ohms for the no load condition, and you'll get close enough to have an idea even though not 100% accurate. If you bother to use the Thevenin formula including the 220 ohms you can get an accurate reading this way.

Thanks. Looking online I see the ST-70 output impedance quoted as ~0.75 ohms but I also see a lot of measurements that don't agree with Amir's so I am skeptical. Looking at the ST-70 response vs SS that I got i.e. increased output below 100 Hz (makes sense with lower damping) and reduced output over 4 Khz (also makes sense with higher output impedance) but they were about 5 times more pronounced than I got when I added in the 1- Ohm resistor which makes me thinks output impedance is more like 4 - 5 Ohms. I will see if I can measure it. I am going to guess the OP transformers have some complex variable resistance based on frequency as well.

 

[Blumlein 88]

Thanks. Looking online I see the ST-70 output impedance quoted as ~0.75 ohms but I also see a lot of measurements that don't agree with Amir's so I am skeptical. Looking at the ST-70 response vs SS that I got i.e. increased output below 100 Hz (makes sense with lower damping) and reduced output over 4 Khz (also makes sense with higher output impedance) but they were about 5 times more pronounced than I got when I added in the 1- Ohm resistor which makes me thinks output impedance is more like 4 - 5 Ohms. I will see if I can measure it. I am going to guess the OP transformers have some complex variable resistance based on frequency as well.

Well the transformer can have a drooping response without it being simple output impedance.

 

[levimax]

Well the transformer can have a drooping response without it being simple output impedance.

Yes but Amir measured this Amp (not just same model but this actual amp) with his AP and it was only down 0.1 dB @ 10 Khz and .5 dB @ 20 Khz so the drop starting @ 4 KHz seems like it must be something else when hooked up to a speaker?

 

[Julf]

Apropos of what I had written before about the sound of real instruments: I just came back from getting lunch and passed by another street band - Tenor Sax, Trombone, Upright Bass, all un-amplified.

Stood there listening from my eyes closed - from far, from med distance, close, off axis etc - and it was constant with every other time I do this.
The sound of each instrument as Big, Rich, Full, Warm, Clear, Relaxed. Just massive sound compared to reproduced. Trombone blattiness, the leading edge itself, was "big and round" and yet "relaxed" by which I mean the leading edge transients that give it "bite" are so clean of any added electronic distortion, and free of any pinching of the frequency range, and so harmonically rich, that listening does not induce in me the "wanting to close down my ears" effect of hearing horns reproduced as squeezed down, extra-sharpened acoustic objects. Sax...warm, reedy, relaxed without any electronic "edge." The timbre of the sax sounded bang-on to what I'm used to hearing from my little Spendors driven by my CJ amps. Mostly just a bigger, clearer version.

As I said, these types of inspections of live sound are what inform and drive my own preferences for choosing a sound system.
(I'm also constantly aware of the sound of the "real world" - what does it sound like walking down a city street? In a small crowd? In a park? etc - because I'm trying to re-create it many days in my work. So the live-vs-reproduced thing is sort of built in to my habits).

"inspections"? As in totally, utterly subjective perceptions?

 

[MattHooper]

"inspections"? As in totally, utterly subjective perceptions?

Yes.

It was a report of "what live instruments sound like to me." By nature: subjective impression.

And...?

Surely you didn't infer that I was trying to suggest you or anyone ought to take my subjective impressions as a scientifically rigorous demonstration?

(I've also directly compared recordings of specific instruments and voices with their live counterparts, at home).

 

[Julf]

Surely you didn't infer that I was trying to suggest you or anyone ought to take my subjective impressions as a scientifically rigorous demonstration?

No, just wondering what your point was.

 

[MattHooper]

No, just wondering what your point was.

How is it obscure?

Or maybe you didn't see the previous minor discussion about the sound of live instruments (e.g. brass).

I related my perception of live instrument and vocal sounds to what I look for and appreciate in reproduced sound, and how I find reproduced sound of those sound sources often depart from the "real thing." Curious what you are confused about.