[Xcalibur255]

I'm in a typing mood so I'll take a swing at this.

I guess it depends upon your school of thought. On the objectivist side, any distortion is bad because it represents a modification or deviation of the original input signal. If what goes out isn't matching what went in then naturally we're not hearing the music exactly the way the microphones heard it.

On the subjectivist side, a number of very prominent and respected amplifier designers who have been doing this for decades have come to the conclusion that some amount of 2nd order harmonic distortion is helpful rather than harmful. The folks at Innerfidelity did an interesting listening trial using a device designed to inject varying amounts of distortion into the musical signal, and they found that people broadly preferred some degree of 2nd order harmonics to be present as opposed to the signal being as "clean" as possible. It's a matter of degrees though. A bit of 2nd order often gets perceived as an "organic" sound that enhances musicality, where as too much makes the music sound overly bloomy or smeared. Think of it a bit like looking through a pair of binoculars that aren't quite in focus. The more 2nd order distortion the less in focus things get, but just a *tiny* bit out of focus can take the hard edge off of things in a pleasing way and can call attention to overtones and harmonics in the music that gives the impression of things sounding more dense or ethereal. I would say a fair amount of what people are tuning in the sound of their tube amps when they roll tubes is the amount of 2nd and 3rd order distortion present.

As for how to interpret the graphs, what it is showing is a test tone at 1Khz. What the numbers represent are sort of ghosts or echoes of the original tone at a much lower intensity or loudness than the original signal itself was. The higher the harmonic, the more "distorted" it is from the original tone and the more different it is. Think of it like shifting the hue of a color. If our original color was pure red, then 2nd and 3rd order distortion would be just a tiny shade off..... maybe coming off as just a tiny bit more pinkish. Now as we get further into 4,5,6 order and so on the shift starts to become more visible and readily identifiable, and maybe by the time we hit 9th order now it doesn't look red at all anymore. Now we can clearly see that it has become mangenta or even purple and is a totally different thing from the original. We perceive harmonic distortion in much the same way. The brain hears 2nd and 3rd order distortion as fundamentally the same as the original tone and kind of just averages it all together as part of your subconscious processes that filter your senses. This is commonly called "masking." The further along you go, the more your brain begins to identify the distortion as its own unique thing that is different from the original sound. Especially stuff past 6th order, these residual harmonics are in contrast to the orignal tone instead of being complementary to it. A very small amount of 8th or 9th order distortion can hurt sound quality a lot, making things sound harsh, or hashy in a way that can be hard to put your finger on. On the other hand you can have quite a lot of 2nd order distortion and not really have anything bad happen to the sound other than a slight softening or smearing effect.

This is, generally speaking, why push-pull tube amps and single-ended tube amps sound different. The push-pull circuit naturally cancels out the 2nd order distortion, but any higher order distortion beyond 2nd will still be present. So you've lost the masking effect and any nasty high order distortion that might be present is that much easier to perceive. That's really a generalization though, and there are plenty of push-pull designs that sound great. In raindownthunda's post comparing the difference between CCS and resistor bias mode in his amp, he's really describing the difference between having more or less 2nd and 3rd order harmonic distortion because that's what the CCS primarily does is make the tube operate as linear as possible which lowers those distortion levels. There's still some present even with the CCS of course, because tubes gonna tube, but a big part of why tube amps seem to run the gamut between being very clear and very lush sounding is the varying degrees of 2nd and 3rd order harmonic distortion their circuit is producing.

 

[David A Silva]

I'm in a typing mood so I'll take a swing at this.

I guess it depends upon your school of thought. On the objectivist side, any distortion is bad because it represents a modification or deviation of the original input signal. If what goes out isn't matching what went in then naturally we're not hearing the music exactly the way the microphones heard it.

On the subjectivist side, a number of very prominent and respected amplifier designers who have been doing this for decades have come to the conclusion that some amount of 2nd order harmonic distortion is helpful rather than harmful. The folks at Innerfidelity did an interesting listening trial using a device designed to inject varying amounts of distortion into the musical signal, and they found that people broadly preferred some degree of 2nd order harmonics to be present as opposed to the signal being as "clean" as possible. It's a matter of degrees though. A bit of 2nd order often gets perceived as an "organic" sound that enhances musicality, where as too much makes the music sound overly bloomy or smeared. Think of it a bit like looking through a pair of binoculars that aren't quite in focus. The more 2nd order distortion the less in focus things get, but just a *tiny* bit out of focus can take the hard edge off of things in a pleasing way and can call attention to overtones and harmonics in the music that gives the impression of things sounding more dense or ethereal. I would say a fair amount of what people are tuning in the sound of their tube amps when they roll tubes is the amount of 2nd and 3rd order distortion present.

As for how to interpret the graphs, what it is showing is a test tone at 1Khz. What the numbers represent are sort of ghosts or echoes of the original tone at a much lower intensity or loudness than the original signal itself was. The higher the harmonic, the more "distorted" it is from the original tone and the more different it is. Think of it like shifting the hue of a color. If our original color was pure red, then 2nd and 3rd order distortion would be just a tiny shade off..... maybe coming off as just a tiny bit more pinkish. Now as we get further into 4,5,6 order and so on the shift starts to become more visible and readily identifiable, and maybe by the time we hit 9th order now it doesn't look red at all anymore. Now we can clearly see that it has become mangenta or even purple and is a totally different thing from the original. We perceive harmonic distortion in much the same way. The brain hears 2nd and 3rd order distortion as fundamentally the same as the original tone and kind of just averages it all together as part of your subconscious processes that filter your senses. This is commonly called "masking." The further along you go, the more your brain begins to identify the distortion as its own unique thing that is different from the original sound. Especially stuff past 6th order, these residual harmonics are in contrast to the orignal tone instead of being complementary to it. A very small amount of 8th or 9th order distortion can hurt sound quality a lot, making things sound harsh, or hashy in a way that can be hard to put your finger on. On the other hand you can have quite a lot of 2nd order distortion and not really have anything bad happen to the sound other than a slight softening or smearing effect.

This is, generally speaking, why push-pull tube amps and single-ended tube amps sound different. The push-pull circuit naturally cancels out the 2nd order distortion, but any higher order distortion beyond 2nd will still be present. So you've lost the masking effect and any nasty high order distortion that might be present is that much easier to perceive. That's really a generalization though, and there are plenty of push-pull designs that sound great. In raindownthunda's post comparing the difference between CCS and resistor bias mode in his amp, he's really describing the difference between having more or less 2nd and 3rd order harmonic distortion because that's what the CCS primarily does is make the tube operate as linear as possible which lowers those distortion levels. There's still some present even with the CCS of course, because tubes gonna tube, but a big part of why tube amps seem to run the gamut between being very clear and very lush sounding is the varying degrees of 2nd and 3rd order harmonic distortion their circuit is producing.

So glad you were in a typing mood! Great stuff!

 

[LoryWiv]

I'm in a typing mood so I'll take a swing at this.

I guess it depends upon your school of thought. On the objectivist side, any distortion is bad because it represents a modification or deviation of the original input signal. If what goes out isn't matching what went in then naturally we're not hearing the music exactly the way the microphones heard it.

On the subjectivist side, a number of very prominent and respected amplifier designers who have been doing this for decades have come to the conclusion that some amount of 2nd order harmonic distortion is helpful rather than harmful. The folks at Innerfidelity did an interesting listening trial using a device designed to inject varying amounts of distortion into the musical signal, and they found that people broadly preferred some degree of 2nd order harmonics to be present as opposed to the signal being as "clean" as possible. It's a matter of degrees though. A bit of 2nd order often gets perceived as an "organic" sound that enhances musicality, where as too much makes the music sound overly bloomy or smeared. Think of it a bit like looking through a pair of binoculars that aren't quite in focus. The more 2nd order distortion the less in focus things get, but just a *tiny* bit out of focus can take the hard edge off of things in a pleasing way and can call attention to overtones and harmonics in the music that gives the impression of things sounding more dense or ethereal. I would say a fair amount of what people are tuning in the sound of their tube amps when they roll tubes is the amount of 2nd and 3rd order distortion present.

As for how to interpret the graphs, what it is showing is a test tone at 1Khz. What the numbers represent are sort of ghosts or echoes of the original tone at a much lower intensity or loudness than the original signal itself was. The higher the harmonic, the more "distorted" it is from the original tone and the more different it is. Think of it like shifting the hue of a color. If our original color was pure red, then 2nd and 3rd order distortion would be just a tiny shade off..... maybe coming off as just a tiny bit more pinkish. Now as we get further into 4,5,6 order and so on the shift starts to become more visible and readily identifiable, and maybe by the time we hit 9th order now it doesn't look red at all anymore. Now we can clearly see that it has become mangenta or even purple and is a totally different thing from the original. We perceive harmonic distortion in much the same way. The brain hears 2nd and 3rd order distortion as fundamentally the same as the original tone and kind of just averages it all together as part of your subconscious processes that filter your senses. This is commonly called "masking." The further along you go, the more your brain begins to identify the distortion as its own unique thing that is different from the original sound. Especially stuff past 6th order, these residual harmonics are in contrast to the orignal tone instead of being complementary to it. A very small amount of 8th or 9th order distortion can hurt sound quality a lot, making things sound harsh, or hashy in a way that can be hard to put your finger on. On the other hand you can have quite a lot of 2nd order distortion and not really have anything bad happen to the sound other than a slight softening or smearing effect.

This is, generally speaking, why push-pull tube amps and single-ended tube amps sound different. The push-pull circuit naturally cancels out the 2nd order distortion, but any higher order distortion beyond 2nd will still be present. So you've lost the masking effect and any nasty high order distortion that might be present is that much easier to perceive. That's really a generalization though, and there are plenty of push-pull designs that sound great. In raindownthunda's post comparing the difference between CCS and resistor bias mode in his amp, he's really describing the difference between having more or less 2nd and 3rd order harmonic distortion because that's what the CCS primarily does is make the tube operate as linear as possible which lowers those distortion levels. There's still some present even with the CCS of course, because tubes gonna tube, but a big part of why tube amps seem to run the gamut between being very clear and very lush sounding is the varying degrees of 2nd and 3rd order harmonic distortion their circuit is producing.

@Xcalibur255 glad you were in a typing mood. Very well-written and helpful post, even to hose of us not technically adept in audio engineering choices as impact perception of sound. Great post sir!

 

[maxpudding]

In summary, if you love tube distortion (lol) especially from power tubes, get the BH+

Or if you just want to roll driver tubes, and enjoy a simple and wonderful tube amp, get the BH.

 

[Xcalibur255]

In summary, if you love tube distortion (lol) especially from power tubes, get the BH+

Or if you just want to roll driver tubes, and enjoy a simple and wonderful tube amp, get the BH.

I do feel it's important to remember that the overall sound of the amp is defined by more than just it's harmonic distortion profile. This is just one aspect of many that contributes to what we hear. Harmonic distortion is also just one of several types of measurable distortion too. Phase shift for example is a type of signal distortion too.

But yes this is probably a fair generalization. Though people should absolutely take Mischa's opinion over mine on this subject if they're having trouble deciding what they want. I'm just trying to help describe what can be a fairly complicated concept with some fun word analogies.

 

[raindownthunda]

I do feel it's important to remember that the overall sound of the amp is defined by more than just it's harmonic distortion profile. This is just one aspect of many that contributes to what we hear. Harmonic distortion is also just one of several types of measurable distortion too. Phase shift for example is a type of signal distortion too.

But yes this is probably a fair generalization. Though people should absolutely take Mischa's opinion over mine on this subject if they're having trouble deciding what they want. I'm just trying to help describe what can be a fairly complicated concept with some fun word analogies.

Good call out @Xcalibur255 and great explanations!

Another factor besides distortion worth mentioning is output impedance influence on driver damping. BH has a fixed output impedance of ~7-8ohm while there is a much wider range depending on type and # of power tubes in BH+.

I’m finding the 300ohm VC drivers perform fairly differently in BH+ with a pair of 6080 (60-70 ohm) than in BH mode.

Here is a table from a guide doc for Blue Halo+ I’m compiling with @A2029’s help:

Tube family	Quantity (Total)	Output impedance (Ohm)
6080/6AS7G	2	60-70
6080/6AS7G	4	~35
6080/6AS7G	6 (Caution: Reduces amp life)	~25
5998/421A	2	35-40
5998/421A	4	20-23
5998/421A	6 (Caution: Reduces amp life)	14-15
6BL7/6BX7	2	75
6BL7/6BX7	4	40
6BL7/6BX7	6	27
6336/6258	2*	~35
**EL34/KT66/KT77/KT88/6V6/6L6GC	2 (Caution: Fast Tube Wear)	90-100
**EL34/KT66/KT77/KT88/6V6/6L6GC	4	45-50
**EL34/KT66/KT77/KT88/6V6/6L6GC	6	30-35

* Requires upgraded power tube heater regulators
** Requires 6AS7 -> EL34 adapters

RES mode increases output impedance ~10% as well according to @A2029

 

[mordy]

I'm in a typing mood so I'll take a swing at this.

I guess it depends upon your school of thought. On the objectivist side, any distortion is bad because it represents a modification or deviation of the original input signal. If what goes out isn't matching what went in then naturally we're not hearing the music exactly the way the microphones heard it.

On the subjectivist side, a number of very prominent and respected amplifier designers who have been doing this for decades have come to the conclusion that some amount of 2nd order harmonic distortion is helpful rather than harmful. The folks at Innerfidelity did an interesting listening trial using a device designed to inject varying amounts of distortion into the musical signal, and they found that people broadly preferred some degree of 2nd order harmonics to be present as opposed to the signal being as "clean" as possible. It's a matter of degrees though. A bit of 2nd order often gets perceived as an "organic" sound that enhances musicality, where as too much makes the music sound overly bloomy or smeared. Think of it a bit like looking through a pair of binoculars that aren't quite in focus. The more 2nd order distortion the less in focus things get, but just a *tiny* bit out of focus can take the hard edge off of things in a pleasing way and can call attention to overtones and harmonics in the music that gives the impression of things sounding more dense or ethereal. I would say a fair amount of what people are tuning in the sound of their tube amps when they roll tubes is the amount of 2nd and 3rd order distortion present.

As for how to interpret the graphs, what it is showing is a test tone at 1Khz. What the numbers represent are sort of ghosts or echoes of the original tone at a much lower intensity or loudness than the original signal itself was. The higher the harmonic, the more "distorted" it is from the original tone and the more different it is. Think of it like shifting the hue of a color. If our original color was pure red, then 2nd and 3rd order distortion would be just a tiny shade off..... maybe coming off as just a tiny bit more pinkish. Now as we get further into 4,5,6 order and so on the shift starts to become more visible and readily identifiable, and maybe by the time we hit 9th order now it doesn't look red at all anymore. Now we can clearly see that it has become mangenta or even purple and is a totally different thing from the original. We perceive harmonic distortion in much the same way. The brain hears 2nd and 3rd order distortion as fundamentally the same as the original tone and kind of just averages it all together as part of your subconscious processes that filter your senses. This is commonly called "masking." The further along you go, the more your brain begins to identify the distortion as its own unique thing that is different from the original sound. Especially stuff past 6th order, these residual harmonics are in contrast to the orignal tone instead of being complementary to it. A very small amount of 8th or 9th order distortion can hurt sound quality a lot, making things sound harsh, or hashy in a way that can be hard to put your finger on. On the other hand you can have quite a lot of 2nd order distortion and not really have anything bad happen to the sound other than a slight softening or smearing effect.

This is, generally speaking, why push-pull tube amps and single-ended tube amps sound different. The push-pull circuit naturally cancels out the 2nd order distortion, but any higher order distortion beyond 2nd will still be present. So you've lost the masking effect and any nasty high order distortion that might be present is that much easier to perceive. That's really a generalization though, and there are plenty of push-pull designs that sound great. In raindownthunda's post comparing the difference between CCS and resistor bias mode in his amp, he's really describing the difference between having more or less 2nd and 3rd order harmonic distortion because that's what the CCS primarily does is make the tube operate as linear as possible which lowers those distortion levels. There's still some present even with the CCS of course, because tubes gonna tube, but a big part of why tube amps seem to run the gamut between being very clear and very lush sounding is the varying degrees of 2nd and 3rd order harmonic distortion their circuit is producing.

Thank you very much for your clear, informative and beautiful explanation - much appreciated.
I often think about this metaphor: A photograph of something beautiful is worth a few cents, whereas a painting of the same subject can be worth millions. Why? Although the photograph is an exact replication, it does not bring out the soul of the object like a great painting can.
I am looking for the soul in the music, the emotional impact. Sometimes you find a tube combination that helps to bring it out, but this depends on a lot of factors in addition to the amp. How do I know? Because only sometimes do you hit those magical listening moments, even though the equipment remains the same.

 

[Xcalibur255]

Thank you very much for your clear, informative and beautiful explanation - much appreciated.
I often think about this metaphor: A photograph of something beautiful is worth a few cents, whereas a painting of the same subject can be worth millions. Why? Although the photograph is an exact replication, it does not bring out the soul of the object like a great painting can.
I am looking for the soul in the music, the emotional impact. Sometimes you find a tube combination that helps to bring it out, but this depends on a lot of factors in addition to the amp. How do I know? Because only sometimes do you hit those magical listening moments, even though the equipment remains the same.

My journey is much the same. If the emotional connection isn't there I'm disconnected, no matter how clear or precise the setup may sound. Something I have come to accept over time, though, is that it's probably a good thing that we only have those truly special listening sessions where we connect emotionally *sometimes* as opposed to all of the time. As the great Bob Ross used to say, there's no light without shadow. If the special listening sessions weren't rare they would no longer feel special at all.

 

[maxpudding]

I do feel it's important to remember that the overall sound of the amp is defined by more than just it's harmonic distortion profile. This is just one aspect of many that contributes to what we hear. Harmonic distortion is also just one of several types of measurable distortion too. Phase shift for example is a type of signal distortion too.

But yes this is probably a fair generalization. Though people should absolutely take Mischa's opinion over mine on this subject if they're having trouble deciding what they want. I'm just trying to help describe what can be a fairly complicated concept with some fun word analogies.

Thanks, I do think your write up is equally important. I cannot put it more eloquently than you did.

 

[Marutks]

I like 6H23P-EB tubes. They are dead quiet in the BH amp.

https://www.thetubestore.com/6h23n-eb-6922

 

[raindownthunda]

Cold morning working in the basement. I'll take the warming glow of a tube amp over a musty space heater any day of the week.

 

[maxpudding]

Back in 2020, when Mischa mentioned that there’s a supercharger circuit in the BH amp that drives the driver tubes, I pitch the idea of the power tube switch to Mischa, not knowing it could work or not, or would it sound as good as a normal OTL amp. Mischa did some calculations and made some initial circuit design for the BH+ and told me a few days later that it could work.

Fast forward to now, seeing the BH+ in all its glory, producing great sounds, glad to see the amp finally becomes a reality. Well done @A2029

 

[raindownthunda]

Back in 2020, when Mischa mentioned that there’s a supercharger circuit in the BH amp that drives the driver tubes, I pitch the idea of the power tube switch to Mischa, not knowing it could work or not, or would it sound as good as a normal OTL amp. Mischa did some calculations and made some initial circuit design for the BH+ and told me a few days later that it could work.

Fast forward to now, seeing the BH+ in all its glory, producing great sounds, glad to see the amp finally becomes a reality. Well done @A2029

Bravo, @maxpudding, for inspiring the inception of this fantastic creation. It continues to amaze me how @A2029 pulled of this design that sounds so phenomenal in not just one, but two completely different output stages. Each with their own unique strengths and individual voice. A true tube rolling chameleon!

Supremely enjoying Blue Halo+ tonight with pairs of GEC L63 and Chatham 6080WB solid graphite tubes and the Verite Closed. In BH mode, the L63 produce tremendous speed, clarity, staging and imaging. In BH+ mode, the extra harmonics of the 6080WB power tubes result in added depth and dimensionality to music, which can only be described as highly euphoric and addicting. The speed and clarity is still very much present - no compromises here. With this combination, electronic music has never sounded better to my ears. Transients projected with laser-precise placement across an unimaginably vast canvas - with just the slightest hint of decay creating a magical effect. Bass extends deep and slams with ferocious visceral impact and speed when called for, yet is never too overpowering. This is bass quality and clarity I never imagined possible in a tube amp. Well recorded rock/blues/guitar/jazz/vocal tracks truly come to life thanks to the excellent clarity/staging combined with extremely natural sounding timbre of instruments and vocals. I keep finding myself asking "Why can't I stop listening??"

 

[raindownthunda]

Listening to the BH+ while working again today and surprised I am actually enjoying RES mode more than CCS mode. I started out this tube roll in CCS mode and was a little too distracted by the clarity and detail to get focus work done. I decided to try Resistor mode and wow! Things just clicked. Sweet, smooth, ethereal, thumpy tube sound unlocked. Still plenty of detail and great sound stage, but the layers are more "smeared" together resulting in a fuller, more blended wall of sound. Perfect for the indie rock playlist.

 

[leftside]

Listening to the BH+ while working again today and surprised I am actually enjoying RES mode more than CCS mode. I started out this tube roll in CCS mode and was a little too distracted by the clarity and detail to get focus work done. I decided to try Resistor mode and wow! Things just clicked. Sweet, smooth, ethereal, thumpy tube sound unlocked. Still plenty of detail and great sound stage, but the layers are more "smeared" together resulting in a fuller, more blended wall of sound. Perfect for the indie rock playlist.

Nice to have those options. If you’re anything like me, you’ll change modes in a week and then prefer that mode I think sometimes our ears just simply like a ”change” which is why you are more likely to see new gear get rave reviews?