I have caught the Class D amp bug lately. I see many hybrid tube / TPX3xxx amps advertised (ex. Douk). Is the tube input stage just a gimmick?
My first radio in the 70's was an AM tube radio... it definitely had a warm sound that was great. My fathers stereo had a Scott integrated tube amp. I don't remember the tube colorations / too young to know a difference / don't think his speakers had the resolution to tell much of a difference.. I get tubes have their own unique sound. Do the tubes in the input stage just add tube coloring / warmth to the audio? I am pretty darned impressed with the "sterile" sound of the TPA3126 and TPA3255 boards I have been playing with. To me adding a tube input section will just alter the more pure sound to a warmer more colored sound?
"Back in the day" I had a Counterpoint SA100 class A/B amp with a triode tube input stage. I ditched it when I bought my used Threshold 400a Class A amp. There was a huge night and day difference between the two amps... but I doubt the difference was in the triode tube input stage. More just Class A (Nelson Pass) vs Class A/B amp. HiFi vs MidFi.
I am interesting in peoples thoughts on this?
My first radio in the 70's was an AM tube radio... it definitely had a warm sound that was great. My fathers stereo had a Scott integrated tube amp. I don't remember the tube colorations / too young to know a difference / don't think his speakers had the resolution to tell much of a difference.. I get tubes have their own unique sound. Do the tubes in the input stage just add tube coloring / warmth to the audio? I am pretty darned impressed with the "sterile" sound of the TPA3126 and TPA3255 boards I have been playing with. To me adding a tube input section will just alter the more pure sound to a warmer more colored sound?
"Back in the day" I had a Counterpoint SA100 class A/B amp with a triode tube input stage. I ditched it when I bought my used Threshold 400a Class A amp. There was a huge night and day difference between the two amps... but I doubt the difference was in the triode tube input stage. More just Class A (Nelson Pass) vs Class A/B amp. HiFi vs MidFi.
I am interesting in peoples thoughts on this?
Last edited:
I'll start the ball rolling by quoting the opinion of Rod Elliott:
"While there's no real reason that a valve front end can't be used with a Class-D amp, that is a rather unlikely combination and serves no useful purpose. There are many combinations that serve no useful purpose, but that hasn't stopped advertising people from extolling their (alleged) virtues."
https://sound-au.com/articles/amp-classes.htm#classd
"While there's no real reason that a valve front end can't be used with a Class-D amp, that is a rather unlikely combination and serves no useful purpose. There are many combinations that serve no useful purpose, but that hasn't stopped advertising people from extolling their (alleged) virtues."
https://sound-au.com/articles/amp-classes.htm#classd
Oh @oughtsix : you may certainly remember these Hybrid Luxman amps, the LV-10x series - I think it was the first "commercial affordable attempt" from a well-known brand to integrate tubes in SS amps.
The tubes were solely inserted as cathode followers between the preamp and power sections, IIRC. Indeed, it was a 🆒 idea, yes, but I'm not sure that it was very useful...
At least, it brought probably some "Tube Magic" in the amp, and it was certainly a good marketing strategy, in the late 80s, when the tubes started to resurrect, for the better and the better... 😎
Personally, I am rather in the "adding a mere tube is a gimmick" camp... But why not, after all ? 🙂😉
T
The tubes were solely inserted as cathode followers between the preamp and power sections, IIRC. Indeed, it was a 🆒 idea, yes, but I'm not sure that it was very useful...
At least, it brought probably some "Tube Magic" in the amp, and it was certainly a good marketing strategy, in the late 80s, when the tubes started to resurrect, for the better and the better... 😎
Personally, I am rather in the "adding a mere tube is a gimmick" camp... But why not, after all ? 🙂😉
T
It simply comes down to what you want. And what you believe should be used to amplify analog signal.
At the end, what sounds good to you matters the most. Money should not be a deciding factor... but it is for many.
If you like tube sound, and believe that class D, powered by SMPS should be used to amplify analog signal... go for it!
I plan on doing just this with XRK’s HyperSET buffer + his 3255 boards. For me the logic is clear; get some of the triode magic but with grunt courtesy of the class D. If you don’t know what I mean by triode magic then go and listen to a well designed SET with some appropriate speakers.
Former member koifarm designed a tube driver stage for the eigentact amp, you should easily find those threads with the search function. The aim was to add tube sound to the otherwise very detailed sounding main amp.
Combining a tube pre with a solid state main amp is not a new idea, there are also some hybrid tube+mosfet amps around. Not sure though whether the TPA3xxx amps need a driver stage beforehand or whether any tube stage would merely be a buffer.
Combining a tube pre with a solid state main amp is not a new idea, there are also some hybrid tube+mosfet amps around. Not sure though whether the TPA3xxx amps need a driver stage beforehand or whether any tube stage would merely be a buffer.
A simple Tube, BJT or Fet transistor follower should create relatively the same harmonic profile.
Basically distortion with a strong 2nd harmonic.
The more simple or good to horrible the circuit is. The stronger the possibility of poor aka " warm" performance.
It isn't really a gimmick, their is technically a tube in the signal, and whatever distortion it adds is what it adds.
Whatever .01% to .1% harmonic rich distortion does to .01% to .1% class D distortion is up to you to decide or imagine.
Depending on power levels below 10K really crude and simple BJT amps can have a similar distortion.
Been well explored, basically a Class A 2nd gain stage in many amps will create the harmonic profile.
Then typical AB output and how much the differential does or doesn't cancel it.
Most just moved to what comes in is what comes out = no distortion, and the harmonics of the instruments in the recording do what they do.
Not all complicated waveforms are even order. The timber or instruments is what it is.
Most of the " Warm" sound is more pleasing for Bass.
And ironically like many simple class A/B amps even LM1875 or LM3886 have rather strong second harmonics below 450 Hz.
And higher below 100Hz
No glass bottles or heaters so the " warm" sound doesn't suit the "imagination" which is 30% of the final sound LOL!!
Do you want .001 or .01 or .1 or 1% of " warm"
listening to radio talk or voice overs in older films, the distortion is annoying so im glad it was just removed.
But technically the harmonic profile of it is considered " warm". some call it junk distortion
Basically distortion with a strong 2nd harmonic.
The more simple or good to horrible the circuit is. The stronger the possibility of poor aka " warm" performance.
It isn't really a gimmick, their is technically a tube in the signal, and whatever distortion it adds is what it adds.
Whatever .01% to .1% harmonic rich distortion does to .01% to .1% class D distortion is up to you to decide or imagine.
Depending on power levels below 10K really crude and simple BJT amps can have a similar distortion.
Been well explored, basically a Class A 2nd gain stage in many amps will create the harmonic profile.
Then typical AB output and how much the differential does or doesn't cancel it.
Most just moved to what comes in is what comes out = no distortion, and the harmonics of the instruments in the recording do what they do.
Not all complicated waveforms are even order. The timber or instruments is what it is.
Most of the " Warm" sound is more pleasing for Bass.
And ironically like many simple class A/B amps even LM1875 or LM3886 have rather strong second harmonics below 450 Hz.
And higher below 100Hz
No glass bottles or heaters so the " warm" sound doesn't suit the "imagination" which is 30% of the final sound LOL!!
Do you want .001 or .01 or .1 or 1% of " warm"
listening to radio talk or voice overs in older films, the distortion is annoying so im glad it was just removed.
But technically the harmonic profile of it is considered " warm". some call it junk distortion
Last edited: