True. But it depends a lot on room gain and how low your high sensitivity channels go. I am horn loaded down to 100Hz at around that 110dB/w/m. Below that are two bass channels that are as sensitive as they need to be to get the appropriate volume in-room. Sub 40Hz is 100dB/w/m thanks to a well sealed room and plenty of room gain which matches my horn channels in volume without attenuation to about 15Hz before falling away, and the midbass channel under construction will be about 103dB/w/m, both channels are direct radiators in sealed boxes. I just add enough drivers in parallel to reach the necessary volume to match the horns.
Not everyone can do this for obvious logistical reasons, but I think it is worth it.
If the cathode were uni-potential, this would be a complete description, but for DHT filaments the model is incomplete. Individual locations on the filament have continuously varying grid to that-individual-small-bit-of cathode voltage. Your model could be restated as: all of these individual voltages integrate to a DC voltage. This is almost but not completely true because valves are not completely linear.
Because filament voltages are quite large compared to typical signal levels, IM distortion from this source is easily measured.
YOS,
Chris
I yet have to see these measurements done right. Same amplifier, with AC vs. DC filaments. What Rod posted are results with two completely different amplifiers, not a fair comparison. The obseraved IMD could be due to reasons other than AC filaments.
I agree that tubes are imperfect, but still cannot see how AC voltage signal from filament gets into tube's input, other than through AC frequency heat fluctuations. But that has been refuted long time ago by Steve Bench.
Btw, IMD closely follow harmonic distortion. Because of high SE 2HD, this is much more of a problem of SE than of PP.
I agree that tubes are imperfect, but still cannot see how AC voltage signal from filament gets into tube's input, other than through AC frequency heat fluctuations. But that has been refuted long time ago by Steve Bench.
Btw, IMD closely follow harmonic distortion. Because of high SE 2HD, this is much more of a problem of SE than of PP.
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I can recall my old argument with Rod. If so scared by IMD from a minuscule amount of AC, one should not listen to amplified music at all because it is a mixture of many frequencies that will intermodulate each other. One should not fixate on AC heater hum, but on decreasing harmonic distortion, a cure for all kinds of IMD.
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Who says it became ´popular?
0.01% of all amps (if that many) does not qualify for that label.
It's an active system with digital crossover (DEQX) so the 8 woofers have separate powerful amplifiers. They are around 96db eff + room gain with around 700 watts per side. I couldn't get the results I wanted with passive crossovers (prefer relatively step filters) and really like to connect the drivers directly to the amplifiers.
I like tube amplifiers but for large diaphragms and 96db of efficiency I woudn't even consider 100 watts PP amplifiers to keep up with the dynamics of the horns. It's not that I listen that loudly but scale and low coloration are rating very highly in my expectation from a good sound system.
While I really like tube amplifiers, I'm not interested in distortion, even pleasing one. I use them because I can build them for very low noise level, low distortion level (if matched to efficient speakers), they are simple and reliable.
I get why some people would put 300b SE on a pair of LS3/5A but the resulting sound is at the total opposite of what I like.
In the past I had very large back loaded horns (big fun horns) corner loaded and tuned to 34hz and around 100 db efficiency. Fantastic speakers for a single drivers and ran them full range on many types of amplifiers from SE PS PP OTL and all SS variants. They were probably the most revealing speakers for the amplifiers hooked to them that I've experienced (full range context). I had good results with SE or PP amplifiers as long as I didn't had to run the amplifiers near their limits and they had similar output power.
Anyway, I'm just not convinced the SE and PP topology are that important in the end results if care is taken to build them properly and they play in their comfort level. The SE I likes are with gapped output transformer though, my experience with parafeed hasn't been very good and would use a gapped SE or PP design over it.
Chris, pondering over your post, I believe that I understood your point. The source of AC filament hum is slight asymmetry of filament, with a peculiar asymmetry of each individual tube. This is why Rod argued that filament hum in PP is not necessarily common mode. But, guys, we are talking about such minuscule hum voltages that they can be disregarded if we consider output stage.
No. Tubes are not linear. As Rod says, they may be pretty linear for very small signals like hum-null. But large signal is always curved, quasi-parabolic. The downside is not as big as the upside.
This was old news in the 1920s.
We could always take some measurements and quantify the effect and see if it is worth disregarding or doing something about. That'd be my approach.
I have several Sound Tech 1700 series distortion analyzers, all with IMD option, and will make some comparison tests, when Covid allows, on my type 845 amplifier. Always been happy enough with AC, FWIW, but need to try something like the Coleman isolation board. Type 845 is pretty low mu, about 5 or 6, so is relatively immune; should make for a conservative test subject.
YOS,
Chris
ps: haven't changed it much in more than 25 years because I can't pick it up by myself any more. Getting old is not for the faint of heart.
YOS,
Chris
ps: haven't changed it much in more than 25 years because I can't pick it up by myself any more. Getting old is not for the faint of heart.
Your cancellation argument is brilliant, so had never occurred to me. Hope to test its application to paralleled valves before the year is through. Tick, tick.
YOS,
Chris
YOS,
Chris
Hear you. Previously I didn't care, but now I have to. Just power supply alone for such amp could be 100+ lb.
If you could measure IMD in your amp with AC vs. DC heaters, that would put the issue to rest.
If you could measure IMD in your amp with AC vs. DC heaters, that would put the issue to rest.
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Rod Coleman,
The symmetry is not at all perfect, but it is generally highly substantial, therefore the "cancellation" of the even order spectral components is highly substantial. If it was not, the elevated system efficiency could not arise, these are the result of the very same mechanism. Everything is physically connected, interference between vibrations always occurs in all systems. Your theory of intermodulation is in need of revision.
(I`m sure Schmitz77 will wholeheartedly agree).
The symmetry is not at all perfect, but it is generally highly substantial, therefore the "cancellation" of the even order spectral components is highly substantial. If it was not, the elevated system efficiency could not arise, these are the result of the very same mechanism. Everything is physically connected, interference between vibrations always occurs in all systems. Your theory of intermodulation is in need of revision.
(I`m sure Schmitz77 will wholeheartedly agree).
Shostakovich may very well remain the last great symphonist, it is unlikely that someone with his talent will ever be born. The 4th symphony is not party background music, but a depiction of terrifying reality.
Gray, dear friend, is all theory and green of life's golden tree.
Faust 1, Studyroom. (Mephistopheles)
The theory behind tube amps, wether they be SE or PP is known since ages. All that
has been chewed, digested and regurgitated by generations of scientists.
The difference lies in its application, and this is where practice comes into play.
I know of a "manufacturer" (yes, he made his gear in the old tradition of manufacturing,
one after the other and not two were the exact same), who used to build its most expensive
line of tube preamps in different versions. Sometimes he chooses to build a small batch (or single unit, I don't know)
by using PP output stage, but mostly he chooses SE output stages. Output principles varied,
sometimes it was parafeed, sometimes not.
The customer of this precious gear didn't know what he received, was it PP or SE.
In the end, it was irrelevant as he managed to let every principle shine the same way.
The basic character of his gear was always the same, with a PP output stage or a SE stage.
Its main function was to portrait the music with its 12 notes in a way, that music could be
understood. Never boring, never hifi-ish. And thats what the customers gladly paid for.
Because with a full tube preamp, in the end for the customer it was irrelevant what principle
in technical terms was behind the sound, the signal strengt, energy, tone, articulation were what they
paid for. And the output stages used the same output impedance, so I bet some customers have
never looked into the gear, they could have changed a PP design for a SE one and nothing would have
changed, looked from the outside of the amps.
Thats what I meant with good designs, if its been done in a proper way, the result in terms
of musicality count.
With power amps, its nearly the same. One could have a big SE amp with high power and one could use a PP amp.
Both will sound different, but what will sound better is a relative term, anybody could
see this different.
In general, with PP power amps its more easy to achieve high power output.
But we have seen, that doesn't mean high energy output.A PP amp could be of high power,
but low energy output, the design isn't able to put out powerfull octaves of voices, instruments etc.
I just watched a series from a Berlin audio dealer, who made those differences clear,
he always distinguishes between the ability to reproduce music and this kind of gear,
which always is only possible to play hifi, turns everything music into low quality
hifi, and therefore some steps far more away from the music and its real interpretation.
It has nothing to do with PP or SE.
Faust 1, Studyroom. (Mephistopheles)
The theory behind tube amps, wether they be SE or PP is known since ages. All that
has been chewed, digested and regurgitated by generations of scientists.
The difference lies in its application, and this is where practice comes into play.
I know of a "manufacturer" (yes, he made his gear in the old tradition of manufacturing,
one after the other and not two were the exact same), who used to build its most expensive
line of tube preamps in different versions. Sometimes he chooses to build a small batch (or single unit, I don't know)
by using PP output stage, but mostly he chooses SE output stages. Output principles varied,
sometimes it was parafeed, sometimes not.
The customer of this precious gear didn't know what he received, was it PP or SE.
In the end, it was irrelevant as he managed to let every principle shine the same way.
The basic character of his gear was always the same, with a PP output stage or a SE stage.
Its main function was to portrait the music with its 12 notes in a way, that music could be
understood. Never boring, never hifi-ish. And thats what the customers gladly paid for.
Because with a full tube preamp, in the end for the customer it was irrelevant what principle
in technical terms was behind the sound, the signal strengt, energy, tone, articulation were what they
paid for. And the output stages used the same output impedance, so I bet some customers have
never looked into the gear, they could have changed a PP design for a SE one and nothing would have
changed, looked from the outside of the amps.
Thats what I meant with good designs, if its been done in a proper way, the result in terms
of musicality count.
With power amps, its nearly the same. One could have a big SE amp with high power and one could use a PP amp.
Both will sound different, but what will sound better is a relative term, anybody could
see this different.
In general, with PP power amps its more easy to achieve high power output.
But we have seen, that doesn't mean high energy output.A PP amp could be of high power,
but low energy output, the design isn't able to put out powerfull octaves of voices, instruments etc.
I just watched a series from a Berlin audio dealer, who made those differences clear,
he always distinguishes between the ability to reproduce music and this kind of gear,
which always is only possible to play hifi, turns everything music into low quality
hifi, and therefore some steps far more away from the music and its real interpretation.
It has nothing to do with PP or SE.
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You may be right, but Philip Glass is one later genius. The Low Symphony and Violin Concerto are of unrivalled beauty, drama, and impact.