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In Reply to: The extreme of that is a 'sound terrain'. (warning: way out stuff) posted by njjohn on March 19, 2007 at 20:12:01:
I experience a phenomena where artist floats in space before you in virtual 3D and the soundstage has real depth every time I sit down to listen. Curiously, the effect is less dramatic after some listening but it always remains three dimensional. In comparison, UL PP is a flat sheet. Everything is there but the depth ... very 2D! PP with minimal NFB and triode operation manages some of the magic but nothing comes close to a good SET. On this we absolutely agree!BTW, my speakers are big ESLs with dynamic mid bass driver arrays and subs only for the lowermost frequencies. Unfortunately you have to be sitting on the centreline to achieve what I'm describing but I wouldn't trade them!
Follow Ups:
that the 3D effect works for all DHT SETs with no global NFB in my experience including 845s, 300Bs 2A3s and 45s (mine are 845s). I have noticed though that a good HF response is important and mids too to a lesser degree. I strongly believe that preservation of phase response throughout the entire frequency spectrum is mostly responsible since spatial cues are heavily reliant on phase relativity. To my mind its this type of distortion that SET topology controls better than others.
I don't have a clue what 'phase' is, so I don't know.
maintaining accurate phase through the full range of audio frequencies from input to output. Every reactive element in the chain has the potential to "distort" phase by leading or lagging (the OP compared to input). This is true at the frequency extremes where the reactive components form a filter and the frequency response begins to fall.What I am suggesting is that if an instrument produces a fundamental of say, 1000Hz it may produce many octaves of overtones. It's relatively easy to design and build an amp that maintains phase accuracy on the 2ndH of 1KHz fundamental but less so at much higher frequencies. So in effect the 9thH may be phase shifted compared to what was input and this shift (compared to the fundamental) could IMO lead to incorrect spatial cues. Playing with phase shift is basically how pseudo surround sound works ... it tricks the ear.
NFB can exacerbate the problem. You can imagine how complex the scenario might become by feeding back phase shifted harmonics (relative to the feedback point) especially if the signal contains varying degrees of phase shift at different frequencies.
The best way of controlling the complex situation is to build a very wide band amp with zero global NFB (common wisdom). Local NFB can also be a problem but this is much easier to control through proper design.
This is kind of DHT talk, but my own system is balanced PP so not totally analagous. It's also totally DHT beginning to end. My observations are that I get more "dimensionality" in space with IDHTs. The DHT experience is right on the speaker, precisely and utterly in the plane of the speaker. So with nothing but DHTs the sound field is quite flat, but VERY immediate, kind of startling in fact. I don't have the opportunity to create soundstage illusions. But I get a whole other kick out of it, which is tone, tone, tone and more tone. The tone is startling - cymbals are totally metallic and shimmering with all the HF energy you expect - you pretty much can see the things right in front of you. Snare drums have snap, rim shots are exactly right - etc etc etc. I'm an ex muso so spent a good 20 years playing jazz on double bass with a drumkit right next to me, and it's the most lifelike reproduction of a drumkit - just in terms of tone - that I've ever heard.So I'm wondering if the holographic stuff isn't coming from
a) SET
b) The IDHTs in the system.
I don't see it coming from the 300b stage just in itself - I reckon there's more going on. If you want the effect, then you may even have to sacrifice the total DHT experience. Not something I'm willing to do, personally.
Am I making sense here? Just wondering if others have had the same kind of listening experience with total DHT and hybrid DHT/IDHT? Andy
That's probably a pretty on-target assessment.But let's not come to a final word about it since it is a work in progress to some extent.
I think my most dimensional amps are the 6sn7/300bs. The 6sn7, especially with a fi primer circuit. At first I attributed some of the dimensional attributes to the opts but later realized that alot has to do with the fi primer 6sn7 circuit.
I agree to that the effect might not be there with the dhts, and that idhts are a key especially say the 6sn7, a double idht, with what seems to me to be a little mystical sounding fi primer circuit. I really kind of like the sound of that circuit.
My favorite amp, by the way, is a 6sn7/26/45. It is not necessary a fully dimensional amp. But just think about what that might throw into the equation: idht/dht driver set-up.
My home brew Phono / Line stage drives my SETs and it exclusively uses IDHTs. It also happens to enhance the 3D effect more than any other Phono stage I've tried, providing exceptional detail and HF response.Funny you should mention DHTs and tone. I tried 26s in lieu of both 6922 and 6H30P in my Phono stage and contrary to other opinions thought that the result was not as extended as the IDHTs. Although the 26 had a nice midrange tone overall I preferred the latter. Interestingly some of the 3D effect was also lost with the 26. I've observed this with many DHTs including some very popular tubes and maybe the right mix of DHT tubes is most important in an all DHT design to prevent limiting HF response too much. My take is that good HF response is a must for holographic imaging but the immediacy of SETs is perhaps the major contributor.
Like you, I too achieved some of the effect with PP but only where the OP tubes were wired in triode mode, which also happened to provide greater immediacy. I'm certain that you can produce 3D to a greater or lesser degree with most types of tubes and even topologies but I think SETs do it better than anything else. DHTs with good HF response work well but if the design implementation is skewed mainly towards great midrange tone at the expense of HF, some "space" will be lost. Often IS coupling is the culprit here unless VERY good trannies are used.
I still think that phase preservation is a must and this stacks up technically with extended HF and little or no global feedback. But but on reflection I think you are right about IDHTs to some extent and perhaps my explanation of frequency and phase response remains consistent with your findings. Maybe a mix of both DHT and IDHT brings about a great marriage in this regard.
The lack of treble in the 26 has been referred to by a few people - it does appear a bit flat on top. For a full sound with good top, try the 12A or 01A, or the 30 which has excellent top but a rather thinner sound. There are some distinct flavours in the DHT cookbook. I'd suggest you experiment a bit more with a greater range of DHTs. I went through a load of them by using bench supplies for the filaments - I just dialled in the right voltage and swapped tubes. I've personally found some nice mixes of DHT that I find promising. The cheapest is the 3A5 which is really peanuts - not the best, but pretty good indeed. Useful double triode, which could probably mate well with another double DHT the 1J6 as a driver. Must try that.I must take a look at SET - never had one but not too hard to build and I have the parts. I hang out here to discuss DHTs!!!
Is a match made in heaven.I have 26's driving various output tubes and I'm a big fan of the tube. But it leads to something very special, perhaps unique with the 45.
I've been talking to Josh about a GM100 driving a 2A3. :)Can you say MUTANT?
Maybe a GM100 linestage....
I did try a 2a3 linestage, but it wasn't the equal of some of the other small DHTs. Others have tried 300b linestages. Haven't heard of a 211 or 845 linestage yet!!
Have you tried 10/801 or 316?These make up very good linestage amps.
There are some radio transmitter tubes, that are 6ft tall, and crank out over 1000W in SE deep class A. Those would make quite a line stage! :)))10 kilovolts on the plate, generate enough X-rays to kill anyone within 20 feet overnight.... sadly, the death of a janitor who mopped the transmitter room on top of the Emipre State Building lead to the discovery that 5+ kilovolts on the plate generate humongous amounts of X-rays..... enough to ignite A-bombs. Special tubes that had focused x-ray bombardment were developed for that puprose........ probably pretty powerful sounding for that split second before the blast. ;)
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