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Romy the Cat wrote:

The events of the last 3 days are incredibly stupid, incredibly interesting and very educational. During the last few days I have discovered some very interesting phenomena, ok might be no a phenomena but a behavior, that would quite alter many of my conclusions expressed in this thread, and in few other threads. I will probably post a summary in a few days about my latest observation when I will have a complete picture.

Next day I got home, turn my audio and it was not just bad electricity day it was probably the worst sound I had for a long time. It was not just bright it was ribs-twisting bright. Also, there was the “character” of those heights. The character of sound was very odd. It was what I call the “sound of the autumn leafs” – it sort of over-burned sound with almost inverted HF, in away remind the sound of BlackGate capacitors that were “just a few month ago” installed. It is very effective sound with a lot of bite into edge of the notes but I very much hate this sound. I was checking everything in playback (the PP2000 was the first to blame), everything was fine but on the back of my mind I felt that it sounded like my MF driver was too idle as it was the very first sign of inadequate load. Yesterday it was perfect, today is unambiguous crap, the quality of electrician is stable – so what went wrong? I could blame the Alfa-rays storm from Sun but I concentrated my attention on the 2R resistor I changed last night.

Now, I replaced the shitty wirewound LPAD with very high quality Milles non-inductive resistor – how wring would it be? Sure, I put the LPAD back and the sound was fixed immediately. OK, I decided the 2R Milles resistor it just too “bad” I need something better. So, being a blind fool who I have ordered the best imaginable 2R resistor out there…

Then I asked myself: why I have those problems? The sound of “bad” resistor shall not affect sound in this way. I had 5 of 6 different types of resistors and all of them hugely change sound. It not supposes to to be this way first of all and second of all why the result so much reminds me the too idle plate load? Further research indicated that I was right – it has nothing to do with resistors.

Thos of you who use large compression drivers with metal diaphragms, and particularly the Vitavox S2 driver, know how the drivers behave when you decrease load. They are getting the “lower distortion” and better transients and then at some point the HF knee of the driver begin to sound like they disintegrated and driver pick some rusty or sandy texture.  What happens is the diaphragm loose the critical dumping by the plate impedance and the cone begin to break-up more auditably. A few years back, what I was playing with Vitavox S2 driver with original metal cones and metal suspension (the configuration that as very sever “sandy texture”) I was trying to cure the problem with a very small low pass filter at 25-40kHz. To a degree it helped than, so I was wondering if in my current situation I deal not with the “bad” and “good” sounding resistors but with the pure low pass filter in my OPT secondary. So, I began to look deeper into the nature of inductance of my resistors.

The working hypothesis was that I might over idle my tube plate and then “correct” the “sound of the autumn leafs” with low-passing sound with LPAD’s inductance. When I put the none-inductive “bad sounding Mills” into game instead of LPAD then I actually have no low-pas and hear sound as it is – too idling plate. I knew that my wirewound LPAD is in away a mind indictor –what the values we are talking about? I was not able to measure LPAD inductance with my inductive bridge as it run at too low frequency.   I took my FM tuner sweep-generator that runs at 100mHz and blew the LPAD with it. The thing was almost not conductive!!! The most horrible was not even the high inductance of the thing but the fact that inductance was almost doubling wish impedance. I did not make a good inductive bridge to get exact numbers but I was OK to get relative numbers.  What I end up was the LPAD in 2R retting had approximately .270millinery and approximately .480millihenry at 6R. The 2R Millls had approximately .035millihenry, the wirewound Vishay-Dale RH had .015millihenry and the military wirewound non-inductive NH version of Vishay-Dale had around .0025millihenry. The crazy Vishay S-102, that is not wirewound but metal file and in addition made with many anti- inductive techniques have whopping .00015millihenry…

Ok, I have 16R load and LPAD at 2R and .270millinery, so had a filter at approximately 9000Hz. That what I need to run 45 tube to attenuate 1dB. With YO184/RE604 I need to attenuate ~3-4 db and with this attenuation I run ~.5millinery. With this inductance I have a filter at 5000Hz. How you understand why I felt that my 45 tube run much higher and cleaner then my 4V tubes? This kind of explains to me a phenomenon that I was not a able to explain to myself. When I was running the YO184 for a first time I was very pleased but then when I put the LPAD into the game and was running YO184 through the LPAD I found that it was “not too extended”. What was in particularly interesting that when I was listening the only one MF channel with YO184 then I did not feel any HF deficiency but did feel it when I was listening the same YO184 integrated into Macondo.  Now it is understandable why – because integrated in Macondo I run my 4 tubes with 3-4dB LPAD attenuation and 5000Hz low-pass filter from the wirewound inductance.

So, to summarize what I was doing: I have an attenuator that very aggressively rolled of HF with attenuator. OK, that all explains my former silliness but what would be the solution to go forward.

First I re-listened all my tube options with no LPAD. With LPAD the 25:1 does well if the attenuation was no more than 1dB. This way the presumably the low-passing coming from the attenuation helped to “fix” the S2’s over-idle fuzziness.  Although the result was very good – in fact seriously good with 45 tube (as it demanded juts 1dB attenuation that was a perfect match in my case). Still I did not feel that it was right way to go. Fists I did not what to have explicit S2 curing inductor   and second I would like to be able to add and reduce the S2’s volume in Macondo. Others ways to do it had to be found. The attenuation at input I discarded as I need a continue attenuation and my high-pass input filter would not allow me to do it. To put the attenuation between the stages did not appear kosher to me as well. So, since the inductors connected in parallel crate the sumizing inductance less than any one of the parallel inductors I asked myself what not to shunt the LPAD with ultra-low inductance and high impedance. This way the high impedance will not impact the LPAD maintains the fix and stable load for my tube and the ultra-low inductance will null out the inductance of the wirewound coils in my LPAD. So, I took a pair of Vishay S-102 resistors and bridged each side of the LPAD. The result was wonderful, the LPAD rolled of volume but maintained the frequency range. The most important was that now my 4V tube, while they were 4dB attenuated, got very nice HF extension. Hallelujah!

With LPAD’s inductive influence contained the 25:1 load sound too idle and I feel that 20:1 would be more suitable load. (The 25:1 works well ONLY with inductive low-pass). Thankfully I still have the Slagle’s 20:1 coil and I put it back. It is what I play now. At this “no inductive” setting my views about the 2A3, 45 and the YO184/RE604 are slightly altered. The 45 still have the super clean and much extended HF but 2A3 and my 4V tube this time do not loose so dramatically in HF department as they did with 4dB attenuation and inductive low-pass. The debate between the 45 and 4V tube not is not around the HF anymore but rather more about the accents. The 45 is still “cleaner” in upper-end but it is restrained in tonal department and in the shadows of MF nuances. The better 4V tubes have less emphasis on the higher notes but they throw magnificent MF with super locative tone. I am particularly like what the YO184 does – it lower range is mesmerizingly good and… this time it does have HF.  The MF channel with 45 and with YO184 shall be truly used differently those tubes basically do different thing…

So, I kind of moved to the right direction but the very major question I ask myself: how better my recent none-inactive setting with 20:1 load vs. my former 25:1 load with a mild inactive low-pass.  Subjectively, after the tweeter and Injection Channel are set in respectably appropriate seething I would that the Sound is the same. The new non-inductive setting has some benefits:

1)   Less reliance upon tonal output of my Injection Channel (-2.5dB then it was with 45 and inductive LPAD)
2)   A flexibility to adjust the MF output practically unpunishable from the perspective of sound quality
3)   An ability to use the 4V tubes.

I for now will stay with the new non-inductive setting and will try to find a setting that would fully capitalize on the MF richness of YO184. I very much like what I get with 45 in the new setting but the 4V tubes and particularly the YO184 have own twist, this time without the HF limitation they had before. It is not about one tube is better then other but rather about what I would like to capitalize upon. The debate about the 45 vs. YO184 is in away remains me the contest between the “quietly” of Maria Callas and Renata Tebaldi. Tebaldi was objectively a better singer but it is imposable to do not fall under hypnoses of the Callas’ throaty timbre, so richly saturated with all imaginary inflictions of drama or excitements. The 45’s slightly tonally not-overblown but still all-together it is about the performing perfection , which is on Tebaldi side, and it is perfect. The YO184’s tone, its ability to arouse the voices of forgotten ancestors and to bring up the smells of wilted flower it something that is very hard to discard and it is more aligned with Callas…

Anyhow, this is the update that I promised. It is what it is. I have updated the circuit of my MF channel where I was trying to depict the logic of my new non-inductive LPAD setting.

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