Rerurn to Romy the Cat's Site

Interesting, Very interesting.

I might make some observations now, claming this recent modification as a success. The minor gain of sensitively certainly did not heart but the major advantage was defiantly the “activation of ceiling”. It is hard to describe, it have to be heard. In a way it sounds like Sound coming from two out of phase with each other loudspeakers only it delivered by a system that is completely time-aligned. What it did in my case was a creation some sort of “out of geometry reference” experience, effectively killing, even with more vigorousness ten before, the soundstage as an audio consciousness… and presenting the necessary imaging WITHOUT the soundstage. I mean the soundstage is here but it has no definitive position and location in the room but rather it behaves like an abstraction of presentation instead of the presentation of itself. It was exactly why I was craving for the idea of the “ceiling loading” since I discovered this effect.

The power handling of the LF section got better as well. Scan-Speak suggests that the drivers I use are 100W but I feel that the more like 20-25W. However, the biggest discovery I had with the fact the since I begin to use the second LF section I was not able to increase the plate current on the LF channel of the Super Milq.

This question I asked to the technical people and it was posted at the Triodemafia.com:

*****************************************************

Hi, guys.

I have question to ask, or more prissily I would like to learn about your visions what might be the causes for the situation that I can’t explain.

CIRCUMSTANCES:

I have a dedicated low frequency amp (Supper Milq) that low-passed at 60Hz.. The output stage is a full 6C33C, 230V-150mA driving a sealed 8R array of woofers with no impedance EQ. It runs all the way up to 33R which is fine. The transformer is 450mA, 15H, 15W, DCR secondary 23R and it’s made to load the 6C33C with 700R. The tube kind of overloaded in this setting and I have less power, fewer distortions and all together the sound that I found appropriate or let call it for the sake of given illustration the “correct sound”.

ACTIONS:

I recently added to the current array of 4 woofers 2 extra woofers. The very same driver, the identical volume of the enclosures and the almost the same boxes resonation frequencies (41Hz and 39Hz) The new enclosure has total of 16R and connected parallel to the old one bringing the combined impedance down to 6R. As the result, I as expected yielded some power, slightly more “loaded” loading of the output stage at the amplifier level and all other (none-related to this subject) benefit in a listening room. Everything sounds kosher and the bass after the new amplitude adjustment still exactly the same “correct sound”.

PROBLEM:

Using a common sense, since I dropped the load impedance I decided to increase plate current. To my huge surprise the increase of plate current for even 20-30mA killed bass instantaneously. The bass still was there but at 170mA it begin to sound like a noise coming out of fourth order port. Interestingly that the word “instantaneously” was the key mystery word in my last sentence as when I used a single old enclosure with impedance of 8R (out of resonance range) then the effect of worsening of sound with increase plate current does NOT manifest itself AT ALL. I mean I could drive a single tower with even 300mA that dissipate almost 70W on this tube but I never had those “ported” distortions. It would be another problem but it will be not so bad.

WHAT THE HELL IS GOING ON?

Really, why is it so? Should I drop voltage? I still way beyond the max tube dissipation (60W) with 230V and 175mA! I did drive this tube at 60W and it dose fine with one single 8R enclosure. Does the impedance of this tube changes too dramatically when it loaded with lower impedance and driven harder and this change in some mystery way affects the speaker’s damping? Why the amp, or the woofer towers, or the interface between them suddenly do not like the increase of current? Are any further thoughts from the member of the Mafia about my quandary?

I kind of do not need “help” with it as I do like what is going in at 150mA and I can perfectly live with it “as is”. However, I would like to UNDERSTAND WHY my higher current kills bass if I’m so far from the saturation point.

*****************************************************

The further experiments leaded to the discovery that those particular woofers of this particular no-feedback amp have some kind bizarre puss in them that makes them superbly sensitive to dumping factor.  Dima discovered that adding 2.7R resistor in series with 5.5R of the new load does return the amp operation into the former state and does allow me to raise the plate current. The interesting part that when I played before with different amps and different speakers I never ever ever ever ever ever seen such a dramatic sensitively to the dumping factor. So, it looks like the need a new 700 :5.5 low frequency transformer.  I still am contemplating if I need to take out of the LF channel more power then I’m taking out now, as I might perfectly fine to live with the current 150mA. If I decided that I need more power then the transformer will be in order, or perhaps I will loose a few turn on the secondary of my current transformer…

Still, I have no idea why my system became suddenly so super-sensitive in regards to the dumping while I dropped impedance juts for 2.5R.

Rerurn to Romy the Cat's Site