Hi Bob, I’m not sure that even the ancient drugstore-type tube testers some of us remember from our childhoods measured heater-to-cathode leakage. Most of the better professionally oriented testers from those days did, however. (I have a vintage Hickok 800a). For most users I suppose the only practical alternative is to see how the tubes perform in the particular application, and hope for the best. And given the many positive experiences that have been reported with Sophia tubes, including the 6SN7, I suppose the odds of success are good. Although note that in some of the cases I referred to the hum problems didn’t arise until the tubes had been in use for some period of time. And of course I have no way of knowing if the problems that I and a couple of others reported represented atypical examples of the particular tube type, or were due to a combination of tube characteristics that are more typical combined with sensitivity of the particular component designs to those characteristics. Note also that as I said in the thread I linked to Ralph has indicated in the past that he rejects tubes having heater-to-cathode resistances of less than 10 megohms (i.e., 10 million ohms). And for the 8 Sophia 6SN7s that were in my possession (4 originally purchased; 4 replacements provided under the warranty) ... The heater-to-cathode leakage in my Sophia’s, as measured on my vintage Hickok tube tester, was as low as 3 or 4 megohms on some sections of some of the tubes, and was in the 5 to 10 megohm area on most of the others.
... Also, I’ll mention that on my Hickok 800a tester all of the vintage 6SN7 tubes I have measure well above 10 megohms, and in many cases are high enough to be unmeasurable.
FWIW, I personally don’t envision Sophia tubes as being in my future, despite all of the glowing praise they have received from others. Best regards, -- Al |
Glad that the Full Music 6SN7s worked out well for you, Ozzy. Your findings regarding their excellent sonics are consistent with many others I’ve seen reported for their Sophia counterpart. Including feedback Ralph mentioned earlier in this thread that he has received from a number of customers. However, I’ll note for the record and for the information of those reading this thread that at various times in the past I and at least two other members here experienced totally unacceptable hum problems with the Sophia version of the tube. See my posts dated 4-2-2017 in this thread, and the link provided therein, and also the post in that thread dated 4-3-2017 by Tubegroover. It can be expected that sensitivity of preamp and power amp designs to what I determined was apparently the cause of the problem (measurably excessive heater-to-cathode leakage, resulting from either a design defect in the tube or a quality control problem in its production) will vary widely among different designs. I would suspect that some designs will be totally insensitive to it. And FWIW, apart from the hum issue the Sophias did sound great in my amp. Best regards, -- Al |
Doesn’t using zero transformers defeat the whole point of an OTL amp? It’s putting a transformer in and makes it similar to a non OTL push pull tube amp. That’s a logical question, which has been stated here in a number of other threads in the past, but basically the answer is "no." From a technical standpoint the following statements quoted from the FAQ at the zeroimpedance.com site are good ones IMO: 12) What is the difference between the ZEROs autoformer and a typical tube amplifier’s transformer?
The ZEROs have a few advantages over "typical" tube amp transformers:
A) The music comes out on the same winding wire that it goes in on so the music does not have to pass from a primary winding to a secondary winding.
B) There is no DC current to contend with. When a transformer is made to accommodate a DC field, its audio transparence is compromised.
C) The impedance ratio is very small (16 ohms to 4 ohms, compared to a few thousand ohms to 4 ohms). This simply means that it is much easier to achieve things like, frequency response extremes, than with a "typical" tube amp transformer. The ZEROs sport a frequency response of 2 Hz to 2 MHz.
13) Doesn’t adding the ZEROs to my Output-Transformer-Less (OTL) Amplifier defeat the benefits of the OTL design?
The ZEROs were originally designed to maximize the full benefits of the OTL amplifier by changing the speaker’s load impedance to the Maximum Power Transfer Region of the amplifier being used.
The ZEROs are not an amplifier fix, they are a speaker fix. It is a great disfunction to music loving audiophiles for speaker manufactures to be making 4 ohm speakers with 3 or 2 ohm impedance dips, and then expect amplifiers and speaker cables to be able to transfer music into a load approaching a dead short. The ZEROs simply multiply the impedance of the speaker in use, and do it so transparently they provide greater benefits than the "penalty" of an added component. As I said, from a technical standpoint that all makes sense to me. Basically, all transformers and autoformers are not created equal :-) Regards, -- Al |
Hi Bob, It is certainly possible to overdo the DEQX calibrations/corrections, resulting in unnatural sound. But as my dealer advised me (Nyal Mellor of AcousticFrontiers.com, who is wonderful), corrections should be applied conservatively. Especially with respect to the natural upper treble rolloff that most speaker/room combinations tend to have at the listening position. My Daedalus speakers are rightly known for having a very natural sonic character, and that was only improved as a result my use of the DEQX. Most notably in the case of recordings having sound quality that is mediocre or worse, especially in terms of harshness or excessive brightness in the treble region. As I said in one of my posts in the DEQX thread: Perhaps most notable among the differences that I and my wife perceived were on some recordings having overly bright string sound, including some string quartets as well as symphonic recordings. Those became much more enjoyable with the filters engaged. Not because the sound was dulled down, but because there seemed to be increased detail and improved definition in the upper midrange and lower treble, as opposed to a more homogenized presentation of those notes, which in turn resulted in the brightness being less objectionable. I can say also, in the case of my HDP-5 and as Ozzy and numerous others in the DEQX thread have attested to in the case of other models, that with the corrections bypassed the unit is amazingly transparent. Even when an analog source is being used (via unbalanced connections, at least; I haven’t used its balanced analog interfaces), and is therefore processed through the unit’s A/D and D/A converters. I can’t say that there is zero effect on the signal, but it is remarkably small, and easily outweighed by the benefits the processing provides. Best regards, -- Al |
Hi Bob, I don’t recall anyone reporting having used a DEQX with a time coherent speaker (e.g. Vandersteen, Thiel, Green Mountain Audio). BTW, time coherence implies phase coherence, but phase coherence does not necessarily imply time coherence. Many speakers are phase coherent without being time coherent. See the post dated 7-15-2014 by Roy Johnson of Green Mountain Audio in this thread: https://forum.audiogon.com/discussions/sloped-baffleAs you've probably seen in the past, though, John Atkinson’s measurements that are presented in conjunction with most speaker reviews in Stereophile sometimes provide impulse response graphs (and associated commentary), and usually provide step response graphs, which can also provide insight into time domain performance. Presumably the time alignments provided by DEQX would not provide a benefit in the case of a speaker that is inherently time coherent, such as your Treo. But of course the frequency response and room corrections it provides would presumably still be applicable. As well as preamp functionality that is provided by some models, and A/D and D/A converter functionality. Best regards, -- Al |
+1 to Charles’ comment. Great job, Ozzy. Between developing the DIY speakers, becoming proficient with the DEQX, and integrating both of them with subs and two very different amps, you’ve certainly dealt with a multitude of challenges.
And Bob, +1 to all of Ozzy’s comments about DEQX. Regarding the graphs, btw, when you go through my posts in the sections of the DEQX thread I referred to you’ll find links I provided to graphs of the speaker and room measurements I took, and the resulting calibrations. As well as descriptions of the necessary measures I took to minimize the effects of room reflections on the speaker measurements, which as will generally be the case included (among other things) moving the speakers from their normal positions. That can be a challenge if the speakers are large and heavy, of course, and for one reason or another it will probably have to be done more than once.
Best regards,
-- Al
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Bob, if you are interested in learning about DEQX, when you have some time available to read through a lengthy thread see the following one: https://forum.audiogon.com/discussions/is-deqx-a-game-changer?And their website is worth visiting as well, of course: http://www.deqx.com/I use their top of the line HDP-5 model, which serves as my preamp as well as providing speaker and room calibrations/corrections. (And yes, to answer your question those can be switched off or on at the touch of a button on either the remote or the front panel). My own experiences getting it dialed in, which at my slow and methodical pace extended over about 6 months, are reported in the above mentioned thread in posts between 5-16-2015 and 12-2-2015. Best regards, -- Al |
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+1 to Jon's wise counsel.
Ozzy, regarding the DEQX calibrations, to be sure it's clear I was envisioning that in addition to the effect of the amp change on the balance between the main speakers and the subs, the DEQX measurements (and the resulting calibrations/corrections) of the DIY mains themselves might change. The reason being differences in impedance interactions between the mains and the very different output impedance of the M-60 vs. the Pass amp.
It sounds, though, like you're intending to re-do the entire DEQX measurement & calibration/correction process, which of course would address this.
Continued best of luck.
-- Al
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BTW, Ozzie, I suspect that the X350.5 spec of "40 watts peak" for the point at which it leaves class A operation is equivalent to only 20 watts based on the usual conventions for defining amplifier power (corresponding to volts x amps with each defined on an "RMS" (root-mean-square) basis, rather than a peak basis).
So you’ve probably been using very little of that amp’s power capability.
Regards,
-- Al
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Hi Ozzy,
I wouldn’t infer too much from that 600 watt number. The amp only operates in class A up to "40 watts peak," and beyond that output power level its AC draw will presumably vary with the dynamics of the music. Also, given the amp’s power ratings of 350 watts/channel into 8 ohms (700 watts total output) and 700 watts/channel into 4 ohms (1400 watts total output), obviously it would be drawing considerably more than 600 watts from the wall outlet when supplying anything approaching its rated output to the speakers. (It can’t put out more power than it takes in, or anything even close to what it takes in given that it is not class D).
Given your earlier mention that your use of the amp has been such that it has rarely if ever left class A, FWIW my rough guess is that the amp has probably been introducing something like 300 to 400 watts into the room.
Best regards,
-- Al
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The M-60 is spec’d as consuming 300 watts per monoblock, and since it operates in class A it will draw that amount of AC power all the time (when it is being operated, of course). And it will convert all of that power into heat, except for the amount of power it sends to the speakers, nearly all of which will be converted into heat by the speakers anyway.
So assuming the spec is reasonably accurate, which I’d expect since it is one of Ralph’s products, the amount of heat introduced into the room by the two amps will correspond to 600 watts. About the same as the heat that would be introduced into the room by six 100 watt incandescent light bulbs.
Best regards,
-- Al
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Hi Ozzy,
I took a look at the photos in your system description thread, and also at the very comprehensive technical info provided at the Aurum Cantus site
My first comment is that it looks like you’ve done an extremely impressive job of assembling a very sophisticated system!
It appears that your G1 ribbon tweeter and whichever of the Aurum Cantus mid-woofers you are using have benign impedance characteristics, which don’t descend significantly below their 8 ohm nominal ratings at any frequency, and don’t have highly capacitive phase angles outside of the deep bass region (in the case of the mid-woofers) which they won’t be handling anyway. Also, it looks like the external crossover you’ve built consists of second order LC filters (low pass for the mid-woofer and high pass for the tweeter, of course), with a resistive pot in the high pass section to pad down the tweeter’s sensitivity to match the mid-woofer’s. I don’t see any of that as presenting any problem for the M-60, used without Zeros.
Also, while most of the energy that is contained in most music most of the time will be present at frequencies that will be handled by these drivers, as opposed to the subs (my understanding is that 350 Hz represents a rough rule of thumb for the frequency at which most music most of the time has equal amounts of energy above and below), the 60 watt capability of the M-60 into 8 ohms should get you to peak volume levels in the area of 101 to 104 db or so at a 10 foot listening distance, with a 90 db speaker that can handle that amount of power without significant thermal compression (as appears to be the case here).
Some further points:
While I’m not totally certain, I think it might be worthwhile to re-do the DEQX speaker calibrations once the new amp is in place. I’m envisioning that the interaction between the amp’s 4.1 ohm output impedance and the characteristics of the cross-over/speaker combination might change the results you obtained with the Pass amp, and its near zero output impedance. Although I’m not certain of that, as I said. Fortunately your DIY speakers are not multi-hundred pound monsters, and should be fairly easy to move, if that is necessary to minimize room reflections during that procedure.
Second, keep in mind that the interaction between the 4.1 ohm output impedance of the amp and the 8 ohm speaker impedance will reduce gain by a few db, relative to what you have with the Pass amp, and will require a corresponding rebalancing of the speakers with the subs.
Finally, I note that the frequency response plots for the Aurum Cantus drivers show some significant variations within the frequency ranges they will be handling, such as a rise of more than 5 db in the response of the tweeter in the top octave, and significant rises in the upper mid-range/lower treble responses of many of their mid-woofers. The DEQX should be very helpful in providing whatever corrections may be needed for those variations.
Best of luck. Regards,
-- Al
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