dazzdax wrote:

what is your experience with passive transformer based preamps? Is this the ultimate way to get a perfect variable gain? Or do you prefer to use an active preamp?

I think the terms of ultimate might be applied only in context of the specific requirements when the definition of success would be a match between the demands and accomplishments. All those passive transformers-based preamps along with the inner-stage transformers are very much should be approached from those positions: in context of what requirements the passive preamps should be observed.

If you have bookshelf, ported or juts in any way LF challenged loudspeakers or for instance not really demanding LF electronics (courtesy to the SET amps) then the passive resistors of transformer attenuators might work perfectly fine for you.

Certainly a resistive attenuation will not drive cables but it you locate them right at the power amp input then the resistors network works juts fine. Once again: they will work fine… depends of the demands of your loudspeaker in your room, primary depends of dynamic and LF demands… Sometimes, going up with your demand and up with your expectations you will reach a point when a passive attenuation extended further form the input stage of your amp will not satisfy you anyhow, primary because it will compress dynamic and truncate LF. Still, my estimate the is that 70% of audiophile systems out there should not worry, or will not able to detect the remote resistors network problems.

With the transformer attenuation everything more completed. It is possible to make a transformer that would preserve or even enrich dynamic range. I said possible not because you can go to store and buy it but because if you chase them for years and years, spending thousands dollars then you might eventually discover one. Also, it is practically imposable to custom order anything serous in magnetics because the manufacturers do not do what it necessary or demanded but what they feel is “comfy” to manufacture…. However, even if you did succeed to preserve dynamics in your line-level transformer then the LF cut off of this transformer will “get” you. The solution is very simple: do not run any transformer attenuators within a really LF capable installations….  I said the “LF capable” and I wonder… how about the LF modulations that must be within any amplification channel? Absents of real bass within amplifier means no properly auditable HF, no proper harmonic modulations… no Sound as far as I concern. (Remember, I did not advised to high pass the HF channel of the supper Milq).

Would it be theoretically possible to bult a properly operating full-range capable innerstge transformer? I did not see any. I am sure Bud, Chris from UK or Torthen if they read it would be violently disagree to my assessments, but I do agree with myself: a line level transformer has more problems then solution, beside that fact that it never sound LF capable, or something that I usually call “good only for Lowther-based systems”....

... there is no really LF potent/transparent line-level transformers.

Rgs,
The Cat

Romy the Cat wrote:

However, even if you did succeed to preserve dynamics in your line-level transformer then the LF cut off of this transformer will “get” you. The solution is very simple: do not run any transformer attenuators within a really LF capable installations….  I said the “LF capable” and I wonder… how about the LF modulations that must be within any amplification channel? Absents of real bass within amplifier means no properly auditable HF, no proper harmonic modulations… no Sound as far as I concern. (Remember, I did not advised to high pass the HF channel of the supper Milq). Would it be theoretically possible to bult a properly operating full-range capable innerstge transformer? I did not see any. I am sure Bud, Chris from UK or Torthen if they read it would be violently disagree to my assessments, but I do agree with myself: a line level transformer has more problems then solution, beside that fact that it never sound LF capable, or something that I usually call “good only for Lowther-based systems”.... ... there is no really LF potent/transparent line-level transformers.

Hi,

dazzdax wrote:

Hi Romy and other fellow audiophiles, what is your experience with passive transformer based preamps?

Thorsten wrote:

I wonder, which specific line level interstage transformers have you tried, it would have to be ALL of them in order for your statement "there are non" to hold... ....But, what specifically do you object to in these transformers?

Applications: To make a properly sounding and really LF frequency capable interstage transformers it would require making it huge with very large inductance that makes it very susceptive to pick all type of problems in a chasses.

Applications: although a transformer independently might measure quite nicely but being placed between the stages it is a perfect second order high pass filter. A interstage transformer is a filter; an output transformer is the filter…. How many filters should be connected in series within one single amplifier? What happen when the slops of the different filters within an amsp come together and begin roll of with very high order at stop band?

Prejudicial disbelieve: transformers are complicated and there are very many variables that would impact their sound. The core material, the winding techniques, the wires, the laminations and so on and so on…. It becomes even more complex when a transformer was placed in a circuit and begin to operate in the real world, when huge amount inductances, capacitances and other sometimes none-linear forces become influential and begin to talk with the rest of the circuitry.  How methodologically correct to assess all of it? How to assess if the transformer is as good as it could be in the given application of the given circuit? A capacitor, quite in contrary, is a self-contained encapsulated element, relatively simple with juts two parameters: material of conductor and material of dielectric. It is very easy to select a correctly sounding capacitor and dance around it’s capacity (no pan intended). Also, a capacitor is mush more “passive” element then transformer. It might affect sounds but it has much less impact to musicality and complex dynamic form of sound reproduction.

Practicality: T. I kind of do not what to sound that I religiously disbelieve in transformer coupling. A properly made transformer should be very interesting but what practical way people like me for instance have to approach those “properly performing transformers”?  I spent quite a lot of tine until I found the phonocorrector step-up transformer that I could lived with and it was a pure accident that most likely will not happen again. Also, I know some serious engineers who constantly bitch that if they come up with a very demanding transformer specification then there is no place when those transformers might be made. And I’m talking about the old generation of engineers with deep international connections who have been doing Sound for 40years! The point is that in the world of transformers we get semi-accidental “as is” result and then juts deal with what we’ve inadvertently got.

My personal experience with transformer coupling was during to my excrements with making “absolutely transparent buffer” when I used Lundahl amorphous transformers. The results that I was getting were constantly less interesting then with best capacitors I had. However, what turned me off very aggressively that the worsening that I experienced with transformer was in a very specific direction. You see, I do not think that I have any reasons or justifications to express my technical opinions on the subject. I  (mostly) do not dive into the minute behavior of circuits (letting the people who more qualified then me to do it) but rather I observe the final result of a topological solution. Interestingly that any single installation that I have hear when the transformer-coupling was advocated had that specific indispensable signature, something that I might characterize as “cold throat sound” or “breathing in a dusty room”. The epicenter of it was my visit the Japanese Sacuma-san when I was listening of his amplifiers with 342 transformers. I can tell you that I was able tofeel that “dry sandy suffocation” in sound each time (to more or less degree) when I heard the transformer-coupled designs. Not to mention that each time when I see a transformer-coupled amplifier I for whatever “mysterious” reasons observed in their listening rooms acoustic systems with LF capacity of the bookshelf loudspeakers. I personally think that problems that I experience with transformer are the ultra low frequency related, as the ULF in transformers do not modulate the necessary “modulation” in the rest of Sound.

Still, if I have a change to have in my disposal unlimited knowledgeable-enough engineering recourses, the unlimited assess to all necessary materials and assembling techniques, unlimited amount of money and time I would wiling to contribute to the projects and if I have people who make transformers did it not juts for money but rather as a LABOR OF LOVE than, knowing what I know about sound, we might come up with a properly sounding transformer – a transformer that would do not only a proper RENDERING OF SOUNDS but the proper transformation of MUSICAL REALTY. I have no such resources and I have not seen any properly performing transformers juts because I did not see any objectives that I might respect among the transformers manufacturers. It is not only because the people who manufacture the transformers have no capacity to perform the musical assessment of their own “reality transforming machines”. The transformers that are being made are juts the devises that are comfortable for people to manufacture and nothing else.

Tell me T, if someone would approach those guys form S&B, agree to pay much more and would demand something very specific and something that is way beyond what S&B put dally to the dealer’s inventory shelves then what S&B would do? Most likely they would send those “someone” to hell of juts take money and do whatever they feel should be done instead what is necessary to do. How good driver would you be if a rack and pinion of your car has own brain and own idea in which direction the wheels of your car should be turned while you are driving?

Anyhow, I am not disbeliever; I’m just a pragmatic realist or a person who was not convinced yet. I would love someone prove me be wrong, I am wiling to pay for it. But so far a really good cap is a way to go for me.

Thorsten wrote:

So, at least in commonly observable and observed terms and when used as intended the S&B line transformers are notably more capable at low frequencies than your LF OPT's in the Super Milq.

I have no doubt but there is something more to it, T. You see an output transformer by cutting LF juts cut LF and nothing else. It dose affect the sound in a room, the “space” qualities, the softness and realistics of the upper bass, the perception of HF and many other things that we attribute to bass. However with bass truncated at output transformer we have juts “no bass” from amplifier.

Nevertheless, if that bass was truncated between the stages then the devastations are way more severe. Those devastations do not affect bass itself (the cut off of the interstage transformer way lower then any output transformer) but the devastations intrude the inner structure of the entire sound and affect sound not horizontally be internally-vertically. I feel that stages, in order to produce the inner-connected sound, should operate in as full range as possible, still they should not be DC coupled….

Rgs,
Romy the Cat

Romy the Cat wrote:

Nevertheless, if that bass was truncated between the stages then the devastations are way more severe.

Romy the Cat wrote:

Applications: To make a properly sounding and really LF frequency capable interstage transformers it would require making it huge with very large inductance that makes it very susceptive to pick all type of problems in a chasses.

Which is why S&B line level transformers (exception, high level 600R 1:1 Output TX410LO) all come in a mu-metal can that has huge levels of rejection of external fields. And yes, the inductances involved are very large, the TX-102MKIII measures around 1,200H primary inductance at 3Hz measurement frequency and around 0.2V level.

Romy the Cat wrote:

Applications: although a transformer independently might measure quite nicely but being placed between the stages it is a perfect second order high pass filter.

Romy the Cat wrote:

A interstage transformer is a filter; an output transformer is the filter…. How many filters should be connected in series within one single amplifier?

Romy the Cat wrote:

What happen when the slops of the different filters within an amsp come together and begin roll of with very high order at stop band?

Romy the Cat wrote:

A capacitor, quite in contrary, is a self-contained encapsulated element, relatively simple with juts two parameters: material of conductor and material of dielectric.

Romy the Cat wrote:

My personal experience with transformer coupling was during to my excrements with making “absolutely transparent buffer” when I used Lundahl amorphous transformers. The results that I was getting were constantly less interesting then with best capacitors I had.

Romy the Cat wrote:

However, what turned me off very aggressively that the worsening that I experienced with transformer was in a very specific direction.

Romy the Cat wrote:

The epicenter of it was my visit the Japanese Sacuma-san when I was listening of his amplifiers with 342 transformers.

Romy the Cat wrote:

I personally think that problems that I experience with transformer are the ultra low frequency related, as the ULF in transformers do not modulate the necessary “modulation” in the rest of Sound.

Romy the Cat wrote:

Tell me T, if someone would approach those guys form S&B, agree to pay much more and would demand something very specific and something that is way beyond what S&B put dally to the dealer’s inventory shelves then what S&B would do?

T, thanks for educational reply. I understand what you are saying and where you are coming from but unit I try better transformer, presumably your S&B TX-102 I would not be able to correlate your observations with my, perhaps too semi-prejudicial findings. I have one extra fully operational full-range Melquiades that I might use for such experiments, sometimes later on… Nowadays I have no motivations to change anything… You know me: I do not change the changeable gust for a sake of the changes…. until I detect what is wrong with the current sound. So far everything sounds all right to me.

Also, nope, I did not see your new changes in your LCR Phonostage, last time when we spoke about it I remember you began using 7721 in output. Later I know you experimented with 10K RIAA filter but I do not know how successfully. If you have a newsiest update version then let know where. If you do not have it posted then feel free to use this site (another thread or I might do a customer page for your corrector). I would like fully indorse that corrector because I remember when I built that 600R thing (I used it “as it was” only with 7721 and with LC supplies) it was a very good sounding machine.

Rgs,
Romy the Cat

Romy the Cat wrote:

T, thanks for educational reply. I understand what you are saying and where you are coming from but unit I try better transformer, presumably your S&B TX-102 I would not be able to correlate your observations with my, perhaps too semi-prejudicial findings.

Romy the Cat wrote:

Also, nope, I did not see your new changes in your LCR Phonostage, last time when we spoke about it I remember you began using 7721 in output.

Thorsten wrote:

I have kept the 600R arrangement, but I cleaned up the circuit a lot. The new stuff was posted over at the AudioAsylum, not a place you are terribly fond of. If you still have the Phonostage you build it might be worth rolling these changes in.... http://db.audioasylum.com/cgi/m.mpl?forum=tubediy&n=88128 I think the biggest improvement came from input terminating and DC coupling the RIAA Module.  Cleaning up the input stage just seemed to get a bit more immediacy and dynamics.

Anyhow, I am jumping off as I’ve moved too far form the subject of the transformers. Your corrector deserves it’s own thread.

Rgs,
Romy the caT

PS: I have added your phono-corrector into the site’s Knowledge Tree

dazzdax wrote:

Thx for this well written and highly educational piece Thorsten! It appears that Romy is not very fond of the Audio Consulting transformers, could you give your opinion regarding those? What is your opinion regarding the use of pure silver wire in transformers?

cv wrote:

RE: the Slagle autoformers and their lower than S&B inductance, that's a deliberate design choice on his part.

cv wrote:

Dave has been known to recommend bigger air gaps for more linearity of the perm and likes low driving impedances.

Allo,

Actually, Dave makes it perfectly clear. Take a look at the forum and FAQ at www.intactaudio.com
He puts a lot of effort in making sure the TVC is suited for the system in mind - there are custom options for those (including higher inductance) and indeed, all his magnetics.

Otherwise, we don't disagree; Dave's is pretty much a custom shop, which is exactly what the dedicated and knowledgeable individual needs for magnetics. The knowledgeable bit is key, because it does take some understanding merely to specify magnetics properly (witness all the BS on tubediy by some *manufacturers* who should know better...).

That's the other big plus of his site to my mind - education. Blend in some good ol fashioned empiricism to find out what does and doesn't work well (no matter what engineering theory tells us) and it's a winning recipe.

Best,
cv

cv wrote:

Actually, Dave makes it perfectly clear. Take a look at the forum and FAQ at http://www.intactaudio.com

Hi Romy,

I just want to add my experience I had last year with a transformer based (actually it was an autoformer based) "passive" preamp.  I thought that this could be the final solution in my preamp quest.  Alas, it was not the case.  Here I will give you some specific reasons why the unit I tried (the Sonic Euphoria passive) did not live up to my hopes.

1) Loss of dynamic contrast.  I am sure you are aware of this problem.  It should not have been such a problem on my system with a 100kOhm input impedance but there it was.  This lack of contrast gave the sound a bland sameness that quickly became boring.

2) Loss of drive to the sound.  This I blame on problems in the low frequencies.  With time-coherent speakers (pair of Stax ELS F81s) it was easy to hear the bass was now lagging behind the rest of the music spectrum.  I think there must be a phase shift occurring to result in such behavior. 

In order to assess the problems more clearly I put an active preamp between the source (cd or vinyl) and the passive preamp.  This made the active preamp a "virtual" source or an output stage with much better driving capabilities than the source by itself. The result was that the sound took on much of the same character as I heard with only the "passive" preamp in the system.   I also tried it the other way around (essentially giving the source a volume control) and found that dynamics were improved but the bass rhythmic problem persisted.  I haven't tried other transformer based preamps so I don't want to over generalize.  However, it occurred to me that anyone who is using a non-time coherent speaker (especially a vented system with a high order and thus high phase shift in the bass) might not be as sensitive to these problems.  Their speaker already makes a mess of this information.   It seems you have had a similar finding with these so called "passive" devices...

If the output transformers cause so much trouble have you thought about remaking the Super M. amp as a Single Ended OTL?  You will need more tubes and generate a lot more heat but the sound should improve.  I recently purchased a pair of Silvaweld OTL monoblocks that use 4 6C33C-b tubes in a SEPP configuration.  It is running Class AB but the sound is really a cut above most of what I have heard (including IMO the Lamm ML2).   Another amazing sounding amp and preamp  that I heard recently is from a German company called Einstein.  Their 6C33C based OTL amps called "The Final Cut" are loosely based on a circlotron theme but the details are not forthcoming from the company except to say that it is a new variation. The preamp called simply "The Tube" is fully differential and interestingly has no input selector switch in the signal path.  It simply activates the filament and heater of the input tube to whichever channel was selected. So each input has its own input tube and the others are simply deactivated.  This gear is definitely worth your investigation as is the top gear from Silvaweld.

Morricab, I perfect concur with your findings and I come to the very similar concussions regarding the autoformers.

Unfortunately my experience with OTLs was much less exiting then yours. I presume that it is possible to get an "interesting" sound out of the OTLs but the entire system, including the speakers should explicitly optimized to handle some OTLs idiosyncrasies.. The Best OTL that I heard in context the SET-minded loudspeakers did not perform well

Rgs,
The caT

morricab wrote:

the unit I tried (the Sonic Euphoria passive) did not live up to my hopes.

Given my somewhat loose but existing ties with S&B and with Music First Audio I need to be careful what I am saying. But let me suggest that just winding some wire around a steel core does not make a good transformer. The unit you tried is very cheap, by comparison. There are reasons.

Given that you very much got the same sound, regardless of having the active preamp in line or not suggests quite clearly that you simply used a device with poor quality transformers.

morricab wrote:

1) Loss of dynamic contrast.  I am sure you are aware of this problem.  It should not have been such a problem on my system with a 100kOhm input impedance but there it was.  This lack of contrast gave the sound a bland sameness that quickly became boring.

morricab wrote:

2) Loss of drive to the sound.  This I blame on problems in the low frequencies.  With time-coherent speakers (pair of Stax ELS F81s) it was easy to hear the bass was now lagging behind the rest of the music spectrum.  I think there must be a phase shift occurring to result in such behavior.

morricab wrote:

However, it occurred to me that anyone who is using a non-time coherent speaker (especially a vented system with a high order and thus high phase shift in the bass) might not be as sensitive to these problems.

morricab wrote:

Another amazing sounding amp and preamp  that I heard recently is from a German company called Einstein.

morricab wrote:

Their 6C33C based OTL amps called "The Final Cut" are loosely based on a circlotron theme but the details are not forthcoming from the company except to say that it is a new variation.

morricab wrote:

The preamp called simply "The Tube" is fully differential and interestingly has no input selector switch in the signal path.  It simply activates the filament and heater of the input tube to whichever channel was selected.