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10-22-2005 Post does not mapped to Knowledge Tree
dazzdax
Netherlands
Posts 32
Joined on 10-22-2005

Post #: 1
Post ID: 1552
Reply to: 1552
Passive transformer based preamp
Hi Romy and other fellow audiophiles, 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?

Chris 
10-23-2005 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 2
Post ID: 1557
Reply to: 1552
Better among worst?

 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?
Chris,

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


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
10-25-2005 Post does not mapped to Knowledge Tree
Bud
upper left crust united snakes
Posts 87
Joined on 07-07-2005

Post #: 3
Post ID: 1573
Reply to: 1557
remotely possible interstage or volume control

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actually I agree with Romy, to a degree.... If the amplifier is a push pull device, using my output and input splitter devices of course, then an interstage transformer is a much better choice than rc coupling. Using transformers designed to the criteria I use will allow a push pull amp to provide a truer musical reproduction than a single ended amplifier with the same tube set, just barely, and only in the case of all out designs.

Using interstages in a single ended design is really a bit hopeless. The requirement for high inductance to offset the dc plate current forces the use of ultra fast core material. This causes the need for slow dielectric material in the coil and a mismatch between E field and B field response. The sonic result is sound with minute but continuous headache inducing dissonances. To cure this problem requires either massive amounts of turns and commercial core, with loss of high frequencies as the result, or fewer turns, gapped core and soggy low frequencies. I am sure there are some applications where triode drivers, step down interstage and low miller effect capacitance in the output tube will allow a specific to need design to work, and work very well at that, but as Romy says you will be throwing money at the problem for a while.

As for transformer volume controls, you can get them. Intact audio has kits for sale. The sound is a bit bland compared to an active linestage and would be better if it was not a tapped autoformer but a full on isolated device with proper coupling will be quite a bit more expensive than the Intact kit. They do sound better than any of the resistor switch devices except for those using $3.50 apeice crushed foil resistors, in a discreet pair type of circuit configuration.

A very interesting possibility is a switched step output transformer driven by a ridulously overkill triode power tube in an active preamp. If a pentode driver stage is used with a CCS to allow no interstage coupling devices and the triode was used, or a pentode as a cathode follower with another CCS attached, this might be a solution worthy of the time and money.

I do thnk you will find that all passive linestage devices have draw backs musically but a transformer volume control is probably the best of the lot and Dave Slagel's kit is inexpensive enough to be worth trying.
http://www.intactaudio.com/ 

Bud
10-26-2005 Post does not mapped to Knowledge Tree
Thorsten


United Kingdom
Posts 65
Joined on 12-06-2004

Post #: 4
Post ID: 1577
Reply to: 1557
Re: Better among worst?
Hi,

 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.



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.

For reference, the current generation S&B TX-101 (Line Transformer, also in an experimental "high level" tube interstage version which may or may not become commercially available) and TX-102 (Line Level Attenuator) are free from any significant (> 0.1db FR deviations or > 5 degrees phaseshift) observable issues down to 10Hz, when driven from a 1k or lower source impedance.

At sensible levels (1V RMS) any distortion is sub -100db with only low order components (<= 5th, 3rd dominant) as far down as that too, in fact to measure any distortion on the transformer you need serious levels at very low frequencies and some really good analysis gear.

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.

If they can be mada better in areas currently overlooked, please let me know, I'll broach it with JB.

But, what specifically do you object to in these transformers?

Ciao T


"It is to Madame Justice that I dedicate this concerto, in view of the holiday she seems to have taken from these parts." V
10-26-2005 Post does not mapped to Knowledge Tree
Thorsten


United Kingdom
Posts 65
Joined on 12-06-2004

Post #: 5
Post ID: 1578
Reply to: 1552
Re: Passive transformer based preamp

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Hi,

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


I have yet to find anything better. If using active try using a TVC as volume control, it takes the active preamp to a new level as well, though personally I prefer it passive overall.

Ciao T


"It is to Madame Justice that I dedicate this concerto, in view of the holiday she seems to have taken from these parts." V
10-27-2005 Post mapped to one branch of Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 6
Post ID: 1587
Reply to: 1577
Some transformer ranting.

 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?

T, I knew that you would disagree but here were we stand. My problems with interstage transformers are following: applications, applications, prejudicial disbelieve and some practicality.

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.

Rgs,
Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
10-27-2005 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 7
Post ID: 1588
Reply to: 1577
Further problems with interstage transformers.

 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


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
10-28-2005 Post does not mapped to Knowledge Tree
Thorsten


United Kingdom
Posts 65
Joined on 12-06-2004

Post #: 8
Post ID: 1598
Reply to: 1588
Re: Further problems with interstage transformers.
Roman,

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


That may be so, however an LF response of less than -0.1db down @ 10Hz is what is normally called "ruler flat", so no "truncation takes place, plus note the LF rolloff of a correctly applied transformer is first order, caused by the limited primary inductance.

So, your note of "truncating bass between stages is bad" may very well be right, but a competently designed line level transformer does not truncate bass.

 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.
 

No, it is not. At low frequencies it is a 1st order highpass, however the tendency of magnetic core material (especially high nickel content permalloy) to show increased induction with reduced frequency limit even this highpass behaviour.

At high frequencies an ideally loaded transformer is 2nd order, however much depends on winding structures. If you make the leakage inductance the dominant mechanism (this works only with a defined resistive load) the HF rolloff will also be 1st order untill load capacitance and transformers parasitic capacitance kick in.

 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?
 

That depends, if one filter dominates, because all other firlters have their turnover frequencies several octaves outside the passband of the dominant filter the answer is "it matters FA how many you connect in series".

 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?
 

That depends entierly where the high order rolloff is situated. If it is several octaves below or above the dominant pole, very little happens.

 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.
 

That is sadly pure wishful thinking.

 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.
 

First, "AM" cores are still usually simple iron. They are basically slightly more ideal generic cores. High Nickel content permalloy or amorphous material is a very different proposition.

Secondly, transformers that have a significant degree of uncompensated DC in the primary can cause sonic probloblems and usually have poor bandwidth. Remove the DC current and use a transformer where it makes sense (that is where step up, step down or galvanic separation is needed and you do not have such issues.

 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.
 

You mean what turned you off was the SPECIFIC way things got worse with SPECIFIC transformers in SPECIFIC applications and you projected the SPECIFIC experience onto the generic subject, which is a logical fallacy. 

Note, non of my designs feature interstage transformers with DC offset in the primary. There are very good reasons why that is so. 

Yet I use a multitap line level transformer as volume control. There are very good reasons why that is so as well..

 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.
 

Sakuma uses transformers in the exact reverse way I do. Clearly he seeks a very different sound to myself.

 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.
 

The ability (or not) of a transformer to pass "ULF" is related to the design. To dismiss all transformers, because some do not pass "ULF" is a logical fallacy, just as to condemn transformers for a lack of transparency is wrong if all that was tested was steel cores and iron amorphous cores.

 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?
 

Right now, polietly decline. However if you have time, once S&B have managed to get past current large bulk orders you may find that such a project, which is basically classifiable as research, would interrest S&B.

In the meantime, why not try a pair of S&B TX-102 for fun? The current generation is really good.

BTW, did you note the most recent changes to my LCR EQ Phonostage circuit?

Ciao T




"It is to Madame Justice that I dedicate this concerto, in view of the holiday she seems to have taken from these parts." V
10-28-2005 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 9
Post ID: 1599
Reply to: 1598
Thorstenisation of magnetism...

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


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
10-28-2005 Post mapped to one branch of Knowledge Tree
Thorsten


United Kingdom
Posts 65
Joined on 12-06-2004

Post #: 10
Post ID: 1601
Reply to: 1599
Transformers & Transformers....
Hi,

 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.


Note, the 102 is designed strictly as volume control for passive (or if you must active) preamplifiers.

If I get JB to make some more 101HL (a version of the TX-101 designed for higher levels with a view to use as interstage transformer for valve circuits, but STRICTLY for push-pull drive with 0mA DC imbalance!!!, 80% Nickel Permalloy Core, sadly not available to the general public at the moment) I'll ask him to make an extra pair.

I found that "interstage" transformers with significant DC in the core call for too many compromises, which I have been so far unable to overcome using off the shelf items.
 
 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.


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.

Ciao T 


"It is to Madame Justice that I dedicate this concerto, in view of the holiday she seems to have taken from these parts." V
10-28-2005 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 11
Post ID: 1603
Reply to: 1601
Very nice, Thorsten!!!

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 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.
Very, very nice, I love it! I still have this corrector assembled and perhaps sometimes during the long dreary Massachusetts winter I might try it again.  The next step would be to stop using the Ansar capacitors as they destroy lowest frequencies (yes they do!!!) and decouple the screen of the 7788 from the circuitry by a regulator, the similar how it done in Melquiades amp. The decoupling should take sound at a very different level… Also, I need to send you a pair of the coupling Cubes 950 capacitors and you will stop to use the tricks :-)

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


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
10-29-2005 Post does not mapped to Knowledge Tree
dazzdax
Netherlands
Posts 32
Joined on 10-22-2005

Post #: 12
Post ID: 1607
Reply to: 1598
Re: Further problems with interstage transformers.
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?

Chris
10-31-2005 Post does not mapped to Knowledge Tree
Thorsten


United Kingdom
Posts 65
Joined on 12-06-2004

Post #: 13
Post ID: 1623
Reply to: 1607
Re: Further problems with interstage transformers.
Hi,

 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?


First, I have no first hand experience of the AC Transformers. Here is what I know about them and how in my experience this impacts on the sound:

1) Primary inductance is 50 - 100H, that is by a factor of 10 to > 20 less than what we ended up with the S&B one. This will seriously impact on the low frequency preformance with sources that have all but the most heroic solid state output stages. I note that Dick Olsher found problems when using the SR with a Lamm LP2 Phonostage, which has around 3KOhm output impedance. I also note that the Dave Slagle Autoformer Volume controls (Intact Audio) have low impedance/inductance as have the Sowter TVC's (85H), which means that if sources have a fairly high output impedance any of these TVC's will experience problems at the bandwidth extremes at much lower source impedances than the S&B TVC and the far eastern "carbon copy" (or should that be amorphous copy?) that is now floating around.

2) Core material is iron/steel in all the lower grade versions (they don't say what the top grade version uses). Our (S&B plus myself) experience was that lowering the nickel content (currently S&B use 80% Nickel Superpermalloy [aka Mu-Metal]) "disimproves" neutrality and transparency, in other words, steel cored (or FE based amorphous) line level transformers are not sonically "wires with gain/attenuations", but fairly strongly manipulative, sonically speaking. It is entierly possible that the colorations and reduction in transparency from this (I also note this with the Opera/DIYHFS Amorphous Iron core equipped TVC's) will be considered to "sound good" by some in some systems, it simply was not the design goal for S&B, that's all.

3) As for silver, S&B have both silver and copper versions of their transformers. I tend to stick with the copper, not just for cost reasons. For utmost transparency silver seems slightly ahead though, but the tonality in my experience becomes slightly washed out, something which may be offset partially by using lower nickel content cores.

Finally, a number of comparisons have been made especially in the HKTA and DJTA Yahoo Groups of various TVC's, including SR & Sowter vs. S&B's earlier offerings (the current MK III are appreciably, if modestly better), it is worth seeking them out.

Ciao T

PS, in my pro-audio days back in east germny we used daisychain several transformers to be able to better hear the effects of core materials, bandpass filter et al. Using Schulze TH-315 Coaxials and even MEG RL-900 Monitors it was difficult to hear with any reliability as much as 4 - 6 daisychanied studio grade line level transformers using high nickel cores and winding techiques that made sure of very wide bandwidth.


"It is to Madame Justice that I dedicate this concerto, in view of the holiday she seems to have taken from these parts." V
10-31-2005 Post does not mapped to Knowledge Tree
cv
Derby, United Kingdom
Posts 173
Joined on 09-15-2004

Post #: 14
Post ID: 1625
Reply to: 1623
Re: Further problems with interstage transformers.
T,
Agreed on the mumetal - it's wonderful stuff for transformers, just wish you could get it in the required core size for big outputs (well, maybe the US DoD can). Heavens know why AC spend a fortune on silver on an iron core.

RE: the Slagle autoformers and their lower than S&B inductance, that's a deliberate design choice on his part. Inductance ranges from 20H to almost 200H for the standard version, from what I recall, depending on how they are gapped.

Dave has been known to recommend bigger air gaps for more linearity of the perm and likes low driving impedances. Having heard his setup and 2A3 OPTs, I'm inclined to agree - the latter were particularly impressive, having a - dunno how to describe it - "inner calm" to the presentation.

Having said that, I appreciate the "impedance"/size-of-market tradeoff you made with the S&B design. Really must wire mine up sometime :-)

cheers
cv
11-01-2005 Post does not mapped to Knowledge Tree
Thorsten


United Kingdom
Posts 65
Joined on 12-06-2004

Post #: 15
Post ID: 1626
Reply to: 1625
Re: Further problems with interstage transformers.

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Hi,

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

 
I am aware of that, however DS does not make that unneccesarily clear to potential customers...

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


I don't disagree.

However, I can either optimise my stuff for a very limited set of conditions (and these should be made amply clear to customers) or I can accept a small possible drop in absolute quality (which can usually be clawed back by putting in more effort in design and manufacturing, make that A LOT MORE) but make sure the product is pretty much compatible with anything out there.

So I guess the question is: "What parameters do you optimise your product for?"

S&B choose (or perhaps more precisely I choose for them) sound quality and general compatibility as core values leaving the price to be what it has to be to pay for materials, work, distribution etc., based on a reasonable markup for all involved. That makes it still bloody expensive (I know) and if you don't need both of the two core values these products embody, as the BBC said, other manufacturers exist. ;-)

And really, wire the whole thing up, you will be surprised (positively I hope).

Ciao T


"It is to Madame Justice that I dedicate this concerto, in view of the holiday she seems to have taken from these parts." V
11-01-2005 Post does not mapped to Knowledge Tree
cv
Derby, United Kingdom
Posts 173
Joined on 09-15-2004

Post #: 16
Post ID: 1627
Reply to: 1626
custom magnetics

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

11-02-2005 Post does not mapped to Knowledge Tree
Thorsten


United Kingdom
Posts 65
Joined on 12-06-2004

Post #: 17
Post ID: 1628
Reply to: 1627
Re: custom magnetics

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Hi,

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


I read, yes, he states the compatibility limts but very technically. Well, i guess his stuff is bought only by serious DIY'ers anyway, who should know.

Ciao T


"It is to Madame Justice that I dedicate this concerto, in view of the holiday she seems to have taken from these parts." V
11-04-2005 Post does not mapped to Knowledge Tree
morricab
Posts 51
Joined on 07-13-2005

Post #: 18
Post ID: 1645
Reply to: 1557
Re: Better among worst?

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.

11-04-2005 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 19
Post ID: 1646
Reply to: 1645
Re: autoformers and OTLs ....

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


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
11-04-2005 Post does not mapped to Knowledge Tree
Thorsten


United Kingdom
Posts 65
Joined on 12-06-2004

Post #: 20
Post ID: 1647
Reply to: 1645
Re: Better among worst?
Hi,

 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.


Steel core transformers without DC bias sound like that. What did you expect? Ever heard a PP Valve Amp? The reasons are in the magnetic core materials behaviour and obvious.

 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. 


You are probably right about the phaseshift, it is a direct result of not having enough primary inductance.

 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.
 

I use timecoherent speakers.

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

I am quite familar with their stuff. I found it okay but unremarkable sounding. It also had that "stressed out" (strained)  sound I have heard from every single OTL that came my way to some degree. You always get the feeling that there is a lot of hard work going on to keep things on track.

The least offending OTL Amp's in that sense where Atmasphere.

 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.
 

It is not much of a variation. It is a pretty straightforward Circlotron with a lot of extra claims.

 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.
 

Yes. And to make up for all that effort they fit a generic Alps "High End" pot as volume control and they use it in the mode that demonstrably causes a lot of non-linearity with that particular device and brand.

I suspect that if you find Einstein "amazing sounding" you are listening for something in music reproduction that I personally pay little attention to and you ignore the things that bother me. Well, different strokes for different blokes.

Ciao T




"It is to Madame Justice that I dedicate this concerto, in view of the holiday she seems to have taken from these parts." V
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