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a friend loaned me a Bent Audio transformer based silver TX102 passive preamp with silver wire to compare to my balanced Placette RVC (remote volume control).i have spent the last 2 evenings comparing these 2 units. the Bent Audio unit is about 3 weeks old but i'm told it is fairly broken in.....i have had my Placette for about 18 months.
after reading about transformer based attenuation and having some people that i respect tell me i should try them i finally got the chance to compare. my system is fairly passive friendly with amps with 40k ohms input impedence, a short 1 meter i.c. from the attenuator to the amps and good output gain from my sources.
i have been very happy with the Placette but figured i would see what all the fuss was about for myself.
i used vinyl, sacd and cd to compare. both units were on the floor between my amps on cones.
i love the speed, openness, air and space that the Placette brings me. every active gain preamp i have tried in my system has been smoked by the Placette.....what would the Bent do in my system?
the Bent unit did not seem to work as well as the Placette in my system. there was a slight softening of edges and an added shimmer.....things were slightly slow and lacking snap and energy.....and yet there was a beauty and ease to it that could probably be helpfull in some systems.
i played about 6 or 7 hours of music.....back and forth....music on the Bent unit compared to the Placette was slightly lacking in pace and drive, voices were beautiful but not as open and textured, and the top end air was reduced. soundstage width and depth were good on the Bent but with the Placette there was a more wrap-around feeling and you could see deeper into the stage. the bass on the Bent was full and voluptuous but also loose and lacking extention and articulation compared to the "best bass i have ever heard" with the Placette.
if i had never heard the Placette the Bent unit might sound very nice.....but the clarity of the Placette is hard to compete with if your system is complimentary to it. my amps have no output transformer.....so adding one in the attenuator might not be synergistic.
the Bent unit in my system reminded me of my perception of the Lamm ML2 amps on Kharma speakers compared to my Tenors.....very nice but just not alive and energetic. are transformers always a good thing?....not in my system to my ears. those of you that love the ML2's may have interpreted things differently.
i don't think this post should be taken as a definitive result one way or another since with passive preamps system synergy is so important. 'transformer verses resistor' is probably not a simple situation. but i will say that it would be a mistake to assume that transformer based attenuation is always better. i'm sure that many systems will greatly benefit from what transformers do.....just not mine.
in fact, i talked to John Chapmann after i listened so i would have an understanding of what was happening before i posted this. he mentioned that passive preamps are all quite system sensitive and that finding the right answer for each situation is part science and part art. my sources have relatively high output impedence and that this was part of the problem with the transformers in my system. the Lamm LP2 Delux phono stage has 3.5K ohms output impedence and i'm not sure what the output impedence of the Meitner DAC6 is. for whatever reason the Meitner DAC6 was a slightly better match in my system than the Lamm LP2 Delux with the Bent unit.....all the deficiencies were there but to a slightly lesser degree.....i assume a better impedence match.
he also mentioned that my system didn't need what transformers can do to help some systems and that my system obviously was particularly synergistic with the Placette. he also felt that his copper transformers would be a better match than the silver transformers in my system and he may arrange to have me try them in the future.....even though in my particular system the resistive approach of the Placette was maybe a better passive solution.
i really appreciated John's lack or defensiveness regarding my experience and his obvious interest in helping people to get the correct solution for their situation. if anyone has purchased the Bent unit they should not take my feedback as a reason to doubt their choice.....but only to be open-minded and listen for yourself. i would also guess that there are systems that would not work perfectly with the Placette......although many of my friends use the Placette with the Tenors and Kharma speakers to their great enjoyment.
i really expected to be bowled over by the Bent silver TX102 unit.....instead i listened and learned.
when it comes to preamps and passives.....keep your mind and ears open.
mikel
Follow Ups:
TX102 is transformer, it's an inductor, and AMP input is a resistor, this two go together form a low pass filter. Has any body looked into this affect?
Congrats on your Rockport (as well as the rest of your system).Have you tried the Shatki Stones on the power transformers of your amps? I would imagine they would have a real nice benefit there.
I've found mine has the greatest benefit on the amp's power transformer, followed by the amp's output transformers (I realize the Tenors don't use them) and other power supplies.
thanks.i did try the Shakti Stones on the Tenor power transformers but since i only have 2 (and have 4 transformer towers) the results for me were inconclusive.....then i got some feedback from a Tenor user that had tried it with all four of his Tenors (he bi-amps Kharma Exquisite 1A's) so he was using 8 Shakti Stones.....at first he liked it......very smooth and natural.....but eventually he determined that the Shakti Stones were robbing the system of micro-dynamics and energy and preferred it without.
i decieded to not pursue it further based on his feedback.
mikel
nt
nice post!its interesting that you are using the tenor amps, since when i sent a pair of autoformers to robert lamarre about three years ago, his results compaerd to his favorite resistive units were very similar to yours... he too preferred the resistive units.
people can argue for one or the other based on theory or design, but the only way you can be sure is to get both and decide for yourself, or get one or the other and don't worry about it...
dave
hi Dave,thanks.
my personal hunch would be to agree with Robert; what the Tenors do so very well is compromised by anything more than a simple resistor......i started with the integrated Tenors which included their own resistive passive attenuator. i just couldn't live without a remote volume control so i tried the Placette RVC.....i could not hear any difference between the Placette in the signal path and not in the signal path (and using the integral attenuators in the Tenors). then i switched to the non-integrated Tenors and the Placette.
i do try to stay open-minded but it will be hard for anything to beat the transparency of the Placette with the Tenors.
i know i am probably over-simplifying things......but it appears that resistors reveal the true nature of your gear and transformers/autoformers 'correct' the true nature of your gear. (this is where all the tech-gurus throw up their hands at the simple-minded audiophiles).
the trick, of course, is to have gear that doesn't need 'correcting'.
regards
mikel
Is a transformer "more than" or "less than" a "simple resistor"?I have a hunch Thorsten Loesch would say "less than".
In my experience one single metal film resistor can make or break the sound of a preamp, speacially in the high impedance grid circuit.
IMS, any metal film resistor attenuator will sound much worse than my autoformer preamp. Metal film resistors bleach the midrange and suck the life out of music (in high impedance tube circuits and IMHO).Riken carbon film sound tubey and very sweet, tantalum Rs sound slightly metallic but very transparent (all were tested as a series resistor in a series/shunt volume pot with a DACT 50 K as shunt element).
I have not tried Vishay or Caddock.
Anyway, my 2c worth, YMMV.
dvb,against my better judgement i will attempt to illustrate just how limited my technical expertise is by explaining why i think a resistor is 'less' than a transformer.
if you connect a cable to the same high quality resistors 5 in a row......to a particular gain......i believe that you would be hard pressed to hear it's difference compared to a straight wire with one resistor to the same gain....there would be a difference......it would simply be difficult to hear.
if you then try the same thing with 5 transformers compared to one transformer i believe you would easily hear the difference......you might like the difference.....but it will be clearly different.
i believe that if my premise is correct; then transformers change things and are 'more there' than resistors.
as far as Thorsten is concerned, his viewpoint as expressed to me in an e-mail is that "in your system some of the advantages of the transformer principle are removed"......OTOH......he also said "we have very different views on what sounds good".
so accuracy and clarity are different than musical taste.
please be gentle....
mikel
Mike,You are likely right that 5 x'forms will sound more colored than 5 resistors. However, there is a basic technical difference between resistor and tranformer based volume control devices.
The output impedance of a typical resistive pot is high, in the range of a few kohm to a hundred kohm depending on total value and volume position. OTOH, a transformer based volume control reflects output impedance of the source through its turn ratio. In normal, attenuating positions the output impedance of it can be lower than that of the source.
Maybe TVC won't be as low coloration as pot, but there can be issues like low driving capabilities and HF roll off associated with pot.
Anyway just to point out possible trade off between these two types.
I've set my mind in trying out TX102. Maybe I will consider a resistor based preamp too.
Ehien
Read your partially finished review couple nights ago and I am glad there your review re-surface again with the follow up. I have John's copper 102 for over 3 months and I love what I get. I must say John is truely a nice man to deal with. BTW, can you the sound of silver 102 at your friend's system?
Hit the entry key too fast. Sorry about the mistake.
hi Walter,i deleted the first post since after further consideration i felt that i needed to talk to John Chapmann regarding my experiences and understand the whole picture first before i posted. i agree that John is a real stand-up guy.....as is Guy Hummel of Placette.
i know my friend is very happy with the silver TX102 Bent Audio unit in his system but i can't really go beyond that. he uses the Berning amp and Audio Physic Avanti III speakers. he has the Hagermann phono stage but i can't remember his digital source as we only listen to vinyl at his home. i have not heard the Bent at his home yet.
regards
mikel
It would be interesting to hear if the Placette sounded better in a system that sounded good with the Bent, given that these things are system dependent.
....the plan is for that to happen soon. he is currently out-of-town.....as will i be starting tomorrow.he may want to post a follow-up.
regards
mikel
Hi Mikel,
That is a gracious move by talking to Bentaudio before posting your thought. I believe Placette is a remarkeble product and you are the lucky one have the opportunity to a/b both.
Walter
Resistive: excellent soundat high volume levels, muffles the music and the dynamics at low volume settings, due to high series impedance.Transformer: sounds as you described;
Advantage: gets rid of most digital upper harmonics.
Disadvantage: soft bass, due to the dual conversion process: electric to magnetic in the primary, magnetic to electric in the secondary. It is THE Ideal solution if you have a few mV DC on your source otput.Autoformer: there is a direct DC path between the input and output.
To my ears they sound excellent at any volume setting. It's fascinating to be able to follow the Keith Jarret trio's intricate bass/cymbal/piano interplay at 3 AM with the neighbors peacefully asleep.
At the loudest volume settings, it is basically a long copper interconnect, no resistive or magnetic effects to speak of.
IMHO it's the most transparent solution, very faithful to the musical emotion hidden in our ceedees .As far as I know, all of the above must be driven from a source impedance of less than 1 K and see a load impedance of more than 10K, to work properly.
I hope this helps clarify the differences
Carlos
It is THE Ideal solution if you have a few mV DC on your source otput.Not sure what you mean here by "ideal."
While a transformer will not pass the DC on to the amplifier (a good thing), DC at the primary or secondary of any transformer will result in a magnetic bias in the core which will increase distortion and cause the core to saturate at lower levels.
se
actually i have seen an instance or two where this is just the opposite.a guy on the joe the other day got substantially better LF response from a SE triode wired 6L6 driving a trannie originally designed for PP when he increased the DC from 10-40ma...
while the DC through the core will reduce the perm, it also makes the perm more linear, much like an airgap (gasp did i say that :-)
in a minimal airgapped high nickel core, i wouldn't be suprised if a slight dc offset didn't linearize the inductance considerably
dig through an old text and find a graph for various values of H showing B vs perm.
do note, i am referring to voltage delivery rather han power delivery...
dave
actually i have seen an instance or two where this is just the opposite.Mmmm. Only instance I've encountered where that was the case was when current in one winding was offsetting current in the other winding.
a guy on the joe the other day got substantially better LF response from a SE triode wired 6L6 driving a trannie originally designed for PP when he increased the DC from 10-40ma...
There's at least one reason why that might have seemed to be the case without it actually being the case.
There's a fairly well known psychoacoustic phenomenon whereby if the brain is fed the harmonics of a bass tone with the fundamental removed, the brain tends to fill in the fundamental. A sort of phantom bass if you will.
In fact this phenomenon is exploted in a number of bass enhancement schemes which produce a perception of increased bass response without actually boosting or extending bass response. For example where the loudspeaker in question wouldn't be able to handle an actual boost in the bass region like a boombox or mini system.
If you look at distortion versus frequency for a typical transformer, you'll see that it's highly skewed toward the low frequency region:
Increasing the DC current would increase low frequency distortion far more dramatically than high frequency distortion, which would just as drastically increase the magnitude of low frequency harmonic components. And because of the interpolative nature of the brain, a perceived increase in low frequency response.
while the DC through the core will reduce the perm, it also makes the perm more linear, much like an airgap (gasp did i say that :-)
That doesn't make any sense. An air gap is used to linearize a transformer in the presence of DC, but here you're saying it's the DC that linearizes the transformer.
in a minimal airgapped high nickel core, i wouldn't be suprised if a slight dc offset didn't linearize the inductance considerably
All I can say is that I've never seen an instance where any amount of DC current has improved the linearity of a transformer except in the case of an offsetting current I mentioned above.
In any case, I'm not saying that a bit of DC current is always and inherently bad. It is if ultimate objective performance is your goal, but its predominantly even-order characteristic can add a bit of "warmth" that in the end may be more subjectively pleasing.
se
hey steve,(SE) There's a fairly well known psychoacoustic phenomenon whereby if the brain is fed the harmonics of a bass tone..
yes, and i would say this is the case, but the guy did it by measurement, and just looked for the best sine wave.... increasing the current made the above sine wave look better! (using a non gapped PP design SE)
(SE)Increasing the DC current would increase low frequency distortion far more dramatically than high frequency distortion
thats the book answer, but increasing current made the above sinewave look like one again... first guess was the lowerd source Z from the increased current caused this, but when he substituted a tube with a lower Rp and less DC offset things got worse!?!
(SE) That doesn't make any sense. An air gap is used to linearize a transformer in the presence of DC, but here you're saying it's the DC that linearizes the transformer.
I know that... thats the conventional thinking, but more and more i think it is dead wrong for audio where sound, and not money is the key desing factor... take money out of the equasion for all the historical work in magnetics, and i suspect the rules would change.
(se)All I can say is that I've never seen an instance where any amount of DC current has improved the linearity of a transformer except in the case of an offsetting current I mentioned above.
i can think of many unique situations where this would be the case, it all stems from the concept of a linear inductance vs. higher nonlinear inductance, and what roles they play in the whole mix, unfortunately... there is no stereophile measurement for such an example, since inductance is such an archaic design elelment.
oddly enough, if high perm (read high inductance) is your only goal, i have seen certain nickels (4-79 permalloy) for example that have very high initial perms, and the addition of a magnetic field actually increases the perm... granted the added field is in the milli-oersted range... but whats not to say that a microvolt or two of DC offset might not accomplish that??? my point is this addition of DC is a unique situation where things become very nonlinear, but a similar alloy of moly permalloy is ruler flat for the small offset of H (which is what DC does)
the big problem is each alloy is specifically designed for a unique use, and info for other uses is not documented, this is not because it is not able to be pressed into other uses, just because there is no way in hell anyone would pay enough for it...i wonder what those guys would say to $5000 interconnects :-)
btw... do you have hosting??? i'll send you some images that are relavant, several of which still confuse the hell out of me with what they say, since i have zero formal education i actually could be missing something obvious, which is why i try to have these conversations.
and to add this final disclaimer... everywhere i look and dig for this info is based solely on what i have heard with my own experiences... i really don't care what is supposed to happen, i just really take note when what supposed to happen, and what really happens doesn't line up... when this is based on listening, its an anecdote, and i search for more anecdotes.... but when a measurement or two show up... i really wonder if there is something there.
dave
Steve, you are correct.
It's not the ideal solution, it's a viable solution if the transformer is specified to take a few mA of current on the primary.
Thanks for correcting my broken English/logic.
Carlos
Thanks for correcting my broken English/logic.It's actually not bad logic. Transformers do block DC. It's just that fine print that gets ya. :)
Oh, and don't worry so much about your English. It's better than a lot of folks whose FIRST language is English. :)
se
hey carlos,actually with the autoformers at full volume, they act as a grid choke, so they are actually a shunt element... its at the lowest settings where nearly the entire length of wire is in series with the circuit.
dave
What are examples of the autoformer type?
Thanks,
Pete
Hello Pete
There are no commercial manufacturers of autoformer preamps. I made a few for friends, they remain good friends (that's a good sign).
I know an audiophile in NYC who made a beatiful preamp with Perspeex and aluminum sheets(he posted pictures on AA).
I believe that several members of Joelist (the Sound Practices gang) have made their own preamps based on Dave Slagle's autoformers.
Dave usually has one or two sets available for trial (no affiliation except admiration for his inventiveness)
For more details, send me an email.
Best wishes
Carlos
I'll take phone #, email, or stork route.
He has posted on this same thread.
Good luck
Carlos
from sunny Rio, Brazil
Try divertech.com.
http://www.uhfmag.com/Issue62/aslpassive.htmlCharmingly, UHF will review a piece, and then offer it for sale.
They currently sell the ASL on-line.
That's supposed to be a nice entry-level solution, though I have not auditioned it, because I can not live with only 12 steps in the volume control.
Also, I hate double volume controls ever since I had an Audible Illusions preamp.
It is totally pointless to have separate volume controls if the steps are larger than 2 db.
Who would want to "balance" channels plus or minus 4 db ?
Just my 2c worth
Carlos
FWIW, the ASL Passive TI has steps of 3 dB, not 4. I had the same concerns as you, but bought one anyway to try it, and would not give it up. Maybe I'm just lucky, but my sides are balanced with the controls set to the same position.
---VikeBoy
one other very interesting thing is 3db steps on an magnetic volume control and 3db steps on a resistive control do not seem to give the same perceived change in volume...one friend claims to his ears, that 3db on magnetic controls is more akin to 1.5 to 2db on a resistive unit.
going between a 600 ohm daven T with 2db steps, and an autoformer with 3db steps, i agree... a single click on each gives a similar boost or cut in volume.
dave
Thanks for your timely feedback mikel!Yes, I wholehearted agree on the part where system synergy plays a very important role in getting the sound "right". In fact, sometimes 1 step forward 2 steps back may get you something sounding evey better!
Audio is known to be a highly "subjective" matter and it all boils down to the particular individual's taste, listening habits, aural health, living environments, also to some extent: knowledge and understanding of sound and music (individualistic approach).
My posting of Bent Audio experience was based on TX-102 Silver (thanks John!) for what seems to be the best synergy to my system. On certain systems (with poor matching) it would sound somewhat "dull" and "lifeless" and I already came across that on several occasions.
I've a motto: "audio (electroncro-mechanical reproduction of music and sound) is just an audible illusion and we audiophiles are dust in the wind"
So please keep your mind and ears open *grin*
My subective feeling on this subject matter. YMMV
Quest;^>
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