Sound of transformers in preamps?

Many of the highest rated preamps around seem to have transformers in the audio chain. The Dude and Coincident tube preamps seem to kick ass when compared to other tube amps and the solid state McCormack VRE-1 is sometimes considered to be the best too. All of these preamps are said to have transformers. Is there a sonic difference with the transformers? What is the subjective difference?
Generally resistors base pre will have more dynamics and midrange than transformer pre. but transformers will outshine in areas like transparency and detail, just my 2 cents. i think it would be hard to notice their musical differences between the two if they are both well design, you need to strain your ears to hear the differences, i guess.
BTW, are you sure Dude has transformers in signal paths?
Not sure at all that the Dude has transformers in the signal path. I just remember on comment in this forum where somebody mentioned it. I haven't seen anything official.

I got curious and searched Audiogon for ‘Dude’ and ‘transformer’ and found a comment by Grannyring where he talked to the Dude designer Paul. He said that Paul didn’t like transformers in the signal path. I guess I was wrong about the Dude.

The Dude has a power transformer, but is not transformer coupled. To answer the posters question, yes the transformer can and does certainly influence the sound of a preamp. Depending on the design of the preamp transformers can be used in several locations. They can and must used in the power supply, can be used as chokes in the power supply and some use them for coupling.

In each instance the transformer can and does impact the sound regardless of use or location.
Also, wether or not a transformer coupled preamp sounds best etc... I have no idea. I think a skillfully designed transformer or capacitor coupled preamp will yield beautiful results. The transformer quality as well as the cap quality in that position is vitally important. I do know this :-)
Transformers have two primary (pardon the pun) issues if used in the signal path, which can be mitigated but not entirely eliminated:

bandwidth limitations
additional distortion

The bigger the transformer the more limited the bandwidth. In preamps where the transformer is fairly small this usually can mean a loss of bass impact. If you consider that you have to have bandwidth to 2Hz in order to reproduce a tone at 20Hz correctly, then the issue is clear. Most good signal coupling transformers are specced to 10Hz; the best are set 5Hz. That means that in the best cases you will have artifacts up to 50Hz.

Distortion is the other issue. Transformers will 'ring' (distort) like any inductor if not properly loaded at the output. There is a point called 'critical damping' where in the inductor is loaded at its optimal point. This is the point of least 'overshoot', but to say there is no overshoot (distortion) would be inaccurate. Anytime distortion is added, you can count on it to obscure detail/transparency.

This is why transformers have usually been avoided in preamps, although cost has something to do with it too. However there seems to be a cult of sorts associated with transformers in the Asian rim and we are seeing products appear here that are influenced by that. IMO the slight overshoot, which is adding a 2nd harmonic, is adding some lushness. That is nice for CDs which are often dry sounding, but not that great if you play analog and like all the detail that if offers.
To degradations of sound quality using transformers in signal path (of preamp or output stages of DAC's) are well described by Athmospere. I will add also mismatch impedance effect on the sound. If your output sstage is passive and transform based you MUST use ultralow capacitence interconnects.

Also, to "Anytime distortion is added, you can count on it to obscure detail/transparency " I wish to add that you are loosing musicality i.e. emotional connection with music which for some of us isTHE most important in interactions with (even reproduced) music.

well then, what is the significant advantage since there has been quite a number using transformer for volume switching and output coupled? do resistors has unstable impedance and cause freq response fluctuation due to feedback from amp? Thanks
The VRE1 manual is available online. On page 6 under Design Highlights Steve McCormack claims a couple of advantages. He says that the input transformer confers a tube like musicality. He also states that it also gives great noise rejection and isolation from DC voltage levels. I can understand the electrical advantages but I am confused what he is talking about with the tube qualities. Maybe he is talking about the second harmonic distortion that Atmasphere talked about. Maybe there are other effects of transformers that give the tube like musicality too like saturation and hysteresis. I don't know.

If I read the manual correctly I believe Steve is using the input and output transformers to attain balanced operation and to achieve 6 dB of gain if required.

I just don't get where he is coming from with the idea that the transformers can create a tube like quality. I have a lot of respect for Steve's knowledge and designs and he is one of the good guys in this industry, but that comment just doesn't make sense to me.
Maybe the comment doesn't make sense but the sound sure does. The VRE beat out my Kondo M1000 all tube unit (which retailed at close to 90k) and yes has more of a tube sound than ss sound IMHO.

(Dealer disclaimer)
Rsimms, yes, single-ended tube circuits are known for 2nd ordered harmonic distortion, which gives them a lusher sound. This is the same effect a transformer can impart. Although it is pleasantly euphonic, the distortion does impair transparency/detail.

Philipwu, generally speaking resistors are more stable with respect to frequency! I'm pretty sure the reason transformers are turning up in preamps is just above in this post.
Yep, it's a fetish. If you want colorama maximus, loss of transparency and destruction of musical timing and loss of coherency then by all means buy more stuff with transformers in it.
Transformers = hysteresis distortion, bandwidth limitations, phase shifts that differ at different frequencies, even order distortion ( in single ended applications ).
This article gives you a good insight -
Well, don't forget: High End
That means, when 20 normally cry loud "NO, that is wrong",
then it is normally the way to go for a Designer who has a better brain.
The customer simply has to find him. But that needs brain, too.... :-)
Dover, thanks for the link to the transformer information. That was very informative. It is probably a little like finding out how sausages are made though. One part of the picture lost is the problems created if you don’t use transformers. The alternatives have a lot of issues and problems too. One time at NASA I tried to find a linear capacitor. That was hard to find. I would think that isolation would be a very significant advantage of transformers, especially in a preamp.

Rsimms, isolation is only a problem if you have a severe ground loop or problem with AC power where you are trying to run the system where part of it is on one line and another part on another line.

However an interstage transformer will not help you with any of that.
Some of the very best natural sounding preamps available use interstage and or input transformers.It will always be about designer talent,implementation and quality of parts selected.Those designers if they were incline to do so could come here and give very valid reasons why they reject the signal capacitor approach.Either method can be quite good with a talented builder.Any and all decisions concerning sound reproduction have some level of trade offs.
Charles1dad you are 100% right. When I search for a pre (or any component for that matter) I don't say OK it has to have A or B or C. Yes I first think tubes and have had more tube amps than most normal people have had cars and the same goes for pre-amps. But I've now landed with a SS pre and never inquired about it's design just plugged it in and knew it was special once heard. Still have not found a SS amp I could live with for the long run but that doesn't mean it's not out there, have yet to hear some of the new Nelson Pass designs.
I have an admiitted bias for tube components but I`ve heard only high praise when the VRE is mentioned(I have`nt heard it).The most musically natural sounding SS power amp I`ve heard(so far) is the Silicon Arts zl-120 built by Masakada Tsuda(Concert Fidelity).Despite the many different amps I`ve listened to,at the end of the day give me a good SET amp.
Agree again...with my current 98 efficient speakers my 8 watt SET is sublime! Many nights I have to wear Depends while listening!!!!
Very interesting thread. I have owned many preamps without interstage transformers (Audio Research, CAT, VTL, Conrad Johnson, Presence. When I received my VAC Sig. Preamp it had the best sound and uses the dreaded interstage transformer. Kevin Hayes of VAC makes two preamps one with and one without the transformer. Guess what his best and most costly one is the one with the transformer.
The VAC Sginature MK II is one of the best sounding preamps I`ve ever heard. Theory aside,it`s always what you "hear" that matters in the end.
Wrt distortion, unbiased transformers create odd order harmonics due to the bh loop symmetry around the origin.

Tubes like solid state devices are nonlinear in an asymmetrical manner so they create predominantly even order distortions.

In order to get transformers to create even order distortion the core must be offset from the origi
n which is typically done by a dc bias.

In order to get nonliner devices to create predominantly odd order distortions, they must be made parallel and summed with one signal inverted. (pushpull, balanced,differential)