Sound of transformers in preamps?

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.

Bob

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.

Bob

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.