Does OTL pre-amplifier exist?

08-30-12: Hifiharv
I believe you need a cap to block DC at either the ouput of the preamp, or the input of the amp. You don't need both, so it may be safe to remove one or the other as long as you keep this in mind when changing to other components. I'm no tech, just a tinkerer, so please, someone correct me if I am wrong.

There are some tube preamp designs that will put out DC voltages on the order of 150 volts or more if the output coupling capacitor is eliminated. The voltage would be sourced through an impedance that is most likely high enough to limit current flow to non-lethal levels in the event of accidental bodily contact. But I would not make any such change to a tube preamp without careful study of the schematic, or input from a qualified person who has knowledge of the specific design.

The input circuit of the amp, and especially the voltage rating of its input coupling capacitor, should also be looked at to assure it can withstand that voltage, and with considerable margin so that long-term reliability is not degraded.

Another concern that occurs to me in that situation, where the preamp design is such that removal of its output coupling capacitor results in a large DC voltage, is the possibility of a significant increase in the severity of the turn-on transient that can result if the preamp is inadvertently turned on after the amp has already been powered up.

Regards,
-- Al

The Sonic Frontiers preamps have cap-coupled outputs to my knowledge.

The only tube preamps with direct coupled outputs are the Atma-Sphere (line stage or with phono) and the Messenger, which is single-ended.

Thanks to you, Al and Ralph.

IIRC there is a direct coupled version of the Cary SLP-98 available from Upscale Audio. I think it is called the F1.