Tube Integrateds...why not a preout for subs.....

I always wonder why tube integrated manufacturers do not provide a preout for the use of a sub.

I'd imagine that it is often because it would require an additional buffer stage (for each channel), to provide a reasonably low output impedance for the pre-outs, and to prevent the main signal path from being affected by what is connected to the pre-outs. Keep in mind that the impedance level at the output of a tube-based circuit stage is usually far higher than at the output of a solid state stage, resulting in greater sensitivity to loading.

That would generally require the addition of at least one dual-section tube and several passive components.

Regards,
-- Al

I believe the ARC VSi60 has a subwoofer out.

Al,
Not necessary it would require to have an extra tube for each channel(buffer). Just like in conventional preamp with one main 'out' that can be disconnected from poweramp 'in' I don't see a necessity to have a buffer stage unless you'd like to have both preamp section connected to amp and another set of preamp outputs together.

My Rogue audio Tempest II Magnum has active and passive pre outs.

02-28-12: Marakanetz
Not necessary it would require to have an extra tube for each channel(buffer). Just like in conventional preamp with one main 'out' that can be disconnected from poweramp 'in' I don't see a necessity to have a buffer stage unless you'd like to have both preamp section connected to amp and another set of preamp outputs together.

Yes, it won't always be necessary to have a separate buffer stage, which is why I said "often." But if the output of the preamp section has to drive an external cable and component (such as a sub, which commonly have relatively low line-level input impedances), as well as the input to the power amp section of the integrated, and if that has to be done without compromising the integrity of the main signal path (into the power amp section of the integrated), not having a separate buffer stage would require a much lower output impedance from the preamp section than would otherwise be necessary.

So either way there may be a much more significant impact to the design than simply adding a couple of wires and connectors.

Regards,
-- Al