First Watt F4 - any users there? (BD-Design)

by Cappy , Wednesday, November 28, 2007, 17:59 (5987 days ago) @ Bert

I believe the amp should work fine with the Orpheans. Lots of people are using the amps with speakers other than full-range Lowther types. Pass designed the amp to be very flexible.

The main thing is that speakers need voltage gain as well as current, but in the case of this amp the voltage needs to be provided somewhere else, i.e. from an active preamp, or in some cases (probably rare, but haven't done the calculations) with a line level source.

From the F4 manual:

The F4 is Class A impedance converting amplifier, having no voltage gain or feedback. Its input impedance is 48,000 ohms, and its output impedance is about 0.2 ohms. It is suitable for driving a high sensitivity loudspeaker with the output voltage of a preamp or other line-level audio source. It is also useful with a less sensitive loudspeaker in a bi-amped configuration where it takes input from the output of a conventional amplifier.

As a stereo amplifier with single-ended inputs and outputs, it will deliver up to 25 watts into 8 ohms with a damping factor of 40. It will do 50 watts into 4 ohms, and as a mono-block amplifier with parallel inputs and outputs, it will do 100 watts into 2 ohms.

The bi-amped configuration is interesting:

There are a number of popular tube integrated amplifiers on the market, the so called “Flea Watt”amplifiers which don’t have much juice, but offer a warm “tubey” sound which is much prized. These amplifiers are good candidates for operation with an F4 in a setup where the loudspeakers have two separate sets of input terminals, one for the woofer and one for the midrange/tweeter.
In such a system the F4 is used to drive the bottom end, where it offers superior damping and higher current, and the flea watt amplifier drives the mid and top end, unburdened by the effort of driving the woofer but preserving the character of the tube amp.

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