Choky,
Found some 10ks last night. Biased up this morning. Driving it with cathode follower at only 3.5v, straight out of my dac. Surprisingly loud enough, but, I’ll need a proper linestage.
It definitely is one of the coolest things I’ve ever built. I’m basically listening to my dac through the loudspeaker. There is a fraction of SS to the sound. But, I definitely see what brilliance this thing is: It really sounds as it’s supposed to sound: like the source.
TDA1541->Class A I/V->5687 follower->F4>Montis
Cheers,
GG
Unbalanced
89db (Martin Logan lists it at 91db, but I don't believe that number. The salient point is that it has a powered woofer, which is obviously makes a huge difference. I run this loudspeaker with SET amps at 2-3 watts. People have tried to school me on the forums that this isn't possible, but they aren't considering the impedance load presented by this design. I do have a HE loudspeaker of my design that is in the 96db range that I need to try with the F4.)
Some of the higher gain tracks I listened to this morning were high enough that I had to turn the volume down (digital volume). OTOH, I still need a proper tube linestage. I've got a gaggle of SS linestages that are wonderful, but these days tube stuff is really where it's at for me). Last year I built a 300b linestage but I sold it to fund another project. DOH!
With just 3.5v, I don't see this as a solution for everyone, but in my case it actually works because of the loudspeaker. So, if you've got a true HE loudspeaker you could drive the F4 with very low voltage and get away with it.
The very simple signal chain that I have is pretty remarkable. After about an hour of warm-up I thought that the F4 did indeed sound like the simple cathode follower driving it: smooth, great separation and scale.
I'm planning two linestages, both single tube.
Cheers,
Greg
Balanced input from a Buffalo DAC, digital volume control. Low sensitivity bookshelf speakers in a small bedroom. I run the volume around 60% at my normal listening levels. There will certainly be situations where it wouldn't be a good fit if you require plenty of drive. I also use an autoformer for another 6db of gain. Sounds really nice though.