good preamp for First Watt F7

I once had a First Watt M2 amp that I employed through a simple tubed pre - I forget what manufacturer.  It sounded beautiful.  After that I always put a tubed pre with my Pass Labs amps, too.  Just a “me” thing but I liked the results. 

Atma-Sphere MP3. 

Rogue Audio RP-5. Output impedance: 500 Ohms.

What's your budget?
And SE preamp I assume?

Linear Tube Audio MZ2. Sounds great with it, output impedance 50 ohms.

the budget is around $1000 (to compete with Freya +), might be tube or SS

bakalovb OP

You need a little gain also with the F7 being only 14db.
Just go with the Schiit Freya-S or Freya-+ both have 75ohm output impedance on rca on their active stages and a gain of 4, and should drive the F7 no problem. Stay away from the Schiit Saga's as they are only unity gain.  

Cheers George

Rowland Capri was recommended to me by Pass dealer and it is a great combination...was told by dealer that the F7 often does not like tube preamps...the original Capri is available often at a little more than your price point...

See bellow the answer of Mr. Pass:
The F7 has a lower input impedance than most, at 10K, and a little less gain than most. Preamps that would have difficulty would be ones where the output impedance is greater than 1000 ohms or so, or tube preamps that cannot driver 10 Kohm, or which have no voltage gain. As it is, I routinely use the the F7 with a B1 which has no voltage gain, but my sources have 2V or more.

I am starting questioning do I really need a dedicated preamp to improve the sound. My PS Audio DS has  gain of 1.414 VRMS for Single Ended outputs (F7 has SE only inputs) and  Output Impedance 100Ω/200Ω . 
Looks like  reasonable preamp for F7! 
I use DS as my only source ( DS CD transport connected to it), so I started looking for preamp because I've been told that both F7 and DS will benefit from preamp . 
I guess I'm opening the can of warm "Do you and when you need a preamp" 

As it is, I routinely use the the F7 with a B1 which has no voltage gain, but my sources have 2V or more.

A lower output impedance than the B1’s 1kohm "may" sound better into the F7’s 10kohm
Maybe trial (14days) the $299 active unity gain Saga-S or one of the others, you can have active tube/solid state or passive and remote. Send it back if not happy
https://www.schiit.com/products/saga-s
Cheers George

I used a Manley shrimp (well matched impedance for a tube pre),  wyred4sound STP SE, and B1 (DIY) preamps with my F7, first 2 worked great, better than the B1 to my ears. Good luck!