FirstWatt F3

I recently finished my DIY FirstWatt F3:

 

@JeffYoung, what was the motivation for the F3 vs.... F5 or another? I’m just curious about your decision process.

Also, tell us about this power supply. Looks really custom. Toroidal has two taps (same voltage?) and you made a custom rectifier and filter board? Indeed, all the boards look custom.

P.s. looks great!

 

Looks super tidy. How does she sound? Haven't heard an F3 myself (got an F7) .

 

More info would be greatly appreciated. I like the looks but to understand all that i am seeing is another beast.

 

Looks like it's time for an HE5 or 5LE.

edit: or maybe some vintage JBLs

 

@skem, the motivation was that the F3 and F5 seemed to sort of be at opposite ends of the spectrum so I'd build them first and see what I like. (The F5 is about 1/2 done.)

Toroid is 500VA with two 36V secondaries. There's a bridge rectifier for each (the 8 diodes on the back of the front panel). The CRC filter is close to a Pass design, but is dual-mono (each side fed from one secondary).

@pedalhead, I was mildly surprised at how good it sounds. I don't have any other Pass designs to compare it to (yet).

@Walderstorn, it's a single-stage, singled-ended class A topology. The little JFET on one end of the heatsink makes the music; pretty much everything else is just its life-support. Going from the other end of the board there's a c-multiplier to further smooth the PS, then a CCS to feed the JFET, and then a cascode to protect it from the full rail voltage. Nelson explains how it all works in the manual (how's that for refreshing?): http://www.firstwatt.com/pdf/prod_f3_man.pdf.

All the boards are custom. (If anyone wants the Kicad files or Gerbers I'm happy to share them.)

@E-Schaaf, I'm going to build some Troels Graveson TQWTs for it: http://www.troelsgravesen.dk/JA8008.htm.

 

Does the F3 use unobtainium transistors like some of the Pass amps, or are they easy to get hold of?

 

The Lovoltech JFETs are indeed out of production. I was bemoaning the fact that I bought some probable fakes on eBay and Nelson sent me a bunch gratis. So if you want to build one give a holler; I still have some spare matched pairs.

 

I’d be very curious to hear the difference between f3 and f5. I have an f5t in the queue but not building yet.

 

My F5 PSU is done, but I haven't started on the amp boards yet:



I'll write up a short comparison once I finish it.

 

Nice looking work. I'm interested to hear the comparisons. I'd like to own a FirstWatt one day, don't know if I have the knowledge required for DIY though.

 

@sphinxvc has F3 in his speaker setup, I've been to his place several times to have a listen. It sounds good, very musical. If you can get over the low wattage, probably a good choice.

 

Good job!

That doesn't look like a typical modushop enclosure or heatsink. Where did you source the case?

 

There's a guy in Thailand that sells the cases on eBay from time to time. He doesn't appear to have an ad up currently, but his email address is [email protected].

 

Ah, Watchara? I’ve been to his factory/shop a few times ,a bit eccentric but very knowledgeable guys who always busy building something.

I think he should have a few enclosures in his stock as he’s preparing to launch his new amp soon.

On topic, Really nice builds you got there! I really wish Pass stuffs are more widespread here so i can audition them.

 

I would be very interested in your thoughts comparing the F5 to the F3

when I started looking at various options to build, I was drawn to the F6 because of the power JFET but then disenchanted because of the JFETs dodo status and although the VFET appealed (also dodo but I had a source), I wanted something more simple which is why I ended up looking at, and building the M2X, which then ended up being alice's rabbit and I tumbled down the hole to find myself in the rare and extinct territory of SITs after all.

BUT I have one spare chassis and that itch is screaming to be scratched

..dB

 

How does the low wattage manifest itself in practice, other than making insensitive speakers incapable of rattling the neighbors’ windows?

 

That's it, you have to stick to high-ish efficiency stuff.

The 3 is 15w per, not even that limiting really.

Truly low eff boxes would sound bad no matter the volume but why would you do that, and if you're married to a pair you can always hook the woofer to a Vidar or a crown or some cheap ooomphbox.

 

I tested it in my daughter's studio (10' x 15') with some 87dB/w Gale 4 speakers, and it will get unsociably loud, but not club loud. Bass was lovely, but not terribly "tight" on something like Duffy's Rockferry. I was using the preamp section of my daughter's NAD 3020, so we also compared the F3 to the NAD 3020's power amp. The NAD did surprisingly well when the music was sparse, but when there was a lot going on the F3 sounded like a bunch of different instruments while the NAD sounded like a single instrument playing a lot of parts at once. The other thing I remember was that Adele's voice was more husky and nuanced on the F3, but that wasn't a night-and-day difference.

One of my few modifications from Nelson's circuit is that I have an additional output in front of the coupling caps. That way if I do use it for just tweeters (which already have caps in their crossovers), I can skip the coupling caps in the amp. The F5 would give a lot tighter bass, but the Vidar is probably a better answer if you want to dance to it.

 

Does anyone ever compare both F3 and F7 ?