DIY F2 clone

[ripson]

dunno, you're stealing current from it where it is already doing squat

theoretically (common sense) yes, but ...

EDIT: it might be possible - not sure - even FR can grab the current at certaing f that is not even able to sing, blocking the ribbon tweeter, aghhh

 

[Nelson Pass]

dunno, you're stealing current from it where it is already doing squat

And probably flattening the impedance seen by the amp as well.

Anyway, easy enough to try...

 

[andynor]

theoretically (common sense) yes, but ...

EDIT: it might be possible - not sure - even FR can grab the current at certaing f that is not even able to sing, blocking the ribbon tweeter, aghhh

The F2 with it’s highish Iq also is fully able to drive but your FR’s and the passive network/cap in front of the tweeter. But you probably allready knew that.

Very happy with mine, but yet to an extra tweeter

 

[andynor]

Edit: both tweets and fr. And yet to try an extra tweet.

 

[Zen Mod]

I'm lucky to find that both amps and spks are much smarter than I am, so they're singing tooooogether even if I usually don't know exactly how

Blessed ZM

 

[Dennis Hui]

Dennis - On your 3U/400 steel chassis - how's the thermal performance on those heat sinks? It's certainly not apples to, but I'm in progress of collecting parts for an F6 and would like to consider the 3U/400 instead of a 4U chassis. Thanks

The heatsinks didn't feel too hot with the F2J when I tried the amp last weekend with a room ambient temp about 22C. I suspect the 3U/400 will be fine for the F6 given it has similar dissipation to the F2J.

I recall reading some members were also looking to build F6 with 3U/400 chassis.

I personally think a 400mm length chassis is the way to go for the F6, especially if you are drilling/tapping the mounting holes yourself. Compared to a 300mm chassis, you get better spacing of the mosfets on the heatsink and greater separation between the input and power transformers.

Cheers,
Dennis

 

[chromenuts]

I thought we had to follow these rules when trying to drive more than a fullrange with a CS amp…

https://www.firstwatt.com/pdf/art_cs_xvrs.pdf

To be honest, I’ve read through it a couple times and it just hurts my head…I have NO passive crossover building experience at all.

The article starts with what I thought was first order (6dB slope) examples and discusses how parallel crossovers are fine with voltage source amps but series crossovers are required for current source amps.

I have a couple of different tweeters I thought about trying with my OB Sonido field coils.

I assume we’re talking about using a single cap to filter a tweeter enough to not allow damage from low frequencies… which doesn’t even constitute a first order filter really?

Can someone show me a correct diagram of how to wire a single filter cap with a tweeter over a fullrange driven by the F2(J)?

 

[Zen Mod]

cap is first order
6db/oct

one end of cap to + of amp
other end of cap to + of tweet
- end of tweet directly to - of amp

 

[chromenuts]

OK…that makes sense to me in that the tweeter then has a cap in series.

For some bizarre reason I thought both drivers had to be in series with the filter being incorporated.

I can just connect the fullrange in parallel with the series tweeter/cap filter at the binding posts of the amp as I normally would then?

 

[Zen Mod]

exactly

 

[ranshdow]

I thought for a series crossover that the filter elements were in parallel with their respective drivers. Instead of a series cap as a high pass for a tweeter, wouldn't you use a coil in parallel? With the full range in series with the tweeter/coil network?

Here's a series crossover calculator. I used it and my ears to design the crossover shown below.

 

[nicoch58]

it hard the series on tw.....and this low to start....

 

[andynor]

I’m surprised how much F2J love we’ve been seeing lately!

Enjoy!

Surprised to see the love it gets?

Just imagine how much love it gives. this is an amp that really thrusts back

 

[Dennis Hui]

Hey Andy, have you tried your new swanky transformer yet?

 

[chromenuts]

Surprised to see the love it gets?

Not at all actually…it’s the first “real” First Watt amp I built after cutting my teeth on a gainclone and ACA.

It just seems like soon after I discovered this forum back in 2008 it was all about the F5, Aleph J and others. Which makes sense I guess, given that was what Papa had recently given to the community.

I didn’t see anyone building or talking about these early current source amps.

I found the articles written about them, but there wasn’t a lot of build documentation and I wasn’t able to find PCBs.

I did come across a webpage documenting a perf board build of the F2…but I wasn’t sure I was ready to take that on.

Eventually I got lucky when I came across kinku wanting to build the F2J and offering PCBs and curve trace matched Semisouth.

The lack of interest seemed strange to me given the fact that they work so beautifully with fullrange drivers which are the perfect place to start for anyone trying to get into this hobby.

Anyway, I’m glad I built them and they are regularly used and loved.

 

[twitchie]

Thanks for sharing Chromenuts! Your journey has many similarities to mine with the F2 being one of my early FW amps. Aleph30 from Peter Daniel's boards was first, home etched F4 from Veteran's drawing was next and then the F2 that I drew and etched was third.

I think the reason why the F2/F2J isn't more widely built is due to folks not having the appropriate speakers, which is a real shame. They don't know what they are missing out on.

Cheers,
Stephen

 

[andynor]

Hey Andy, have you tried your new swanky transformer yet?

Yes. Got it in a few days ago.

In fact, it too makes a bit of noise. Though less than the Toroidy.

I guess my mains is full of crap, or that’s at least my main theory. Need to dig into it but right now I can’t prioritize it.

How are you finding the sound of your amp?

 

[andynor]

Now this pic ain’t much, and also it shows them crapass boxes. But adding an improvised test-network with some parts I had laying around, meaning non-optimized at all, really made a difference, friends!

Values concocted from Papa’s article from drivers with similar impedance curves. I set the 3db @ 1900-ish hz with the parts I had, hoping for primarily two things: reduced midrange level, less treble peaking and in turn: more bass for the buck. Allready added 3x47R across the terminals on my Alpairs iot tighten up the bass (increasing damping factor). Now there is just more of that ****.

And waddaya now, I can play extremely loud and it is just really all relaxed and detailed at the same time.

Need to make this **** serious, and buy a mike. But for now, I’ll enjoy it as is

For those wondering: RC consists of 8R/10uF. A bit high for both, but it’s a start. In time, finding ideal values, I’ll prolly make a box or something for the network.

Sorry for the lingo, Boyz N’ tha Hood is rolling as I write

 

[Studley]

example recipe when I'm ordering custom Donut from Trafomatic:
********************************
Toroid xformer, 300VA

Primary 230Vac (or 2x115Vac if needed)

2 (two) secondaries of 18Vac each, under nominal load

wound for decreased flux to prevent buzzing - A Class amp, so constant load is 90W

all leads stranded wire, 25cm long, secondaries at 180deg from primary

Static shield, magnetic shield
*****************************

so, please - Boyz at Trafomatic are knowing their ****, no need to contemplate about core size, number of windings etc. - everything stated above is just right for proper order; if you start adding more info, you're just being smarta$$, so better wind your own if you're so smart

MZM: You said in a subsequent post that this was your recipe for a dual mono build. Am I being stupid but why spec for dual secondaries when going dual mono (2 trafos) ?

 

[Analogico]

Studley,
As a picture is worth a thousand words, follow the link below to an 'Octopus Technicus' post, and see the attached drawing of a dual mono PSU with dual secondary trafos:
https://www.diyaudio.com/community/...ated-build-guide.241729/page-386#post-6833135