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Old 14th February 2012, 10:10 PM   #401
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Yes, the three IRF fets should be matched. Do you already have the Lovoltech JFETs? If not I would recommend ordering a kit from tech-diy as the kit also includes matched fets.

Last edited by Aleksi M; 14th February 2012 at 10:15 PM.
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Old 15th February 2012, 07:37 AM   #402
djkiwi is offline djkiwi  United States
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Default F3 Build and caps

Originally Posted by tp147 View Post

if you don't have fun to read the whole thread, do yourself a favour and read from this http://www.diyaudio.com/forums/pass-labs/137145-f3-builders-thread-3.html#post1724304
the following 10 or 15 posts - there ar much infos about C1

Hi Thorsten, thanks for pointing those posts out. Believe it or not I have read through the entire thread more than once. It's a addictive reading and there are some very talented amp builders out there.

Your points are well noted on a "fridge size" bank of capacitors. One thing I do know is that the circuit is 80% of the sound so if you don't get that right then you are wasting money on the remaining 20% i.e parts

I am continually impressed with this F5 circuit on the Tad horns. I'm fortunate to own a pair of custom designed SET 45 monoblocks 2 gain stage with very high quality parts which is the best amp I've heard to date. I'm a great fan of SET amps and have owned a variety of 211s, 845 300b, 2A3 and 45 type amps among many other different amps over the years.

The fact that this little F5 amp can get as close sounding to my 45s is quite remarkable.

In its current state I'd say it sounds more like a typical sounding 845 amp. In fact it reminds me very much of the New Audio Frontiers 845 I had a few years ago. Much more power than the SET45 but did not have the ultimate refinement or texture.

So I'm curious to hear the F3 now compared to my SET 45s to see how close a single gain stage full optimized circuit can get. From what I have read it should solve the texture issue with the F5. I don't care about bass because it is being used at 110 db 8 ohm speakers 650 hertz up.

So on the discussion of caps it sounds like nobody has heard the F3 with anything but electrolytics in the signal path given the size of the values. One thing I do know is the coupling caps have quite a big impact on sound. I've rolled many over the years and rolled some mundorfs and audio notes and various others. I also tried a fully charged blackgate as well which frankly was dreadful compared to the others. Now I'm only talking about a single coupling 0.47uf cap and we could hear how poorly the blackgate performed. So that is my concern with the 15k in electrolytics. On solid state amps it may have lesser impact.

In any case I've managed to track down an F3 and hope to audition it in the next couple of weeks. I will then compare that to the F5 then make a decision which one of these amps to build as monoblocks. I may have an impedance issue with my Bent TAP-X preamp with the F3 so will be checking on that carefully.

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Old 15th February 2012, 08:48 AM   #403
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No doubt, some people will be a bit puzzled with this, but ...

I found that the F3 was a fairly "slow" amp in comparison to the F5, particularly noticeable in horns, very light cone drivers and also headphones!!
So I systematically changed the capacitors to see about changing this aspect of it without losing any of it's magic -It goes a bit like this ...

If you replace the 1uF film cap on the o/p (C8?) to 200uf film (in // to the 10,000uF electro C1) you will notice quite a difference in the sound - it seems to get "faster" then, but it also changes the "balance" of the sound, so you have to go to your Cmultiplier to "fatten" it up a bit - this is where the Silmics or the Nichicon FineGolds come into their own - if not enough, you may have to change the power supply caps to something like the Mundorf's, Jensen 4Ps, Sikorels, etc that "seem to" (sorry!) produce a bit more "weight" in the bass.

However, as you're only driving the horns above 600Hz, don't need to worry about any of this bass balance stuff and can go straight to something like the BHC T-Network caps (or maybe the Slit foils) for C1 plus maybe something as simple as 50uF of film in // to that - maybe the Russian K73's caps will do okay - for some reason, Auri's seem to be a bit "rough" here as they don't seem to like sharing at all - might be because of reasonances - Sonicaps were okay, Mundorf's okay, K73-16s okay, etc

Another point of contention regarding "speeding the amp up" was to replace the 220uF electro at position C3 with a 40uF film cap - surprising thing is that the Auri's are fine here, altho I prefer the big red Jantzens - also, once again, the "balance" of the amp's sound changes again and it takes a bit more 'stuffing about' to set it up the way you want it to sound -

Just to raise a few eyebrows, C2 ended up as a Rifa peg124 (those axial caps) with initially, an R-C snubber across it (0.1 + 22uF K73) and then just one of those Epcos 20uF blue block caps, forget the number) and C4 also became a 470uF Rifa peg124.

Another curious thing was to replace the power resistors with the Manganin PBH 3/10W units from Issabellenhutte in Germany - not exactly the cheapest things but a much softer, more detailed sound than, for example the Caddocks or the Isotan power resistors.

I had quite a bit of fun with this remarkable amp - A bit of an adventure if you want something a bit different to the standard F3.

... my 2 cents
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Old 15th February 2012, 07:46 PM   #404
tp147 is offline tp147  Germany
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Originally Posted by Aleksi M View Post
Yes, the three IRF fets should be matched. Do you already have the Lovoltech JFETs? If not I would recommend ordering a kit from tech-diy as the kit also includes matched fets.
... ooahah, I thought as much.
Are there any best practices out there to match these IRFP240 for F3?
I bougth 2 sets of F3 boards from a german guy and 1 set of the LUIS where included.
I've already matched 2SK170 for my aleph ono and there was a wide spreading between the JFETs. I'ver odered 10 of the IRFP240 in hope they are much closer - is there a chance to get a proper triple?

The LED in the schematics: In my german translation is the LED marked as BLUE - I hope also a green one will work, with blue LEDs blood runs out of my eyes

thanks & cheers
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Old 16th February 2012, 01:38 AM   #405
wildburro audio
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Originally Posted by Tea-Bag View Post
Audiophile Jelly Rolls. LMAO.
I have to admit that was stolen from one of SY's articles.
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Old 21st February 2012, 09:06 PM   #406
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Hello, i am building my F3 amplifier, but i didnt see any schematic from the power supply
Anybody can help me out?
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Old 22nd February 2012, 03:33 PM   #407
tp147 is offline tp147  Germany
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just have look at Peter Daniels F3 PSU boards here F3 PS Options using PD boards

it is quit simple: AC in - rectifier diodes - 15,000F - R (0R5) - 15,000F - DC unreg out.
These are boards for standard PSUs, you also can install a little LM 317 reg for preamps or s. th. like that, not nesseccary for F3.

I've also a set of these boards but there is not too much space for real big elctrolytics. I bought some Panasonic TS HA with 35mm diameter, the biggest I've found are Evox Rifa 22,000F, but they won't fit into my case.


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Old 22nd February 2012, 06:09 PM   #408
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You should also use caps with a higher voltage rating. For example 63 V to have some headroom. I think the original design uses 25 V caps but two caps are always connected in series to get 50 V rating.
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Old 22nd February 2012, 06:20 PM   #409
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Has anyone tried the paralleled silmics and decided to go with the original panasonic output cap afterwards? I went for the silmics right from the start but in the end felt I didn't quite get the right sound out from the amp even though everything else seemed to be alright (voltages etc. can't measure the output distortion). Would it be worth trying out the original combination of 15000uF Panasonic + 220uF silmic and 1uF PP?
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Old 23rd February 2012, 09:00 AM   #410
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Hi thanx for the info, but actually i am talking about another way off building the supply board.
First convert ac into dc with sckotty diodes then 22.000 uF - coil - 22.000 uF.
Anybody knows the value off the coil between the capacitors?
I like coil there better then resistors.
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