Hi,
I am looking to build the F2J. I would just like some information on some parts which I view as being the critical parts, which may affect sound.
1) Is this transistor by semisouth a good replacement for the original one (which has become unobtainium).
SEMISOUTH|SJEP120R100A|JFET, SIC, AUDIO, 1200V, 17A, | element14 Singapore Products
2) The output capacitors, which type/suitablity part number etc would useful too. Or any 15,000 uF capacitor will do?
3) Capacitor for power supply, can I use a 33,000uF cap instead of 2 pcs of 15,000uF.
4) Is it advisable to switch to a lower current (bias if speakers are 8ohm)? by changing R16 and R1 to 1 ohm.
5) What size of transformer do I need? 200VA (18V X 2) sufficient?
Thanking all in advance.
Oon
I am looking to build the F2J. I would just like some information on some parts which I view as being the critical parts, which may affect sound.
1) Is this transistor by semisouth a good replacement for the original one (which has become unobtainium).
SEMISOUTH|SJEP120R100A|JFET, SIC, AUDIO, 1200V, 17A, | element14 Singapore Products
2) The output capacitors, which type/suitablity part number etc would useful too. Or any 15,000 uF capacitor will do?
3) Capacitor for power supply, can I use a 33,000uF cap instead of 2 pcs of 15,000uF.
4) Is it advisable to switch to a lower current (bias if speakers are 8ohm)? by changing R16 and R1 to 1 ohm.
5) What size of transformer do I need? 200VA (18V X 2) sufficient?
Thanking all in advance.
Oon
Hi,
I am currently collecting parts for a F2J at the moment also. Here are a few bits that you might find useful:
Peter Daniel (on this forum) has F2 boards that can be used for the F2J. I have a pair waiting to be stuffed with components and they are really good quality.
The SJEP120R100A is equivalent (for our purposes anyway) to the SJEP120R100 (the A denotes 'Audio' apparently). It is possible that these are JFETs that didn't quite make the grade as far as power switching applications are concerned so they are a bit cheaper.
Another forum member - Tea-Bag - was providing a matching service for these parts at a modest additional cost, you can PM him through the forum. Not sure if there are any left, see:
R100A JFET Group buy
Of your questions that I can answer:
2) This is in the signal path, I am sure that you could spend mega $ buying some esoteric capacitor. Depends on taste - I will go for something snap in with low ESR (most likely Panasonic as that is what usually comes up when I look on Farnell - same company as element14 BTW).
3) Yes.
4) I can't really comment on that one I'm afraid - you can always build as per the spec and then change after and let your ears decide.
5) Maybe a touch low running at ~2.5A at 25V each side will draw 62.5W for 125W total. Most people like to overrate by double so 250VA is maybe more appropriate for cool running, but 200VA would work.
Ian
I am currently collecting parts for a F2J at the moment also. Here are a few bits that you might find useful:
Peter Daniel (on this forum) has F2 boards that can be used for the F2J. I have a pair waiting to be stuffed with components and they are really good quality.
The SJEP120R100A is equivalent (for our purposes anyway) to the SJEP120R100 (the A denotes 'Audio' apparently). It is possible that these are JFETs that didn't quite make the grade as far as power switching applications are concerned so they are a bit cheaper.
Another forum member - Tea-Bag - was providing a matching service for these parts at a modest additional cost, you can PM him through the forum. Not sure if there are any left, see:
R100A JFET Group buy
Of your questions that I can answer:
2) This is in the signal path, I am sure that you could spend mega $ buying some esoteric capacitor. Depends on taste - I will go for something snap in with low ESR (most likely Panasonic as that is what usually comes up when I look on Farnell - same company as element14 BTW).
3) Yes.
4) I can't really comment on that one I'm afraid - you can always build as per the spec and then change after and let your ears decide.
5) Maybe a touch low running at ~2.5A at 25V each side will draw 62.5W for 125W total. Most people like to overrate by double so 250VA is maybe more appropriate for cool running, but 200VA would work.
Ian
Hi,
Thanks for all the tip... will contact tea bag. Alternatively might just get it from element14/farnell who is just down the road, (yup I know the name change, been buyibng from them for the last 15 years). I think the matching o the transitor may not be so critcal in this one, since this is left and right. It would probably be more critical in those cases where they are in parallel
1) How much did you have to pay for the F2 board? I suppose the circuit is so simple a veroboard with point to point wiring would be about the same.
2) Well that's the ironic thing about currents, they are the same in series circuit. So putting on an esoteric capacitor may not make any difference... in which case I might as well save the money and pay for a plain old vanilla capacitor..
Oon
Thanks for all the tip... will contact tea bag. Alternatively might just get it from element14/farnell who is just down the road, (yup I know the name change, been buyibng from them for the last 15 years). I think the matching o the transitor may not be so critcal in this one, since this is left and right. It would probably be more critical in those cases where they are in parallel
1) How much did you have to pay for the F2 board? I suppose the circuit is so simple a veroboard with point to point wiring would be about the same.
2) Well that's the ironic thing about currents, they are the same in series circuit. So putting on an esoteric capacitor may not make any difference... in which case I might as well save the money and pay for a plain old vanilla capacitor..
Oon
The F2 boards came to $22 US for the pair delivered to the UK IIRC - which I thought was pretty good value.
Ian
Ian
Thanks for the tip again. I think the price is pretty fair...thanks for the tip again.
Oon
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Oon
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If you guys are both building the f2j at roughly the same time, I'd like to suggest that perhaps you use this thread as a dedicated build thread. I'm also interested in the f2j, and the original f2 thread has gotten very long, and also not "J" specific which is the main problem I think. I'm still a few months from getting into the project, but as always I look forward to seeing these amps develop.
OK so the case for my F5 has been canabalised for the F2J which is now 99% complete (just need to wire up the LEDs on the front panel and check the bias later this week). I feel sorry for the F5 but as I listen to the F2J I am getting over it really fast. The F5 could make a reappearance sometime in the future if I ever have the option to bi-amp a pair of speakers.
So how does it sound - really, really good. My F5 was fast but a touch dry in the bass. The F2J is just as fast, sweeter through the midrange and the bass has much more weight (if very slightly less control - but not much). I may play around with the output resistance a little see what it does to the sound. It is worth noting that it only has a couple of (long) evenings play on it so far - so I expect it to get even better as it breaks in.
I have a tiny bit of hum on the left channel, but that is due to the power wiring running down that side of the bank of capacitors in the middle. I can't hear it more than a couple of feet away from the speaker. I may rewire this bit so that the incoming power comes straight down the middle of the PSU caps.
I am running it with a pair TB W8-1772 in 45 litre BR cabinets and in my smallish room; it provides plenty of volume.
I will post some photos a little later in the week when I open it up again to wire the afore mentioned LEDs.
I'd just like to take a second to thank NP for a fabulous design (and being so generous opening them up to the public), and also Peter Daniel for the boards and Tea-Bag for the JFETs (starting to sound like an Oscars acceptance speech so I'll stop now!).
Ian
So how does it sound - really, really good. My F5 was fast but a touch dry in the bass. The F2J is just as fast, sweeter through the midrange and the bass has much more weight (if very slightly less control - but not much). I may play around with the output resistance a little see what it does to the sound. It is worth noting that it only has a couple of (long) evenings play on it so far - so I expect it to get even better as it breaks in.
I have a tiny bit of hum on the left channel, but that is due to the power wiring running down that side of the bank of capacitors in the middle. I can't hear it more than a couple of feet away from the speaker. I may rewire this bit so that the incoming power comes straight down the middle of the PSU caps.
I am running it with a pair TB W8-1772 in 45 litre BR cabinets and in my smallish room; it provides plenty of volume.
I will post some photos a little later in the week when I open it up again to wire the afore mentioned LEDs.
I'd just like to take a second to thank NP for a fabulous design (and being so generous opening them up to the public), and also Peter Daniel for the boards and Tea-Bag for the JFETs (starting to sound like an Oscars acceptance speech so I'll stop now!).
Ian
Hey Ian, congratulations on almost completing the journey. I am in the midst of looking for the most difficult part of this project- time ... which becomes unobtanium when you have a 4 month old baby...
Oon
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Oon
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Fantastic Ian! Looking forward to more info and pics of your build. Will be building one very soon I hope... cheers.
Hey Ian,
Just checking. Did you have any problem stuffing the transistor from semisouth into peter Daniel's board?
Oon
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Just checking. Did you have any problem stuffing the transistor from semisouth into peter Daniel's board?
Oon
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Hi,
I actually didn't mount the large transistors directly on the board itself. I run some wire from the board to the FETs. My heat sinks were all ready tapped for my F5 so this was the path of least resistance.
It is possible to run short wires without too much issue with oscillation. In this build I am actually using slightly longer runs of wire (due to the existing tapped holes) but am having no oscillation problems.
Ian
I actually didn't mount the large transistors directly on the board itself. I run some wire from the board to the FETs. My heat sinks were all ready tapped for my F5 so this was the path of least resistance.
It is possible to run short wires without too much issue with oscillation. In this build I am actually using slightly longer runs of wire (due to the existing tapped holes) but am having no oscillation problems.
Ian
Hi Ian,
Thanks for the info. I will most likely do the same. Saves a lot of problem figuring out the assembly.
Oon
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Thanks for the info. I will most likely do the same. Saves a lot of problem figuring out the assembly.
Oon
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My F2J soundstage bests the F5 (IMO). I build it using as cheap as parts as I had around and it sounds amazing. I am stuffing another PD board and getting some better parts to see if actually sounds any better.
The new parts are low PPM Mills resistors, PRP signal resistors, 10Uf Auricaps for input ,Mudorf New 10,000uf E-caps for the output.
I use 25R Mills-MRA-12 on the output running into a 15R Lowther PM5T with copper VC.
The new parts are low PPM Mills resistors, PRP signal resistors, 10Uf Auricaps for input ,Mudorf New 10,000uf E-caps for the output.
I use 25R Mills-MRA-12 on the output running into a 15R Lowther PM5T with copper VC.
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I was lucky enough to have some more 'exotic' parts in my parts bin from some previous valve projects, so I had a load of Elna Silmic IIs, Russian surplus teflon caps and some bigger Russian surplus polystyrene caps. Needless to say they all got used.
I can't compare my F2J to any other version, but it beats my F5 (that it replaced) on my single driver speakers hands down. The F5 was no slouch either.
The mids and highs compare with my PX25 single ended mono blocks and the bass on the F2J just blows them away.
I can't compare my F2J to any other version, but it beats my F5 (that it replaced) on my single driver speakers hands down. The F5 was no slouch either.
The mids and highs compare with my PX25 single ended mono blocks and the bass on the F2J just blows them away.
I am thinking of using this cap at the output of the F2J. A 490uF PP cap maybe bypassed by something of higher quality such as a mundorf M-cap. I believed it is probably not one of the best cap but I believe better than an electrolytic. I don't really need the bass, since I am using it for my fullrange (I have a separate amp for the woofers).
Any thoughts on this?
Oon
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Any thoughts on this?
Oon
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Oon, I only use my F2 for 200hz up, after electric x-over.
I use only 200uf of Elna Silimics now.
I use only 200uf of Elna Silimics now.
Oh yeah. Forgot to mention that. Received your transistors last week. Looks great. Now just need to round up the rest of the components.
Oon
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Oon
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Just realised my earlier post is missing the link.😱 The polyproplene Cap I want o use is this one.
CORNELL DUBILIER|947C491K801CBMS|CAPACITOR, 490UF, 800V, DC LINK | element14 Singapore
Weighs a kilo, i've never heard of a cap this heavy and huge, doesn't seem to cost to much for its value so why not give it a shot.
Oon
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