If the Ebay Jfet are genuine (and unfortunately there is a high probability they are fake...) being GR grade will require more resistance across the bias pot, as Andrew says.
This means you will need to increase the value of the resistor in parallel with P1 P2, which are R3 R4 (or R5 R6 if you are looking at the schematic that includes P3)
My F5 build guide with the Peter Daniel boards used GR Jfet, it took quite a bit more resistance to get everything operating as planned, but it worked wonderfully and sounds great.
To you mean F5Tv3? which version of the amp are you building?
This means you will need to increase the value of the resistor in parallel with P1 P2, which are R3 R4 (or R5 R6 if you are looking at the schematic that includes P3)
My F5 build guide with the Peter Daniel boards used GR Jfet, it took quite a bit more resistance to get everything operating as planned, but it worked wonderfully and sounds great.
brunogiovs said:
To you mean F5Tv3? which version of the amp are you building?
Th1 and th2 why the amp needs it?
I thought MOSFETs had a self protection to runways ?
Anyone can confirm the right specs ? Or part ?
I thought MOSFETs had a self protection to runways ?
Anyone can confirm the right specs ? Or part ?
Lateral mosFETs have a near zero tempco when Ic is ~200mA
Vertical mosFETs have a near zero tempco when Ic is 10A to 40A.
Laterals when biased to less than 200mA can self protect since total dissipation is acceptable at this lowish Ic, whereas Verticals will simply blow up due to excessive dissipation that rises as temperatures rise.
Vertical mosFETs have a near zero tempco when Ic is 10A to 40A.
Laterals when biased to less than 200mA can self protect since total dissipation is acceptable at this lowish Ic, whereas Verticals will simply blow up due to excessive dissipation that rises as temperatures rise.
R19 run hot
Hi
Just finished my F5 V3 and are ready to bias.
Power supply steady with 24,4v - I'm using softstart and speakerprotection boards.
Powering with a variotrafo - one/some resistor close to the LED runs hot, and start to smoke. I think its R19 (100R 1/4w).
I havent started biasing, but both R11 and R12 measure just few mV.
Any advice?
Hi
Just finished my F5 V3 and are ready to bias.
Power supply steady with 24,4v - I'm using softstart and speakerprotection boards.
Powering with a variotrafo - one/some resistor close to the LED runs hot, and start to smoke. I think its R19 (100R 1/4w).
I havent started biasing, but both R11 and R12 measure just few mV.
Any advice?
Ahhh- found out that I'm using resistor no from the BOM - they have changed to new numbers according to schematics from the F5Turbo article.....
like this one?
2x 18V toroidal transformer 500VA
you mentioned 18 or 20v, where is that based or depends on?
That'll do. Either 18v or 20v will do fine. If your line voltage was on the low side you may go with 20v. And some transformers are rated slightly different than the Plitrons. But not a big deal.
I'm hoping the JFETs will be back soon as I want to order full transistor set and boards in one go.
You've built a million F5s at this point, you should really build an Aleph J... 😀 😀 😀
Matched Jfet are still an issue, we are actively working on it. They will return, we promise. Hopefully soon.
Matched Jfet are still an issue, we are actively working on it. They will return, we promise. Hopefully soon.
Thanks good to know
Hehe.. I've built an F5 for a friend and a F5 turbo for another friend that sounded amazing but had issues.. So now am wanting to build a F5T for myself using the new revision diyaudio boards.
I'll have a look at aleph J
Hehe.. I've built an F5 for a friend and a F5 turbo for another friend that sounded amazing but had issues.. So now am wanting to build a F5T for myself using the new revision diyaudio boards.
I'll have a look at aleph J
The F5T boards are not much different, if at all. The F5 (standard, single output pair) are in their v3 revision. (Has the "P3" pot)
F-5 – diyAudio Store
There's a new parts kit for that PCB in the store, everything for the amp channels except the Jfets - F5v3 Kit – diyAudio Store
As for the Aleph J, that needs the differential (j74/J74) matched pair Jfets, those are in stock - J74/J74 Stereo Differential Kit – diyAudio Store
The matched transistors can be found here - Aleph J Transistor Kit – diyAudio Store
And PCB - Aleph J – diyAudio Store
Build guide - Aleph J illustrated build guide
As for sonic differences, Zen mod summed it up the best years ago - With the F5 you see the cockroach crawling around the violinist's feet, with the Aleph J the cockroach turns and smiles at you. 😀
F-5 – diyAudio Store
There's a new parts kit for that PCB in the store, everything for the amp channels except the Jfets - F5v3 Kit – diyAudio Store
As for the Aleph J, that needs the differential (j74/J74) matched pair Jfets, those are in stock - J74/J74 Stereo Differential Kit – diyAudio Store
The matched transistors can be found here - Aleph J Transistor Kit – diyAudio Store
And PCB - Aleph J – diyAudio Store
Build guide - Aleph J illustrated build guide
As for sonic differences, Zen mod summed it up the best years ago - With the F5 you see the cockroach crawling around the violinist's feet, with the Aleph J the cockroach turns and smiles at you. 😀
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