A guide to building the Pass F4 amplifier

[KevinHeem]

@Alan Cohen
Don't place your order just yet. I think I have some I can just drop in the mail to you.
i'll check and get back.

 

[KevinHeem]

I do have some 750R. They’re probably 1/4 watt and I don’t recall the brand (could be KOA/Spear). They do meter at 750 ohms. PM me if you want a few.

 

[Alan Cohen]

So I think I did a bad thing. I accidentally mixed up the mosfets that I bought from the diystore. There are 6 in each bag. I'm assuming they were matched? Anyway I can check them?

 

[Mark Johnson]

Regrettably, I suspect you will ultimately decide, it is faster and cheaper to buy them again, than to assemble the apparatus needed to test them properly. I hope I'm mistaken but, uhhhh ....

 

[myleftear]

So I think I did a bad thing. I accidentally mixed up the mosfets that I bought from the diystore. There are 6 in each bag. I'm assuming they were matched? Anyway I can check them?

Mine had the values noted on the body‘s back-side (the metal side), hence my bragging about the precision of the match (#2302)... yours not?

 

[KevinHeem]

Do the N’s come in one bag and the P’s come in another, or was it 3 N’s and 3 P’s in each bag?

 

[Alan Cohen]

Do the N’s come in one bag and the P’s come in another, or was it 3 N’s and 3 P’s in each bag?

I don't know. They're all mixed up now.

Part numbers are 6 x IRFP 240 and 6 x IRFP 9240. 240s are Ns, 9240 are Ps. I guess there was 3 of each in each bag?

Any chance all 12 are matched?

 

[myleftear]

I think I got it. Part numbers are 6 x IRFP 240 and 6 x IRFP 9240. They are clearly marked on the devices. Whew! Thanks!!

Is that the engraving/print on the front-side? If so, you‘d still need to sort out the triplets. I‘m confident diyaudiostore did note the value on the other side (they came wrapped as triplets?)

 

[Alan Cohen]

They came in bags of 6. I assume one for each channel. There are no other markings. The text in the store reads:


Included in this kit are the semiconductors needed to complete an F-4 amplifier or BA-3 output stage, with the exception of the input JFETs. MOSFETs were matched in accordance with standard operating conditions. This is enough transistors for 2 channels (one stereo amplifier).

6 x IRFP 240 (F4 and BA-3)
6 x IRFP 9240 (F4 and BA-3)
2 x TL-431 (BA-3)
The IRFP9240/IRFP240 MOSFETs were matched at the rail voltage and current that the BA-3 and F4 articles suggest, specifically, 22v and .4A, and then grouped by VGS to within .1V.

I dropped a message to the store to see if, per chance, all 12 are matched.

 

[6L6]

Are their numbers written on the plastic or the metal of the mosfets?

 

[2 picoDumbs]

They might have a record of what they supplied you.
You might be lucky.

 

[Alan Cohen]

Are their numbers written on the plastic or the metal of the mosfets?

Not that I can see

 

[Alan Cohen]

Enough for day 1.

 

[PJN]

I have been slowly been gathering parts for a F4 build. I also bought the transistor set from the Diyaudio store. None are marked with any measurement numbers. All the N's in one bag and all of the P's in another. I guess I'm going to have to trust that the store did the matching and didn't bother writing the numbers down. But then again how would they sort them out after measuring a bunch.

 

[Alan Cohen]

Ah-ha! That's good to know that the Ns and Ps were in separate bags, not 3 each in each bag. That would lead me to believe that all 12 are matched.

The bags were not marked in any way indicating to keep bags separate.

 

[PJN]

It still would be reassuring to get confirmation from the store.

 

[Alan Cohen]

Elena from the store does not know and passed on the question. It might take a bit for an answer. I'm still waiting for the chassis, so no rush. I also posted the question in the DIY store in the question section for the F4 devices.

But if they came with Ns and Ps in separate bags, with no individual labeling, then they should all be matched...if they're matched at all.

I have enough time to build the matching rig and do it myself. Might be fun to try.

 

[myleftear]

I‘d be quite sure they wouldn‘t match triplets just to toss them in a bag of six. They‘re good (@diyaudiostore) and your devices are most probably nearperfect matches.
Still, better to know than to believe.

 

[JR_W]

I bought an F4 kit from the store quite a while back, mine were just loose in the bag. The JFETS always come taped together in pairs, so I guessed the MOSFETS were close enough for rock and roll.

 

[myleftear]

Connection question, just to be sure…

Next to the Connectors "ST_V+", "ST_G1", ST_G2", "ST_V-" are the screw-terminals, they're marked X1, X2, X4, X3
…
I guess they are corresponding, right?
(ST_V+ being X1 etc.)

thank you!