Hi VictoriaGuy,
If you want to save a few bucks, you can ask for 2 matched pairs in the 10 to 11.2mA
Idss range. (I used parts with ~11mA idss in my build).
Cheers,
Dennis
If you want to save a few bucks, you can ask for 2 matched pairs in the 10 to 11.2mA
Idss range. (I used parts with ~11mA idss in my build).
Cheers,
Dennis
To save other 'beginners' for asking the same questions that I have asked, please note that the comment about the power supply is for a STEREO (2 channels) amp but the semiconductor list is for a MONO (one channel) amp. So multiply all the semiconductor requirement$ by two for stereo. And check the BOM for the full transistor list. For a stereo Aleph J, it looks like 16 transistors need to be on my list IF they are matched. If not matched, more (number of IFRP240 is a gamble?) must be bought to allow matching . How the matching works -i.e. which pairs exactly need to be matched in the output stage of each channel, and how closely the channels need to be matched (I don't want different gain in the R&L channel!)- isn't clear.
(4) per amp channel, so a total of (8) IRF240 for a stereo Aleph J.
The N-channel mosfet are usually fairly close if from the same production batch, so if buying from Mouser or DigiKey, they probably will be. If you buy your Fets from Ebay you are totally on your own.
I'd buy 3x the devices you need, match them up, you'll most likely have enough for another whole amp, and you can sell those as matched to the next guy and recoup most of your $. 🙂
Specifically talking about the Aleph J, there are 2 sets of (2) per amplifer PCB, one set are the output devices, the other set is the output Constant Current Source. (Looking at the schematic, the top is the CCS, the bottom is the outputs.)
Each set should be populated with a pair of Mosfet that has been matched for Vgs (Voltage gate to source), this is to make sure that the paralleled Mosfet turn on at the same time. If they are not matched, one will turn on before the other, hog all the current, and overheat, while the other one doesn't do much at all.
The output fets and the CCS fets do no need to be matched to each other, you basically need 2 patched pair per PCB, not a matched quad.
Matching the fets in this case has nothing to do with gain.
Actually, that's 18 transistors, not 16 for a stereo Aleph J
And there's no matching required for the ZTX ones, AFAIK.
8 IRF240
4 SJ74
4 ZTX450
2 ZTX 550
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Thanks - the reference to the schematic makes it a lot clearer.
So this matching Vgs is different than the matching for the SJ74s which is current matching? At any rate I need to do some searching to see what is involved in the matching process (jig setup).
This means that: The output fets and the CCS fets in one channel do not need to be matched to the ones in the other channel. The transistor current/voltage properties don't affect the gain of the amplifier.
For each channel, the two CCS mosfets need to be a matched pair and the two output mosfets need to be a matched pair.
Correct ???
Correct.
I thought we were talking about the Mosfets that need matching. 😀
ZTX need no matching.
It's similar, but not difficult. You could use a 19v laptop brick for the PSU (in lieu of a 12v source), see diagram below -
An externally hosted image should be here but it was not working when we last tested it.
And more info on matching here - Embedded Hybrid Headphone Amlifier
Yes, and actually the Mosfet don't need to be matched to anything other than the one they sit directly next to. Which is to say you could build a stereo amp with (4) pairs of IRF240s.
Yes.
I didn't expect this many replies to my question...but thank you.
The F6 looks like it's the next one up in difficulty from the ACA so I think I will go with that one. Especially since the power supply can be used in other amps as well as the chassis.
The F6 looks like it's the next one up in difficulty from the ACA so I think I will go with that one. Especially since the power supply can be used in other amps as well as the chassis.
My apology for hijacking your thread!🙂
Hopefully some of the answers to my beginner questions will be helpful to others. Thanks again (from me) to all the folks who have helped to 'point me in the right direction'.
In many ways just knowing there are other beginners is helpful. One reads so many posts by people that really understand the engineering details of these amps that it is easy to think you are the only one baffled by some step in the process.
There's here ( Pass Lab forum ) everything for beginners to make an Pass amp the way it should be done , you just have to be able to :
search , read , understand , spend the right amount of money , and MAKE IT ....
you'll love it ;-)
.
search , read , understand , spend the right amount of money , and MAKE IT ....
you'll love it ;-)
.
I see on some power supplies people have used 2 transformers and others only 1.
If I've read the build threads right then a single 400va transformer like this AS-4218 - 400VA 18V Transformer - AnTek Products Corp will power both channels, correct?
If I've read the build threads right then a single 400va transformer like this AS-4218 - 400VA 18V Transformer - AnTek Products Corp will power both channels, correct?
....and to add to the confusion some have, what is the suggestion for a 500VA, (iron belted) x2, 18-0-18v toroid? Also, what is the sensible max uF per rail?
(Don't want what Zen Mod calls a 'Sissy PS! 😉)
(Don't want what Zen Mod calls a 'Sissy PS! 😉)
Max? Well, overkill kicks in somewhere north of 88,000uF per rail. (8) 22,000uF caps total
If using normal diyAudio PCB use 15,000-22,000uF caps in each position. Nelson uses 15,000 in the factory-built ones, so anything more is just vanity... 😀 😀 😀
If using normal diyAudio PCB use 15,000-22,000uF caps in each position. Nelson uses 15,000 in the factory-built ones, so anything more is just vanity... 😀 😀 😀
Member selling Jfets - http://www.diyaudio.com/forums/swap-meet/304379-fs-2sk170-2sj74-matched-jfets.html#post5001641
The J74 Quads would be great for Aleph J, the K170/J74 sets for anything else (F5, BA-3, F6, F4, etc...)
The J74 Quads would be great for Aleph J, the K170/J74 sets for anything else (F5, BA-3, F6, F4, etc...)
6L6 & Pico!
Thanks.
And - for Pass clones - how about a PS using an at hand 500VA x2 18-0-18? Treat as single traffos? Earth problems?
Thanks.
And - for Pass clones - how about a PS using an at hand 500VA x2 18-0-18? Treat as single traffos? Earth problems?
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