??? It should clip at about a volt input. Do you have input resistors of the proper value?
B&D inc. has genuine Jfets. And they charge as such.
Yikes! I have audited previously but will most certainly double check the input resistors when I pull it apart. It needs to 'play nice' in a bi-amp rig where the other balanced amp has 20X gain.
the issue reappeared even with input wires soldered to the pcb, must be some other problem
Rail Voltage
Hi,
I've searched the threads but haven't found an answer. Has anyone (or does anyone know of someone) who has successfully bumped the rail voltage up to 30V to get more power without sacrificing sound performance (if that's possible in the design)
I fully appreciate that heatsinks will need to be larger.
Thanks!
Hi,
I've searched the threads but haven't found an answer. Has anyone (or does anyone know of someone) who has successfully bumped the rail voltage up to 30V to get more power without sacrificing sound performance (if that's possible in the design)
I fully appreciate that heatsinks will need to be larger.
Thanks!
Afaig, we haven't seen a polarity swapped version with 50V rails and 3-4 parallel JFET pairs yet. (smellyfish-j ?)
You are essentially describing an Aleph 5 vs Aleph 30 - same circuit, more voltage.
I think there should be no issue with an Aleph j and 30V rails with no other modifications other than 35V caps.
Send Nelson an email to verify.
Thanks for the replies everyone. I did note that the 2SJ74 is a bit over spec at 30V which would cause it to run a bit hotter and perhaps may not be good for long term reliability. A TO92 heatsink is an option...
I just cruised through the Nelson Pass document "F5 Turbo". Since this is also a Class A design as well, any opinions on sound between the F5 and AJ?
The only stumbling block is the obsolete FQA devices. It would take some datasheet detective work to find a close sub.
use plain dumb IRFP240
me likee Aleph more
call me spoiled brat
You like...Aleph J more? or Aleph 5?
I should get off of this thread with F5 questions, but I'll throw out 1 more since I see you've been on this thread for quite a while. (sorry thread moderator) I see that some are using IRFP240/IRFP9240 pairs. Why would Nelson Pass not have specified these in 2012, with the FQA parts going obsolete?
moi - J .
Papa is also spoiled brat (though , self-spoiled one
) having gazzilion of obsolete parts under the verrrry big mattress
Papa is also spoiled brat (though , self-spoiled one
) having gazzilion of obsolete parts under the verrrry big mattress
They are used in the F5Tv2 at 32V with no ill effects.
Nelson probably has thousands (no exaggeration) of the FQA laying around to use.
IRF, FQA, Toshiba (if you can find them) -- they all work in these circuits.
Thanks 6L6. Nice Moniker, BTW... 🙂
I'm now leaning toward the F5Tv2 as the power in the J is a bit low for my speakers. Really need to be around 50W/channel plus. IRF240/9240 seems to be the best choice as getting the original FQA is out of the question. Specs on current production FQA's too far from FQA19/FQA12.
Was the biggest issue with 240/9240 getting a good Vgs match? Again, I've spent the afternoon cruising the forum threads but couldn't seem to get a good handle on what the issues were with the 240/9240 devices. Did anyone successfully use them, and did test measurements appear quantitatively close to using original devices?
Thanks!
P group matched
N group matched
there is no benefit in trying to match N with P
so , again , use IRFP outputs , as many already do
"issue" with P type IRFP outputs is sort of different capacitive performance in voltage domain , comparing to N ones
however - nothing to write home about .... some Greedy Boyz even prefer that "mosfet mist" to more linear ones
N group matched
there is no benefit in trying to match N with P
so , again , use IRFP outputs , as many already do
"issue" with P type IRFP outputs is sort of different capacitive performance in voltage domain , comparing to N ones
however - nothing to write home about .... some Greedy Boyz even prefer that "mosfet mist" to more linear ones
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it's just that greed that keeps these forums going! ha! 🙄
When I was referring to matching, it was matching Vgs in their respective types - P and N. So probably buying a rail of each should be sufficient to get close enough Vgs with each type.
Also - Mr.Pass also indicates that using lateral MOSFETs is OK, but says they have lower current ratings. (pg.9 of his pdf doc) The ALFET ALF16N16W/ALF16N20W have Id of 16A, so that should be adequately sufficient. The only issue is bias spread of which these have a much lower threshold.
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