No one for a Rigorous reply
Then me again
I would suggest you try to look in the www for a Explanation
Search for:
How do a Differential pair works
JFET bias
CCS for LongTailed Pair / differential amp
Some Basics that can give you a answer
Nothing Nelson Pass has invented.
So no reason to stop him from doing important work
Everyone knows that it is difficult to explain the circuit of the Nielsen Pass with textbooks. Can you explain? ? I also have the basics of these textbooks. If you can't explain it, don't talk about it. . . . . .
The input stage is a classic differential amplifier with a CCS (constant current source) on the positive rail.
R8 controls current through the pair.
R7 controls the DC operating point of the positive output node, and hence the DC offset further down the circuit, as this amplifier is DC coupled.
R8 controls current through the pair.
R7 controls the DC operating point of the positive output node, and hence the DC offset further down the circuit, as this amplifier is DC coupled.
we were all newbies once, when there is a word or a phrase that i do not understand, i highlight it with my mouse and then right click, search google, that is my little secret how i learned a lot of things, and you can too...do not take things personal....
edit: we are all here to help, but you should help yourself too...
I’m still a newb but was grateful 6L6 was gracious enough to answer my endless questions till I had a better understanding of what I was doing. I think the hardest part of learning this stuff is not knowing the proper term(s) to search on the forum or net. One sentence could have 3 different terms and a newb like me had to learn how to correctly search for each phrase/concept, understand them, then move to the next just to understand a sentence or two.
yes to this....even if i read the textbooks over and over again, having someone to talk it with and applying it with real work, makes learning faster...that is why when i discovered this board many many years ago, i stayed on....i learned a lot of things here than in my 5 years of college....
Had nothing to to with newbie or not.
I thought about to explain it. (at least as far as I understood it)
Maybe its my bad english. But the way the question was asked...
...in germany no one will get a answer this way.
Sounds like... Here i am, i want an answer...
...then i think -> go and look for yourself.
A question like:
I`ve no idea how this or that works. I`ve looked in the www. found something but
i do get it. can some help or explain?
Will get another response from me.
I thought about to explain it. (at least as far as I understood it)
Maybe its my bad english. But the way the question was asked...
...in germany no one will get a answer this way.
Sounds like... Here i am, i want an answer...
...then i think -> go and look for yourself.
A question like:
I`ve no idea how this or that works. I`ve looked in the www. found something but
i do get it. can some help or explain?
Will get another response from me.
I work in a similar way. Some explanation of the journey that includes giving those with the knowledge an understanding of what the query holder understands helps a lot. It means that redundant advice is not offered and the query holder is likely to get a useful answer with less fuss.
Hello all,
The Aleph J that I built gives a bit too much presence and zing in the upper mids / lower treble with my speakers (Klipsch Forte II). I've built a pair of ACAs and and an M2, which both work very well with the speakers. Maybe it is just how the Aleph J sound with the Forte II, but I am wondering if swapping some caps or other part might mellow the amp a bit.
I built the amp pretty much according to the BOM linked in the beginning of the thread. For the power supply, I used a 300 VA 18 volt Antec transformer, and eight 22,000 uf 35 volt Cornell Dubilier caps on the store's board, using packaged bridge rectifiers recommended elsewhere on the Pass threads. It is very similar to the power supply I used on the M2.
Maybe the amp is supposed to have this quality to the highs, but if anyone has any ideas, I'd enjoy trying some suggestions.
Thanks,
Alan
The Aleph J that I built gives a bit too much presence and zing in the upper mids / lower treble with my speakers (Klipsch Forte II). I've built a pair of ACAs and and an M2, which both work very well with the speakers. Maybe it is just how the Aleph J sound with the Forte II, but I am wondering if swapping some caps or other part might mellow the amp a bit.
I built the amp pretty much according to the BOM linked in the beginning of the thread. For the power supply, I used a 300 VA 18 volt Antec transformer, and eight 22,000 uf 35 volt Cornell Dubilier caps on the store's board, using packaged bridge rectifiers recommended elsewhere on the Pass threads. It is very similar to the power supply I used on the M2.
Maybe the amp is supposed to have this quality to the highs, but if anyone has any ideas, I'd enjoy trying some suggestions.
Thanks,
Alan
The input jfets are Toshiba 2SJ74 matched pairs from Punkydawgs, and the rest are from the DIY Audio Store Aleph J kit, which are ZTX450, ZTX550 and IRFP240.
Hi Aljordan,
I built my J as per the BOM just as you did, but with a 400VA transformer. Your mention of the J being a little bright in the treble at first was exactly the same for me. Not that it sounded badly. It did smooth out after a couple of weeks listening to music daily. Maybe it’s a little more sensitive to break in?
Hmmm,
LTP... long term paranoia?
OS Iq... the IQ of my operating system?
I tried googling these things, but didn't find much to aid in my understanding. I see a resistor on the circuit board labeled LTP. Would I measure the LTP current after that resistor, with my black lead connected to ground?
Unfortunately I couldn't finding anything on measuring OS Iq.
I can tell you that, with the inputs shorted and no load on the outputs, each channel measures .401 V across the source resistor, and the offset at the speaker terminals measures about 0.49 mA. I tried to get the offset closer to 0.00 mA, but it gets touchy. Seems like half a mA is pretty good, but I don't really know.
If I can figure out how measure the other things you asked about, I'll report back.
no need for that ....... after I was humbled by some real good and passionate people, I'm really trying to be lesser pompous prick than I really am , so typing sentence or two isn't that hard
LTP means Long Tailed Pair - and that;s exactly funny looking arrangement of input JFets - their sources are connected together , so can limp together , doing all the magical things in computing and singing
OS means Output Stage , and that are big ones , you screwed to heatsink
so , even without knowing Magical Words needed to be introduced in Hidden Community of Initiated Ones , you've done half of work , even if written sorta funny
400mV across 0R47 source resistors is OK
DC offset on output is usually meant to be some sort of Voltage [V] , and that one is having (always) some relation with current [A] , but let's talk in mV rather than mA , at least while we are at voltage ; in light o that , I hope you're having your DMM set at "200mV" range (probes placed accordingly ) while you're poking between speaker outputs
it will be nice if you can put resistor (any value between 1R and 1K you have in drawer) in place of "R30" jumper (and leave it permanently in , thus relieving some heat from Q2 for good) and measure voltage across it
write here what you measured and which value of resistor you soldered in
that would confirm is there enough juice (means mA) through input LTP , and tell us is there possible culprit for sound being funny
edit : oh yes ...... Iq is short for Quiescent Current ; above I'm writing about determining of LTP Iq , while OS Iq means steady current in output stage , and you already confirmed that with figure of 400mV across source resistor(s) of big one(s)
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>>Klipsch Forte II
Klipschs - it's been years since I've heard a pair - aren't exactly known as mellow speakers. Efficient - yes! - but a lot of horn tweeters, like my departed UREI 813As - were very sensitive to everything upstream. Tube amps were the best for my horn drivers; perhaps the higher output impedance acting as some sort of high frequency filter? Dunno, but that's what worked best for me.
Anyways - second 6L6's recommendation. My build sounds very similar to yours, straight down to the measurements, punkydawg 2SJ74s, and Antek transformer. I would not call the amplifier zingy on a pair of Wharfedale Denton loudspeakers (which have a rather soft treble out of the box).
To my ears - subjectivity alert - the Aleph J is quite neutral, but more colorful than say my backup amp, an Adcom 545.
Klipschs - it's been years since I've heard a pair - aren't exactly known as mellow speakers. Efficient - yes! - but a lot of horn tweeters, like my departed UREI 813As - were very sensitive to everything upstream. Tube amps were the best for my horn drivers; perhaps the higher output impedance acting as some sort of high frequency filter? Dunno, but that's what worked best for me.
Anyways - second 6L6's recommendation. My build sounds very similar to yours, straight down to the measurements, punkydawg 2SJ74s, and Antek transformer. I would not call the amplifier zingy on a pair of Wharfedale Denton loudspeakers (which have a rather soft treble out of the box).
To my ears - subjectivity alert - the Aleph J is quite neutral, but more colorful than say my backup amp, an Adcom 545.
no need for that ....... after I was humbled by some real good and passionate people, I'm really trying to be lesser pompous prick than I really am , so typing sentence or two isn't that hard
LTP means Long Tailed Pair - and that;s exactly funny looking arrangement of input JFets - their sources are connected together , so can limp together , doing all the magical things in computing and singing
OS means Output Stage , and that are big ones , you screwed to heatsink
so , even without knowing Magical Words needed to be introduced in Hidden Community of Initiated Ones , you've done half of work , even if written sorta funny
400mV across 0R47 source resistors is OK
DC offset on output is usually meant to be some sort of Voltage [V] , and that one is having (always) some relation with current [A] , but let's talk in mV rather than mA , at least while we are at voltage ; in light o that , I hope you're having your DMM set at "200mV" range (probes placed accordingly ) while you're poking between speaker outputs
it will be nice if you can put resistor (any value between 1R and 1K you have in drawer) in place of "R30" jumper (and leave it permanently in , thus relieving some heat from Q2 for good) and measure voltage across it
write here what you measured and which value of resistor you soldered in
that would confirm is there enough juice (means mA) through input LTP , and tell us is there possible culprit for sound being funny
edit : oh yes ...... Iq is short for Quiescent Current ; above I'm writing about determining of LTP Iq , while OS Iq means steady current in output stage , and you already confirmed that with figure of 400mV across source resistor(s) of big one(s)
Thank you for nicely trying to explain LTP (long term patience) and OS Iq. I see the possibility of a blooming symbiotic relationship. You can develop practices of pleasantries and patience towards technical morons, and I'll happily put those virtues to a test, as most of the stuff you will write will pass through my brain like a neutrino.
Regarding DC offset in mV (for others like me, that means millivolt... 1/1000 of a volt... take one volt, divide it by 1000, and you get a millivolt... my spell checker does not seem to think that millivolt is a real word, so the existential nature of the millivolt remains in question). Regarding the DC offset, I let the amp cool down until the heat syncs felt about room temperature, then turned the amp on while measuring at the binding posts. It started at about 22 mV, and declined over the next few minutes to about 5 mV. After 30 minutes or so, the offset was 0.6 mV in the left channel, and 0.0 mV in the right channel.
Is this normal behavior? Wait, what I mean is, is the DC offset showing normal behavior? Please don't comment on my own behavior. Should I worry about the +-1 mV values? As I recall, it was touchy thing getting to a near 0 value when I first set the offset of the amp. That was a month or so ago.
I think this might be a moment for a little deep breathing exercise, but here goes anyway. Regarding output stage quiescent current, do I measure this at the drain pin of Q7 and Q8, or elsewhere? Do you want this measurement in milliamps or millivolts? I am guessing milliamps, as I think amps when I see the word current, but I guessed wrong on the DC offset thing already, so I figured I'd better ask.
I haven't yet removed the boards to install a resistor at the R30 jumper. But I will happily do so if it is suggested. I have some 10 Ohm, 18 Ohm, and 100 Ohm. I'll choose 10 Ohm, unless otherwise directed.
Thanks again for the help that you and others have selflessly offered. I will dig out some other speakers to listen to the amp with. I have a nominal 8 ohm pair with normal (non-horn) high quality drivers, but at very low 86 dB efficiency.
Alan