I agree. And statisticians needn't worry, the statistics are staying within long-term averages considering some exchanges over in the blowtorch thread.
indeed, probably this is due in part to the majority wanting to actually see something produced out of this exciting event; instead of degenerating into the usual squabble.
ssshhh geniuses at work
The part number and the specs strongly suggest this is two J310 die moulded into a single package. 6nV noise is quite far removed from the BF862 but fairly respectable for a JFET opamp input stage.
Acrimony
Yeah, and as such is becoming quite un-entertaining on that level, in order to re-direct those who are here awaiting such antics: (with all credit to Monty Python):
_________________________________________________
Q: WHAT DO YOU WANT?
M: Well, I was told outside that...
Q: Don't give me that, you snotty-faced heap of parrot droppings!
M: What?
Q: Shut your festering gob, you tit! Your type really makes me puke, you vacuous, coffee-nosed, maloderous, pervert!!!
M: Look, I CAME HERE FOR AN ARGUMENT, I'm not going to just stand...!!
Q: OH, oh I'm sorry, but this is abuse.
M: Oh, I see, well, that explains it.
Q: Ah yes, you want room 12A, Just along the corridor.
M: Oh, Thank you very much. Sorry.
Q: Not at all.
M: Thank You.
(Under his breath) Stupid git!!
_________________________________________________
Indeed...I have read this on other DIYA threads, couched in slightly different prose...
Howie
Yeah, and as such is becoming quite un-entertaining on that level, in order to re-direct those who are here awaiting such antics: (with all credit to Monty Python):
_________________________________________________
Q: WHAT DO YOU WANT?
M: Well, I was told outside that...
Q: Don't give me that, you snotty-faced heap of parrot droppings!
M: What?
Q: Shut your festering gob, you tit! Your type really makes me puke, you vacuous, coffee-nosed, maloderous, pervert!!!
M: Look, I CAME HERE FOR AN ARGUMENT, I'm not going to just stand...!!
Q: OH, oh I'm sorry, but this is abuse.
M: Oh, I see, well, that explains it.
Q: Ah yes, you want room 12A, Just along the corridor.
M: Oh, Thank you very much. Sorry.
Q: Not at all.
M: Thank You.
(Under his breath) Stupid git!!
_________________________________________________
Indeed...I have read this on other DIYA threads, couched in slightly different prose...
Howie
Cgd of the input devices is one of the major paths for +ve PS noise into the i/ps. That's why the PSRR nulls with a particular source Z cos that's when the Zs presented by the feedback network & the source are equal and the CMRR of the amp ignores it. Cascoding the input helps make this effect innocuous.
Having separate CCS for both input devices re-introduces the problem from the -ve supply .. which then need extra cascodes.
But if we
doesn't this eliminate the problem from the -ve rail?
GuruWurcer said:
Scott, could you explain a little for us unwashed masses why we can't?
ricardo "wannabe a SPICE guru but failing" lee
I'll get around to the explanation, promise.
A thought occured to me last night, there are several build to print houses in Taiwan that offer some surprising value. With Stinious' BOM down in the $1 range in even modest volume the need to solder all those tiny packages could be eliminated.
Another fine point, the resistors along the rails are in a 2,1,3 ratio so 6 resistors of the same (~125 Ohm) value off of the same reel would eliminate having to only get close on the ratios. I would use either 124 or 127 Ohms. It adds 3 resistors but eliminates 2 values. In any case the 375 Ohm ones are not critical so doing this at the input only adds one resistor.
A thought occured to me last night, there are several build to print houses in Taiwan that offer some surprising value. With Stinious' BOM down in the $1 range in even modest volume the need to solder all those tiny packages could be eliminated.
Another fine point, the resistors along the rails are in a 2,1,3 ratio so 6 resistors of the same (~125 Ohm) value off of the same reel would eliminate having to only get close on the ratios. I would use either 124 or 127 Ohms. It adds 3 resistors but eliminates 2 values. In any case the 375 Ohm ones are not critical so doing this at the input only adds one resistor.
thats an interesting idea mate, but I actually think its a good opportunity for some of these guys that are seasoned veterans otherwise, but are a bit scared of SMD to get to know the new packages they will have to be dealing with, on a small scale project with not many parts, easy to troubleshoot and not much of a loss if it goes up in smoke. some of course are totally comfortable with it, but some could use a push IMO.
I mean no disrespect here, many are much more accomplished DIYers than I am, just not so comfortable with SMD and these are small, but really not very difficult parts to solder
I mean no disrespect here, many are much more accomplished DIYers than I am, just not so comfortable with SMD and these are small, but really not very difficult parts to solder
BC846BPN ?? How well matched are these complementary devices? They are obviously on the same substrate. Probably more matched that trying to match them ourselves??? Also the resistors around the diff amp: How well matched should those be: .01, .001?? Also I would like to know which transistors need to be thermally coupled to the output transistors. It seems this has been redrawn to suit each contributor and I'd like to stick to Scott's latest schematic. I know that diff amps and constant current sources and sinks if they are current mirrors need to be matched and thermally coupled to not drift. Obviously this simulation will need to be built and go through a parts substitution phase before it is safe to order parts? Waiting in the wings. Very enthused and interested! Ray
http://www.nxp.com/documents/data_sheet/BC846BPN.pdf
They appear to have done an admirable job of matching current gains and base-emitter voltages in the vicinity of 2mA Ic. However, the statement early on in the datasheet, "no mutual interference between the transistors", suggests that they are NOT on the same substrate.
Unless it's SOI. Note there are no side to side specs. I think I will order some and give a look, if anyone has some a fine sandpaper disk in a Dremel should be enough to see if there are one or two die.
Matching BF862
Hello Scott,
I feel like I'm asking a stupid question but the input stage of the discrete opamp is a pair of BF862 don't these need to be matched for optimum performance. How do you get matched parts , I suspect matching these smd parts is not so simple and a lot of work. If this aspect has been covered in this thread could somebody point me to it.
Arthur
Hello Scott,
I feel like I'm asking a stupid question but the input stage of the discrete opamp is a pair of BF862 don't these need to be matched for optimum performance. How do you get matched parts , I suspect matching these smd parts is not so simple and a lot of work. If this aspect has been covered in this thread could somebody point me to it.
Arthur
Unfortunately, test sockets for SOT-23 devices are expensive. I recently bought one for about 35 dollars iirc and specifically to match parts like the BF862. Ideally, sort them for Idss and threshold voltage, and make sure to put some damping R in series with the gate lead connection to prevent high frequency oscillations.
But testing and sorting is tedious, no doubt about it.
The LSK389 works almost as well for those who can't bother. I took a PC board with some pads at SOT23 spacing and set it up to measure Idss. Using a plastic tweezers I pressed the parts down one at a time, you can do almost a whole tube in less than an hour. The plastic is both non-conductive and prevents finger heating.