Hartono, you have a good understanding of low noise fets, but some others here don't, and they are unwilling to take my word for it. If you wish to lay it out for them, I don't mind, but I like to just give answers and leave the classroom 'proofs' to others.
john curl said:
It does depend on the cartridge, and I would say that your
comment is more true now than then. We assumed a maximum
input impedance of 100 ohms, and had different inputs for
lesser values.
I did have a dissected copy of the JC-1 (not easy teasing the
devices from the epoxy) but of course I would never copy
anything of yours...
😎
Nelson Pass said:
That's for sure and the same is for JFET input stage opamps, compared to BJT ones.
"If you wish to lay it out for them, I don't mind"
Mr Curl, I'm not that knowledgeable. still learning.
Hartono
Mr Curl, I'm not that knowledgeable. still learning.
Hartono
IF3601(single) and IF3602 (dual) JFETs from InterFET have typical 0.3nV/rtHz @100Hz and 5mA . These are mighty expensive, thought!
x-pro
x-pro
2SK369 for as low as 2 quarters, and that's about 15 times cheaper than the price of an MAT03 or an MAT02 cost (me) two decades ago, some folks even bothered to build phono stages with MAT03/MAT02 in parallel back then.(The A versions as listed on the AD schematic)
Maybe Mr Curl can estimate what the cost of the Vendetta phono would have amounted to if he had gone for low noise matched AD parts.
Seemed to me that the initial Vendetta research msrp was on the optimistic side anyway.
Maybe Mr Curl can estimate what the cost of the Vendetta phono would have amounted to if he had gone for low noise matched AD parts.
Seemed to me that the initial Vendetta research msrp was on the optimistic side anyway.
So is a 2SC2547, question is what will be cheaper in serial manufacture ?
oft:
Mr Curl, the BT that's for sale on Audiogon has the initials JDG.
Was it made for Jeff or are those the initials of the person who's offering it coincidently ?
oft:
Mr Curl, the BT that's for sale on Audiogon has the initials JDG.
Was it made for Jeff or are those the initials of the person who's offering it coincidently ?
x-pro said:
Thanks X-pro.
I wasn't aware of the existence of these devices. So probably, they are the winners, that is, if you don't mind a max. offset of 100mV. Any idea how much they cost?
BTW, the subject has apparently changed from a theoretical point of view to more practical design issues, in particular
/ dBnNevertheless, I insist that it is NOT a good idea to replace the input BJTs in Glen's design by JFETs for quite an other reason. As he's using a full-complementary topology, it's important that gm of the two LTP's are equal (<1%), otherwise the two VASes started to "fight each other". This condition is easily met with BJT's but not with JFETs, as full-complementary JFETs are hard to find (as far as I know).
Cheers, Edmond.
Wow! You folks know how to 'dance' around a design problem! ;-)
I did NOT say that bipolar transistors cannot be quiet. In fact, if you took my patented design and used the very quietest bipolar transistors available today, the input noise might be as low as .2nV/rt Hz.
However, I used the quietest devices that were known at the time, and 'only' got .4nV/rt Hz back in 1973. Yes, 1/3 century ago!
With a very low impedance input, the very best bipolar transistor always has a slight advantage, BUT the FET will win over a wide range of input impedances, and this can be useful with amps and preamps of all kinds to keep the input stage quiet. Does anyone know why?
I did NOT say that bipolar transistors cannot be quiet. In fact, if you took my patented design and used the very quietest bipolar transistors available today, the input noise might be as low as .2nV/rt Hz.
However, I used the quietest devices that were known at the time, and 'only' got .4nV/rt Hz back in 1973. Yes, 1/3 century ago!
With a very low impedance input, the very best bipolar transistor always has a slight advantage, BUT the FET will win over a wide range of input impedances, and this can be useful with amps and preamps of all kinds to keep the input stage quiet. Does anyone know why?
> IF3601(single) and IF3602 (dual) JFETs from InterFET have typical 0.3nV/rtHz @100Hz and 5mA . These are mighty expensive, thought!
And enormous capacitances.
I have a pair. I still have not figured out how to use them as input diff pairs, yet (even with cascode and degeneration).
Patrick
And enormous capacitances.
I have a pair. I still have not figured out how to use them as input diff pairs, yet (even with cascode and degeneration).
Patrick
Glen, why is Estuart's contention that your input stage is always balanced with respect to input stage gain in the complementary device pairs, bogus? Hint: Think servo. ;-)
Yes, input capacitance can be a problem. However, with low source impedances, capacitance usually is not very important. However, cascoding input fets can be very useful and important to prevent capacitance multiplication due to Miller effect.
Posted by Mr. J.Curl -----------> "BUT the FET will win over a wide range of input impedances, and this can be useful with amps and preamps of all kinds to keep the input stage quiet. Does anyone know why?"
input current noise (looking at textbook)
yawn.....
Hartono
input current noise (looking at textbook)
yawn.....
Hartono
I agree with JC. In a real world situation, JFET input is much more universal. The BJT input Vn advantage is more less academic only. The large In for common Zout of previous stage is a real problem.
Regarding input capacitance - I do not think it is a big issue. For many good reasons, it is advantageous to buffer outputs of link stages and keep their output impedance low.
What about small signal MOSFETs for input? I think I have only come across one or two amp schematics using them, so I suppose they have some obvious disadvantage that I haven't realized.