Post from Scott: "I thought from reading the audio reviews Boulder has superceeded the CTC BT anyway with discrete op-amp modules (Dick Burwen did it first but that's another story) and more than doubled the price point. So I think we should do a group discrete op-amp and give it free to the community." {my bold}
Back when transistors cost a lot of money, circa 1970, I had a "supervisor" (a grad student with an instrumentation bent --- I was hired so he would have to focus on his dissertation) who got to the point that he would specify how many of them I could use.
Transistors, most of them, are not that expensive anymore. And most are also very good.
Just for fun how about lateral MOSFET output stage? Charles Hansen swears by them 😀 I don't know how available they are though, perhaps CH already cornered the market.
Semelab makes laterals that are similar to Hitachi-Renaisas. They are quite big but can be used in line stages too.
There are complementariness two.
Renaissas made them since two years ago so there should be some.http://documentation.renesas.com/doc/products/transistor/rej03g0122_2sj76ds.pdf
Renaissas made them since two years ago so there should be some.http://documentation.renesas.com/doc/products/transistor/rej03g0122_2sj76ds.pdf
Topology
I have built and bought numerous broadcast components utilizing the venerable 990 (some still operating 24/7 after 30 years!!!), and it still is a decent design, especially with regards to drive capability, stability, and speed of overload recovery into different line loads (300M+ of quad-star cable...😱). I have often thought it would be great have an updated design, considering how much better semis are these days than they were in the 990's day in the 70's.
Since Scott has also been so intimate with the limitations of IC processes and he posed the idea; I too would like to see what he and John and you other geniuses do when size/power/heat dissipation limitations are relaxed.🙄 Not to the extent that we end up with a power amp, but a true no-holds barred line-level opamp. Sort of a logical continuation of the BT thread which gave this one life...
Just my $0.02 worth as usual...
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
I believe that the design exercise posed by Scott would be best expressed as a topological exercise. From this perspective, the size and parts count should not be a constraint, because if you want small, well, we already know we can do REALLY well with just a tiny chip.
I have built and bought numerous broadcast components utilizing the venerable 990 (some still operating 24/7 after 30 years!!!), and it still is a decent design, especially with regards to drive capability, stability, and speed of overload recovery into different line loads (300M+ of quad-star cable...😱). I have often thought it would be great have an updated design, considering how much better semis are these days than they were in the 990's day in the 70's.
Since Scott has also been so intimate with the limitations of IC processes and he posed the idea; I too would like to see what he and John and you other geniuses do when size/power/heat dissipation limitations are relaxed.🙄 Not to the extent that we end up with a power amp, but a true no-holds barred line-level opamp. Sort of a logical continuation of the BT thread which gave this one life...
Just my $0.02 worth as usual...
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
Maybe Toshiba made them too but this is a long time ago. They are pretty good though.
I use them in my privat line stage on very high idle.
I like laterals a lot. Very easy to design with.
i use them not as followers though but use the drain output. They are awesome constant current sources but Gm is not particular steep.
I use them in my privat line stage on very high idle.
I like laterals a lot. Very easy to design with.
i use them not as followers though but use the drain output. They are awesome constant current sources but Gm is not particular steep.
at op amp V, even audio line driving should be fine with few 100 MHz BJT - maybe SO-223 package for a few watts of power
the gm, parasitic C will be better than available (oversize die for the current) MOSFETs
even if the Beta isn't "infinite"
of course I'd really use the TPA6120/THS6012 DSL driver chip with GHz BJT - as a complete looped feedback amp you can have a V gain of 10x, @ 100 MHz, and with 400 mA output current, uA input the "beta" is pretty high too
the gm, parasitic C will be better than available (oversize die for the current) MOSFETs
even if the Beta isn't "infinite"
of course I'd really use the TPA6120/THS6012 DSL driver chip with GHz BJT - as a complete looped feedback amp you can have a V gain of 10x, @ 100 MHz, and with 400 mA output current, uA input the "beta" is pretty high too
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Digikey is listing both the J76 and K213 series as obsolete. So that looks like a dead end then.
Toshiba has some high-gm FETs (even better on paper than Renesas) but they're rather low voltage and have higher thresholds than the laterals. Along with negative Vgs threshold temp coeff.