I hope the mini beast uses through-hole parts.
Well, I discovered that SMD is not really much harder to solder than through hole
It may actually be much faster too, no wires to cut
The original "Beast" is made of multiple push-pull stages so with both N and P channel JEFTs?
The Beast we try to make here will be a single ended beast?
How do we drive all those jfets? …..will they need an input stage as driver? ….or is the input impedance that high that 2000 in parallel is still very high so a normal preamp can drive them?
The Beast we try to make here will be a single ended beast?
How do we drive all those jfets? …..will they need an input stage as driver? ….or is the input impedance that high that 2000 in parallel is still very high so a normal preamp can drive them?
Problem is there are no more complementary low noise JFETs in production, that's why I'm contemplating a B1 style beast, in order to use N-channel only (2SK209) which are still in production
I don't see a problem driving them, this design is quintessentially a buffer isn't it ?
Igss = -1nA
so 1000 in parallel will be 1mA, I think it's OK
I'd just plug it straight to the CD player
.....or actually use the soldered band described above as the interconnect between the CD-player and the speakers lol
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In the FirstWatt article there is written this about driving them:
"A word about input capacitance. The Jfet pairs here have an input capacitance of about 38 pF, and as you start paralleling them up, you multiply this value, Fortunately, running balanced results in halving the ultimate values, but in the end the two 294 pair in series works out to about 5.5 nF capacitance as an input, or about 5 times the old IHF standard.
If you wish to get the performance presented, a 50 ohm source will get you about 600 Khz bandwidth, but a 600 ohm source will roll off at 50 Khz. I run about 100 or 200 ohm sources, so I don't have much problem with this, however I did consider the possibility that this would not be acceptable to someone (isn't that always the case?).
So I provisioned the circuit board so that first cell of each rank of 21 Jfet pairs can be set up as a driver to the remaining 20 simply by strapping that section accordingly. This way the input capacitance is reduce by a factor of about 20, down to around 250 pF, and allowing for a 1 megahertz bandwith with a 600 ohm balanced source.
The same people who might complain about the capacitance might also complain about the added complexity of drivers. Well, you can't have it all. I have listened to and measured it both ways, and I find it comes out about the same."
So there is a driver pr. row…...a schematic about this may tell a bit more.....how it is done. Probably obvious for the more experienced guys inhere…..
70W peak into 2 ohm...….not bad....
"A word about input capacitance. The Jfet pairs here have an input capacitance of about 38 pF, and as you start paralleling them up, you multiply this value, Fortunately, running balanced results in halving the ultimate values, but in the end the two 294 pair in series works out to about 5.5 nF capacitance as an input, or about 5 times the old IHF standard.
If you wish to get the performance presented, a 50 ohm source will get you about 600 Khz bandwidth, but a 600 ohm source will roll off at 50 Khz. I run about 100 or 200 ohm sources, so I don't have much problem with this, however I did consider the possibility that this would not be acceptable to someone (isn't that always the case?).
So I provisioned the circuit board so that first cell of each rank of 21 Jfet pairs can be set up as a driver to the remaining 20 simply by strapping that section accordingly. This way the input capacitance is reduce by a factor of about 20, down to around 250 pF, and allowing for a 1 megahertz bandwith with a 600 ohm balanced source.
The same people who might complain about the capacitance might also complain about the added complexity of drivers. Well, you can't have it all. I have listened to and measured it both ways, and I find it comes out about the same."
So there is a driver pr. row…...a schematic about this may tell a bit more.....how it is done. Probably obvious for the more experienced guys inhere…..
70W peak into 2 ohm...….not bad....
Ok.....then pre-amp will only drive the parallel drivers which is much less…..but still many. Lets us see if this turns out to be a project. Previously this project has been done also with only one type of jfet:
BF862 based SE Class A Headamp without the HEAT
A small amp to begin with could be a nice way to test the concept.
BF862 based SE Class A Headamp without the HEAT
A small amp to begin with could be a nice way to test the concept.
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