Yep, the new Grado is quite a strange MM animal. Can't imagine how they got to 2ohm and 2mH, that sounds pretty odd to me.
Power supply
I have decided to do a PCB for the raw power supply (rather than using perf board and wiring). See the attached pictures.
Testing went very well, 0.28-0.3nV/rtHz and 0.008% distortions at all frequencies and output levels up to 40Vpp. I also got only 25uV output hum (input shorted), before even throwing everything in the steel case. This is an excellent level, equivalent to 2.5nV input hum. It's actually a little better than HPS3.1 in the same stage (before case), probably because of a better layout of the input stage. But the key to low hum is the dual mono construction and the ground loop(s) handling, as described on my web site under "wiring".
I have decided to do a PCB for the raw power supply (rather than using perf board and wiring). See the attached pictures.
Testing went very well, 0.28-0.3nV/rtHz and 0.008% distortions at all frequencies and output levels up to 40Vpp. I also got only 25uV output hum (input shorted), before even throwing everything in the steel case. This is an excellent level, equivalent to 2.5nV input hum. It's actually a little better than HPS3.1 in the same stage (before case), probably because of a better layout of the input stage. But the key to low hum is the dual mono construction and the ground loop(s) handling, as described on my web site under "wiring".
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http://www.synaesthesia.ca the Low Noise Designs part was updated with HPS4.1 schematics, Gerbers, comments, etc... Measurements to follow ASAP (they were mostly posted here, anyway).
Comments welcomed, as usual.
Comments welcomed, as usual.
http://www.synaesthesia.ca the Low Noise Measurements page was updated with the HPS 4.1 measurements.
Currently, continuing the listening tests. So far, I was able to identify two significant differences to HPS 3.1: low level resolution/imaging and the vinyl noise handling.
Compared to HPS 3.1, I like better HPS 4.1 at low listening levels. It seems to have better resolution/imaging. With HPS 3.1 I can't resist turning up the volume
Pops are, to me, better handled by HPS 3.1. The entire vinyl noise appears more distinctly in HPS 4.1. HPS 3.1 has a more "soothing" effect on the vinyl noise. I guess it's related to the head amp pulse response (less overshooting in HPS 3.1) because this changes with the MC capacitive loading. 47Kohm/220pF is HPS 3.1 is audibly equivalent to 47Kohm/470pF in HPS 4.1. But also switching both to 100ohm input impedance levels the field?!
I'll invite a few friends to capture their opinions as well, then I'll draw the conclusions of this exercise. HPS 5.0 will be a new generation of Peltier cooled devices...
Currently, continuing the listening tests. So far, I was able to identify two significant differences to HPS 3.1: low level resolution/imaging and the vinyl noise handling.
Compared to HPS 3.1, I like better HPS 4.1 at low listening levels. It seems to have better resolution/imaging. With HPS 3.1 I can't resist turning up the volume
Pops are, to me, better handled by HPS 3.1. The entire vinyl noise appears more distinctly in HPS 4.1. HPS 3.1 has a more "soothing" effect on the vinyl noise. I guess it's related to the head amp pulse response (less overshooting in HPS 3.1) because this changes with the MC capacitive loading. 47Kohm/220pF is HPS 3.1 is audibly equivalent to 47Kohm/470pF in HPS 4.1. But also switching both to 100ohm input impedance levels the field?!
I'll invite a few friends to capture their opinions as well, then I'll draw the conclusions of this exercise. HPS 5.0 will be a new generation of Peltier cooled devices...
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HPS 5.0 is going to use BF862 in SMD. Probably the best low noise JFET available today, so sorry a P-channel equivalent doesn't exist...
You have to compare the equivalent paralleled BF862's to that FET. The gm/C is the important figure of merit.
Yup, last time I've checked it was $50 a pop, in quantities.
BF862, I got 200 pcs for half of that. All you would save with Interfet is SMD soldering points, paralleled BF862 for the same transconductance are, performance wise, significantly better.
The point was to enable everyone to DIY something of real performance. BF862's typically equal 2SK170's on noise at 1/3 the C's. Yes there is a risk as the noise is not guaranteed, but they can be had for as little as .05$. A front end that requires $50 FETs (invariably only available as part of a group buy) is another matter entirely.
On a technical point the Interfet C's are specified at a reverse bias of 4V. Depending on junction grading this can be only 25-33% of the extrapolated zero bias capacitance (the SPICE parameter). Still 200mS at 5mA is impressive in a single package.
On a technical point the Interfet C's are specified at a reverse bias of 4V. Depending on junction grading this can be only 25-33% of the extrapolated zero bias capacitance (the SPICE parameter). Still 200mS at 5mA is impressive in a single package.
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