Further refinements of the BOM. No changes to the component lists.
Also an early version of the kit instructions, just as a sample work-in-progress.
Also an early version of the kit instructions, just as a sample work-in-progress.
Have you made even a first attempt to determine that the J113 FET's have a suitable noise performance?
It's right there in the datasheet. The noise performance is broadly comparable using an audio op amp for the same purpose. A little better at high frequency, the same or perhaps a little worse at low frequencies. I've shown a bipolar op amp by way of example, a FET input type like the OPA134 is a little worse again.
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I meant actually measure a few typical samples. They are not speced for audio and other Fairchild switches need to be screened for audio frequency noise i.e. the spec is typical not guaranteed. For some parts the opposite is true the data sheet looks bad but the yield to low noise is excellent, BF862 for instance.
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Hi Scott,
That the J113 is marketed as a switch was a area of concern. We'll just have to see how it plays out, while hoping that the datasheet is a reasonable approximation of actual performance.
I certainly will be able to confirm the noise floor once I have the first prototype running. This should be in a week or so.
That the J113 is marketed as a switch was a area of concern. We'll just have to see how it plays out, while hoping that the datasheet is a reasonable approximation of actual performance.
I certainly will be able to confirm the noise floor once I have the first prototype running. This should be in a week or so.
a9 BOM
Fix: in previous BOM resistor R7 part number was incorrectly given as the 221 ohm resistor rather than 221 kohms.
Fix: in previous BOM resistor R7 part number was incorrectly given as the 221 ohm resistor rather than 221 kohms.
This would interest you.
http://www.tubecad.com/2004/AikidoAmp12.gif
Aikido Tube Amplifiers
It has good PSRR without using a CCS.
Instead it feeds the PS noise to both top & bottom FET of the follower for self cancellation.
Very clever.
Patrick
http://www.tubecad.com/2004/AikidoAmp12.gif
Aikido Tube Amplifiers
It has good PSRR without using a CCS.
Instead it feeds the PS noise to both top & bottom FET of the follower for self cancellation.
Very clever.
Patrick
Ok, real quick: a sketch-up of the circuit in the previous post.
note the original circuit is missing the source resistor on the input jfet, I, uh, took the liberty of fixing that. 🙂
(You can also deconstruct the circuit back to the CrystalFET by removing the two CSS stages. You can see the distortion is very similar. Basically what you get for your pains is about 12 dB of PSRR and the ability to run at much lower supply voltages.)
note the original circuit is missing the source resistor on the input jfet, I, uh, took the liberty of fixing that. 🙂
(You can also deconstruct the circuit back to the CrystalFET by removing the two CSS stages. You can see the distortion is very similar. Basically what you get for your pains is about 12 dB of PSRR and the ability to run at much lower supply voltages.)
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> I like the look of the other variant even more.
You will change the sonic signature using a high NFB as that one.
Might as well use an opamp then.
Patrick
You will change the sonic signature using a high NFB as that one.
Might as well use an opamp then.
Patrick
It's only about 12 dB of global feedback. But on a wider front I absolutely agree with you: some circuit topologies are best kept for what they are, optimized with only a light hand. Throw in the kitchen sink to "improve performance" and the results rarely satisfy.
Oops!
I made an error when transferring the LTspice circuit to Eagle.
Boards need a re-spin. The fix is easy enough, but doing another run will take some time.
Existing boards can be fixed with a trace cut and a couple of flying leads.
I made an error when transferring the LTspice circuit to Eagle.
Boards need a re-spin. The fix is easy enough, but doing another run will take some time.
Existing boards can be fixed with a trace cut and a couple of flying leads.
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And here it is powered up, DC bias operational state but no signal wiring.
Mosfet regulator section works as expected. R20 full CCW V+ is about 15-20 V, adjusts to 35 V after a few turns CW. Output voltage falls about 1~1.5 V after being powered up for a few minutes. Current source output 30 mA, about 20% less than simulation, probably because the transistors used are different types.
I found the jfets bias a little hotter current than calculated, pulling the drain voltages to between 7~8 V when 9~10 V was calculated. I'm not sure why, but it's pretty close and can be easily redressed by decreasing R2 and R8 a little.
Mosfet regulator section works as expected. R20 full CCW V+ is about 15-20 V, adjusts to 35 V after a few turns CW. Output voltage falls about 1~1.5 V after being powered up for a few minutes. Current source output 30 mA, about 20% less than simulation, probably because the transistors used are different types.
I found the jfets bias a little hotter current than calculated, pulling the drain voltages to between 7~8 V when 9~10 V was calculated. I'm not sure why, but it's pretty close and can be easily redressed by decreasing R2 and R8 a little.
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