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JFET-MOSFET headphone amplifier J-Mo 3
JFET-MOSFET headphone amplifier J-Mo 3
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Old 2nd August 2017, 04:56 PM   #11
ammel68 is offline ammel68  United States
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JFET-MOSFET headphone amplifier J-Mo 3
It's been pointed out before in the PS section to NOT use large(1kuF) after any LM-series regs.

I asked about it specifically after receiving a Chinese board that used 1kuF output caps.
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Old 2nd August 2017, 11:20 PM   #12
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JFET-MOSFET headphone amplifier J-Mo 3
The main boards already call for 1000 uF, so this cap just brings the total output capacitance for a stereo build up from 2000 uF to 3000 uF.

I remember there was some discussion of IC V-regs showing peaking when loaded with over 220 uF output capacitance.

While in general I agree with keeping capacitance on the light side, I'd recommend scaling that estimate according to the circuit current draw. If you would use 100 uF with an op amp at 5 mA for example, a circuit drawing 100 mA should see 2000 uF.
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Old 3rd August 2017, 02:59 AM   #13
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JFET-MOSFET headphone amplifier J-Mo 3
A MOSFET shunt-source voltage regulator, with better PSRR than your typical ICs. Under development.

Originally used configured as a phono stage power supply.
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Old 3rd August 2017, 04:49 AM   #14
ammel68 is offline ammel68  United States
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JFET-MOSFET headphone amplifier J-Mo 3
Yeah, I think a shunt regulator will be a better option than LM-series regulators with large output caps hung out on the end of them.

Having just built and tried the Jung/Didden super regulators with several circuits, the SQ is definitely improved over LM-series regulators at the expensive of added complexity.
Not sure how your MOSFET shunt-source regulator compares to the Jung regulator, though.

Press on Richard!
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Old 3rd August 2017, 01:37 PM   #15
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JFET-MOSFET headphone amplifier J-Mo 3
I have a question.

About the heatsinks - they have two retaining pins which in Eagle can be connected to circuit elements. Is it better to ground the heatsinks or leave them disconnected from the circuit? The former will require isolation from the MOSFETs, the latter allows the fet substrate to be in electrical contact with the heatsink...
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Old 3rd August 2017, 01:51 PM   #16
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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Default Suggestion

Why not to add a decoupling cap in series, at the signal input on board, for safety reasons?
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Old 3rd August 2017, 05:38 PM   #17
ammel68 is offline ammel68  United States
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JFET-MOSFET headphone amplifier J-Mo 3
Quote:
Originally Posted by rjm View Post
I have a question.

About the heatsinks - they have two retaining pins which in Eagle can be connected to circuit elements. Is it better to ground the heatsinks or leave them disconnected from the circuit? The former will require isolation from the MOSFETs, the latter allows the fet substrate to be in electrical contact with the heatsink...
I've always left the retaining pin pads disconnected from the circuit altogether.
Why would you want to ground them?
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Old 3rd August 2017, 05:53 PM   #18
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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I always ground any heatsink in order to KNOW its potential. Leaving it unconnected may lead to confusion. Also, it (most of the times) cooperate reducing EMI in switching devices.
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Old 3rd August 2017, 06:16 PM   #19
JPS64 is offline JPS64  Germany
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JFET-MOSFET headphone amplifier J-Mo 3
Osvaldo de Banfield is right, ground heatsink.

V+ to capacitors then dispatched. Electrolytics to place considering COM as return.

Still in process and progress, a lot to do...

JP
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Old 3rd August 2017, 11:11 PM   #20
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JFET-MOSFET headphone amplifier J-Mo 3
Quote:
Originally Posted by Osvaldo de Banfield View Post
Why not to add a decoupling cap in series, at the signal input on board, for safety reasons?
Unless I'm misreading what you are suggesting, I don't see the need as the output of the circuit is not DC coupled. There is no way to damage the headphones leaving the input DC coupled, and the JFET has no gate current that needs to be isolated from the volume control.

re. the heatsink connection, I detect some difference in opinion in line with my own waffling ... I see the arguments for grounding it, but I also see its unlikely to offer much real world advantage. I suppose it comes down to whether anyone is likely to want to mount the FETs to the heatsink without electrical insulation.
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