[sdiy] 2SK170 FET alternative - more info

[Seb Francis]

By the way, the FET's purpose is described in the design note as ...

"a FET to buffer the [storage] capacitor's voltage"


Seb Francis wrote:

> Hi,
>
> I'm building a compressor based on this circuit:
> http://www.thatcorp.com/datashts/dn115.pdf
>
> It uses a 2SK170 FET as part of the adjustable attack/release bit in 
> between the RMS level detector and VCA.
>
> Neither of my 2 regular shops stock this FET, and while I'm sure I'd 
> be able to track one down, I'm wondering if a 2SK30A-Y would work 
> instead. They look fairly similar from the datasheet, but unfortunatly 
> my experience of FETs is pretty non-existant, so I wonder if some kind 
> person could cast a quick glance at these specs and tell me in what 
> situations the differences would matter (or not)..
>
> 2SK170
> Gate cut-off current IGSS = −1 nA (max) (VGS = −30 V)
> Drain current IDSS = 2.6 to 20 mA (the FET suffix isn't specified on 
> the schematic so I can't be more specific about this)
> Gate-source cut-off voltage VGS (OFF) = -0.2 to -1.5V
> Forward transfer admittance Yfs = 22mS typ
> Input capacitance Ciss = 30pF typ
> Reverse transfer capacitance Crss = 6pF typ
> Noise figure NF = 0.5dB typ or 1.0dB typ
>
> 2SK30A-Y
> Gate cut-off current IGSS = −1 nA (max) (VGS = −30 V)
> Drain current IDSS = 1.2 to 3 mA (this is for the Y suffix that I have)
> Gate-source cut-off voltage VGS (OFF) = -0.4 to -5.0V
> Forward transfer admittance Yfs = 1.2mS min
> Input capacitance Ciss = 8.2pF typ
> Reverse transfer capacitance Crss = 2.6pF typ
> Noise figure NF = 0.5dB typ
>
> The max ratings look very similar apart from the drain power 
> dissipation which is 4x higher (400mW) for the 2SK170, but I don't 
> think I'm going to be running the device anywhere near its max ratings.
>
> Seb
>
>