Keantoken's CFP cap multiplier

Jump to Latest
keantoken

keantoken

Member
Joined 2006
I know that Jung uses it in "Don't Shunt the Shunt Regulator". But it's outdated and uses the ancient 2N3638. Does it make sense that lower noise transistors will make lower noise references when reverse biased like this?

I think I remember there being another app note or something by Jung where he does this again with a more modern transistor.

- keantoken
 
H

HiFiNutNut

Member
Joined 2004
I spent a day experimenting my Marantz SACD player with the K-Multiplier.

I have to say that I like the resistor (47R) much better than the jFET (2SK170BL with Idss=11.2mA) at R1 position. I have no technical explanation. To me the resistor version sounds correct and more musical, while with jFET it sounds a bit harsh. I have 47R for R1 now. I have not compared different values of resistance, but only compared the resistance to jFET. The result was so obvious that repeatitions were not needed.

Bad jFET?
 
Last edited:
keantoken

keantoken

Member
Joined 2006
1/4W resistors will work for all resistors.

The capacitors I used for the 1000uF cap are Panasonic FC (25V), but I don't know how much it matters. The output decoupling can be film, I tested with polypropylene snubbers and 6.8uF polycarbonates here.

- keantoken
 
Last edited:
keantoken

keantoken

Member
Joined 2006
To get the low output impedance specs I gave, you need 15-17mA through the driver transistor. Output impedance is directly related to the quiescent of the driver (bigger is better). Try not to go above 20mA, because this is the onset of beta droop for the BC550/560. So say the outputs have an Hfe of 100 and your load draws max 300mA. Well give some headroom by biasing the driver 3mA lower, at 17mA.

Zout is impacted dramatically by the driver bias current. IE, for 1mA it's 800mR and for 10mA it's 80mR, or you get the idea.

- keantoken
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Slang for Mouser among DIYers. So I just found J109 is available at Mickey's. It has 40mA IDSS @ 15V VDS. He can get that and degenerate with a source to gate resistor. Taking current from the gate node. How much VDS will it see in your CCT?
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Abort!:) Revert to a resistor. J111 is -3 to -10V Vgs(off). Bill in Australia could put a K170BL 11mA (just about for adequate pinch off) but still did not like it if you remember. That ties with your explanation that just 10-11mA to 17mA recommended impacts the Zo of the complementary Darlington negatively, since each mA in the driver counts in lowering Zo enough.
 
You must log in or register to reply here.
Top Bottom