Power supply options?

[stevew_w]

I have done a few successful tweeks to my NAC 72 mainly with better capacitors. The 72 is currently powered by a HiCap.

Following various threads on this forum and other articles on other sites it appears that improvements can be made by improving the power supply arrangements for the 72. The problem is that some of this information has been contradictory

I think I have norrowed the options down to:

1) A pair of super regs inside the 72, one for each feed from the HiCap

2) 4 LT1086, one for each board. May be using a voltage ref (LM4040DIZ-10) instead of a resistor to set the voltage.

3) Gyrator on each board a la Les W Avondale

Comments please...

 

[teddy_pardo]

If you do #1 and #3 you don't really need #2 (IMHO)

For the Gyrator, instead of the single transistor build a darlington from two transistors (almost any couple of small size NPN transistors will do), use much larger resistor values than sugessted by Les diagram (>50K), use film capacitors of 3uF or more (polypropylene or polyester).

If you do #3 right, you may even not need #1, but others may argue...

 

[stevew_w]

Thanks for the reply

For the gyrator:

To keep things small how about using a darlington pair device e.g. ZTX605 ?

I have some spare Evox Rifa 10uF MMK caps, would these work OK ?

Anyone have any formulas for using gyrators? Voltage drop, resistor size etc?

Anyone got a rough idea how much current the 321 & 729 boards require?

 

[teddy_pardo]

Monolithic Darlingtons usually have an internal resistor that makes them faster in some situations but decreases their hfe in low currents, which is the case in preamps. My advise, build your own from two transistors.

The 10uF MMK are very good, I use them too.

For a Darlington, if you don't have a resistor between the base and the ground, the dropout is about 1.2-1.4V. If you encounter above 2.0V I'd suggest reducing the value of the resistor between the collector and the base. Basically, the current on this resistor is the output current divided by the hfe. One channel of a Naim preamp uses about 100mA, a good home made darlington has an hfe of 100,000, so a resistor of 100K will only add 0.1V dropout.

If you're looking for more dropout use a resistor between the base and the ground, it will make a voltage divider.