james - shunt reg q

[dave dove]

was talking to nick the other day
and now i'm confused
so

with your bouncy shunt reg design

do i need to shunt 120% of idle current
or
120% of signal current
and if the latter
how do i calculate it

dave

[James D]

For SE the best sound is when you shunt 120% of the idle current... for PP its about 50% of idle current

ciao

James

[dave dove]

)^&(£)&_^_%6

[Andrew]

Hey Dave,

Is it for a phono? Then somewhere between signal current double the signal current should be more than enough. As James said elsewhere, there's usually quite a bit of standing current in a phono by keeping gm high and noise down, no point shunting this - as its a fixed load.

cheers,

-- Andrew

[James D]

But you can start from about 50% of the idle current and work upwards as and when able. Just make sure you have some good capacitance before it to buffer the shunt when it runs out of current on peaks...

As with all music most of the time the amp is cruising at 20% of peak or less and thats where the shunt works best - of course it helps deliver clean peaks and cleans up after the peak really well if you have the current capacity in the shunt but it is still worth doing if you can get to 50% of idle current - or there abouts...

Andrews point is accurate for some/most phono's but ones that run at 2 or 3 mA per stage should have full idle current shunt reg

James

[Andrew]

Hi Dave and James,

Of course my mind is on the the 1k5, you are, as usual, quite correct!

cheers,

-- Andrew

[NickG]

Now I am getting more confused, why is a SE output stage stage best at 120% when there is a big inductor to reduce the variation in current, whereas in a phono SE stage, where there is no inductor and the PSRR is higher because of that, and you have huge gain, especially at low frequencies, less is ok?

I can see the point of 120% if you are actually regulating the DC voltage, but I thought the shunt was only operating at AC in this case, and at DC was just a constant current load,

Confused of Halifax.

[dave dove]

andrew

no
already done the phono
just trying various choke:cap combos

chaps

for a few moments there was light
now i find myself all damp + extinguished
slapped by a wet herring or something.....
that's 560mA current plus headroom for the tx

dave