Lower noise floor tweak for Extended Foreplay III

[Doc B.]

PJ and I have been studying the limits of noise floor administration on the Extended FPIII after my 2007 CES experience, where four extended FPIIIs were running into Pass Labs amps with a whopping 26dB of gain in the TAD room. While our own amps are all well below 20dB of gain, some SS amps have crazy levels of gain like this, and in these cases a wee bit of white noise from the shunt regulated, actuve loaded cathode follower can be heard when you stand close the the speakers.

After a bit of analysis PJ came up with something to try. We tack soldered one of the original brown 2.2 uF caps that come with the stock FPIII in parallel with each of the two 147K resistors on the shunt regulator PC board (the middle board). Made for an audible improvement in noise floor, and does not seem to degrade the sound.

[trioid]

Hi Doc:

So, even if I have a low gain amp (say on the order of 15 db), there would be no disadvantage to doing this tweak, right?

Cheers
Jim

[Doc B.]

I have not experienced any disadvantage. But you should probably try it yourself and form your own opinion since it takes all of ten minutes to put the caps in.

[trioid]

I think this is a good thing to do, based on what I hear (my system, my ears).

[grufti]

Doc, I am thinking this would be applicable for any Bottlehead regulated power supply.  

Are the brown 2.2uF caps the stock output coupling caps?  And for the Extended Foreplay III, is the 147k Ohm resistor the resistor above or below the reference input of the three pin regulator?  I don't have an Extended schematic but I'm looking at the Eros schematic.  Eros has two resistors, one "above" and one "below" the reference input.

On the new board what component, label, would this bypass be across?

Grainger, did you hear back on this question?

[Doc B.]

This is for cathode followers.