Recommended cap for PSU bypass

[Strikkflypilot]

Thanks for the heads up, Jamie.
I spent some time reading through that post to see if I understand correctly.
Does this mean that I replace the 270Ohms Resistor between 13-15 with the C7X, and can replace the stock 220uF between 12-13 with anything from 10-220uF? In that case would there be a sonic difference between low and hi uF cap?

[JamieMcC]

Unfortunately I am also still a newbie and have a lot to learn on the topic so am not very well qualified to speculate and hesitant to offer any advice on areas that are outside of any mods I have not tried myself.  All I can add is that I did not notice any significant differences  between the 89uf and 200uf caps I tried in this position. 

[Strikkflypilot]

Interesting input anyways.
Maybe Caucasian Backplate will enlighten us.

[Grainger49]

  .  .  .    Does this mean that I replace the 270 Ohm Resistor between 13-15 with the C7X, and can replace the stock 220uF between 12-13 with anything from 10-220uF?   .  .  .   

Yes.

The film will do the final smoothing and can release energy (voltage) into the circuit faster than the stock electrolytic.

Now each manufacturer's film will add a slightly different flavor.  Going to the high end of the range, in microfarads, might make a small audible difference.  It is just a try it and see situation.  It is very system/listener dependent. 

[Strikkflypilot]

Thank You Grainger49!

Since I have a slight problem leaving it alone, do You have an idea why exactly 220uF was chosen? A smaller cap would have been a cheaper choice, I guess, for the stock Crack, wouldn't it?

[mcandmar]

In general the more capacitance the smaller the ripple, i.e. the smoother the DC voltage will be and the quieter the power supply.   At what level you reach the point of diminishing returns i don't know, but i suspect Paul calculated it from a combination of testing, experience, and utilizing the parts bottlehead already stocked.

Using a choke to filter the supply is far more effective than bulk capacitance so capacitor size can be reduced when using a choke with little to no negative side effects.  I tried to simulate the Crack circuit with the information i had at hand and estimated around 1.5mv ripple with the stock configuration of three 220uf caps, with a C-7X choke i kept lowering the capacitance of the caps until i got back to ~1.4mv ripple and was using 220uf, 100uf, and 22uf.  The advantage of downsizing the caps would be the availability, lower cost, and physical smaller size of Poly film caps to replace the electrolytic.  But if you can put 220uf poly films in there go for it.

[Paul Birkeland]

Yeah, I amended that recommendation for a bit more filter capacitance. 

[Strikkflypilot]

Fantastic feedback, guys!

I am sure many more than myself will also profit from this.

[thomas27]

The Speedball should decrease the benefits in terms of noise from a film cap as 3rd power supply cap + choke, shouldn't it? Or am I getting confused?

[Paul Joppa]

A current source improves power supply rejection in grounded-cathode gain stages, but not in cathode followers (the Crack output stage).

[thomas27]

Got it, thanks!

[Strikkflypilot]

I should receive the choke soon.
Will try to replace the 270 Ohm 5w resistor only first and post impressions.
Sadly have no oscilloscope.

[Strikkflypilot]

I ordered a Mundorf MCAP  150uF 250VDC.
It measures (w/l) 56mm/66mm.
Getting crowded in there.

[Strikkflypilot]

So now I've gotten the C7X choke. Any reason for not installing it already? (Before I install a film cap as the third cap in the PSU)
Also many threads seem to recommend 200uF and upwards for the third cap. Hope my 150uF will suffice.

[JamieMcC]

Personally I think your going to be pleased with the results after fitting the 150uf and am looking forward to hearing your impressions.

Heres a pic of the 89uf caps I tried for both coupling caps and as the last psu cap they worked well.

(https://www.head-fi.org/image/id/6109323/width/900/height/900/flags/LL)