Using R+C instead of LED.

[Paul Birkeland]

I'd try better source material.  Spotify's ability to resolve complex orchestral music over an internet stream may well be the issue.  (You also still haven't mentioned the headphones you're using)

[garfo]

Beyer DT990Pro 250ohm (waiting for a pair of Senn HD600).

[garfo]

Went back to LED. Not huge difference to be honest but def more clarity, breath and dynamics. Maybe female voices sound more sexy but otherwise way better the little red light
Thanks everybody for help and for their thoughts ! See u soon.

[Paul Birkeland]

I can remember working on a very early Crack prototype a long, long time ago for a musician who wanted a high end headphone amp.  I remember sitting down and listening to at least 15 different tube operating points, then I finally found one that just sounded really good.  I took voltage measurements, scratched my head a little bit, then realized the operating point was one that I had run into building Bottlehead kits with the same tube.

The biggest improvement to be had in the Crack, beyond the Speedball, is shunt regulation.  Unfortunately, you really need a bigger power transformer and chassis to accomplish that.

-PB

[garfo]

It is probably worth building a Crack II with a sister chassis for PSU only. I'd be a buyer !

[Azimuth48]

So what IS the accepted load resistor here to use with a capacitor?

I have seen everything from 390 to 470 to up to 1.5k or even 2.2k. A friend wants me to mod his Crack by removing the cathode LED's for 2.2K resistor and 2000µf bypass cap. Just running the values, it seems 2000µf is way overboard where a 470µf will do given 2.2k. Thoughts?

[Paul Birkeland]

It is probably worth building a Crack II with a sister chassis for PSU only. I'd be a buyer !

I have done a lot of repairs on audio equipment with umbilical cords over the years, and only once was the umbilical not at least part of the issue.  There really is nothing to be gained by doing this.

[Paul Birkeland]

A friend wants me to mod his Crack by removing the cathode LED's for 2.2K resistor and 2000µf bypass cap.

I would let your friend know that the designer of the amp said this is a pretty substantial downgrade in performance. 

[Doc B.]

It is probably worth building a Crack II with a sister chassis for PSU only. I'd be a buyer !

You could just build a Crackatwoa.

[Azimuth48]

I would let your friend know that the designer of the amp said this is a pretty substantial downgrade in performance.

Yes, and a couple of other friends did the RC mod on their Crack and raves about it. I’m sure it IS different, and I highly doubt “better”. I did the reverse mod for a similar design, the Darkvoice 336 SE and I loved the LED’s. So much better transients and speed. It dropped the hazy slow blunted sound.

But if this person INSISTS on the changes, I just want to say on the same operating point as close as possible.