My Crack Diary

[orson]

Finished my basic build about a month ago and got the wood case done last week.
I wanted the Crack to look like it was build in the sixties or seventies.
Under the hood everything is still stock but prepared for the upgrades coming.
I will update this thread with every upgrade I do: inside the Crack as well as periphery.
At the moment I try to find the right combination of tubes that suites my taste. In the pics you see my favourites at the moment but a Chatham JAN CAHG 5998 arrived yesterday and gets some burn right now.

 

[Paul Birkeland]

The roundover on the base is a nice touch.  I wonder if you could get some nickel/phenolic input jacks to fit the factory holes.

 

[orson]

The roundover on the base is a nice touch.  I wonder if you could get some nickel/phenolic input jacks to fit the factory holes.

Now that is a nice idea - will put that on my list (although you won't see much of the jacks with the rca-cable plugged in).

 

[orson]

Modding PSU Part I

I decided to start my modding where it all begins - at the PSU. I want the music to be amplified and not crap and ripple.
I already have a Furman AC 210 between the wall plug and DAC/ Crack. It´s main purpose is to protect against voltage spikes. But it has a linear filtering stage as well to clean up the AC before it goes via braided and shielded power cables to the Crack.
For the PSU I followed the recommendations here: changing the filter stage from CRCRC to CRCLC with a Triad choke and replace the last cap with a film cap. The choke is mounted on a grounded alloy plate to add shielding because of the close neighborhood to the transformer.

To my ears the Crack plays everything with more ease and superior now. Better bass, better mids. And better low level resolution - it reveals tracks/ samples coming into the mix with a noisy background that I did not mention before. As my Crack was already dead silent before nothing changed in this regard.

For me absolutely worth the investment as the huge cap had a broken leg and was very cheap.

PSU Part II is already in preparation.

 

[Doc B]

That's a nice mod. I just want to point out that the Speedball upgrade gives around 60dB of additional PSRR to the amplification stage.

 

[orson]

Speedball is already here - it goes into the build right after I´m done with the PSU Part II.
Do you have a figure at hand how many db of PSRR there is with Speedball and choke? I read somewhere here that the Stock PSU has about 30db and adding a choke gives about 60db. I think the figures do not simply add up so maybe it is at about 70-80 db with Speeball and choke?

 

[orson]

Modding PSU Part II

Schottkyfied!!!
Man, I thought replacing the already good UF4007s with Cree Schottkys gives not more than a slight improvement if at all.
But this one is definitely clearly audible: in terms of tonality much smoother mids and highs. The bass did not change itself, but: as the upper range is smoother and less distorted you can turn up the volume a bit more for a comfortable level and therefore the bass is more at least (hope that explanation makes sense for you).
In terms of resolution the Crack digs even more into the fine details (for example the shaker in the middle part of Chris Jones „No Sanctuary Here“ is more prominent, new strumming sounds on Dire Straits „Sultans of Swing“) and the imaging is more accurate. especially with the tracks from the Chesky´s binaural series. The stage is much more believable.
My last listening evenings were very long...
For 15 bucks this mod is incredible value, though it is not the easiest.
PSU Part III will follow.

 

[JamieMcC]

Nice implementation

 

[orson]

Two things to add to the Schottkys:
The voltage readings at the output tubes changed from 166V to 164V - so nothing to worry about.
The transformer runs cooler (though only measured with my fingers). I read somewhere about the advantages of the Schottkys for the transformer itself but cannot recall it exactly and did not save the link.

 

[mcandmar]

The voltage drop of the Cree vs UF is pretty much the same so the voltages of the power supply shouldn't change.  If anything its inconsequential vs the varying mains voltages throughout the day.  +/- 10% is the norm in a 240v world.

I don't believe it will make any difference to heat, the whole point is the cleaner switch on/off as the diode conducts which translates into less switching noise and transformer ringing, which can translate into a lower noise floor.  Never tried to measure it in practice so that's just an assumption.

 

[Grainger49]

The lower voltage could be a result of the incoming voltage.  And the lower heating could be due to the lack of Reverse Recovery Spikes which would feedback into the transformer.  Or not.

 

[orson]

Modding PSU Part III

Bypassed the first and second cap in the PSU with Mundorf MKPs 2,2uF.
22uF would have been better but too large.
For this mod I really can´t comment on sound changes. If there are some they are too small to be audible without A-B-ing.
I did not expect that anyway, just did it for the good feeling to have a Mundorf signature throughout the PSU.
I consider myself done with the PSU given the fact that I neither want to build a larger chassis nor mount something on top of the plate.
The remaining space under the hood is reserved for the future mods to come.
Now it´s time for listening fun before the Speedball goes in.