California Audio Labs Sigma II DAC review

Clipdat

I purchased a used California Audio Labs Sigma II Tube Analog Processor (DAC) from our very own @MrBlackCrow back in April of this year. I was contacted via PM with the offer to purchase it, and after a day of research I accepted. Thanks again @MrBlackCrow for reaching out to me and for the great deal!

This 25 year old DAC uses a 12AX7 direct coupled tube output stage. This unit came with a NOS Sovtek 12AX7WA tube. It also boasts a few other impressive specs:

S/N Ratio: 102db
THD: .005%
Channel Separation: 101db

Also, an interesting note from the owner's manual: "As with any tube product, we recommend that you leave the unit off when not in use. It takes about thirty minutes for SIGMA II to warm up once it is switched on, but it may be used for non-critical listening during this warm up period."

A few photos showing the no nonsense plain exterior, and internal components:









I've listened to a few DACs recently, but this is the first one I've heard with a tube output stage. Before I listened to it, I was using a Schiit Bifrost and a North Star Design Intenso. If I had to list a "reference" DAC that I own, it would be the Cirrus Logic CS4398 inside my Marantz CD6004.

I hooked the CAL Sigma II up to my Rotel RCD-1072 via an MIT AVt 1 digital coax cable. I logged roughly three weeks of listening on it, and was happy with what I heard!

Immediately with some of the first CDs I played through it, I noticed that it had a rich and full bodied sound, with strong bass and pleasant highs. The sound was easy to listen to, and seemed to make the music sound less "digital" and a little more "vinyl-like". I really cranked up the third CD I played, and everything just sounded so smooth and nice.

It has a great musicality and timing to it, it does justice to the rhythm of the source material perfectly! I was also impressed by the tonal character that it provided to instruments like piano, saxophone, and acoustic guitar. There was a naturalness to them, and it gave me a good idea of the tonal characteristics of the instrument I was hearing.

I was really losing myself in some of the songs that I was testing with, and thoroughly enjoying it. I got goosebumps from my arms down to my legs during one track. That's never happened to me before with this particular song, and it didn't happen with I listened to this track on the previous two DACs I tested out. I'd say that's a good sign!

There's a few areas where the CAL Sigma II can't match it's SS brothers, at least with the currently installed tube. The first is soundstage width and depth. The presentation just doesn't have as deep of a sound where you can "see" the distance between the performers. In terms of details, it's not going to give you that extremely detailed and resolving aspect, in my experience. The Bifrost and Intenso easily beat it in terms of resolution and detail.

That being said, the overall musicality and engagement that I get with the CAL Sigma II puts it squarely as the #1 DAC currently in my collection. It's hard to adequately describe how enjoyable and fun it is to listen to!

Obviously we all have different personal tastes in what we look for with our DACs and playback equipment, but for me this one is great. I highly recommend that anyone who loves music give this DAC a try at some point.

tonyb

CAL made some really nice gear, It's no surprise that you like it. Try a few different NOS tubes in it and you may find what it lacks now, will improve. Congrats on the new toy.

Clipdat

Thanks Tony. It's a real special piece of gear, and I'm thrilled to have it in my collection. It's a nice feeling to have found a DAC that meets your personal tastes and seems to "tick all the boxes".

Would be open to trying some different tubes in it! Any suggestions?

tonyb

Not sure if the 5751'S are a viable replacement, usually they are. The RCA or Sylvania blackplates triple mica are nice sounding.

The Slov's like you have in there now where more so know for their ruggedness, which is why they came with some gear back in the day. Sound wise....not so much.

halo

I have some Japanese made 5751 tubes that I got from @snow which I used in my Jolida Glass FX Tube DAC III. Best tubes I had in it IMHO. Should be a good replacement for the Sovtek since the Jolida uses two 12AX7 tubes.

snow

The 5751 tubes will work but like the 7025 and other variations will have less gain then a standard 12AX7 tube so it will play at a lower volume.


Regards Snow

pier65

Buongiorno al gruppo,
sono alla ricerca dello schema elettrico del dac CAL sigma per sostituzione
del trasformatore di alimentazione perchè in corto.
Qualcuno può aiutarmi?
Qualcuno conosce le tensioni del secondario del trasformatore?
Grazie.

tonyp063

.

audioluvr

Wi' Wi'!