What's wrong with my Cal Delta/Sigma?

How long has it been powered up and what were you using as a source before? Might want to check the tubes in the DAC as well. Most of the tubes that I receive in the mail sound like crap for a couple of days (both signal and output) as they seem to be full of static electricity. The same goes for most anything else that has been shipped.

I was using a marantz 63se. The tubes should be operational and well burned in because I purchased this trans/dac from a private seller who's been using it for years, and they sounded fine when I demoed them on his system.

Replace the 12AX7 output tube with the low noise version from Cal Labs (~$40). Also, ditch the optical digital interconnect and get a high quality (preferably silver) unshielded .5M digital coaxial interconnect. Set the units aside of one another and not stacked. Do not use vibrapods. Make sure that you NEVER turn off the DAC other than to move / change connections / service the tube, etc.

Had this Combo for 8 years and have experimented much. This is what worked for connection to ARC LS-25 / VT-100.

Another good upgrade is to change the 3 connectors to the upgrade versions from CAL ($60). Don't attempt this on your own unless you are confident in soldering skills, electronic technician abilities, and are very careful. The unit must be totally disassembled, connectors desoldered from PC Board, new connectors mounted in the Bulkhead, and wires run from the new connection to the PC Card. Just another tip...

Yohjixme: I am just fishing here, but the digital IC does effect the sound quite a bit (regardless of what the bits is bits crowd has to say about it). It could be the cable, but I kind of doubt it would make the sound awful, as you describe unless there is something wrong with it. I have tried some pretty cheap ones myself and though they did not sound great at all, they were still OK. My DAC (a Bel Canto) needs to be powered up a minimum of three days (a week is better) for the detail to shine through, otherwise it is a little muffled, but I am talking very little here and as the cheap cable went, it still sounds not great but OK. What you may want to try is to clean all of the RCA connectors (both male and female) and then reinstall the cabling (both the digital and analog IC's). It is advisable to power down when doing this, but it should just take a few minutes. If you do not have a special cleaner for this an inexpensive one is electricians grade Isopropyl alcohol (available at electronics stores and probably even Radio Shack), which should be above 99.95% pure and have no additives. I use a cotton T-shirt over a pointed wooden skewer to clean the insides of the male RCA's, but most anything small enough will work fine (I just don't use knife blades for fear of scratching the metal). Following this leave it powered up for a week and see what happens. This won't cost you much ($3 or so) and is good maintenance anyway. Dirty contacts can severely degrade the sound from my experience and even if this does not work at least you will have eliminated this possible cause of the poor sound. Also why you are at it you might as well clean the power cord and IEC contacts.