DCX2496 problem - distortion with multiple outputs

[ComputerJLT]

Ok i've developed a weird problem with my dcx2496.

a little back info - i have a dcx2496 running a stock power supply and stock dsp board but the output board is gone, i've gone direct spdif in to the oem trafo with a 75ohm terminating resistor in place of the 110ohm. Outputs are passive single ended using 6.8uf Dayton 250V audio grade caps from parts express (here) for ac coupling and i'm also using these 3.3nf filter caps.

so far so good but today when i went to crank it up i was getting horrible distortion and popping/crackling at moderate levels. no where near clipping my amp or distorting my speakers. Meters on the dcx are only about 1/3 way up then they start jumping/clipping as the noise starts. After playing with it i found if i have more than the 2 outputs i'm using enabled (even if they're muted it doesn't matter) then i get the popping and distortion. only way to get rid of the noise is to change the input on my 4 unused outputs to sum or C neither of which I am using.

Any inputs? is something starving the DACs for power?

The only thing i've done to this dcx since i did the passive out was try to power it with a modified power inverter. Per another users recommendation i modded a cheap power inverter to output 160v DC instead of modified sine ac (bypass the output h-bridge basically) and made sure it worked (and it did, no weird artifacts or overheating components after about an hour). I plan on using this dcx in my car with a carputer source (digital out only) is why i wanna power it with an inverter.

AFter I did that i plugged the dcx back into wall mains and all was well until today?


any ideas whats wrong or where i should look to see if somethings up? i have a 40mhz scope and decent DMM and am used to fixing car audio amps but idk where to look on this dcx. Maybe meter the 5v power to the DACs and maybe scope it see if i get nosie?

[Radugazon]

Try to disconnect and reconnect the multicable connector that remains (behind the 6 little electrolytical capas). maybe ????

[ComputerJLT]

I forgot to mentiin I reseated all conectors and hard reset the unit, no change. Also reseated rcas and physically moved them in case they were picking up emi/rfi. I even added a wire from the dcx chassis to my amps negative/chassis same issue.... Ill meter and scope all the power supply rails tomorrow if I. Have time.

One more bit of info, 2 caps before the inductors in the psu were bulged and replaced when i got the dcx. I used slightly higher value and voltage caps.

[ComputerJLT]

So i changed sources and spdif cables and issue is gone. I have it playing with everything at -0db with some clipping on loud songs and no distortion. I guess that cables picking up rfi or something weird

[Radugazon]

Good lesson to remember, but strange. When I do measurements I use sometimes a 6 meters cable plugged in the SPDIF input. 75 ohms load, no trafo, no problem, but the ground of all the system is very good.