what did I do? channel hiss in McCormack DNA 0.5.

Robert you've definitely done some damage but it's not real serious since the amp still plays. Definitely contact Steve McCormack & get the amp to him for repair. While you're at it you might consider an upgrade: SMC Audio has 3 levels of upgrades available. Check these out at his website & then talk to the guys at SMC; really good people there.
http://www.smcaudio.com/

The amp was on when I changed cables. I tried switching the left cable into the right channel and vice versa, and I still got the hiss from the left channel, so I think it's in the amp - and I tried another amp the other day, and the hiss was absent. With this amp, there's always a hiss if your ear is right next to the tweeter. But you can hear the hiss on the left speaker a few feet away. I have a feeling I messed something up in the amp, and I don't know who I should contact about it. I bought the amp used here. I could talk to Steve McCormack, a local store who carries this line, or someone else.

Thoughts?

Thanks,

Robert

You might have jarred the connection loose on an interconnect or the input jack on the amp. Not that uncommon. Do the basic troubleshooting procedures that are mentioned above and in other threads and try and track the problem down. Power amps should always be turned off or at least muted as a safety measure when hooking / unhooking cabling. Otherwise, one very quick and simple mistake can take a BIG toll on your system and wallet. Sean
>

Suggestions:

Put the original pre-amp back into the chain - Is the noise present?

If so - most likely the amp

If not - most likely the new pre-amp

If the original pre-amp is not available try this -

switch the interconnects at the amplifier end only (ie right to left input and left to right input)

Is the noise present in either channel? - if not, could be a grounding issue with the interconnect.

Is the noise in the left channel? - if so, most likely the amp.

Is the noise in the right channel - if so, most likely the pre-amp.

Hope this helps