Has anyone else noticed audible interference when using the serial port on the 990 for automation?

I have my 990 connected to a 7700 power amp with balanced connections except for right-surround which is connected with an RCA cable (that balanced output is non-functioning on my 990).

I have a serial cable connected to the 990 from a URC master controller (MSC-400) which is used to automate my entire system, mostly via IR.

When operating the IR repeaters of the MSC-400 or sending serial commands to the 990, I can hear audible clicks on all output channels, regardless of the 990's volume settings. It's loudest on the right surround channel that's not using a balanced connection, but all channels make the noise.

It's been a great pre-amp, but noise isolation like this is irritating. The RCA-connected channel also has a constant hum which is not present on the balanced connections. Very low, but loud enough to bother me if the room is otherwise silent. Easy to take care of by playing some music or a movie of course.

I have noticed that when I (manually) advance the volume control quickly, I sometimes hear clicks. Are the commands that you are sending (i.e. changes in volume) small steps (i.e. 1-2 dB) or large steps? I only ask because if I smoothly advance the volume control, I do not hear clicks.

On the other hand...the RS-232 interface does rely upon signals that are akin to impulses (digital strings at a high baud rate)...so that *could* be part of the reason...and I would start by checking the shielding of that cable. Then again, that it does it with IR commands suggests otherwise.

As far as one of the balanced outs no longer working, you could employ a high-Z to Low-Z impedance transformer going from the RCA output (to the "High-Z" side of the transformer), and the XLR side going to the balanced input on the 7700. At least this would convert the RCA single-ended signal to a balanced one.

Thank you very much for the assistance, especially the recommendation on the transformer.

The audible clicks aren't' heard when changing volume on the 990, only when passing IR through my URC MSC-400 controller. The controller is currently connected with a master IR-input which is automatically echoed out to 12 output ports. 6 of those ports are double-duty and can also be used for serial connections. One of them is currently assigned to be serial and is connected to the 990, though I have yet to employ full use of the serial commands since I'm still programming the controller. I've sent individual commands during testing however.

I see two things troublesome in this setup. #1 is that the IR signals are not completely isolated from the port where I have the serial cable plugged in on the MSC-400 even though I have it set up for serial use, not IR (using URC-branded serial cable). #2 is that the 990 is making audible noise in its audio path when receiving communication over its serial port.

Do you have any links for a suitable transformer that might already have an RCA connector on one end? I'm coming up with matches for products that have a phono connector built-in like this one:

http://www.americanmusical.com/Item--i-A...0807AFLHAMS0000

The AT transformer you cited will work, but you'll need some gender changers. I know that HOSA makes one that is 1/4" TS to XLR male (just can't recall the part number). I also found this (see page 40):

http://conquestsound.com/images/products/ConquestCatalog2012.pdf

The part you would want is the SI3230.

There are many otehrs...I have heard good things about SESCOM and though they are much pricier, they claim their transformer technology is 'better than the competition' (I suspect lower hysterisis).

It sounds like you are technically competent though, so if you were up to it, you could do this with something like a JFET op-amp (TL-082). With a small bi-polar DC supply, you could easily make a balanced line driver. JFETs are pretty low noise...and you would work-around the whole non-linearity of transformers issue (i.e. when they are close to saturation).

Anyway, the AT XMER you cited works fine - I use some of them in my whole-house audio (they receive balanced sends from a balanced distribution amplifier) and then via 1/4" female TS to RCA male mate with the preamplifier in a given room. Also, if you look, you can find 'em on eBay for around $10 each - you just have to (in your case) get the proper gender changing adapters, because XLR females are (by convention) inputs, so you need a XLR male to XLR male adapter, but then you're off to the races.

Just remember one thing...keep the RCA portion as short as is practically possible - you want the balanced signal (XLR portion) to be the longer of the two sections so as to minimize any chance of hum, or RFI. You may need to adjust the gain of that channel relative to the others, but you can esily do that in the 990.

I think the quickest path is using an adapter like this one: http://www.monoprice.com/products/produc...=1&format=2

Along with a transformer that has the 1/4 connector on a short lead, like the Sescom ones I've seen. Not only is that simple to procure and install, it may also be the solution to fit into the tightest space. I don't have very much clearance behind the 990. It already took a custom-designed/made cabinet *and* a recessed pocket in the awl behind the cabinet to accommodate the 990 and the XLR and power connectors.

It's a shame the 978 isn't going to be 5" or so shorter in depth. The cabinets on many pre pros are definitely way too big. Then again, I may just have to jump onto something else toward the end of the year if the 978 isn't released.

Yep...that's the shortest path - I use those on my AT XMERs, with them plugged into an RCA male to RCA female (male end going to the preamp input - remember, I'm using these at the 'receive' end rather than what you will use them for (the 'send' end).

However, it sounds like you are space-challenged (depth of cabinet), so yes...you could use a very short RCA male (perhaps even right-angle?) to 1/4" TS female...plug the AT XMER into that, then plug the gender-bender into its other side (XLR male to XLR male)...and now you can use any garden variety XLR mic cable to go to the amplifier.