The 4V refers to the DIFFERENCE between the non-inverted and inverted signals that are provided to pins 2 and 3, respectively, of the XLR connector. Each of those signals individually has a maximum amplitude of 2V. By adapting the XLR output to an RCA input, you would only be using one of those signals (the non-inverted one), so the RCA input would see a maximum amplitude of 2V.
Something to keep in mind, however: Most XLR-to-RCA adapters, and perhaps some adapter cables, short the inverted signal on XLR pin 3 to ground (XLR pin 1). Many components won't have a problem with that, but some will (if it is done on an XLR output; it is no problem on an XLR input). Use an adapter or adapter cable that leaves pin 3 unconnected. Talk to the supplier to be sure that is what they will provide.
Another approach to consider would be to just use the RCA output, via a y-adapter that would allow you to connect it to two destinations. That should work fine as long as the total of the two cable lengths is not extremely long.
Regards,
-- Al |
Hi Scott, Is the solution different for converting RCA to XLR vs converting XLR to RCA? Yes, absolutely. The two situations are very different. It is highly preferable, and will be necessary in many cases, to ground pin 3 when adapting to an XLR input. Otherwise that input connection would be referenced to the component's circuit ground only through a high impedance (the input impedance of that input), which would create a susceptibility to hum and noise. On the other hand, grounding pin 3 of an XLR output accomplishes nothing constructive, and creates the risk that the circuit or device providing that output signal will misbehave (or even be damaged if it is not well designed) as a result of the excessive amount of current that will be drawn by the short circuit. See this thread for an example. Best regards, -- Al |
Yes, that looks like a good choice, Scott. FYI, this Jensen paper may be of interest, with respect to long term applications as opposed to the temporary situation you are addressing. Best regards, -- Al |
Granny, as shown at the bottom of this page the "xx" in the part number gets replaced with letters specifying the type of input and output connectors. For RCA in and XLR out the model Bob mentioned would be DM2-2RX. Before ordering, though, you should call Jensen and discuss your particular application with them, to be sure that is the most optimal model for your purposes. Regards, -- Al |
Granny, wow, that's mystifying. Sounds like you've tried pretty much all of the logical things.
Cheater plugs would have broken a ground loop, if that was the cause of the problem. And the Lightspeed wouldn't be susceptible to ground loop problems, because its power supply is optically isolated from the signal path, as I understand it. And also because it has a two-prong AC plug, with no safety ground connection.
You've probably already tried this, but if not try connecting the preamp and amp to the same dedicated line, and try doing that on each of the two dedicated lines.
I assume, btw, that nothing is connected to the outputs of the amplifier other than the passive speakers. I see that the Atlas is fully balanced, so if for instance a powered sub were connected to its outputs in the wrong manner, hum problems (or worse) could result.
The only other thing I can think of is that I see there is no switch on the back of the amp to select between the RCA and XLR inputs. Perhaps therefore the RCA input is wired directly to the same circuit point as pin 2 of the XLR connector (the non-inverting XLR input signal), in which case a jumper might be needed between pins 1 and 3 of the XLR connector when the RCA input is being used. Perhaps the manual addresses that. Perhaps the EMI environment is different now that the powered electrostatic speakers are no longer present, resulting in a difference in the amount of hum that is picked up by the floating input on pin 3.
Just some wild guesses, but I can't think of any other possibilities.
Regards,
-- Al |
I see in John Atkinson's measurements that the Atlas has extremely high input impedance, which adds credibility to my theory that the problem may be due to hum pickup that occurs via the unused XLR inputs. If you happen to have a multimeter, check for continuity between the center pin of an RCA input and pin 2 or pin 3 of the XLR connector for the same channel, and let us know. If you don't have a multimeter, but you have a piece of wire of suitable gauge, try jumpering pin 3 to pin 1 on each XLR connector. Obviously, the jumper should only be inserted when the amp has been turned off for at least a minute or so, to assure that a transient won't be injected into the speakers. And the wire gauge should be such that its contact with the pins is secure, so that the connection won't be intermittent when the amp is turned on. Alternatively, for experimental purposes you could order an RCA-female to XLR-male adapter, which would short XLR pin 3 to pin 1 (ground). Markertek, B&H Photo Video, and Musician's Friend are suppliers of that kind of thing, among many others. You could connect to the RCA input as usual, while having the adapter connected to the XLR input but in turn connected to nothing. Alternatively, for experimental purposes you could connect your RCA cable to the adapter, although depending on the design of the amp it's possible that could result in no signal going through one half of its balanced signal path, which would greatly reduce power capability and probably also have some adverse sonic effects. If a jumper or adapter eliminates the hum, then yes, a Jensen transformer would be a good permanent solution, as it would provide a balanced signal pair to pins 2 and 3 of the XLR connectors. Regards, -- Al |
That all continues to be pretty baffling. Does the buzz still occur if the preamp is connected to the amp but the preamp is not turned on, or is not plugged into the AC outlet?
-- Al |
The preamp need only be in the system and not turned on. Just the ic's hooked up to it. What if the preamp is hooked up to the amp but not plugged into the AC outlet? And what if the ic's are connected to the amp but left unconnected at the other end? Sam -- good luck on your issue as well! Best regards, -- Al |
My experience with hooking up ic's to an amp and leaving them open on the other end is a very loud and seemingly dangerous noise through the speakers. Yes, if the RCA center pin comes in contact with, or perhaps even close to, a source of static electricity (such as your body), or anything that is at a different potential than the amp's ground. I should have thought of that when I posted. In any event, you've established that the problem is not due to a ground loop, since it occurs when the amp is the only thing that is connected to AC power. So it would seem that the problem must be due either to EMI (electro-magnetic interference) pickup in the cabling and/or the preamp, from some nearby source of EMI, or to some defect in the input circuit of the amp. I found the Atlas manual online, and I see that it has a front panel switch to select among four possible inputs (balanced and unbalanced, direct and high-passed). I'm just speculating, but perhaps something is messed up in the switching circuit which causes the ground side of the RCA connectors to not be properly switched in. If you haven't already, you might try switching among the various inputs, and/or unplugging the amp for a few minutes, to see if that clears out any improper states in the circuit that selects among the inputs. As the manual indicates, MAKE SURE THE AMP IS MUTED when the input selection is changed. Also, it might be worthwhile seeing if the same problem is present when you connect to the high-passed RCA input. And if all of that leads nowhere, perhaps purchase an RCA-female to XLR-male adapter, that would allow you to try the XLR input on an experimental basis. Beyond that, I'm pretty much out of ideas. Best regards, -- Al |
All the ic's caused a buzz, but turning off the system and placing them in different positions changed the volume and channel of the buzz. What happens if you don't change the cabling at all, but you turn the amp off, wait a few minutes, and then turn it on, and you repeat that whole cycle a few times. Does the volume of the buzz on each channel stay the same? With the ic's connected to the direct inputs (RCA) on the amp no matter which input I chose on the selector the buzz was there. Did not matter as long as the ic's were connected.
When I connected the ic's into the crossover RCA inputs on the amp the noise was there wether I selected the RCA or XLR inputs on the crossover inputs. But with the ic's still connected to the crossover RCA inputs and selecting the direct RCA or xlr selection on the display the buzz went away. This increases my suspicion that something is defective in the amp's input selection circuit. That's just a guess, though. Regards, -- Al |
Could it be a speaker issue? I know it is passive, but..... I can't envision a way in which a passive speaker could cause the symptoms you have described. But I guess it is conceivable that a problem involving the front end of the amp, or the interconnect cables to the preamp, could be AFFECTED differently depending on whether an electrostatic speaker or a passive dynamic speaker is being used. Regards, -- Al |
