I believe that your Rowland amp is fully balanced, and it appears that you may have a REL sub in the system which uses that amp. If so, are you connecting the sub at speaker level, and if so are you making the mistake (that is not uncommon when connecting a sub to amps that are balanced or bridged) of connecting the ground (black) wire from the sub to one of the amp's negative output terminals?
If so, I can envision a technical scenario in which that would be responsible for the problem, even if the amp didn't used to get hot under the same circumstances.
In any event, good luck with the problem. Regards,
-- Al
|
Ideally the black wire from the sub should be connected to a circuit ground point on the amp, but it appears that the Rowland 8 does not provide a binding post or other terminal corresponding to its circuit ground. (There are some balanced amps, such as some of the Pass models, which do provide such a terminal). Given that, connecting the black wire to a chassis screw on the amp will most likely work well, and at least some of the REL manuals suggest doing exactly that when connecting a sub to the outputs of a balanced (or bridged) amp.
Although it is unlikely, if doing that results in a hum or some other issue, and if your connections to the amp's inputs are balanced (so that its RCA input connectors are not in use), you could solder the black wire to the ground sleeve connection point of an RCA plug, leaving the center pin unconnected, and insert that into one of the RCA input jacks on the amp. That would establish a suitable circuit ground connection.
The issue that I indicated I was envisioning, given that on a balanced amp the negative as well as the positive output terminals have full amplitude signals on them, is that depending on the internal grounding configurations of both the sub and the amp connecting the black wire to the negative output terminal could result in a near-short being applied to that output. For example, if as is commonly done both components connect their circuit grounds to their chassis through a low resistance, by connecting the black wire to the negative output terminal a path would be established from the negative output terminal of the amp through that low resistance in the sub to the sub's chassis/AC safety ground, then through the AC power cords of both components and the external AC wiring to the chassis/AC safety ground of the amp, then through another low resistance to the amp's circuit ground. Voila, a near short will have been created between the amp's negative output terminal and the amp's circuit ground! And perhaps over time the resulting excessive current flowing through those resistances, and the resulting heat, have caused one or both resistors to become lower in value, or even to short out completely, increasing the load on the amp and causing it to heat up more than previously.
In any event, even if this is not what turns out to be causing the problem, it would be good practice (and perhaps sonically beneficial) to connect the ground wire as I've described.
One final point: You might have to readjust the level control on the sub a bit after changing the connection of the black wire as I've described, to keep the sub and main speakers in balance.
Good luck. Regards,
-- Al
|
You're welcome! Pin 1 on the XLR connectors would also be a circuit ground point. Perhaps a convenient means of making use of that would be to obtain an XLR-to-RCA adapter, such as this one, inserting it into one of the unused XLR inputs, connecting the black wire to the ground sleeve connection point of an RCA plug as I described, and inserting the RCA plug into the adapter. That and most such XLR-to-RCA adapters will connect the RCA ground sleeve to XLR pin 3 as well as to pin 1, but I'm pretty certain that won't matter in this case. Regards, -- Al |
Correction to my previous post. When I said: That and most such XLR-to-RCA adapters will connect the RCA ground sleeve to XLR pin 3 as well as to pin 1, but I'm pretty certain that won't matter in this case. ... upon looking at the manual for the 8T (I couldn't find one for the 8) I see on page 8 a statement that "When the RCA position is selected, pin 2 of the XLR input is shorted to pin 1." That is unusual, as in most cases involving USA equipment if any of the two signal pins on the XLR connector were grounded when the RCA input is being used it would be pin 3. Given that, I suspect that the center conductor of the RCA connector is connected internally to XLR pin 3, so using an XLR-to-RCA adapter which connects pin 3 as well as pin 1 to the RCA ground sleeve would kill the input signal on the RCA connector. I believe that Cardas can supply, at least on special order, XLR(male)-to-RCA(female) adapters that do not ground pin 3. Those would be suitable. But surely there must be some screws on the case of the amp to which you could attach the wire? Best regards, -- Al |
Dave, rather than using an adapter you might also consider simply purchasing a 3-pin male XLR connector and wiring the one connection (black wire to pin 1) yourself. For one thing, that would undoubtedly be a good deal less expensive than using a Cardas adapter. Parts-Express.com has lots of choices of suitable connectors, costing just a few dollars. Good luck. Regards, -- Al |
09-05-15: Daveyf
Al, one more question...could I connect the ground wire from the sub to my preamp, with the other two connections going to the amp? The preamp has a ground connector for a turntable, which I use for that purpose; could I hook up the sub ground there too? That might work ok, and it's well worth trying. In fact REL manuals I've seen suggest doing that if a single sub is being used with monoblock amps. The one downside I can envision is the possibility that hum might result. It would be prudent to turn down the level control on the sub before powering up the system with it connected that way, and bringing the level control up gradually while listening for hum. 09-05-15: Jea48
If the bias was off for the power transistors of one channel or both, wouldn't that cause the amp to run hot? Yes, that's certainly a possibility, as are a number of other things of course. As I mentioned, though, even if the problem is being caused by something other than the way the sub's ground has been connected, it would still be a good idea, and very possibly sonically beneficial, to change that connection as I've described. 09-05-15: Daveyf
Main question is have I damaged my amp due to the subwoofer hook-up. It seems so based on the heat it is now giving off.Ugh I don't think we can say at this point, with any certainty. It could be that some damage has occurred as a result of the connection issue, but of course it could also very well be that the overheating is being caused by something else altogether, such as a bias problem as Jim mentioned. Best regards, -- Al |
Dave, if you happen to have a multimeter there are some measurements you could make that might provide insight into whether the overheating problem has resulted from the sub connection issue.
You would disconnect the sub and the amp from each other and from everything else, including the AC outlets, and on each of them you would measure the resistance between the AC safety ground pin on the power plug and the ground sleeve of an RCA connector. If that resistance is just a few ohms or less in both cases, it would increase the likelihood that damage resulted from the connection issue. If either or both resistances are significantly higher, say tens of ohms or more, it would mean that the cause of the overheating is most likely something else.
Although it's probably all academic at this point, as it seems probable that the amp has to be sent in for repair in any case.
Best regards,
-- Al
|
Good! The 100 ohm figure is easily high enough, regardless of what the number is in the amp, to make it unlikely that the sub connection damaged the amp. That resistance would have limited the current through the roundabout path I described earlier, involving the safety ground wiring, to low levels that the amp would have had no problem with.
I don't know what to make of the fluctuating readings for the amp. Perhaps some capacitance is involved that hadn't fully discharged when you took the measurements, which might have resulted in fluctuating (and erroneous) readings. But yes, values that are very close to zero are possible, and some designs connect circuit ground and chassis ground/AC safety ground directly together (which would result in a resistance of essentially zero ohms). Although that is generally not good practice, as it can make the design susceptible to hum and other ground loop issues, especially if single-ended connections to other components are involved. In this case, though, my guess is that residual charge on some capacitance was just confusing the measurement.
Best regards,
-- Al
|
Dave, based on the info in the manual that I referred to earlier, about XLR pin 2 being shorted to ground when the RCA inputs are selected, I suspect that the only thing that switch does is to put that specific short in place when the RCAs are selected, and remove that short from the circuit when XLRs are selected. I suspect that XLR pin 1 is always connected to either circuit ground or chassis ground, regardless of the position of that switch.
And regardless of which of those grounds pin 1 is connected to, it should serve as a suitable point for connecting the sub's ground (the black wire). Certainly if pin 1 is connected to circuit ground, and most likely if it is connected to chassis ground (although in that case there is a slight possibility of some hum resulting).
What I'm envisioning is that XLR pins 2 and 3, through which the balanced pair of signals would be supplied if the XLR connectors were being used, are routed to the + and - inputs of a differential receiver circuit. With the center pin of the RCA connector being connected directly to one of those inputs (the one corresponding to XLR pin 3), and the switch providing a ground (0 volts) to the other input of the differential receiver (the one corresponding to XLR pin 2) when the RCA input is selected.
You can verify what I'm envisioning, with respect to the grounds, by disconnecting the RCA cables and measuring the resistance between the RCA ground sleeves and pin 1 of the XLR connectors. If XLR pin 1 is connected to circuit ground, that will measure 0 ohms, or at most a tiny fraction of an ohm, regardless of the position of the switch. If it is connected to chassis ground, you may get a fluctuating reading similar to what you previously reported when you measured between the RCA ground sleeve and AC safety ground. In that event, take a measurement between the AC safety ground pin of the power plug and XLR pin 1. If that reading is 0 ohms or very close to it, regardless of the position of the switch, it would confirm that pin 1 is connected to chassis ground, and you would also be good to go.
Best regards,
-- Al
|
Strange that the two channels gave different results. Not sure how to explain that.
Just to confirm that the correct pins were measured, pin 1 of each of the female XLR connectors would be the pin closest to the right side of the connector, when viewing the connector from the rear of the amp.
Given those results, additional measurements that might be useful to know would be the resistance between the ground sleeves of the two RCA connectors, and the resistance between pin 1 of the two XLR connectors.
In any event, I would still expect connecting the black wire to XLR pin 1 to work, although using the right channel XLR connector seems like the surer bet.
Best regards,
-- Al
|
Sounds good! So pin 1 on either XLR connector should be a good point for connection of the black wire from the sub.
Best regards,
-- Al
|
