Rotel RB980-BX switch-off thump

[murone]

Does anyone here have the Rotel RB980-BX power amp? I just bought a used one and when I switch the amp off there's a very loud "thump" or pop in the speakers and I was wondering if anyone else with this amp experiences this. Is this a fault or a characteristic of the amp? Thanks.

[emaidel]

I've had one for years, and never experienced any "pops" or "thumps" whenever I turn it on. I'd suggest checking with Rotel for a fix.

[murone]

Thanks for the reply. It only happens on switch OFF. When I turn it on there is no noise as there is a delay but there seems to be no delay on switch OFF. Do you get any noise on switch OFF emaidel?

[Luvin Da Blues]

Is the loudness of the "thump" dependent on were the volume is set when you turn it off?

[murone]

No, the thump happens even with the preamp disconnected.

[AndrewRH]

Yes, I have heard that thump or pop - it isn't much, but it is there. And only when you power down the amplifier, not in normal operation. I have a Canadian version (110V)...which I'm looking to sell soon...

[niles300z]

Late add as usual for me, but mine does the same thump only not so quietly, This thump has me worried. It is common for this amp I guess, but I am not liking it. However, the deep controlled sound this amp can pump has me looking for a preamp that may work better with it than the AMC 1100 I was using which I really like. I will continue to try to isolate the issue. Let us know if any one figures out a fix.
Also,while here, can anyone shed light on how to utilize an amp like this capable of 80amps but the wall will only give me 15? Thanks
Niles

[Glen B]

Late add as usual for me, but mine does the same thump only not so quietly, This thump has me worried. It is common for this amp I guess, but I am not liking it.

The RB-980X has no output relays, that is why you may hear thumps of some kind. Now, if the thumps are unusually loud, this could be the result of excessive DC offset at the outputs. The only way to know for sure is to have it checked.

As parts such as those in the input differential stage age and drift off their values, this will cause increased levels of DC to appear at the amp outputs. If there are offset trimpots, these can be adjusted to correct the DC imbalance.

Some amps (like the RB-980X) lack such adjustments, and the solution would be to replace the out-of-value parts. It is always a good idea to have DC offset and bias in an older amp checked by a technician as a matter of routine.

However, the deep controlled sound this amp can pump has me looking for a preamp that may work better with it than the AMC 1100 I was using which I really like. I will continue to try to isolate the issue. Let us know if any one figures out a fix.

A better preamp than the AMC may be worth a try. This is a subjective matter based on your likes/dislikes. If you have a specific budget in mind, I and others here can recommend some options in your price range worth considering.

Also,while here, can anyone shed light on how to utilize an amp like this capable of 80amps but the wall will only give me 15? Thanks

Do not confuse the two items. That 80A figure is the absolute maximum current the amp is capable of delivering into a low-impedance load, under laboratory conditions, for a fraction of a second. Look at the published spec again. It states that this 80 amps is attained for a single pulse of 10 microseconds duration, into a 0.1 ohm load.

All this is telling you is that the amp can supply a lot of instantaneous current into a low impedance on a one-shot basis. This does not occur in real-life normal music playback and is meaningless to the average music enthusiast.

Now, the 80 amps is possible on the test bench, because of the massive energy stored in the main power supply caps. These caps provide a reserve of high instantaneous current for moments of high output demand.

A 15A or 20A branch circuit is capable of supplying several times it nominal rating for a few milliseconds at a time without tripping a circuit breaker or blowing a fuse. This allows for turn-on surges without nuisance tripping. I have measured inrush current of more than 200A on a 15A circuit.

The rear panel of the RB-1080 has a 4A fuse and marked power consumption of 400 watts. Actual average consumption at normal listening levels will be significantly less.

[Happy Camper]

I don't have that model but I do use two RMB-100 monoblocks for my planar headphones and they are great. I used them on a pair of Martin Logans in a rear channel set up and they served flawlessly. For planar/electrostatic loads, they are a good value amp.

(and yes, I said headphones)