Rotel RB-1070 problem?

[specialized]

Hi there.. I got last RB-1070 they had on stock. Im using for rears (for my 805S)

After listening session when i turn off after 2-3 seconds there is sound on the speakers like emptying of capacitors of RB-1070 (Something like fiuuuuuuuuuuu). If i just turn on and turn off there is no such sound.. Only if i played a little bit.. While it's playing sound is ok..

Is this a sign that some of capacitors are gone? Should i return the unit?

Or is not a problem to worry about? I tried connecting to different speakers and the same thing happened. Also i tried to different power cords and definitly it's RB-1070 not something else..

Greetings

Darko


p.s. I have something like that (but more short and more silent ), from one of the RB-1080, and after a while the sound gone.. I keeped the RB-1070 turned on for few days, but the same. .Nothing changed

[miner]

First of all, the amp does not power down completely until a few seconds after turning off - so sounds normal to me what you are experiencing. Yu need to be sure your volume on the preamp is turned all te way down when you power off. Is the amp connected to the preamp via a 12V trigger?

[specialized]

First of all, the amp does not power down completely until a few seconds after turning off - so sounds normal to me what you are experiencing. Yu need to be sure your volume on the preamp is turned all te way down when you power off. Is the amp connected to the preamp via a 12V trigger?

No. Its not.. And also Im turning off preamp first.. When i turn off amp last same thing happened


Darko

p.s. Seem like capacitors are emptying.. Becouse When i dont listne music just turn on and then turn off after few minutes, nothing happenes.. This sound i'm getting only if i have listen few minutes

[Glen B]

I believe the RB-1070 and RB-1080, like some other Rotel models, have no output relays, so the speakers are always connected to the amp output stage. If you cut power to the amp while music is playing, the sound should continue for a few seconds and become increasingly distorted as it dies down.

I think what you are hearing is indeed the sound of the power supply caps discharging, a normal occurence and nothing to worry about. When you listen to the amp for several minutes versus just letting it idle momentarily, IMO its going to be hotter and behave a little differently when you power down.

[specialized]

I believe the RB-1070 and RB-1080, like some other Rotel models, have no output relays, so the speakers are always connected to the amp output stage. If you cut power to the amp while music is playing, the sound should continue for a few seconds and become increasingly distorted as it dies down.

I think what you are hearing is indeed the sound of the power supply caps discharging, a normal occurence and nothing to worry about. When you listen to the amp for several minutes versus just letting it idle momentarily, IMO its going to be hotter and behave a little differently when you power down.

It's strange that when i turn off after beeing used for sound after i listened and stopped the sound, the sound that im getting is like wistle and starting 5-10 seconds after i turned off .. If i wait and dont turn off imediatly after i stopped the sound and leave the amp turned on for maybe 30 minutes, when i turn off after nothing happened.. I have three more Rotel RB-1080 and nothing happened like this.. Also i had older Rotel then RB-1070 (his precessor), also nothing happened..

Darko

p.s. I tried connecting to different power plug and also i changed the surge protectors i had. Now im using Belking vs MGE before

[Glen B]

Darko,
I've discussed your issue with several techs and all concur there is no fix to the amp that will eliminate the noise. What you're likely hearing is some oscillation as power to the rails drop off. If you find the noise intolerable, the best solution would be to install an output relay, if there is room in the amp.

A suitably rated DPST (double pole single throw) relay, with power for its coil taken either from the transformer secondary, ahead of the diode bridge, or AC mains, right after the power switch, would be easy to implement. As soon as the amp is turned off, the relay will drop out, disconnecting the speakers. The relay contacts would be wired in series with the "+" side of each channel's output. Any competent technician should be able to install an output relay for you, as long as there is space in the chassis.

Glen

[specialized]

Darko,
I've discussed your issue with several techs and all concur there is no fix to the amp that will eliminate the noise. What you're likely hearing is some oscillation as power to the rails drop off. If you find the noise intolerable, the best solution would be to install an output relay, if there is room in the amp.

A suitably rated DPST (double pole single throw) relay, with power for its coil taken either from the transformer secondary, ahead of the diode bridge, or AC mains, right after the power switch, would be easy to implement. As soon as the amp is turned off, the relay will drop out, disconnecting the speakers. The relay contacts would be wired in series with the "+" side of each channel's output. Any competent technician should be able to install an output relay for you, as long as there is space in the chassis.

Glen

It's not that noise is intolerable.. I can live with that as soon as there is no more damage to the amp or speakers or preamp..

Do u suggest that except the noise i listen there is no other negative things that would produce in the future some more serious problems?

Darko

[Glen B]

The problem is in the circuit design. There is no damage risk, its just a nuisance issue. That is part of the reason why manufacturers include output relays (to mute turn on/turn off noises). It would have cost Rotel less than $10 worth of parts to include an output relay.

[specialized]

The problem is in the circuit design. There is no damage risk, its just a nuisance issue. That is part of the reason why manufacturers include output relays (to mute turn on/turn off noises). It would have cost Rotel less than $10 worth of parts to include an output relay.

U want to tell me that all Rotel RB-1070 have this? It's strange that i have three more RB-1080 and non of them have this.. Also i had a chance to try the model before RB-1070, also no something like this..

Darko

[Glen B]

I did not say that ALL Rotel have this problem. Amplifier operation/behavior depends on the design. The tolerance of parts (resistors, caps, transistors) vary and values drift over time, values change with temperature, and the circuit designer has to take all of these factors into consideration. When you power down your amp, as the caps discharge and the rails lose power, parts of the circuit are probably maintaining bias while some parts are not. This is likely causing a slight oscillation, which you are hearing. This is a shortcoming in the circuit design that probably manifests itself only rarely because of a combination of factors.

If the amp had an output relay that disconnected the speakers upon turnoff, you would not be aware of any noise, and we would not be having this discussion. You can't use other models as a reference since they are of slightly different circuit design and have output relays. Maybe some other amps do have this oscillation but you just don't know it because the speakers disconnect when the units are powered down.

[specialized]

I did not say that ALL Rotel have this problem. Amplifier operation/behavior depends on the design. The tolerance of parts (resistors, caps, transistors) vary and values drift over time, values change with temperature, and the circuit designer has to take all of these factors into consideration. When you power down your amp, as the caps discharge and the rails lose power, parts of the circuit are probably maintaining bias while some parts are not. This is likely causing a slight oscillation, which you are hearing. This is a shortcoming in the circuit design that probably manifests itself only rarely because of a combination of factors.

If the amp had an output relay that disconnected the speakers upon turnoff, you would not be aware of any noise, and we would not be having this discussion. You can't use other models as a reference since they are of slightly different circuit design and have output relays. Maybe some other amps do have this oscillation but you just don't know it because the speakers disconnect when the units are powered down.

Thanks Glen for u'r help.

Greetings

Darko