Rotel AMP sounds Excellent but slight Humming

[pcsolutionz]

I just got my first AMP, Rotel RB-956AX. I am absolutely amazed how much of an improvement it has brought to my system for just over a bill. Only problem is it is making a slight humming buzz when you put your ear up to the speakers. I dont want to damage my speakers and have tried different outlets, cables and moved all my wires away from each other. I cant get rid of the hum. Will it hurt the speakers? Also, there are no power inputs on my receiver or the amp itself. My old receiver and components were able to be plugged into each other. When i turn the AMP on or off it makes a loud pop from the speakers. What do i need to eliminate the pop and be able to turn my receiver on with the amp at the same time. From reading around, it sounds like a power conditioner may be in order. I dont have much more to spend and could certainly use advice for a cost effective solution to my problem. Thanks in advance for all replies!

 

[j_garcia]

The fact that there are no outlets on your receiver is a good thing. You should NEVER plug an amp into those sockets on ANY receiver. To have it power on and off at the same time, you would use the 12V trigger from the receiver.

A power conditioner is not likely to solve the issue if different outlets did not. Hum may be caused by a number of things, but it is often an issue between a device connected to the receiver or the connection between the receiver and the amp. So start disconnecting sources and see if the problem goes away.

 

[AcuDefTechGuy]

The fact that there are no outlets on your receiver is a good thing. You should NEVER plug an amp into those sockets on ANY receiver.

I noticed they stopped putting outlets on AVR. What is the reason for not plugging amps to those outlets on AVR?

Because power is limited?

 

[j_garcia]

I noticed they stopped putting outlets on AVR. What is the reason for not plugging amps to those outlets on AVR?

Because power is limited?

Yes, it states on pretty much all of them that you should only connect low current devices to those outlets. The typical external amp won't qualify as a low current device Plus it saves cost and space.

 

[KEW]

Yes, it states on pretty much all of them that you should only connect low current devices to those outlets. The typical external amp won't qualify as a low current device Plus it saves cost and space.

Is it okay to leave cd player or tuner plugged in? (I don't plug in amps because of the limits stated on the back).

 

[PENG]

Is it okay to leave cd player or tuner plugged in? (I don't plug in amps because of the limits stated on the back).

Those should be fine but you should always read the owner's manual to find out what the outlets are rated for, then find out what is the rated power consumption of the CD player or tuner to make sure they don't exceed the rating of the outlet(s).

Just for a good laugh, my 3805's outlet is rated for only 120W and the manual says "do not use them for hair driers, etc."

 

[M Code]

I noticed they stopped putting outlets on AVR. What is the reason for not plugging amps to those outlets on AVR?

Because power is limited?

The issue is their max current handling rating, most are < 100W. Fine for a CD player or turntable but not a power amplifier. The current rating could be increased by using a higher current power relay but that would drive up the unit cost significantly....

My preference is to use a smart power strip, these can handle power switching ON/OFF of high current drawing power amplifiers and are not expensive.. Typically, < $50..

Just my $0.02...

 

[TLS Guy]

I just got my first AMP, Rotel RB-956AX. I am absolutely amazed how much of an improvement it has brought to my system for just over a bill. Only problem is it is making a slight humming buzz when you put your ear up to the speakers. I dont want to damage my speakers and have tried different outlets, cables and moved all my wires away from each other. I cant get rid of the hum. Will it hurt the speakers? Also, there are no power inputs on my receiver or the amp itself. My old receiver and components were able to be plugged into each other. When i turn the AMP on or off it makes a loud pop from the speakers. What do i need to eliminate the pop and be able to turn my receiver on with the amp at the same time. From reading around, it sounds like a power conditioner may be in order. I dont have much more to spend and could certainly use advice for a cost effective solution to my problem. Thanks in advance for all replies!

First if all the issue of the turn on thump. This is severe and noted in original reviews. As I understand it, it might well damage some drive units. Solving this would require a unit redesign.

The next issue is the hum. Does it hum just connected to the speakers, with nothing plugged into the inputs? If it does then the unit has a poorly designed ground plane, a well known Rotel feature by the way.

If the hum is only present with other devices connected, then you have a ground loop to sort out in your system.

This is an older unit and not a good one. It is 40 watts per channel, but performs poorly with four ohm loads and really hits the wall if any part of the impedance curve drops below four ohms.

You will not solve these issues with a power conditioner. Your best bet is to sell it on, and we will be ready to deal with the next guy's post!

 

[pcsolutionz]

Thanks to all of you for the pointers. I didn't notice the replies until now. After your comments, my research and a couple days of trying to get this sorted. I have come to terms with the fact that I bought a cheezy first amp. I have to say though, if this is a poor amp and has so many flaws, I'm excited to see what a better amp will provide. The comparison of my system without this amp and with it are night and day. The detail and response I get in movies with the amp is extremely impressive. Being that I have accepted my loss and poor choice, do any of you have advice as to which amp brand / type I would be able to pick up for a reasonable price point and get better results. I'd like to have headroom with my speakers and have them all run off of amps. My fronts are rated to 125w, I am thinking about a 2 channel amp of 150 or 200 watts for those. For Center (100w), Surrounds (50w), Surround Back (50w), I am thinking of a 5x100 five channel amp. Am I on the right track here? Any suggestions would be greatly appreciated. I can probably sell the 956ax on Craigslist where I found it. Thanks in advance guys!

 

[TLS Guy]

Thanks to all of you for the pointers. I didn't notice the replies until now. After your comments, my research and a couple days of trying to get this sorted. I have come to terms with the fact that I bought a cheezy first amp. I have to say though, if this is a poor amp and has so many flaws, I'm excited to see what a better amp will provide. The comparison of my system without this amp and with it are night and day. The detail and response I get in movies with the amp is extremely impressive. Being that I have accepted my loss and poor choice, do any of you have advice as to which amp brand / type I would be able to pick up for a reasonable price point and get better results. I'd like to have headroom with my speakers and have them all run off of amps. My fronts are rated to 125w, I am thinking about a 2 channel amp of 150 or 200 watts for those. For Center (100w), Surrounds (50w), Surround Back (50w), I am thinking of a 5x100 five channel amp. Am I on the right track here? Any suggestions would be greatly appreciated. I can probably sell the 956ax on Craigslist where I found it. Thanks in advance guys!

Since you are on a budget, I think you are on the wrong track. To best the amps in your receiver will require a significant expenditure.

The amp you purchased is certainly inferior to the amps in your receiver.

I have to conclude that you like distortion. Some people do for some strange reason.

 

[audiofox]

Mark, can you be more specific regarding your comment about the Rotel's poor ground plane design? Have you seen evidence of this flaw in all their amps or just certain models?

 

[PENG]

The comparison of my system without this amp and with it are night and day. The detail and response I get in movies with the amp is extremely impressive.

Looking at the specs of your Rotel amp it is hard to see how it could make night and day difference unless the amp section of your AVR is defective. According to the manual, the Rotel is rated 30W (cont.) per channel with 2 channel driven or 90W when bridged for mono operation. It has 3 groups of stereo pairs, 6 channels altogether. Even it's peak current specs is unimpressive, 20A into 0.1 ohm for 10 micro second for just 1 pulse. It is highly unlikely that your speaker's impedance would drop below even 2 ohms under any conditions.

It may welll be more powerful than the Yamaha under all channel driven to near rated power conditions but in 1, 2 or even 3 channel situations I would bet my money on the Yamaha. So I would say it is not that the Rotel can sound superior than the 765 but rather your 765's amps section is the problem, I mean something wrong. Just fyi, I have a little Yamaha RX-V659 that sounds as good as any of my separate amps when working well below its output limit. I think you can expect at least the same kind of improvements by going with just about any reputable amps rated for 100W per channel including the low cost Emotiva UPA amps that are often recommended on this forum. Lastly, if you serious about wanting to have more power reserve on hand, that 30/40W Rotel is not a good solution even without the hum and the power on thumb.

 

[AcuDefTechGuy]

Looking at the specs of your Rotel amp it is hard to see how it could make night and day difference unless the amp section of your AVR is defective. According to the manual, the Rotel is rated 30W (cont.) per channel with 2 channel driven or 90W when bridged for mono operation. It has 3 groups of stereo pairs, 6 channels altogether. Even it's peak current specs is unimpressive, 20A into 0.1 ohm for 10 micro second for just 1 pulse. It is highly unlikely that your speaker's impedance would drop below even 2 ohms under any conditions.

It may welll be more powerful than the Yamaha under all channel driven to near rated power conditions but in 1, 2 or even 3 channel situations I would bet my money on the Yamaha. So I would say it is not that the Rotel can sound superior than the 765 but rather your 765's amps section is the problem, I mean something wrong. Just fyi, I have a little Yamaha RX-V659 that sounds as good as any of my separate amps when working well below its output limit. I think you can expect at least the same kind of improvements by going with just about any reputable amps rated for 100W per channel including the low cost Emotiva UPA amps that are often recommended on this forum. Lastly, if you serious about wanting to have more power reserve on hand, that 30/40W Rotel is not a good solution even without the hum and the power on thumb.

It's that low voltage gain again.

Unless people level match by increasing the speaker channel levels, it's going to sound differently night and day because a 4-6dB difference is night and day.

 

[TLS Guy]

Mark, can you be more specific regarding your comment about the Rotel's poor ground plane design? Have you seen evidence of this flaw in all their amps or just certain models?

Yes, I had an RSP 1098 pre/pro, for a couple of years. That has significant ground plane issues as well as being very sensitive to RF interference. I believe the problems were related. My dealer admitted that these problems have been a significant issue with Rotel equipment.

I moved on to Marantz, which has been much more satisfactory, except for one power supply failure, which was handled by Marantz in exemplary fashion.

 

[PENG]

It's that low voltage gain again.

Unless people level match by increasing the speaker channel levels, it's going to sound differently night and day because a 4-6dB difference is night and day.

Are you saying that the Rotel may have higher gain, like the Emotiva amps?

 

[PENG]

I am impressed with the relatively detailed specs Rotel had provided in the owners manual.

 

[AcuDefTechGuy]

Are you saying that the Rotel may have higher gain, like the Emotiva amps?

Not as high as Emotiva, but perhaps higher than some AVR from Denon, Yamaha, etc.

I think the Rotel is 28dB gain for both balanced and unbalanced.

 

[pcsolutionz]

I have a feeling my Yamaha amp is faulty. I'm looking into a warranty replacement now. Either way, I'd like to merge to separates without getting divorced. My attempt to save a buck did not work out so good. TLS guy states I like distortion, I'm no genius audiophile like some in here, but do know good from bad sound. Was just trying to take a cost effective move toward better sound. I put the Rotel on Craigslist and am thinking of ordering a UPA-500 and UPA-200. I know they are not the best they have but do you think I'd be happy with the results from these two? Would it be a good move toward separates? I'll eventually get an Emotiva Pre. The 200 would cover surround and surround back along with center. Only thing is my center is rated to 100w and it the 200 is only 80w. Quintets are rated for 50w. The 500 puts out 125, which is exactly what my WF-34 Fronts are rated for. Any suggestions before ordering are welcome. I don't mind spending the money if it is a wise investment and will be impressive. Thanks for all your help!

We all have our own area of Expertise!

 

[AcuDefTechGuy]

I have a feeling my Yamaha amp is faulty. I'm looking into a warranty replacement now. Either way, I'd like to merge to separates without getting divorced. My attempt to save a buck did not work out so good. TLS guy states I like distortion, I'm no genius audiophile like some in here, but do know good from bad sound. Was just trying to take a cost effective move toward better sound. I put the Rotel on Craigslist and am thinking of ordering a UPA-500 and UPA-200. I know they are not the best they have but do you think I'd be happy with the results from these two? Would it be a good move toward separates? I'll eventually get an Emotiva Pre. The 200 would cover surround and surround back along with center. Only thing is my center is rated to 100w and it the 200 is only 80w. Quintets are rated for 50w. The 500 puts out 125, which is exactly what my WF-34 Fronts are rated for. Any suggestions before ordering are welcome. I don't mind spending the money if it is a wise investment and will be impressive. Thanks for all your help!

We all have our own area of Expertise!

If your budget is under $2K, I think it's best to just stick with a nice AVR.

Going separates the cheap route is no better at all IMO.

 

[PENG]

If your budget is under $2K, I think it's best to just stick with a nice AVR.

Going separates the cheap route is no better at all IMO.

Are you going to point him to a $1,299 4311 (I can never find such deal on that thing) just to tempt him? I do think the 4311 will sound as good and as powerful as those little UPA amps for most applications especially two channel stereo.