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Discussion Starter · #1 ·
Hi,


I'm getting an RX-V663 receiver for use with my 5.1 system. The 663 is rated at 95W/channel.


I have a 6 channel external amp just sitting around unused - it's an older Rotel RB-976 rated at 60W/channel. There's an option to configure ("bridge mono operation") the channels together to get 3 x 150W/channel amps as well. But the restriction is that in "bridge mono" mode, the connected speakers must be 8 ohms (my center and 2 surrounds are 8 ohm, but my fronts are 4 ohm)


Given the Rotel has a lower power rating, but is a 26lb external amp, would I be better off:

a) using the RX-V663 only and leaving the Rotel aside, or

b) using 663 as pre-pro only and using Rotel for amping all channels (even with lower power rating), or

c) using 663 to power my 2 front channels and bridging the Rotel to drive my center and 2 surrounds at 150W each (can't power my fronts and the center due to 4ohm fronts).


The answer may be "try it all ways and listen for yourself". But I'm just not confident that by the time I unhook, re-hook, and re-balance levels that I'll remember how the previous configuration sounded well-enough to make a judgment. I'm hoping some of you have a strong opinion on this based on your experience.


Thanks in advance!
 

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I've always believed that dedicated amp is better than the amps in a receiver. In your situation I would leave the Rotel out of the loop. If you could do the front three channels then I would say go for it but your speaker situation doesn't allow it.


Just my 2 cents.
 

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It should be noted that the Yamaha cannot put out 95 watts x 7 at the same time. With movies though, that's not necessarily a concern. So it's hard to say whether an all channels driven rating of 60 watts / channel (I assume the Rotel is ACD rated,) beats a 95x7 rating with all channels driven.


Of course people will tell you the Rotel sounds better or it's watts are better. Of course they don't know this, they are just assuming Rotel > Yamaha. I am not saying it's not true, I am just saying people will make that assumption without knowing.


One advantage to using the Rotel to drive at least some of your channels is that it can theoretically take some load off the 663's power supply if the 663 can be configured to turn off those channels being driven by the Rotel.
 

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It is was a question of whether to go out and buy a multi channel amp or use the 663 the decision would be more difficult.


If I had the amp sitting around, unused, there is no way under the sun that I would not hook it up and do a comparison. No way.


My experience with external amps is that they always put a bigger smile on your face than the amps in a receiver. How big a smile often depends on the pre amp section of the receiver feeding the amp.
 

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I'd bridge the 976 into 3x150. One such channel should power your center -- you should do this regardless of what else you do. Almost certainly you should use the other two channels to power your surrounds.


I'm curious why you would hesitate to do this -- the heavily mixed center channel will get extra headroom, and the Yamaha's power supply will only have to deal with the two 4 ohm main speakers, increasing headroom to them as well. Other than connecting the wires, all you'd have to do is re-adjust the channel level trims in the Yamaha's setup menus.


Is there a downside I'm missing?
 

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Discussion Starter · #6 ·

Quote:
Originally Posted by ggunnell /forum/post/14167437


I'd bridge the 976 into 3x150. One such channel should power your center -- you should do this regardless of what else you do. Almost certainly you should use the other two channels to power your surrounds.


I'm curious why you would hesitate to do this -- the heavily mixed center channel will get extra headroom, and the Yamaha's power supply will only have to deal with the two 4 ohm main speakers, increasing headroom to them as well. Other than connecting the wires, all you'd have to do is re-adjust the channel level trims in the Yamaha's setup menus.


Is there a downside I'm missing?

Hi Ggunnell,


Thanks for the advice. I asked the question because of the disparity in the power specs (95 watts vs 60W watts) and I wasn't sure to what degree "discrete watts" outranked "receiver watts". I had wondered whether the Yamaha would benefit from not having to drive 3 of the speakers, but wasn't sure whether it would have the headroom benefit you pointed out. If that's the case, then I should definitely try it. I was a little worried that Yamaha had made the 663 amplifiers a little less beefy than the 659 model I'm currently using (based on people's comments about 661 vs 659), so this may equalize things a bit if that's the case.


I also had some "inertia" related to a couple of mostly minor points:

* RB-976 is a 220V model, so I need to use a 120V-to-220V converter (I already have this, but it's a big mother and subject to the WAF)

* Have to create space in my rack which is already pretty full

* No easy way to avoid plugging everything into one outlet, so I was wondering whether I'd overload the circuit (plasma, DVR that never seems to shut off due to HDD, 663, subwoofer. . .and now add the voltage converter and RB-976). I should add up the amp load to make sure I'm still OK.


Thanks again - I appreciate your and other people's taking the time to comment/advise.
 

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Quote:
Originally Posted by eitakura /forum/post/14164138


Hi,


I'm getting an RX-V663 receiver for use with my 5.1 system. The 663 is rated at 95W/channel.


I have a 6 channel external amp just sitting around unused - it's an older Rotel RB-976 rated at 60W/channel. There's an option to configure ("bridge mono operation") the channels together to get 3 x 150W/channel amps as well. But the restriction is that in "bridge mono" mode, the connected speakers must be 8 ohms (my center and 2 surrounds are 8 ohm, but my fronts are 4 ohm)


Given the Rotel has a lower power rating, but is a 26lb external amp, would I be better off:

a) using the RX-V663 only and leaving the Rotel aside, or

b) using 663 as pre-pro only and using Rotel for amping all channels (even with lower power rating), or

c) using 663 to power my 2 front channels and bridging the Rotel to drive my center and 2 surrounds at 150W each (can't power my fronts and the center due to 4ohm fronts).


The answer may be "try it all ways and listen for yourself". But I'm just not confident that by the time I unhook, re-hook, and re-balance levels that I'll remember how the previous configuration sounded well-enough to make a judgment. I'm hoping some of you have a strong opinion on this based on your experience.


Thanks in advance!


I'm not sure that either the bridged Rotel or RX-V663 will be happy with 4 ohm main speakers. I suppose if it were me in your shoes, I would bridge the Rotel and drive the center and surround speakers via preamp outputs from the 663. then, I would set the 663 internal amps for use in a 6 ohm system via the advanced setup menu. Run YPAO and adjust the calibrated setup to final taste. YMMV.
 

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Discussion Starter · #8 ·

Quote:
Originally Posted by Magmatic /forum/post/14169631


I'm not sure that either the bridged Rotel or RX-V663 will be happy with 4 ohm main speakers. I suppose if it were me in your shoes, I would bridge the Rotel and drive the center and surround speakers via preamp outputs from the 663. then, I would set the 663 internal amps for use in a 6 ohm system via the advanced setup menu. Run YPAO and adjust the calibrated setup to final taste. YMMV.

You're right - the Rotel manual specifically says the speakers need to be 8ohm in bridged mode. I'm using Infinity RS3's as my surrounds and a Paradigm CC370 v3 as my center, and both are listed as 8ohms, so I should be OK. My fronts are Paradigm 11SE MKII's (yeah, Frankenstein system, speaker-wise) and the label there says 4ohms. I've been running my 659 in 8 ohm mode to drive all 5 speakers (based on the Audioholics review that advised not to change this setting), but not sure yet whether I should do this with 663 or use the 6-ohm setting.


Can you use a common voltmeter/ohm meter to confirm the ohms of a speaker - or does it require driving the speaker to see the true load?
 

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Quote:
Originally Posted by ggunnell /forum/post/14167437


I'd bridge the 976 into 3x150. One such channel should power your center -- you should do this regardless of what else you do. Almost certainly you should use the other two channels to power your surrounds.


I'm curious why you would hesitate to do this -- the heavily mixed center channel will get extra headroom, and the Yamaha's power supply will only have to deal with the two 4 ohm main speakers, increasing headroom to them as well. Other than connecting the wires, all you'd have to do is re-adjust the channel level trims in the Yamaha's setup menus.


Is there a downside I'm missing?

I considered doing the same thing with my 663 and that Rotel amp. Definitely use it bridged with the center and surrounds if you are going to use the Rotel.


Trust me the 663 does just fine with 4 ohm speakers even when left in 8 ohm mode. This was near reference levels also!

http://youtube.com/watch?v=7cdxUkfK2Os
 

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In my last car audio project I added a 4 channel amp @ 25 watts/channel to a head unit that claimed 100 watts/channel.


All I can tell you is that 25 real watts grossly outshine 100 pretend watts anyday.
 

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Discussion Starter · #11 ·

Quote:
Originally Posted by mpgxsvcd /forum/post/14169980


I considered doing the same thing with my 663 and that Rotel amp. Definitely use it bridged with the center and surrounds if you are going to use the Rotel.


Trust me the 663 does just fine with 4 ohm speakers even when left in 8 ohm mode. This was near reference levels also!

http://youtube.com/watch?v=7cdxUkfK2Os

Thanks. I read a review that said I could also run my amp at 70W x 5.


What do you think: Use 663 as pre-amp for all channels and get 70 discrete watts for all channels (including fronts)? Or stick with the plan to put 150W to center and surrounds and use 663 to drive fronts?
 

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Discussion Starter · #12 ·

Quote:
Originally Posted by mpgxsvcd /forum/post/14169980


I considered doing the same thing with my 663 and that Rotel amp. Definitely use it bridged with the center and surrounds if you are going to use the Rotel.


Trust me the 663 does just fine with 4 ohm speakers even when left in 8 ohm mode. This was near reference levels also!

http://youtube.com/watch?v=7cdxUkfK2Os

mpgxsvcd,


i saw your video review - nice job. i understand that discrete vs receiver didn't make much difference for you except at highest sound levels. but if you had the rotel amp already, what were your reasons why didn't you end up using it in your setup?
 

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Well. lets see, where to start . . .



First, no, the DC resistance of a loudspeaker is not the same as the impedance which varies with frequency. The relative phase of voltage and current also varies with frequency, and this is also a factor in how 'difficult' a load the loadspeakers present to an amplifier. Not an issue here.


The 663 will drive 4 ohm loads -- but as with most receivers, the power supply becomes the limiting factor as you increase the number of channels driven.


Your single circuit should be enough -- remember your true RMS power rarely exceeds [email protected] I was able to hear what I thought was dynamic compression on loud bass peaks by driving two Rotel 1095's, four SVS Ultras, and everything else off one 15 amp circuit (it did go away when I put in dedicated circuits) -- I don't think you have a problem (yet!)


The voltage converter scares me. I have no idea who rated it or how, what it's frequency response, noise profile, etc. are. If you've used it before with no audible issues fine, otherwise I'd type up all the specs you can find on it and email them to Rotel and see what they say.


Frankly, if you plan to continue residence in a 120V area, I'd sell the Rotel and the converter. With power amps like the Emotiva XPA-5 (5x200 for $800) around (and of course you could look into used amps and even trading -- maybe someone in a 220V area is struggling with a 120V unit). At least worth looking into IMO.


You've mentioed wanting to use the Rotel in unbridged [email protected] mode.

It's definately possible (if it were a more recent Rotel I'd say it's certain) that it will sound better than the Yamaha's output stage at low to moderate listening levels -- there's a lot more to amp design than max RMS output.


Some information that might help you decide whether to bridge the Rotel's channels or not would be distortion specs on the Rotel in both bridged and unbridged modes -- some amp designs sound better bridged, others not. Again, an email to Rotel might get you a knowlegable anwer.
 

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Discussion Starter · #14 ·

Quote:
Originally Posted by ggunnell /forum/post/14172906


Well. lets see, where to start . . .



First, no, the DC resistance of a loudspeaker is not the same as the impedance which varies with frequency. The relative phase of voltage and current also varies with frequency, and this is also a factor in how 'difficult' a load the loadspeakers present to an amplifier. Not an issue here.


The 663 will drive 4 ohm loads -- but as with most receivers, the power supply becomes the limiting factor as you increase the number of channels driven.


Your single circuit should be enough -- remember your true RMS power rarely exceeds [email protected] I was able to hear what I thought was dynamic compression on loud bass peaks by driving two Rotel 1095's, four SVS Ultras, and everything else off one 15 amp circuit (it did go away when I put in dedicated circuits) -- I don't think you have a problem (yet!)


The voltage converter scares me. I have no idea who rated it or how, what it's frequency response, noise profile, etc. are. If you've used it before with no audible issues fine, otherwise I'd type up all the specs you can find on it and email them to Rotel and see what they say.


Frankly, if you plan to continue residence in a 120V area, I'd sell the Rotel and the converter. With power amps like the Emotiva XPA-5 (5x200 for $800) around (and of course you could look into used amps and even trading -- maybe someone in a 220V area is struggling with a 120V unit). At least worth looking into IMO.


You've mentioed wanting to use the Rotel in unbridged [email protected] mode.

It's definately possible (if it were a more recent Rotel I'd say it's certain) that it will sound better than the Yamaha's output stage at low to moderate listening levels -- there's a lot more to amp design than max RMS output.


Some information that might help you decide whether to bridge the Rotel's channels or not would be distortion specs on the Rotel in both bridged and unbridged modes -- some amp designs sound better bridged, others not. Again, an email to Rotel might get you a knowlegable anwer.

Thanks for clarifying the impedance issue and circuit issue. I feel better about the overloading my circuit issue.


I don't know the specs of the power converter, but I'll find out. I know the wattage is sufficient, but the other specs I don't know. I'm trying to do this w/o spending more $, so spending much more ($800 is much more!) than I could recover by selling the RB-976 and converter would be tough - but good point about potential trade. I can also get the 976 converted to a 120V supply by a Rotel-authorized dealer, but not sure how much that would cost.


The specs for Rotel in both modes are:

6-channel mode: 60W/channel power output, 20Hz-20kHz,
 

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As long as the output (220V side) amp/watt rating of the converter is at least equal to the back plate amp/watt rating of the Rotel it's worth try.
 

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Discussion Starter · #16 ·
All,


I set up my system with the Rotel driving the surrounds and center. But I'm getting a semi-loud pop/thump when the Rotel powers on.


I have the Rotel set on a delayed turn on using a 12v trigger. Powering on the 663 triggers the 12v trigger to a Power Center, which then turns on the outlet that goes to a 120-to-220v transformer (always powered on) which feeds the Rotel (always powered on).


Is the pop/thump normal? If not, how much danger is there to damaging the speakers?


BTW, I did try to leave the outlet on, with transformer already powered up, and then just toggle the on/off switch of the Rotel (I wanted to make sure the simultaneous "rush of power/current" to the transformer then to the Rotel wasn't causing this). But even if the Rotel goes on alone (663 already on as well, but no source driving), it makes this same sound.


Maybe the amp need to be serviced? I have another amp (B&K EX442) that doesn't make a loud sound (different setup) when it's powered up after the pre-amp, so this doesn't seem normal.


Any thoughts?
 

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A lot of amps thump when turned on. The Rotel may be designed to not do so, however and something is not working quite right.


As for it hurting speakers, I couldn't say. A lot of amps do this though, in a lot of PA systems, and I doubt speaker damage is ocurring regularly.
 

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Discussion Starter · #18 ·

Quote:
Originally Posted by MichaelJHuman /forum/post/14235133


A lot of amps thump when turned on. The Rotel may be designed to not do so, however and something is not working quite right.


As for it hurting speakers, I couldn't say. A lot of amps do this though, in a lot of PA systems, and I doubt speaker damage is ocurring regularly.

Thanks Michael. I sent an email to Rotel and will also post in the Rotel owner's thread to see if other people have experienced this on theirs.


Thanks again.
 

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I've triggered various power amps from various Yamaha receivers with no problems. Most applicably I've triggered Rotel 1095's with several Yamaha receivers, most recently the 3800, with no problems.


I think you are bypassing the Rotel's internal startup sequence, which eliminates turn on transients, by triggering power to it instead of by leaving the power to it on and triggering the amp itself. I don't think there is any other way to avoid this problem.
 

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Discussion Starter · #20 ·

Quote:
Originally Posted by ggunnell /forum/post/14236780


I've triggered various power amps from various Yamaha receivers with no problems. Most applicably I've triggered Rotel 1095's with several Yamaha receivers, most recently the 3800, with no problems.


I think you are bypassing the Rotel's internal startup sequence, which eliminates turn on transients, by triggering power to it instead of by leaving the power to it on and triggering the amp itself. I don't think there is any other way to avoid this problem.

Actually, I did try the same thing by leaving the transformer on (which supplies power to the Rotel) and then turning on the amp with the front button. Still get the same pop/thump.
 
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