Stick to RSX1065 or go to 1055/1075 separates?

[BleakShore]

I guess I'd like to hear/learn advices/experiences from those who have gone this route.

That is, stick with the RSX1066, or exchange it for the RSX1055/RMB1075 combo? I bought it from Myer-Emco so I can do the exchange with no penalty.

The reason I'm contemplating this is because I am *so very* happy with the RSX 1065. It is everything I was looking for. It really makes me want to turn on the receiver and be around all day if I my wife and kids let me. So am I satisfied? I should be, but, Nooo. I keep wondering how the separates might sound even better!

I had bought and returned NAD T762 and the Outlaw 950/7100 combo before I found the Rotel and settled on it. The NAD and Outlaw, while excellent in their own rights, just were not what I was looking for. Rotel, on the other hand, just sounds great to me. And it looks totally cool. I love it.

Then I find Club Rotel. Some seem to indicate that perhaps the way to go is get the RSX1055 as pre/pro and RMB1075 for the power amp. After reading some posts by A. Pratt, et. al., I am pretty much set to go that route at the moment. So unless I hear otherwise between now and qutting time today, I plan to go and do the exchange in a few hours after work.

Reservations...

I do have a bit of mixed feelings. On the one hand, I feel I should get the RSP1066 if I'm going separates to be purist like. On the other hand, 1055 and 1066 have identical features and almost similar performace specs for the pre/pro section, with the additional tuner and the amps, and $200 cheaper. Seems like a tremenous bargain.

But 1055 is a receiver, not a dedicated pre/pro. That bothers me just a wee bit, but not enough.

My findings so far:

Seems the RSX1055 SNR is about 3 dB worse than that of RSP1066 from the published specs, but 1055 specs are for the entire front to amp chain. E. Johnson (hope I got his name right) did a review, and his measurements for the pre/pro section indicates much lower THD for the preamp section alone. So I'm speculating that the SNR for the preout section is probably much better, and almost just as quite as the 1066.

The plan...

I will use the 1075 to drive BW 604S3 fronts, LCR6 center, and 603S2 rears.

I'm toying with three possible configurations.
1. Use 1075 for usual main amplification, and use 1055 front amp to power the 3 back surrounds, as 1055 is flexible to let us do that.

2. Use 1075 to biamp the two fronts, power the center, then use 1055 to power the rears.

3. Use 1075 and 1055 to biamp all speakers: 1075 powering the woofers and 1055 powering the tweeters.

Any suggestions / experiences you can share is welcome!


Thanks! Happy to be a Rotel owner.

Jong
Herndon, Va

[Andrew Pratt]

Given there's no penatly I'd say go for it:T

As for your options regarding power the speakers I'd advise you to try bi amping the mains with the 1075 and see if you find it worth while. It seems some speakers sound better bi amped while others sound worse. Assuming it doenst' sound worse I'd say let the 1075 power the fronts and centre then let the 1055 power the sides and rear surround(s)

[aud19]

I say go for it as well.

I'd compare the 1075 bi-amping the mains and the 1075/1055 bi-amping all scenarios and see which you like better.

J.R.




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[art vandeleigh]

this is the same question that i am struggling wiht right now. i just picked up the 1055, but the upgrade bug has bitten and i would love to another amp to power the fronts...but im thinking about maybe going with something other then a rotel though.

i have not really seriously auditioned any of the rotel amps, but from the short listenening i did of the 1075, i was not really blown away. i felt it to sound very similar to the internals of the 1055...but again i really did not get a chanec to do a serious listen.

i was thinking about maybe goign with an aragon...the older model ones, liek the 8008BB ro something similar...i was also thinking about just biting the bullet and picking up a used krell on audiogon. but if you can keep us updated of what you decided to go with. i would really like to know what you decided on and why...and of course your review.

[will1066]

The 1075 won't sound much different. If you're not happy with the "company sound" now, moving up the line won't make that much difference. You'd do best trying another brand.

I love my Rotel but my aspirations for sometime within 2004 is to sell my Rotel and move up the food chain. Krell is one candidate I'm thinking about.

[BleakShore]

Well, the dealer did not have the 1075 amp on hand, so I have to wait until Wed night. I did pay for the exchange, so I will at least give it a listen and see if it was worth it.

Perhaps going with something different altogether might be an alternative.

Will keep you posted.

[4_everyman]

Given there's no penatly I'd say go for it:T

As for your options regarding power the speakers I'd advise you to try bi amping the mains with the 1075 and see if you find it worth while. It seems some speakers sound better bi amped while others sound worse. Assuming it doenst' sound worse I'd say let the 1075 power the fronts and centre then let the 1055 power the sides and rear surround(s)

This is the route i've taken. I just added the 1075 and i think it sounds fantastic. I had been driving two Polk RTi150s, a CSi40 center, and two FXi50s from the RSX-1055. Driving the mains in a bi-amp configuration has made a noticable (although not a night/day) difference.
Rgds,
--Pete

[BleakShore]

Well, I got my RSX1050/RMB1075 combo in exchange for the RSX1065 two nights ago. After much grunting moving the old stuff out and hauling new stuff in, and sweating bullets to plug/unplug all the cables :M, I was quite buzzed. Took some beers to go through all that pain 8x):B

The 1050/1075 combo sounds fantastic! :T Even better than the RSX1065, as I hoped it would. It just seems to play with more ease and composure. After playing quite loudly for some some, I noticed that both the 1050 and 1075 were only slightly warm to the touch. Not the kind of hotness I felt from the 1065, NAD T762, and Outlaw 950/7100.

What's puzzling is that the Outlaw 7100 is quite a bit heavier than RMB 1075, by 13 lbs or so, with a total capacitance of 140,000 µF total (20,000 µF pch) whereas the Rotel has 80,000 µF (16,000 µF pch). Yet the Rotel ran cooler (definitely) and sounded sweeter to me (subjective) . Nice satisfying brass and strings. It really lets you feel and hear the rosin.

I was so pooped and feeling rather grim at the prospect of having to rewire/replug wires for various bi-amping configurations, I chose to use the 1075 only to power the speakers for the time being. Besides, I thought, by not using the amp section in the RSX1055, its pre/pro section would run with the least noise and power drain. I wanted to hear the 1055 at ist best.

If 1055/1075 were any noisier than the 1065, I could not tell (1055 SNR is 3 dB worse.) Yes, there is a faint hiss if I turn up the gain beyound 70%, but unnoticeable for all practical purposes.

I am very glad that I got the 1055/1075 instead of the 1065. At a reasonable price, I now have flexibility and near par performance of the separates, i.e., 1066/1075. And they look great. Although I was a bit sad to see 1065 go... it was such a nice looking machine.

When I recover from the exhastion, I will eventually try bi-amping the fronts. Has anyone tried bi-amping a pair of B&W DM604s (S3) with 1075? Notice any difference?

Well, I think I'm done upgrading for a while. For a long time, I hope. This year, in addition to the 603 S2 and LCR6 S2 I bought last year, I've added the Rotel 1055, 1075, 604 S3s, and an SVS 20-39PC+ sub. Rotel/B&W/SVS sounds quite good to me.

Final System:
Rotel RSX1055 as pre/pro
Rotel RMB 1075 as main amp
B&W 604 S3 fronts
B&W 603 S2 surrounds
B&W LCR6 S2 center
Infinity RS5b back center (1985 vintage)
SVS 20-39 PC+ sub
Behringer BFD 1024 for sub equalization

B&O Beogram RX2 turntable
Adcom GFP550 preamp (for phono)
Sony NV700S DVD player
Hughes HD receiver
Mitsubish 65809 RPTV

Took a while to get here. Movie time! opcorn: :beer:

[aud19]

Congrats! That's a pretty nice list of equipment there

J.R.




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[will1066]

Hey Aud, when are you going to receive yours??

[aud19]

Still getting the perpetual "today or tomorrow" response, sigh.... and yes the wait is killing me. :? On a good note they told me the reason was that they were making sure I got the latest remote etc. so it's taking longer.

J.R.




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[sikoniko]

You have a very similar speaker setup to me. if you ever had time, i would be interested to hear what advantage the 1075 added when using that over the internal amp of the 1055.

I spoke to my local dealer and he doesnt think i would get as much out of an amp (1075/1095) as i would if i switched to def tech speakers, or moved up to CM or 700 series speakers.

My b&w's are s1. I dont know if there is much of a difference between s1 and s3. i know they put the tweeter of nautilus in the new ones.

in all honesty, i have no issues with my setup. i know there is better out there, but if i dont sit mine directly next to higher level speakers, i dont notice the difference. ignorance is bliss.

I do know that I will require an amp though when i want to go 7.1 so that is something i will have to face eventually.

[BleakShore]

Sikoniko,

If you are happy with your system as is, don't do anything. Why mess with a good thing? Just enjoy. That is my sentiment.

Besides, too, the longer you wait to upgrade, the more state-of-the-art stuff you are going to get, so why hurry?

That said:

There has been a significant upgrade from s1 to s2 for 603. 603 s2 was definitely an improvement as it employed a bona-fide woofer driver rahter than a passive radiator. The passive radiator in S1 with ports resulted in a rather sluggish bass. Don't know about 604. I think as far as 604s are concerned, the improvements are more subtle. A slightly more extended highs, the Nautilus tweeter, etc. But I suspect, the nature of the sound really did not change that much.

Now, I did notice an improvement in sonic quality when I went from the RSX 1065 receiver to using the 1055/1075 combo. I am very happy with the result. It just sound cleaner and better defined. With the 1065, at the loudest loudness level *I* usually play when mood strikes, I noticed a hint of harshness. But not with 1055/1075. The system just seem to coast right through. Easy and smooth.

I have not heard the 1055 through its amp section. But the 1055 has less powerful amps than the 1065, slightly hight THD, and 3 dB lower SNR figure, so I imagine the difference you'd notice would be greater when you do add an external amp like the 1075.

Regards,

[BleakShore]

Just an update for those who are curious,

Finally tried a few different configurations and settled on this.

Final set up
1055 drives:
- 2 back center speakers (Infinity RS5b) via redirected two front channels
- 2 side surrounds (603 S2)
- center tweeter/mid drivers of (LCR6 S2)

1075 drives:
- center bass driver of (LCR6 S2)
- 2 channels drive left front (604 S3)
- 2 channels drive right front (604 S3)

With this configuration, I am using all 10 channels of amplification from 1055 and 1075.

- The two fronts are pseudo bi-amped wiht 1055.
- The center is pseudo bi-amped with 1055/1075 combo.
(Pseudo bi-amped because I am not using active crossover with internal defeated)

Findings
- I measured SPL to make sure there is no gross mismatch of signal levels out of 1055/1075 to drive the center. There was practically no difference in SPL levels, so the combo tracked well.

- The 1055 and 1075 runs cooler than before.

- The system sounds, to me, smoother (less strained) and very pleasing.

Conclusions
If you have the amps anyway because you are using a respectable receiver as a pre/pro, then I think it is definitely worth bi-amping. Now the two fronts get 240 Watts each, and the center gets 185 Watts.

To me, it really made everything sound with so much definition and authority. I really like the sound. It was well worth the effort.

I'd not hesitate to encourage anyone to try this configuration, if you hhave a 1055/1075 setup. I am hoping this set up is now closer to the performance of the 1066/1095 combo.

[alkaline6]

BleakShore,

I am trying to decide between the Rotel 1055 / 1075 vs. 1066 / 1075 combos. Based on your observations, it sounds like the 1055 / 1075 is the winning pair.

I do have a question though about the 'bi-amping' issue. Could you describe in detail how you wired the 1055 and 1075 to your speakers? Did you install a crossover between the receiver and amp? I will be powering the B&W 704's as my mains.

[BleakShore]

... Could you describe in detail how you wired the 1055 and 1075 to your speakers? Did you install a crossover between the receiver and amp? I will be powering the B&W 704's as my mains.

As I mentioned in my post, it was "pseudo bi-amping", not the true bi-amping. No external crossovers employed between the receiver and the amp.

This is what I did

Center:
1. Remove the metal clips from the speaker's 5-way binding posts.
2. Connect the 1055 power amp to center tweeter/mid terminals.
3. Connect the 1075 power amp to center bass terminals.

Fronts:
Use two 1075 amps to power the left and right speakers, similar to the center above.

If you want to truly biamp the speakers, you have to open up your speakers and bipass the internal crossovers, and put active/passive crossovers in between the 1055 and 1075 as you suggest.

Note that, if you have a three way speaker, the bass driver will be amp'ed separately (with external crossover ensuring proper spectrum being delivered to the bass driver).

But the mid/tweeter will still have to use the internal crossover even if you use an external crossover.

What I did was a quick and dirty: I figured since I have the amps, why not. There was nothing to lose. At the least, you get doble the power to speakers.

[alkaline6]

How did you connect the 1055 to the 1075 amp. Did you split the L and R Pre-outs to the 2 amp channels each?

[BleakShore]

Hi,

Ok. This is what I did.

1. Buy 2 Y cables of your preferred brand (one male to two females).

2. Split the front left front pre-out from 1055 using the Y connector and connected to two left-most 1075 amps. This allows connecting a single RCA L/R stereo cable to two adjcent amps for neat cable arrangement.

Note: You can connect the split preouts to any two 1075 amps. Just keep track of it.

3. Do the same for the right front pre-out from 1055 and connect to two right-most 7055 amps.

4. Set 1055 to reroute two front amps to two back centers.

5. Connet all speakers.

7. You got some powerful 7.1 set up!

Good luck. I dare say you will like it. I enjoy it emmensly!

[Mike Hayes]

If you have the amps anyway because you are using a respectable receiver as a pre/pro, then I think it is definitely worth bi-amping. Now the two fronts get 240 Watts each, and the center gets 185 Watts.

I don't think that you are getting 240watts of overall wattage for your mains but rather, you have a dedicated 120 watts for the tweeter and a dedicated 120 watts for the midrange. I don't believe that this necessarily equates to a doubling of overall output.

[BleakShore]

I don't think that you are getting 240watts of overall wattage for your mains but rather, you have a dedicated 120 watts for the tweeter and a dedicated 120 watts for the midrange. I don't believe that this necessarily equates to a doubling of overall output.

I beg to differ.

1. One 120W channel is dedicated and connected to the BASS driver. After going through the internal crossover (low pass filter), all of the 120W is going to the BASS driver with the exception of the loss in the crossover itself. There is no load on the amplifier for the high freq range (normally for the tweeter) as there is no tweeter connected to this. Therefore, all of the 120W is available to the bass driver.

2. Another 120W channel is dedicated and connected to the MID/TWEETER drivers. This 120W is in turn split by the internal crossover that feeds the tweeter and the mid driver. Likewise as explained in #1 above, all of the 120W of power is being delivered to the tweeter and mid drivers.

Think about what you just said. If what you said were true, there would be no power goint to the bass deriver, and the you would not get any bass at all!

Regards,

[aud19]

I personally still think you'd be better off using the 1055's internal amps and speaker outputs for the mid/tweeter and then just the 1075 for the bass. This way you don't have to split the signal anyway externally which can only do some harm, no matter how minor, no matter what quality splitter you use to the signal. Just my 2 cents.

J.R.




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[Mike Hayes]

Okay, so 120w is going to the bass driver and 120w is going to the mid/tweeter. Still don't think that this equates to doubling your overall wattage. It just means that you are using a dedicated 120 watts for each part of the speaker. Are you saying that your configuration is delivering the same wattage to your mains as a 240 watt amp would?

[BleakShore]

Mike,

Yes. Pretty close to delivering all of 240 Watts.

There have been numerous studies done on the required powers by the low freq drivers (woofers) and the high freq drivers (mid/tweeters) on two-way and three-way system speakers.

I don't recall and have the links, but surf the net and you will find various articles on the subject of bi-amping. There are tons of information out there. Some good and some snake oil ("the problem with the world is not that people know too little, it is that people know too many things that just ain't so", M Twain).

These articles point out that, for typical speakers with the low crossover freq of 350 Hz, the high and low freq drivers require about the same amount of power.

Restated, if your speaker cross over is at 350 Hz, and if you drive the speakers with a 100 Watt amp, then 50W will be used by the bass drivers, and the other 50W goes to the high freq drivers (tweeter/mid).

If the crossover is set at higher than 350 Hz, then more power is required by the bass drivers than the mid/high drivers, and vice versa. The required power ratios as a function of the crossover freq is tabularized in some of the articles on the subject.

My B&W speakers crossover is 400 Hz. So the low and high freq drivers require about the same amount of power. If I use a single 120W amp, then 60W and 60W will go to the low and high drivers, respectively. If I use two 120W amps for each low and high drivers, then each driver will use the same amount of power, i.e., 120W each.

If my crossover freq is, say, 1 kHz, then the required power ratio may be 70:30. In that case, it would make more sense to use 120W and a 50W amps for the bass and high freq drivers, respectively. 1075 and 1055 combo would deliver the required powers with fairly close to this ratio.

To answer Aud16, I prefer to use the same amps for bi-amping for the followinf reasons:

1. It is unlikely that two different amps (1075 and 1055 for example) will have identical voltage gains, not to mention other subtle attributes. I asked Rotel about this and was told that this is so with the 1075 and 1055 combo. This means, at the same volume setting, there will be a mismatch in the delivered power to the low and high freq drivers.

So before I used the 1075/1055 to biamp the center, I did a quick check how much "off" the two amps were. I found them to be close enough for "government work", and decided the sound was more pleasing to me than not. So I went ahead with it.

2. The mismatched gains of the amplifiers will result in an effective shift in the crossover frequency, affecting the tonal charcteristics of the speakers.

3. Different rise times, slew rates, etc, etc, will all affect sonic characteristics of the speakers.

4. For these stated reasons and knowing that my speaker's low and high freq drivers would require about the same amount of power, I knew: a) I wanted to use two identical amps with equal power, and b) I did not want to use two different amps (even with same powers) for the my speakers, especially for the mains.

5. Also the way I biamped my system was the only option for me to get the 7.1.

6. I won't touch splitting issues.

7. So all things considered, the way I have it set up is optimal for MY system.

Regards,

[Mike Hayes]

Hmmm.... do you have links? If what you are saying is true, my next logical amp upgrade would be a second 1075. I have a 1066/1075 and so, adding a second 1075 would allow me to biamp everything at 120watts (I am using a 5.1 system with 2 ways all the way around). I had always thought about adding a nice 2 channel, 200 watt amp like the 1080 but maybe a second 1075 would be the ticket instead. I am not terribly interested in 7.1 at this point.

[espo]

Are any of the amps bridgeable? If they are I think you would be better off since the bridged power is usually more than double the single channel power. Also the power would be available to all drivers in the speaker to draw from as needed, depending on the demands of the music/soundtrack you are playing.

[BleakShore]

Mike,

Here is the link Rod Elliott on Bi-Amping.

The article is by Rod Elliott titled "Benefits of Bi-Amping (Not Quite Magic, But Close)". In particular, see Section 1.3 "Power Distribution and SPL". For convenience, this is that power distribution table from the article:

Xover Freq (Hz) Power to Bass (%) Power to Mid+High (%)
========== ============ ===============
250 40 60
350 50 50
500 60 40
1,200 65 35
3,000 85 15
5,000 90 10

I found his article to be one of the best I've read in a while. Well written and he knows his subject. Learned a thing or two from it. .

In your situation, Mike, I don't know which is the better way. If the 200 2ch amp is cheap, that might be a cost effective way to go about powering the two mains. And you will have two extra amps for 7.1 if you wish to do that some time. On the other hand, if the amps cost about the same, that I'm inclined to agree with you; i.e., getting another 1075 just may be the ticket.

Incidentally, for the one who asked the question, these amps are not bridgeable.

Regards,

[Mike Hayes]

Thanks for posting that link, it was elucidating. I was thinking of bi-amping in the sense of adding a 2nd amp but leaving the speaker's crossover intact and bi-wiring. The author indicates that the second amp is basically worthless in terms of the benefits of bi-amping in a bi-wired system with the speaker's built in crossover still intact. He encourages disconnecting the crossover inside the speaker (to me it seems like there are warranty issues for those who choose to do this). For those of us using all 2 ways, it sounds like disabling the (in my case) 3 Khz crossover inside my 2 ways would provide nominal and maybe even 0 benefit. It sounds like the biggest bi-amping winners are those with 3 way speakers and the biggest gain is to be had by disabling the mid/low bass crossover inside the speaker as it looks like there can be some very large losses at this crossover point. The electronic crossover is not a problem . After reading this article, it appears that the biggest bi-amping gain for me would be a bigger amp for the sub. My Adire Rava has a 250w amp but next time, I think I will look for a sub with a somewhat beefier amp. I am back to thinking a 1080 2 channel amp is the way to go for the mains.

[Mike Hayes]

Actually, I think the 1095 would be even better for my 5.1 needs rather than 1075/1080. At some point, I think I will sell the 1075 and upgrade to the 1095. This is quite a ways down the road and don't get me wrong - the 1075 is a fantastic amp for the $$. It is doing a fine job driving my 805s/HTM2/601s. However, I have been wondering about the 1095 for awhile now.

[Mike Hayes]

Bleak,

If I am reading your posts correctly, you have not disabled the crossovers within your speakers? It sounds like, based on the article, to reap the benefits of bi-amping you must disable the speaker's internal crossovers and use an external crossover? And so, it is still not clear to me that you are really getting the 120w split that you are trying to achieve. This guy seemed very clear - the benefits of a second amp in a bi-wired configuration with the speaker's internal crossover intact sounds negligible. I'm not trying to be a jerk but rather, simply trying to understand the concept. As you indicated, since you have the extra amps in the 1055, you really have nothing to lose but it sounds like it may be a stretch to conclude that you are getting a true 240 watts to your mains unless you take it to the level that he has indicated. I do agree with you though that in theory, it sounds like 240w to your mains could be achieved with your current amp capabilities by going with a truly bi-amped system rather than a pseudo bi-amped system.

[Mike Hayes]

The most common question I get (three or four times each week) is

"Do I need to disconnect the passive crossover in my speakers?"
The answer is ... YES, otherwise you are not really biamping at all.
Generally speaking, the mid to high section needs to be retained since a typical biamp setup will only eliminate the bass to mid+high network. These sections are nearly always completely separate networks, although it may not seem like it when you first have a look at the board.

Equally important is the selection of the electronic crossover frequency. It must be the same as the original, within a few 10s of hertz. The only exception is where you might obtain information from the manufacturer of the speaker that allows the frequency to be modified. In general, I strongly suggest that you determine the original crossover frequency, and stay with it.

When the crossover is modified, make sure that you retain all the parts, along with the original connections. A drawing (including all component values) and photograph will be of great assistance when you want to restore the speakers to normal prior to selling them - it is unlikely that you will ever want to do this for your own use - not after you have enjoyed the benefits of biamping for any length of time.

Passive biamping (where two amplifiers are used in a bi-wiring connection) is, IMHO, a waste of money. Although there may be some moderate sonic benefits, they are not worth the expense of the extra amplifier.

The above quote is the basis for my last post. :?

[BleakShore]

Mike,

In my previous posts, I made it clear I did not bypass the internal crossovers. Let me also state at this time that I'm not advocating the approach I took. Rather, for those in similar situations as I am, I was simply pointing out what one can do to fully utilize all the resources that are avialible to them.

There are many issues to consider when one does this. If you use internal amps of teh1055 when it is being used as a pre/pro, the added noise level from the power amps being used in full force in one concern. The power drain on the buss is another. It goes on. All these will affect the pre/pro performance. It's all about trades and personal prefereances.

That said, let me summarize.
There are two advantages to true biamping as Mr. Elliot points out in his article:

1. it employs extrenal crossover to avoid less than ideal performance of internal passive crossovers under time varying, nonlinear, and dynamic loading of the speakers.

2, you get additional powers from multiple amps.

What I did is sort of like the biwiring; however, it does offer one of the advantages. viz, you get additional powers from multiple amps .

If you want to read more about biwring, do some more surfing on the subject of biwiring and biamping.

True,I do not get the full benefits of true biamping. The reason I did what I did is:

1. I had extra amps sitting around in 1055 doing nothing anyways.
2. I did not want to mess with internals of my speakers. I like keeping my gear in their original conditions.
3. I did not want to spend tweeking with external crossovers at this point. It is the can of worms I did not wish to tackle at the moment. I have set up my church's audio system using some heavy duty gears and bi-amped them. It sounds good, but it took a lot of work to get it right.

[Mike Hayes]

Bleak, thanks. I do agree that you are getting the extra power benefit (sometimes it takes me awhile) I spoke with a couple of dealers yesterday about 2 1075s verses a single 1095 and both felt that they are nearly equivalent options with the 2 1075s holding a slight advantage powerwise.

Also, I realize that you were not trying to advocate what everyone should do but rather, sharing an option with the members of the forum. Like you said, if you have the amps, use them. Congratulations on an ingenious use of the amps at your disposal

I am still pondering what Mr. Elliott said regarding the sonic benefits of passive bi-amping (leaving the speaker crossover intact) verses active bi-amping. It almost sounds like he would conclude that the 2nd 1075 would be a waste of money if you stick with the passive route. Not sure what to conclude at this point. Doubling the power seems like it would have very noticeable sonic benefits. I guess I will leave it at that for now.

[Mike Hayes]

Okay, just want to add a few more thoughts:

1. Since my speakers crossover at 3 Khz, my current 1075 splits the 120wpc in a ratio of roughly 85:15. This equates to roughly 102w below 3Khz and 18w above 3 Khz.

2. The only thing that would change with a 200wpc Rotel 1095 would be the amounts, not the ratio and so, the amp would send roughly 170w below 3Khz and 30w above 3Khz.

3. Here is the big difference as I see it. 2 1075s passively bi-amped (bi-wired) would alter the ratio to roughly 50:50, ie, 120w below 3Khz and 120w above 3Khz.

Based on the 85:15 ratio, leaving the intenal 3Khz crossover intact, it does not appear that I really need 50% of the overall wattage directed above 3Khz and so, using 2 1075s in a passive bi-amp (bi-wire) configuration appears to be a waste of the second 1075's available wattage. It seems like the 1095 would actually be a more efficient amp because more power would be directed below 3 Khz where apparently, the speaker manufacturer intended it to go. Am I completely missing it or does this seem correct?

[NonSense]

Hello all.

I've been following this forum for quite some time. Enjoying all the great postings, but having very little to contribute thus far. Thought I would finally join, and likely increase the entertainment of all those in the know.

I have no expertise with the design of audio amplification electronics (or in that matter, anything in general), but a couple design principals often used in the design of small signal electronics may in fact also apply to the bi-amp/bi-wire topic.

If you were to look at a specification for an op-amp. One of the key specifications you would consider in your design would be the Gain/Bandwidth product. This is a performance spec that implies that the broader range of frequencies the amplifier is required to handle, the lower the gain capability of the amp before it begins to compress (ie: clip).

Let's make the stretch for a moment and consider that this model is applicable to the audio power amplifier characteristic. (Did I mention this would be entertaining) (We all know that the amp must still be capable of covering the audio band regardless of the limited BW it is presented. Lets forget that for now.)

In the 1xAMP/1-Wire situation, you deliver frequencies (20-20KHz+) to the loudspeaker. The passive crossover network (ie: 2Way) has some insertion loss, with the power for the highs going to the tweeter/Midrange and the lows to the woofer, and some power split to both within the crossover point of the network.

In the 2xAMP/Bi-Wire situation, your pre-amp is still delivering a full spectrum of frequencies (20-20KHz+) to the input of each amplifier and delivering it (the full spectrum) to the loudspeaker crossover binding posts (even when separated). The separated passive crossover network will again have some insertion loss as before, but now all the unwanted frequency power (which would normally be sent to the other network) will be dissipated as heat in the separated crossover network. (No need for concern, the designers will have considered this when they decided to give you two sets of binding posts.)

In the 2xAMP/Active Crossover/Bi-Wire situation, you now limit the frequencies into the power amplifier by removing the unwanted high and lows at the pre-amp output levels. If the Gain/Bandwidth model holds true, then you should see a significant gain in performance of your amplifier, because each unit will now be responsible for a reduced range of frequencies. The amplifiers energy lost as heat in the passive crossover network configuration, may be put to use in the dedicated frequency band of the active crossover configuration. And you will also regain the insertion losses associated with the passive network. Direct control of each driver for better or worse?


Having said all this, I have no idea if this model holds true. Wouldn't I love to have enough capital to do some tests.

Would a higher wattage amp outperform two lower wattage separated amps? It's possible. I would expect each situation to differ, and the listener could be the judge.


IMHO: If you were to compare 1xamp vs. 2xamps of the same type (wattage) in the first two situations. I would expect to hear a better performance from the two amp configuration. What comes to mind, is that the dissipation in the crossover would be stable vs. the extra effort the 1x amplifier requires to control backlash from the mechanically loaded (wildly inertial) drivers on the other network.

Something to ponder.

[espo]

NonSense,
If your conclusion is correct, then bi-wiring should always be better than single wiring. Also if the 1xamp is the same power as the 2xamps combined, and the speakers are bi-wired, the larger amp should be much better, due to the increase in dynamics, soundstage, and openness usually associated with a larger amp.

[BleakShore]

Okay, just want to add a few more thoughts:
... It seems like the 1095 would actually be a more efficient amp because more power would be directed below 3 Khz where apparently, the speaker manufacturer intended it to go. Am I completely missing it or does this seem correct?

Hi Mike,

If your speakers are indeed crossed at 3 kHz (a two-way system, is it?), then you are indeed correct, sir.

Getting 1095 would make more sense. 2 1075s would be a waste.

Regards,

[BleakShore]

...
In the 2xAMP/Bi-Wire situation, your pre-amp is still delivering a full spectrum of frequencies (20-20KHz+) to the input of each amplifier and delivering it (the full spectrum) to the loudspeaker crossover binding posts (even when separated). The separated passive crossover network will again have some insertion loss as before, but now all the unwanted frequency power (which would normally be sent to the other network) will be dissipated as heat in the separated crossover network.
....

Greetings NonSense, Welcome to the discussion.

What you said above is not quite true. Let's take the bass side first. The amp for the bass is delivering a full bandwidth signal to the speaker (let's say it is 20-20k for now).

The internal crossover network will indeed introduce insertion loss. This insertion loss will show as dissipated heat.

To simplify the discussion, let's assume that the crossover for the bass is a very simple first order L curcuit; i.e., there is just an inductor in between the amp outputt and the input of the bass driver, the load.

At the risk of boring some, let me present a quick overview of the inductive impedance, Z. Z will tend to infinity as frequncy increases, as Z = j2 pi f L, where j is sqare root of -1, f is the frequency, and L is the inductance. This represents a 6 dB/octave impedance curve (a line in this case), tending to infinity as freq increases. It's 6 dB because every doubling of frequency, the impedance also doubles.

For a more complex crossover network, the impedance of the network would be very low and is constant below the crossover freq, and would increase linearly as frequency increases. For a first order network, this would 6 dB/octave, for a 2nd order, 12 dB/octave, etc.

Simplifying further, if we use an ideal "brick wall transfer function of the crossover network, the impedance of the network is infinite right about the crossover freq.

What that says then is that above the crossover frequency, the amp is looking at an open circuit, viz a viz, there is no load presented to the amplifier. No current flows to the speaker, as the crossover is now an open circuit. It is as if nothing is connected to the amp.

So the all the power from the amplifier is available to the operating band of the bass system, that is 20 Hz to crossover frequency. In Mike's case, this bandwidth would be 3 kHz.

Same analysis holds true for the tweeter side, except a capacitor would be the simple crossover network, with its capacitive impednace going to zero as freq increases, and open circuit at DC.

So, just as in the external active crossover case, you will get the benefit of the extra amplification. The only difference is the less than ideal performance of the internal crossover network due to the highly nonlinear impedance of the speaker drivers itself.

Regards,

[BleakShore]

Accidentally posted twice. Stupid PC..

[espo]

BleakShore I qote:
"Simplifying further, if we use an ideal "brick wall transfer function of the crossover network, the impedance of the network is infinite right about the crossover freq.

What that says then is that above the crossover frequency, the amp is looking at an open circuit, viz a viz, there is no load presented to the amplifier. No current flows to the speaker, as the crossover is now an open circuit. It is as if nothing is connected to the amp."

I thought impedance is resistance, therefore infinite resistance is the opposite of an open circuit. If I am correct more power would be dissipated. However I see imperically that V/I=Z, so if Z is infinite, then I approaches 0.

[BleakShore]

Infinite resistance/impedance is not the opposite of an open circuit. It is the opposite of a short circut.

Impedance is a more general case of resistance. Impedance Z is complex and is defined as:

Z = Zreal + jZimg,

where Zreal is the real part of the impedance (is the resistance if Z is purely real, ike a resistor), Zimg is the inductive or capacitive "resistance", and j is the imaginary operator.

High impedance (if real, is equal to high resistance) limits the ability to conduct current, i.e., it impedes or resists the current flow of a circuit. If something infinitely impedes or resists the current flow, no current flows through it.

An open circuit has infinitely high resistance, i.e., no current flows through it. An example of an open circuit is a broken wire or an "open" switch. If a speaker wire is broken, no current flows through it, and no sound will come out of the speaker.

Power dissipated through an open circuit is (as you pointed out):

P = i^2 R = 0, as i (current) is 0.

So for a bass driver crossover, the impedance is infinite above crossover freq, no current flows, no power is delivered to the speaker (as the crossover looks like a broken speaker wire), and no high frequency sound comes out. As power for the high freq specrum is never delivered to the speaker in the first place, no power is "wasted". The amp is only delivering power for the low frequncy spectrum.

The opposite of an open circuit is the short circuit. That happens when you connect two ports/devices/lines with a 0 impedance (or resistance) device. An example of a 0 resistance device would be a piece of common, nice copper wire. The power dissipated in the wire is:

P = i^2 R = 0, as R is zero. So, the piece of wire does not get hot. In practice, all copper wires have small resistance (like .01 ohm per meter), so if you stick a pirce of thin copper wire in the household 120V socket, it will blow, because it gets real hot. Because of near zero resistance of the wire, the current through it would be near infinite. Poof.

Hope I was not too tedious.

Regards,

[espo]

Thanks BleakShore,
I thought current actually flowed into resistance(load) and either powered the load (light bulb) or was dissipated as heat (resistor). I didn't realize resistance actually "opened" the circuit, or put up a wall to current flow. Live and learn!

[Mike Hayes]

If your speakers are indeed crossed at 3 kHz (a two-way system, is it?), then you are indeed correct, sir.

Yep, a 2 way system consisting of:

B&W N805s - fronts (crossover = 3 kHz)
B&W HTM2 - center (crossover = 3 kHz)
B&W 601s - surrounds (crossover = 4 kHz)

Thanks for confirming

[dirk67]

Hi,

why are you always talking about using the RSX 1055 as a prepro and kind of "waste" the built in power amp section when there is the RSP 1066 as a dedicated prepro? In Germany the RSP 1066 is 1649 Euro while the RSX 1055 is 1999 Euro, so the 1066 is even less expensive. Ok, with the 1055 you also get a tuner, but I think with a 1066 you get more amp for the money.

Greetings,
Dirk

[BleakShore]

Hi dirk67, Greetings.

..In Germany the RSP 1066 is 1649 Euro while the RSX 1055 is 1999 Euro, so the 1066 is even less expensive.

Here in the states, the 1066 costs $1600 USD and 1055 costs $1300 USD. WIth a slight discount (Rotel holds their MSRP fairly tightly), I got my 1055 for $1200. I could've gotten the 1066 for $1500 or so I guess.

So, I get 1055 which has the same pre/pro features as 1066 albeit slightly compromised performance in terms of SNR, etc., but I get 1) the tuner, 2) built-in 65W x 5 amps, and 3) save $300 in the process as well. Apply the $300 toward the purchase of 1075, and it is a bargain.

That's why all the discussions.....

Regards,

Haben zie ein guten tag (one year of German in high school , hope I got it right)

[BleakShore]

..I thought current actually flowed into resistance(load) and either powered the load (light bulb) or was dissipated as heat (resistor). I didn't realize resistance actually "opened" the circuit, or put up a wall to current flow. Live and learn!

Hi espo,

What you say is actually true. Current flows into a load which has a finite impedance/resistance. Depending on the impedance (8 Ohm typical for speakers), the amount of the current the load (speaker) draws (demands) vary.

The lower the impedance, the more current it will draw. That's why the 4 Ohm speakers or speakers with very low impedance (like Maggies, in 1 to 2 Ohm range, i think) are such a hard load for amps. The amp must be capable of supplying the current before it dies.

For example, if you connect two 8 Ohm speakers, they look like a single 4 Ohm speaker. It is easy to see that two 8 Ohm speakers will demand more current (twice, in fact) than a single 8 Ohm speaker.


Given the load, think of the crossover network as a valve like water faucet. Fully open, water (current) is allowed to flow freely into a load. How much water actually flows depends on what you have connected as a load (speaker).

If the load is a garden sprinkler with a couple of tiny holes, not much water would flow, as the load has high resistance. If a hose with a large opening is connected to the valve, then the water will now flow like crazy (low resistance load, Maggies).

So, your statement "current actually flowed into resistance(load) and either powered the load (light bulb) or was dissipated as heat (resistor)." is absolutely correct.

The resistance of the crossover (the valve) controls the flow of current into the load (speaker). When high, it blocks current flow into the load (speaker), so no sound comes out. Except the crossover is frequency selective.

Regards,