Bi-amping Rotel RB-981s.

[Baz Tench]

Hi all. My home set up at the moment consists of a Rotel RB-981 power amp and a RC-971 pre-amp. I've just won an eBay auction for the same combination again as I am going to go down the bi-amping route.

My plan is to possibly sell the pre-amps and get a really nice one to power the two power amps. Is this a good idea, and if so - what pre-amp would you recommend? They would be powering a bit of a home Dj set up (twin technics SL1210 record decks and a mixer, so I'm not looking for audiophile qualities, just a fun meaty sound.

Also, a speaker upgrade will be on the agenda next, but I can't see many options with a power handling rating above 200 watts per channel (budget for speakers is around £800- £1000 at the moment).

Thanks in advance for any suggestions.

[clived]

Why change the pre-amp? In fact - why use one at all - your mixer is a pre-amp after all

[Baz Tench]

Hmm, I didn't think of it like that!

[Crackie]

I've been using RB-981 / RB-971 power amps for almost 20 years and would advocate going bridged mono rather than bi-amping.

I have three RB-981s and three RB-971s running in an active system and have been able to get them all into the lab, where I used to work, to measure them. Both models measure very well in conventional stereo or Bi-amp mode but they're much better in bridged mono. Just under 400w per channel into 8 ohms for a 981 should give the power you need and configured this way will also help with fun meaty sound you're looking for.

Regarding the RC-971 pre amp, I've not used one. I've seen Hi-Fi News' and Hi-Fi Choice's tests of the pre and both said it was average at best. Using the mixer is a good plan but please check out the mixer's output voltage spec first. The RB-981 has a high input sensitivity; full output is reached with only 1.0v input and most DJ type mixers are likely to be capable of supplying far more than 1.0v. Mixers are likely to supply 1.0v when their output meter is showing 0.0dB. Certainly worth checking out.

The RB-981 and RB-971 both appear to be gaining a bit of a reputation; their second hand prices are often higher now than twenty years ago when new.

For the alternative speakers, how about these http://www.lean-business.co.uk/eshop/ldeb152-ld-sy...
LD rate that model's power handling as 500wpc....should work well with bridged 981s. They'll be capable of huge volume levels even in big rooms.

Edited by Crackie on Friday 2nd September 08:21

[anonymous-user]

I've been running a pair of RB 971's in bridged mono with an RC850BX pre amp, also have a phono pre amp as well, (a 20 squid bargain at the audio jumble in Tonbridge Wells) They drive a pair of TDL floorstanders and it sounds mighty fine to me. I'm not surprised that they are going up in value, for the money they are great bits of kit. Scuse rotten photo..no idea why it's sideways.

[Some Gump]

Baz Tench said:

Hi all. My home set up at the moment consists of a Rotel RB-981 power amp and a RC-971 pre-amp. I've just won an eBay auction for the same combination again as I am going to go down the bi-amping route.

My plan is to possibly sell the pre-amps and get a really nice one to power the two power amps. Is this a good idea, and if so - what pre-amp would you recommend? They would be powering a bit of a home Dj set up (twin technics SL1210 record decks and a mixer, so I'm not looking for audiophile qualities, just a fun meaty sound.

Also, a speaker upgrade will be on the agenda next, but I can't see many options with a power handling rating above 200 watts per channel (budget for speakers is around £800- £1000 at the moment).

Thanks in advance for any suggestions.

OP,

First, good choice. the 981 is epic. You only need 1 preamp - sell the other immediately.

You can do 2 things with them, depending on what speakers you have and desired outcome.
1 - run them bridged, 1 amp per speaker as monoblocks. They're epic this way.
2 - Run them as bi-amp - needs speakers with 4 posts / links removed. You just need 2 sets of interconnects - use both outputs on the 971 to the powers.

Few things:
Never, ever ever switch between stereo and bridged with the unit switched on. If you're lucky, it'll blow a fuse (easy fix). If you are unlucky, it's about 80 quid to fix. Ask me how I know that.
A poster above suggests going mixer-amp. I can't disagree more - leave the pre amp in. Your mixer can very easily be kncked / twiddled by a mate into blowing stuff up territory. The pre protects from this.

Finally, if you're upgrading speakers later, then B+W 600 series S2 or S3 are epic. 602 (stand) or 604 (floor) are the picks of the bunch imo.

[Baz Tench]

Thanks for the suggestions! It seems I have a few interesting options. My speakers are Acoustic Energy floor standers (bi-wired) at the moment (power handling is 200w per channel).

I thought bi-amping and bridging was basically the same thing btw. Some more research needed!

[Some Gump]

Generally, bi-amping is using 2 amps to drive treble and bass. The beard types argue that this gives better seperation of high and low, and make it sound purer.

Bridging your amps means that it uses "more" to drive 1 channel. The rotel designs are brilliant at it. Non beard people would say that this is the better bet, because you have such a vast amount of power / current on tap that you never get the amp "stressed" and so it sounds better.

I used to use 981's with 1210's to play drum and bass. Loud. bks to detailed treble (my cartridges were only cheapie 500's) - I just wanted epic bass with loads of punch. bridging made that epic.

PS - IMo you'd get a LOT more out of better cartridges than a better pre amp, if that's something you're considering later on. Next I'd look at your mixer, and only after you've gone to daft levels there change the pre. You're rellay not going to notice the difference on your DJ setup even if you swapped that 971 to a 1070 pre or similar (at loads more money) - even though e.g a CD from a decent player might get a wee bit better.

[Crackie]

Baz Tench said:

Thanks for the suggestions! It seems I have a few interesting options. My speakers are Acoustic Energy floor standers (bi-wired) at the moment (power handling is 200w per channel).

I thought bi-amping and bridging was basically the same thing btw. Some more research needed!

Rotel's power rating on the 981 amp was conservative; the spec was 130w into 8 ohms but they are able to deliver over 33amps continuously i.e. 160w into 8 ohms loads. They'll also pump 35amps ( 200w ) for dynamic peaks. This is what a 981 will deliver when used in conventional stereo or bi-amp mode. The improvement when using two 981 amps to bi-amp was noticeable but subtle. imho of course.

Bridging an amp ( converting to mono ) involves feeding the positive cycle of the signal to one amp channel and the negative cycle to the other channel. Consequently the current/power available to drive each speaker will be doubled because left and right are configured/combined to behave as one. Changing to mono on a 981 is a, very simple, two minute job and is just a case of moving three jumper links on the circuit board. It is clearly explained ( with pics ) in the instruction manual. The improvement in sound quality when using 981s as mono amps is far from subtle........10-15% better to my ears.

Hope you enjoy your new amp, whichever way you decide to configure.

All the best,
Beardy Crackie.

Edited by Crackie on Friday 2nd September 14:48

[Baz Tench]

Being a non-beardy type, I think bi-amping is more for me based on the info above. Thank you all very much for clarifying!

My cartridges are Ortofon 'Nightclubs' which are very impressive tbh.

I'm going to pick up the amp I've won tomorrow, and will sell one of the pre-amps and use the other one, again - based on the above information.

Thanks very much!

[Baz Tench]

A little update. I brought the amp home earlier and wired it up (bi-amp). Wow! I'm very impressed! It definitely sounds a lot better as a whole system. Smoother, deeper bass, higher highs, greater detail... For me, it's got the lot now.

I will probably go down the bridging route in the future, but it is plenty powerful enough at the moment for my little two bed semi. I suppose I am curious at doubling the power by bridging though.

A sweet thing about this is the price I paid, £210 for the amp and pre amp (the pre amp I will sell), and about 20 quid in fuel means it was a bit of a bargain.

Very happy with the results!

[Some Gump]

Bridge it and stop being a ponce.

Then play a bass heavy tune.

Crackie is a professional, listen to him =)

PS - with hindsight it seems that I had both 870's and 981's. The "blow the up" switch was removed in the 981. Both were the same design =)

[Baz Tench]

I've decided to shelve the new speaker thing for the moment, but I can't see that lasting long .

My current AE floorstanders would struggle with bridging, whilst they seem to be very comfortable with bi-amping.

I'm enjoying the learning curve though, it's nice having these options.

[benz0]

Struggle? This is nonsense. An amp will only output as much power as you tell it to. Having an amp with more headroom in reserve should reduce the possibility of clipping and therefore maximise the dynamic range available when listening to music.

Having a 400w amp doesnt mean it will blow your speakers up

[Baz Tench]

benz0 said:

Struggle? This is nonsense. An amp will only output as much power as you tell it to. Having an amp with more headroom in reserve should reduce the possibility of clipping and therefore maximise the dynamic range available when listening to music.

Having a 400w amp doesnt mean it will blow your speakers up

Again, I'm learning. I didn't realise this. I've blown a few sets of speakers in the past, but that was apparently from setting the master volume on the mixer too high. It's made me a bit paranoid.

Edited by Baz Tench on Sunday 4th September 16:54

[Crackie]

Baz Tench said:

benz0 said:

Struggle? This is nonsense. An amp will only output as much power as you tell it to. Having an amp with more headroom in reserve should reduce the possibility of clipping and therefore maximise the dynamic range available when listening to music.

Having a 400w amp doesnt mean it will blow your speakers up

Again, I'm learning. I didn't realise this. I've blown a few sets of speakers in the past, but that was apparently from setting the master volume on the mixer too high. It's made me a bit paranoid.

Understood regarding your concerns if you've blown speakers in the past.

Using a mixer, rather than a hi-fi pre amp could cause a problem whether using bridged mono or bi-amped stereo. 1.0v from the mixer into a standard 981 will feed 200w into the AEs. 0.5v from the mixer into a bridged 981 will also supply 200w. Bearing in mind that the mixer can probably supply at least 2.0v, care needs to be used in either configuration.

What model of mixer is it ?

[Baz Tench]

The mixer is a Pioneer DDJ-SX. I have no idea what voltage it's putting out. I keep the master volume at half way and the 'trim' volumes for each channel at around half way too.

[Crackie]

I had a search to find info about the Pioneers but didn't find anything; 2.0v max from the unbalanced RCA and 4.0v from the balanced XLR outputs is a good rule of thumb. If you have your master set at halfway then that should be unity gain, 0.0dbfs on the Pioneer's output meter and 1.0V max being fed into the Rotel's input. That should be ideal.

To be sure, you could download these files and use Track 4 to check max level.
http://www.wavecor.co.uk/testdisk.html

[Some Gump]

BAz,

There's an easy way to get the level out of the mixer right - if you have a CD player.

If you put CD player into the preamp, and play a CD - then switch inputs to what you're playing on the decks, they should be roughly the same volume. Depending on the mixer, you can then either use the master gain rotary (my preference) or the master fader to control overall level. I don't like the fader option as much, because your mates can knock it / get enthusiastic and cause issues.

On the subject of faders and rotaries - personally I'm a bit scared of going over about 1/4 "+" on the bass / mid / treble controls using a hifi system. Most clubs have clever boxes that control / stop clipping, but hifi systems don't. Overenthusiastic treble skullduggery can blow tweeters =( not that treble needs boosting anyway, everyone just wants more bass!

[benz0]

Some Gump said:

BAz,

There's an easy way to get the level out of the mixer right - if you have a CD player.

If you put CD player into the preamp, and play a CD - then switch inputs to what you're playing on the decks, they should be roughly the same volume. Depending on the mixer, you can then either use the master gain rotary (my preference) or the master fader to control overall level. I don't like the fader option as much, because your mates can knock it / get enthusiastic and cause issues.

Not necessarily; there's a long thread on the harbeth user group which documents how many CD players output is way too high for the input sensitivity of many amplifiers, so they are clipping at the input stage.