Rotel Preamplifier

[Paul_Over]

Hi,

This is a totally newbie question, so please bear with me.

I have just bought 2 Rotel RB971 power amps, and I'm looking for a preamplifier to suit. Someone has offered me a Rotel integrated amp, and they told me that this can be used as a preamp' for my power amps. If that is true, how would it be connected if it doesn't have a pre-out? The only RCA outputs I can see on the unit are "tape out".

Also, these amps are monoblocks that are bridgable - I know some of the other Rotel RB range power amps from this era were capable of being pseudo-balanced; does anyone know if these amps are capable of that also?

Any advice would be appreciated, thanks.

[stuofsci02]

Hi,

This is a totally newbie question, so please bear with me.

I have just bought 2 Rotel RB971 power amps, and I'm looking for a preamplifier to suit. Someone has offered me a Rotel integrated amp, and they told me that this can be used as a preamp' for my power amps. If that is true, how would it be connected if it doesn't have a pre-out? The only RCA outputs I can see on the unit are "tape out".

Also, these amps are monoblocks that are bridgable - I know some of the other Rotel RB range power amps from this era were capable of being pseudo-balanced; does anyone know if these amps are capable of that also?

Any advice would be appreciated, thanks.

If the integrated has pre-outs then you can use as a preamp, however, if you already have the power amps I don't see the purpose of using an integrated purely as a preamp. It doesn't sound like the one you are looking at has pre-outs anyways so it probably cannot be done.

What is your price range for pre-amp. Then people will be able to make some suggestions.

It sounds like your amps are actually stereo amps that can be bridged into a a single channel. I suggest that you try running in a horizontal bi-amp configuration and also in bridged mode and determine what you like best. In bridge mode always remember that the amplifier sees the speaker as a half load. This can cause some amps a problem if the impedance becomes too low.

Cheers!

[Paul_Over]

If the integrated has pre-outs then you can use as a preamp, however, if you already have the power amps I don't see the purpose of using an integrated purely as a preamp. It doesn't sound like the one you are looking at has pre-outs anyways so it probably cannot be done.

What is your price range for pre-amp. Then people will be able to make some suggestions.

It sounds like your amps are actually stereo amps that can be bridged into a a single channel. I suggest that you try running in a horizontal bi-amp configuration and also in bridged mode and determine what you like best. In bridge mode always remember that the amplifier sees the speaker as a half load. This can cause some amps a problem if the impedance becomes too low.

Cheers!

Hi stuofsci02, thank you for your detailed response and recommendations.

These amps share only their power supply, so I believe that makes them monoblocks? That is what they are listed as anyway - sorry to be vague, but like I said, I am new to this.

My budget for a pre-amp is only around £100, hence why I am trying to broaden my horizons so to speak.

Your suggestion with bi-amping horizontally - Am I right in thinking that if they are stereo amps, and I ran them in bridged mode whilst being bi-amped horizontally, wouldn't that make me lose any balance control on the pre-amp? And if I bi-amped them vertically in bridged mode, it would be pointless bi-wiring each speaker, right? Or am I completely barking up the wrong tree? :alol:

[stuofsci02]

Hi stuofsci02, thank you for your detailed response and recommendations.

These amps share only their power supply, so I believe that makes them monoblocks? That is what they are listed as anyway - sorry to be vague, but like I said, I am new to this.

My budget for a pre-amp is only around £100, hence why I am trying to broaden my horizons so to speak.

Your suggestion with bi-amping horizontally - Am I right in thinking that if they are stereo amps, and I ran them in bridged mode whilst being bi-amped horizontally, wouldn't that make me lose any balance control on the pre-amp? And if I bi-amped them vertically in bridged mode, it would be pointless bi-wiring each speaker, right? Or am I completely barking up the wrong tree? :alol:

I had a peek at the specs for the RB-971 and it appears to be a 70wpc stereo amp that is bridgeable to a mono channel. That means on the back usually there is a stereo/bridge switch. Most often when running in bridge mode you use the two positive speaker posts and not the negatives.

If you will Bi-amp the speakers you have to first make sure your speakers have two sets of binding posts. If they do not, then biamping will not be possible. When you Bi-amp you will not have the amps in bridge mode, it will have to be done in stereo mode. See link below for diagrams for vertical/horizontal biamp.

http://www.symphonysound.com/articles/biamp.html

[Paul_Over]

@stuofsci02

Great article from symphonysound, thank you.

The configuration that you list is exactly as these amps are, but as I said before, wouldn't bridging each amp in a horizontal bi-amped setup lose control of the balance between the channels, hence why you stated that I should use the amps in stereo mode? I am assuming that in bridged mode, it means that you are joining the 2 channels together, making one more powerful mono channel, but maybe my perception of that is wrong?

My speakers are Kef iQ7SE's, so yes, each speaker has 2 pairs of binding posts to allow for bi-wiring.

Lots of people have raved about using these amps in bridged mode, so it's probably best if I try both horizontally bi-amping in stereo mode, and vertically bi-amping in bridged mode (forgetting about bi-wiring the speakers), and see which gives the best results.

Just to get a suitable preamplifier now!

If you could clear up my above questions, I will be grateful, just so I know that my train of thought is correct (or incorrect, as it maybe ).

[stuofsci02]

Hi Paul,

You are correct in what you say about Bridging. When you do this you "bridge" the two channels in the amp together making a single more powerful channel. Usually when you do this your amp should be 4 times as powerful (so for you this would be 280 wpc). Since your amp is rated a 180 wpc in bridge mode, this tells me that the amp cannot deliver the current required to get all 280 wpc. This means you need to be extra careful when running in bridge mode since the amp will see the speakers as half their impedance (so a 8 ohm speaker will look like a 4 ohm speaker to the amp).

When you are in bridge mode you cannot biamp (unless you have 4 of these RB971) because you will only have two mono amps. One per speaker. You can still bi-wire them, but the jury is out on if this improves performance.

If you leave it in stereo you will have 4 channels (two per amp). You can then biamp them either vertically or horizontally. You will need to remove the jumper on the speaker binding posts and run two sets of cables to each speaker.

[srb]

Although the KEF iQ7SEs are rated at a nominal 8 ohm impedance, they do dip down to a 3.2 ohm minimum at some unspecified frequency(s).

This would present a 1.6 ohm minimum impedance to your amplifiers in bridged mono mode. Although there are amplifiers that can operate comfortably at 2 ohms and below, I don't think that the Rotel RB971s would.

Because the low frequency portion of the speaker will consume a larger percentage of the power, I would recommend vertical bi-amping.

Steve

[Paul_Over]

Perfectly explained, and much appreciated, stuofsci02.

I'm yet to understand why the amp sees the speakers at half of their impedance when in bridge mode, but I trust your judgement, and believe that bi-amping in stereo is probably the way forward.

Yes, the bi-wiring from the same output theory makes no sense to me either, but like you said, the jury is out on that one.

Thank you very much for your time and help.

[Paul_Over]

I've just seen your help/explanation, so thanks to you too, Steve.

Like I said before, just to find a half reasonable control/pre-amplifier now. Would it be a bad thing to mix n' match with something outside of the Rotel stable?

[stuofsci02]

Paul,

I don't see any issue in another manufacturer pre-amp. For 100 pound it may be necessary. Depending on the number of inputs you have and the output voltage of your source you may be able to us a nice passive pre-amp.

Cheers

Stuart

[stuofsci02]

Although the KEF iQ7SEs are rated at a nominal 8 ohm impedance, they do dip down to a 3.2 ohm minimum at some unspecified frequency(s).

This would present a 1.6 ohm minimum impedance to your amplifiers in bridged mono mode. Although there are amplifiers that can operate comfortably at 2 ohms and below, I don't think that the Rotel RB971s would.

Because the low frequency portion of the speaker will consume a larger percentage of the power, I would recommend vertical bi-amping.

Steve

Steve,

This is a good point... 1.6 ohms might make the Rotel unstable...

[Paul_Over]

@Stuart

As I'm sure you can tell, I'm just trying to get back into this after many years with all-in-ones. My budget is pretty low at the moment, so I thought the best thing to do is buy separates that are older, but still very functionable, then upgrade components as and when I can afford to. I paid £180 for this pair of Rotel power amps, which I know are old and a mediocre amp by Rotel's standards, but they are in great condition and I thought the price was okay, and maybe I won't lose a fortune when I comes to replacing them. The same will go for the pre-amplifier that I end up buying - it will just be a stop-gap, but hopefully a reasonable one. That's the reason why I am half considering using an integrated amp, as long as it has at least one pre-out, because there seems to be a lot more of those around than dedicated pre-amp's. They also seem to be somewhat cheaper pre-owned; maybe that is because there are more around within my budget.

[stuofsci02]

@Stuart

As I'm sure you can tell, I'm just trying to get back into this after many years with all-in-ones. My budget is pretty low at the moment, so I thought the best thing to do is buy separates that are older, but still very functionable, then upgrade components as and when I can afford to. I paid £180 for this pair of Rotel power amps, which I know are old and a mediocre amp by Rotel's standards, but they are in great condition and I thought the price was okay, and maybe I won't lose a fortune when I comes to replacing them. The same will go for the pre-amplifier that I end up buying - it will just be a stop-gap, but hopefully a reasonable one. That's the reason why I am half considering using an integrated amp, as long as it has at least one pre-out, because there seems to be a lot more of those around than dedicated pre-amp's. They also seem to be somewhat cheaper pre-owned; maybe that is because there are more around within my budget.

Paul, I completely understand.. This is also what I did when getting into it.. I was using two NAD2200 PE amps (bridged) and my reciever as the the preamp.

Where are you shopping used? Is there a website that I could look at?

Cheers,

Stuart

[Paul_Over]

Paul, I completely understand.. This is also what I did when getting into it.. I was using two NAD2200 PE amps (bridged) and my reciever as the the preamp.

Where are you shopping used? Is there a website that I could look at?

Cheers,

Stuart

Nowhere in particular, Stuart. I have been checking the hi-fi forums like pinkfish/wam etc, but mainly I have been looking on eBay. Not the ideal place I know, because prices seem to go extremely high at times, whether something is great, or looks like it has been dragged behind a truck for 50 miles, it appears to make no difference to the price; where as at least with the hi-fi forums, the guys seem to know what they are selling, and are much more honest and straightforward in their approach - generalising on both counts, of course. The only trouble with those forums is volume - not so much comes up for sale, and I want one now.... I'm sure you know how that story goes too.

Funny that you mentioned using a receiver, because I was offered a Sony 6 channel receiver very cheaply by a friend, but I ruled it out immediately, because so many people have said that it's not the way to go, and will never come close to matching a hi-fi pre-amp with hi-fi, as it should be. Of course, the receiver had no HDMI inputs or output, so it's pretty much classed as obsolute for home theatre now, but probably not in the terms of what I am looking to do with it.

I meant to ask, is there a sales section to this community?

Thanks again, Stuart.

Paul

[stuofsci02]

Paul,

Recievers are a tricky thing. So much sound destruction can go on inside you wouldn't believe it. If you are happy with your analog source, keeping it analog is an important thing, so when using a reciever (especially an AVR) make sure that there is a pure analog path (analog direct or bypass they sometimes call it).

I am using an Emotiva USP-1 right now, which was $349 US and it is phenominal for the price. I have it paired with my Chord amp which was 10 times the price and have found it to be quite capable. If you were on this side of the pond I would suggest one in a heart beat.

That said, a passive pre-amp might be a good choice and be on budget.

[Paul_Over]

Hi Stuart,

Sorry that I have taken my time in getting back to you; it's been a busy day.

Yes, I saw your list of kit. Very nice - love the Chord amp, and of course the B&W 804s, which are the speakers I'd love to own, or maybe the older 703's.

What are your thoughts on using an Arcam Xeta2 as a pre-amp? It's an old pro-logic AV processor, but has had very good reviews, and it has analogue pre-outs too! This particular one is very clean, mint in fact, and is priced at £70. It's remote has gone amiss, but I have the IR codes, so an all-in-one remote is compatible.

Thanks for all your info again - I have probably taken up too much of your time already.

Paul

[stuofsci02]

Hi Stuart,

Sorry that I have taken my time in getting back to you; it's been a busy day.

Yes, I saw your list of kit. Very nice - love the Chord amp, and of course the B&W 804s, which are the speakers I'd love to own, or maybe the older 703's.

What are your thoughts on using an Arcam Xeta2 as a pre-amp? It's an old pro-logic AV processor, but has had very good reviews, and it has analogue pre-outs too! This particular one is very clean, mint in fact, and is priced at £70. It's remote has gone amiss, but I have the IR codes, so an all-in-one remote is compatible.

Thanks for all your info again - I have probably taken up too much of your time already.

Paul

Paul,

Sounds like you found something that will do the trick. The nice thing is it was designed to be used with a power amp on the main speakers, so that is nice..

Let us know how it goes...

Cheers,

Stuart