Pundit
Post by LinnBoy on Mar 1, 2020 10:39:34 GMT 12
I am a fan of bi and tri-amping, and in particular active operation. In my office system I have a Linn 5103 Pre amp, into a little Rotel RB930 power amp. (Replaced the cheap chinese valve amp) The speakers are 1/4 wave folded little towers I was involved in the development of, and are bi-wire/amp-able. Do any of my fellow Lanterneers know about the gain of Rotel amps? Were I to bi-wire, would I have to have another RB930, or can I choose from elsewhere in the range? This in order to ensure same volume output for a given volume level on the pre-amp. I prefer to use one amplifier for treble, one for bass, rather than one per channel, and prefer stereo to a stereo amp changed to mono. I used to know, but cannot remember and can't seem to find the answer online. There is such an abundance of second hand Rotel power amps, and I am a real fan of these and their CD players. They are not giant power hogs, but I think 30wpc done properly is better than 100wpc done poorly. 
I am a non-recovering audioholic, and Ivor is my higher power.
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Post by jon on Mar 1, 2020 12:24:14 GMT 12
I do not know the gain for the Rotel amps. You have not indicated whether you are using an active X-OVer or are relying on the passive crossover in the speaker...
For horizontally amped set ups as you have described and I am assuming you are using (using the loudspeaker passive x-over network)I would suggest amps of the same type so have 2 X RB930. I've done this in the past, and have come across a few issues with balance when using unmatched amps.
However for fully active x-overs (which is what I am running at home, currently) then there is no reason to restrict yourself to having the same amp for each band pass. Quite the reverse, feel free to mix and match. Just remember that bass drivers are power hungry so scale up a little to allow for this. The active X-over should be able to compensate for any power imbalances to a degree.
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Pundit
Post by LinnBoy on Mar 1, 2020 13:47:41 GMT 12
Does anyone know if Rotel amps have a standard gain?
I am a non-recovering audioholic, and Ivor is my higher power.
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Post by colinf on Mar 1, 2020 21:38:36 GMT 12
Looking at the schematic, the RB-930’s gain is set to 25dB (voltage gain of 18). The higher powered ones have slightly more gain. As an example I looked up the RB-951. It has switchable gain of 14 on low and 27 on high (22.9dB and 28.6dB). If you’re thinking of another Rotel to match the RB-930 let me know which and I can possibly work out the gain. But generally if you have a higher powered one with more gain, make sure it has a volume control or gain control on it so you can reduce it to match the lower powered amp.
AMR-iFi R&D
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Pundit
Post by LinnBoy on Mar 2, 2020 7:28:10 GMT 12
Thanks Colin, I might just keep an eye out for a pair.
I am a non-recovering audioholic, and Ivor is my higher power.
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Post by Owen Y on Mar 2, 2020 8:29:03 GMT 12
Looking at the schematic, the RB-930’s gain is set to 25dB (voltage gain of 18). Hi colinf - can you just look at an amp's specifs & work out gain using input sensitivity? eg. 1V input sensitivity => 30Wpc/8 ohms. Using Ohm's Law... gives a gain of 15.5V from 1V input?
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Post by Owen Y on Mar 2, 2020 8:41:26 GMT 12
I prefer to use one amplifier for treble, one for bass, rather than one per channel,.... I remember when I experimented with bi-amping using 2 x Leak Stereo 20 amps... I found that I got noticeably better bass when using one amp er ch - usually called 'vertical' bi-amping (confusingly). Paul McGowan explains here. See also this KEF page - Beginner's Guide to Bi-Amping.
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Pundit
Post by harvey on Mar 2, 2020 10:38:56 GMT 12
Rotel have 5ch amps that show up second hand once in a while, this may be an option?
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Post by michaelw on Mar 2, 2020 13:36:48 GMT 12
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Post by colinf on Mar 2, 2020 19:33:17 GMT 12
Hi Owen, that will give a rough idea of the gain, but as the power output might be more than 30w (it varies with power supply voltage and headroom of the power supply) it’s not as accurate. You can determine the actual gain gain from the schematic with the negative feedback resistor ratio. (R feedback+ R ground) / R ground = the gain (in parallel with the amplifier open loop gain). The open loop gain is very high in most negative feedback transistor amps so you can mostly ignore it, but for a valve amp you need to add that into the equation. Eg. Say the ratio of the feedback resistors results in a gain of 18 and the amp’s open loop gain is 100 (like a valve amp). The total gain would be 15.25. For 2 stereo amps the same I prefer vertical bi-amping too, where one channel runs the bass and the other the tweeter in each amp. Only one channel of each stereo amp puts out the higher power of the bass needed and doesn’t tax the power supply as much as horizontal bi-amping. Also you get dual-mono operation which can open out the soundstage. Let me know if I get too technical!!
AMR-iFi R&D
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Post by jon on Mar 2, 2020 20:03:21 GMT 12
For 2 stereo amps the same I prefer vertical bi-amping too, where one channel runs the bass and the other the tweeter in each amp. Only one channel of each stereo amp puts out the higher power of the bass needed and doesn’t tax the power supply as much as horizontal bi-amping. Also you get dual-mono operation which can open out the soundstage. Let me know if I get too technical!! Ok, would someone like to take a stab at defining vertical and horizontal bi-amping?
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Post by Owen Y on Mar 2, 2020 20:14:25 GMT 12
See diagrams on the KEF page above.
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Post by foveaux on Mar 2, 2020 20:26:34 GMT 12
Some pertinent advice from from the KEF article? "...So once again, if you are considering bi-amping your system, tread carefully and do as much research as you possibly can before taking the plunge. You may be better off spending your money on a really good, clean, 500WPC integrated amp, than buying 2 250WPC amps..." many advantages in the KISS principle?  
"I see music as a lifetime affair." [Rory Gallagher]
"Free - I miss that band, but when I look back, we were very young" [Paul Rodgers]
848 posts
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Post by colinf on Mar 2, 2020 23:23:53 GMT 12
Sure, but not too much thinking or research! Vertical bi-amping is easier than it sounds.
AMR-iFi R&D
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Pundit
Post by LinnBoy on Mar 3, 2020 7:06:51 GMT 12
Bi-amping takes minutes to experiment, and is a gateway drug to active.
I am a non-recovering audioholic, and Ivor is my higher power.
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Post by foveaux on Mar 3, 2020 8:07:29 GMT 12
Bi-amping takes minutes to experiment, and is a gateway drug to active. Yaha Linnboy Been there, done that, and still there with my Sanders 10e ESL system.  You're there too - with your Linn main system? f
"I see music as a lifetime affair." [Rory Gallagher]
"Free - I miss that band, but when I look back, we were very young" [Paul Rodgers]
848 posts
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Post by jon on Mar 3, 2020 8:39:09 GMT 12
See diagrams on the KEF page above. Phew, I did have it right! Thank you
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Pundit
Post by LinnBoy on Mar 3, 2020 9:39:15 GMT 12
Bi-amping takes minutes to experiment, and is a gateway drug to active. Yaha Linnboy Been there, done that, and still there with my Sanders 10e ESL system. You're there too - with your Linn main system? f Yes, Active Linn Espek speakers which are 3 way. 2 x 5 channel Linn Power amps with the active boards mounted inside. Rocks. I have had Linn Active systems for the last 30 years, pretty much.
I am a non-recovering audioholic, and Ivor is my higher power.
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