RMB-1075 vs RMB-1095

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  • Glenn
    Senior Member
    • Jun 2003
    • 109

    RMB-1075 vs RMB-1095

    Is there an "optimum" point on the volume dial with respect to an amplifier?

    For example, if I were to want an actual room sound volume of say 85db, would it be better to use a smaller 1075 amp running at 70% of its max capacity to achieve this volume level, or would it be better to use a larger 1095 amp running at 35% of its max capacity. (the percentages are for illustration purposes only, unsure of the actual percentage valules)

    I am thinking of the comparison to a car where you want to get it revving in a proper range, not redlining it but also not lugging it. Is there such a sweet spot when it comes to amplifiers? Can you "underuse" an amp, equivalent to lugging it?


    ps - This initially was a question regarding the 1075 vs the 1095, but perhaps this should be posted elsewhere?
  • Andrew Pratt
    Moderator Emeritus
    • Aug 2000
    • 16507

    #2
    Your example of RPM isn't really valid for amps since they always run at 100 percent...its the job of the pre amp to control the volume as in how much gas you're sending to the engine.

    that said I understand what you mean and really what we're talking about here is headroom which is more like horsepower in a car. Both a 100 HP engine and a 200HP engine can both push a car along at 100 mph with ease but where you'll notice the extra power is when you want to accelerate. With the larger amplifiers you'll gain more motor control over the drivers esp at louder volumes which should equate to cleaner sounding music...but like with cars horsepower isn't everything. Depending on the effiency of your speakers you may or may not need the added watts from the larger amps since an efficient speaker will be able to play louder for a given watt then a less efficient speaker....so much so that if we take two extremes with say a magnepan vs a klipshe the maggie speaker would need nearly 4 times the power to keep up with the klipshe (or there abouts)




    Comment

    • Glenn
      Senior Member
      • Jun 2003
      • 109

      #3
      Ah, ok I now understand re: amps always running at 100% (There needs to be a light bulb icon I can add for effect )

      However, as I turn the pre-amp volume dial farther and farther up (without any source material being actually played), I can hear more and more hiss coming from the speakers. I was thus thinking, if I could get my room 85 db volume level at a 30% pre-amp dial number, vs. say a higher 75% dial level, would it not be "cleaner" sound? Or would the 30% level on the bigger amp = the 75% level on the smaller amp (for both to generate the desired 85db), so the same amount of hiss would be generated.

      Comment

      • Danbry39
        Moderator Emeritus
        • Sep 2002
        • 1584

        #4
        That's a very interesting question and I'm not sure if my answer is correct, but I'm still going to try and logic it out. If, as you're assuming, the hiss is coming from the preamp, then, as you say, the hiss escalates as the volume control of the preamp is turned up. That would mean that the hiss might be constant and the elevated loudness level was the result of the increased volume, which, in effect, was working to amplify the hiss louder. If this is so, the increase to a more powerful amp wouldn't impact the hiss level at a given volume, as no matter what the volume would be amplified uniformly.

        Again, I have no clue here, but am just trying to grasp at whatever logic my brain cells have left in them.

        Others, who might have an idea, please feel free verifying or correcting my hypothesis. This could be the one new thing I learn each day.




        Keith
        Keith

        Comment

        • Wilfred
          Junior Member
          • May 2003
          • 27

          #5
          Here's my attempt:

          Given a constant source input, preamp voltage out (hence, power amp input) will vary in proportion with volume dial % (0%=0V, 100%=Full output).

          While holding speakers efficiency constant, at any given preamp %, the output loudness of speakers should be the same. Reason being, with everything being equal, most importantly same gain factor, an amp is to ampilfy an input signal X times and deliver it to the output.

          With that said, a higher wattage rating amp will allow you to turn the dial to a higher % (ie louder) before "overloading" the amp (distortion). If both amps can do 85db comfortably, you should hear the same hiss level as both amps amplify the same signal by the same amount.

          And here where the fun begin.

          Introducting speakers sensitivity (ability to turn electricity into sound - dB/Wm), as mention above - Magnepan (Maggie) is very inefficient low 80s dB, while Klipsch is very efficient 90s+. So, in order to produce 85dB, one might need to set dial at 40%, while Klipsch only requires 35% (numeric values for example purpose only).

          From a noise stand point, and assuming it is from your pre-amp before the dial stage, I would have to say the hiss will be more audiable for Maggie over Klipsch.

          Humm, after saying all these, I will have to try it myself just to prove my 'theory' is right... :roll: oh darn, it's only Monday...

          Wilfred

          Comment

          • sikoniko
            Super Senior Member
            • Aug 2003
            • 2299

            #6
            Originally posted by Glenn
            However, as I turn the pre-amp volume dial farther and farther up (without any source material being actually played), I can hear more and more hiss coming from the speakers. I was thus thinking, if I could get my room 85 db volume level at a 30% pre-amp dial number, vs. say a higher 75% dial level, would it not be "cleaner" sound? Or would the 30% level on the bigger amp = the 75% level on the smaller amp (for both to generate the desired 85db), so the same amount of hiss would be generated.
            I think it has more to do with the point at which distortion occurs at higher levels.

            of course a higher rated amp will be louder, but thats just part of the equation. a lot will probably have to do with your room size and room acoustics just as much as your amp.

            you will find that the higher rated amp will reach the same volume with less effort and will allow more overhead, but you may also find that your room acoustics are not optimal either and are causing the sound to be distorted at no fault of the amp.

            With as many speakers as are in a home theater, you have a lot of sound reflecting. This is why bands carpet their practice space from top to bottom. to absorb the sound instead of allowing it to bounce.


            I am debating the same thing. which amp to get. Im a ways off though.

            I have similar concerns as I had to turn my 1055 up to 60 to calibrate my stereo to 65. I feel more comfortable at or below 50% of the power curve.
            I'm just sittin here watchin the wheels go round and round...

            Comment

            • Glenn
              Senior Member
              • Jun 2003
              • 109

              #7
              Originally posted by Wilfred
              If both amps can do 85db comfortably, you should hear the same hiss level as both amps amplify the same signal by the same amount.
              Perhaps the hiss level can be thought of simply as a precursor of what's to come, regardless of where the relative dial settings are set at between the two amps.

              To get 85 db from the small amp, 75% volume dial is needed. To get 85 db from the large amp, 45% volume dial is needed. Both will produce 85 db when the signal is fed. AND both will produce the same amount of hiss BEFORE the signal is fed, at their respective 75/45% volume settings.

              Comment

              • Andrew Pratt
                Moderator Emeritus
                • Aug 2000
                • 16507

                #8
                Its an interesting thought but I doubt you'd notice that much difference in the where the volume knob would be even if one amp were 10 times more powerful then the other since even a very inefficient speaker only needs a couple of watts tops to reach quite loud levels. That means that the vast majority of the time you're only using 1-5 watts at the most so your volume knob which is log scaled will almost always be very low (even if its at 50% max) if that makes any sense?




                Comment

                • Todd S
                  Junior Member
                  • Jan 2003
                  • 21

                  #9
                  In my opinion there are 2 different types (or points at which noise occurs within the pre-amp) that are relevant here:

                  The first being noise that occurs before the preamp's gain stages. This noise will be attenuated/amplified by the preamp depending on the preamps' gain setting (volume knob position). This type of noise will eventually produce the same audible level at the speakers no matter how powerful the amp is. This is because the bigger amp's gain will be offset by the fact that you will be turning down the preamp's gain to produce the same source signal output level.

                  The second type of noise will be noise introduced after the preamp's gain stages. This noise level (which is probably relatively small compared to the first type of noise I described) will produce the same voltage output from the preamp no matter where the preamp's volume setting is at. Since normal amp's are usually designed to produce full rated output with let's say 1 volt signal input, a bigger amp will amplify this type of noise more than a smaller amp. So according to my theory, a correctly ‘sized’ amp will sound less noisy than an ‘oversized’ amp. Now this is theory, and like I stated earlier, this type of noise in all likelihood is probably pretty small, and you may not be able to hear it unless you put your ear up to the speaker.

                  What do you all think?

                  Todd
                  Todd

                  Comment

                  • Glenn
                    Senior Member
                    • Jun 2003
                    • 109

                    #10
                    Originally posted by Andrew Pratt
                    Its an interesting thought but I doubt you'd notice that much difference in the where the volume knob would be even if one amp were 10 times more powerful then the other
                    So with respect to the two amps originally referenced, do you mean to get the 85 db example volume, both the 1075 (120w) and the 1095 (200w) amps, would require the preamp volume dial to be set at the same level/position?

                    And just another way of rephasing/reasking, would a preamp set at 50% on the dial, first connected to the 1075, then connected to the 1095, be outputting the same db? Wouldn't the 1095 be generating more actual db at the same 50% preamp dial position?

                    I'm confused ...

                    Comment

                    • Todd S
                      Junior Member
                      • Jan 2003
                      • 21

                      #11
                      So with respect to the two amps originally referenced, do you mean to get the 85 db example volume, both the 1075 (120w) and the 1095 (200w) amps, would require the preamp volume dial to be set at the same level/position?
                      No, not exactly. Theoretically, using the 1095 would require you to set the preamp's dial lower by 2.2dB. Keep in mind that the apparent loudness difference is very small. Most people would not even hear a difference except for a sine wave.

                      This is assuming that the both amps are designed the same way. Meaning that for a given input level (let's say 1Vrms) the amp produces rated output. This I think would be true when both of the amps we are talking about are made by the same company.

                      Todd
                      Todd

                      Comment

                      • Todd S
                        Junior Member
                        • Jan 2003
                        • 21

                        #12
                        From 1095 owners manual:
                        Input Impedance/Sensitivity
                        33 k Ohms/1.5 volt (unbalanced)
                        33 k Ohms/±1.5 volt (balanced)

                        From 1075 owners manual:
                        Input Impedance/Sensitivity
                        33 k Ohms/1.0 volt

                        So the 2 amps are actually designed differently. So if my figures are correct the 1095 would actually require the preamp to be turned up by 1.34dB.

                        Todd
                        Todd

                        Comment

                        • ht_addict
                          Senior Member
                          • Dec 2002
                          • 508

                          #13
                          Let me take a try at this. Take a speaker that 1m away and 93db sensitive.

                          1w/1m: 93db
                          2w/1m: 96db
                          4w/1m: 99db
                          8w/1m: 102db
                          16w/1m: 105db
                          32w/1m: 108db
                          64w/1m: 111db
                          128w/1m: 114db
                          256w/1m: 117db

                          So as you can see with using the same speaker in a perfect room the 1075 tops out at 111-114db and the 1095 tops out at 114-117db. Add other speakers for 5.1 and you get a 7db gain. So to reach the 85db your looking for both amps will have no problem. Checkout the following link to a db calc for more info.

                          http://www.myhometheater.homestead.com/splcalculator.html

                          Where the 1095 will have an advantage is in those intense transitions of some soundtracks. Due in part to the 2/1.2KVA toroids, 8/15,000uf Caps, and 30-150w/15A output devices compared to the 1075 with 1-1.5KVA toroid, 8/10,000uf caps and 20-150w/15A output devices. In the end I think it boils down to which one you can afford or get a better deal on. Personally I'd get the 1095. I did.

                          ht_addict

                          Comment

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