Hi,
I am amazed at the stupidity of my own question, but missing knowledge, even if basic is still not there!
I am very partial to my current hifi setup (when in a large room).
The Acoustic Energy 309s are large sensitive, precise speakers that faithfully reproduce whatever you throw at them.
The Rotel RB-991 has a wonderful warm sound and has oodles of power.
The problem is that the RB-991 only sounds good when the RC-995 is at least 9 o'clock.
The problem is with the 991 not the 995, when running the 991 at low power levels it is known to be a bit weak.
but at 9'oclock the volume is significant due to 93db/w speakers and a small room.
My question is:
Is there any way of making the speakers or amp less efficient, so that the amp is operating in it's comfortable range?
The car analogy is I want to make the amp run in it's power band, currently the revs are almost at a stall.
So is this a stupid question, and is it possible?
I am amazed at the stupidity of my own question, but missing knowledge, even if basic is still not there!
I am very partial to my current hifi setup (when in a large room).
The Acoustic Energy 309s are large sensitive, precise speakers that faithfully reproduce whatever you throw at them.
The Rotel RB-991 has a wonderful warm sound and has oodles of power.
The problem is that the RB-991 only sounds good when the RC-995 is at least 9 o'clock.
The problem is with the 991 not the 995, when running the 991 at low power levels it is known to be a bit weak.
but at 9'oclock the volume is significant due to 93db/w speakers and a small room.
My question is:
Is there any way of making the speakers or amp less efficient, so that the amp is operating in it's comfortable range?
The car analogy is I want to make the amp run in it's power band, currently the revs are almost at a stall.
So is this a stupid question, and is it possible?
I presume that when you say 9 o’clock you mean that the volume is at 75% or ¾ of its travel. If that is correct then what you’re really saying is that the RB-911 only sounds at its best when played loud. Your problem appears to be combining efficient speakers with a powerful amp resulting in a sound that you’re not completely happy with. There is no easy way to make a powerful amp less efficient without resorting to a resistor to absorb most of the output from your amp, which is analogous to driving your car with your foot on the brake. If for instance you put an 8 Ohm resistor in series then it would absorb about half the power of your amp, so it would need to be rated at over 100 watts. I’ve never heard of this being done and am extremely doubtful of the outcome; however in theory it’s possible.
The HIFI site
The HIFI site
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Just adding a bit more... adding a resistor is no good. That wastes power, meaning the resistor would get hot, but more than that, it drastically alters the response of the speaker as the load a spaeker presented to the amp is not constant but varies wildly with frequency. For example, a nominal 8 ohm speaker may have an actual impedance of anywhere as low as 3 ohms to as high as 20 or 30 ohms depending on the frequency.
Your problem sounds familiar... I suspect you find you want to sit and enjoy some music, you sit down to listen and find it hard to really get into the performance... you probably have certain recordings that sound good... but not maybe not many, you perhaps blame the recordings... after all if one or two are good the equipment must be good... it's also very critical as to what volume level does sound good. In the end you get bored and do something else instead.
Is that way off the mark or not ?
Bias
with all due respect to Jaycee, I suspect that increasing the bias will be more a case of wishful thinking, in that it has changed the sound significantly.
Your problem sounds familiar... I suspect you find you want to sit and enjoy some music, you sit down to listen and find it hard to really get into the performance... you probably have certain recordings that sound good... but not maybe not many, you perhaps blame the recordings... after all if one or two are good the equipment must be good... it's also very critical as to what volume level does sound good. In the end you get bored and do something else instead.
Is that way off the mark or not ?
Bias
with all due respect to Jaycee, I suspect that increasing the bias will be more a case of wishful thinking, in that it has changed the sound significantly.
Not I suspect without changing the amp unfortunately.
It might be worth you looking at some of Hugh Deans offerings on here, look under Aspen amplifiers and his AKSA designs.
Or would you go down the DIY route perhaps.
beefing up the bias will help but this will be marginal and also will produce some extra heat for sure less than this """100W """ resistor
then gain a passive input and probably a small change in the gain of the amplifier will also might help ...
i wonder what type of drivers exist inside the amp ( will look for a schematic ) often if the amp is designed properly but gets dirty very easy changing to faster drivers will also have effect on your problem
doing all three of the above will alter the amplifier totally i think
then gain a passive input and probably a small change in the gain of the amplifier will also might help ...
i wonder what type of drivers exist inside the amp ( will look for a schematic ) often if the amp is designed properly but gets dirty very easy changing to faster drivers will also have effect on your problem
doing all three of the above will alter the amplifier totally i think
Thanks for the help so far, but afraid some of the ideas were above me, could you please elaborate.
Changing bias, simple, is 60mA agreed OK? there is thermal protection on this amp, so worst come to worst should still be fine!
Now for the embarrassing bit, never heard anyone refer to drivers in an amp =-(
Even my search on line for a quick self teach did not help.
So what are the drivers, and what should I change them too?
Sorry for needing all the hand holding,
P
Changing bias, simple, is 60mA agreed OK? there is thermal protection on this amp, so worst come to worst should still be fine!
Now for the embarrassing bit, never heard anyone refer to drivers in an amp =-(
Even my search on line for a quick self teach did not help.
So what are the drivers, and what should I change them too?
Sorry for needing all the hand holding,
P
Drivers are the transistors that work in conjunction with the output devicesto, well drive them The gain of a single output device is low... it needs "help" and that's the purpose of the driver stages. It's actually a lot more complex than that but it gives you the general idea.
Bias... only one value is normally correct for any given design, but that said it's always a compromise. The idea that upping the bias to make the amplifier work that little bit more in class A is doubtful, and it can often worsen the overall performance figure.
I wouldn't advise you to start changing "drivers" without knowing exactly what you are doing and again, the sonic effects of all this are half of a quarter of nothing imo. The sound of the amp is determined by the circuit topology that's used... and you need to explore the alternatives.
The gain of a single output device is low... it needs "help" and that's the purpose of the driver stages. It's actually a lot more complex than that but it gives you the general idea. Bias... only one value is normally correct for any given design, but that said it's always a compromise. The idea that upping the bias to make the amplifier work that little bit more in class A is doubtful, and it can often worsen the overall performance figure.
I wouldn't advise you to start changing "drivers" without knowing exactly what you are doing and again, the sonic effects of all this are half of a quarter of nothing imo. The sound of the amp is determined by the circuit topology that's used... and you need to explore the alternatives.
A loudness control button boosts the bass and treble at lower volume levels, and a proper implementation requires a "tapped" volume control so that the effect is progressive... but it's not the answer
partially my mistake i am sorry for that since what i ofered can only by evaluated from experts ...again sorry for that .....
some aditional info ....in plane Greek
in a class AB amplifier like the Rotel you have sound signal passes through positive and negative output transitors .... in order to pass easier we use some way to actually keep transitors "open" or working or contactive so actually sound signal will find an open path to pass from. Also keeping them open means that signal passes from postive to negative tranistors while tranistors are allready open and have meet eachother so passing through from pt to n is easier ....
now ho much open these transitors will be ditermine the Class of your amplifier ...in class A amplifiers ( not your rotel ) transistors are almost totally open and active all the time ( or as much is possible to be ) so signal will have an absolutelly open path to pass from that will provide ultimate quality of sound but open tranistors will consume a hell of a lot of power in heat to stay open
In class AB transitors are partially open ...very very litle so signal will find a small open path to pass through or lets say to start passing through and after that since this "start" is made things are easier ....that will perform with increased efficiency compaired to a class A amplifier and consume by far less heat and power but also will not have a warm tubish sound like class A ....
fact !!! all class AB amplifiers the first few watts are really class A watts ... very few though how much few think that you can find a board for reference in passdiy.com .... beefing up the idle will alter that and if the first 7 watts of your amp is class A this will might goto the first 12 watts ... that is of course marginal and if this level of power is enough ( together with sensitive speakers ) might actually help you a bit....
Now from design aspect and the comment of the drivers above you have in plane Greek the basis of things ....the rest of the design choise of parts style of biass and overall design makes the diference from amplifier to amplifier....
Designers often compromise between cost power and efficiency and small changes here and there will make big diference in the performance of the amplifier ....
Altering the biass , changing drivers,changing the overall gain will effect the way your system works but skills and instrumens are required to do that ....
kind regards sakis
some aditional info ....in plane Greek
in a class AB amplifier like the Rotel you have sound signal passes through positive and negative output transitors .... in order to pass easier we use some way to actually keep transitors "open" or working or contactive so actually sound signal will find an open path to pass from. Also keeping them open means that signal passes from postive to negative tranistors while tranistors are allready open and have meet eachother so passing through from pt to n is easier ....
now ho much open these transitors will be ditermine the Class of your amplifier ...in class A amplifiers ( not your rotel ) transistors are almost totally open and active all the time ( or as much is possible to be ) so signal will have an absolutelly open path to pass from that will provide ultimate quality of sound but open tranistors will consume a hell of a lot of power in heat to stay open
In class AB transitors are partially open ...very very litle so signal will find a small open path to pass through or lets say to start passing through and after that since this "start" is made things are easier ....that will perform with increased efficiency compaired to a class A amplifier and consume by far less heat and power but also will not have a warm tubish sound like class A ....
fact !!! all class AB amplifiers the first few watts are really class A watts ... very few though how much few think that you can find a board for reference in passdiy.com .... beefing up the idle will alter that and if the first 7 watts of your amp is class A this will might goto the first 12 watts ... that is of course marginal and if this level of power is enough ( together with sensitive speakers ) might actually help you a bit....
Now from design aspect and the comment of the drivers above you have in plane Greek the basis of things ....the rest of the design choise of parts style of biass and overall design makes the diference from amplifier to amplifier....
Designers often compromise between cost power and efficiency and small changes here and there will make big diference in the performance of the amplifier ....
Altering the biass , changing drivers,changing the overall gain will effect the way your system works but skills and instrumens are required to do that ....
kind regards sakis
I modified my friend's Rotel RB991 until he sold it being quite dissatisfied with its sound. In my judgement the 991 is a well engineered product but of mediocre sound quality. Low level resolution is bad. It tends to sound good when driven to high output levels. I increased the feedback resistor to obviate the rail fuses from blowing; I think the stock version is a near oscillator. This further adds to the bad sound.
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