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Pre-amp/ power amp pairing

Tadaoo

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Hello from Paris, France

This would be my first post on this forum that I have been reading with great interest in the limit of my technical ability…

My question concerns a possible mismatch between my pre-amplification device and my power amp.

My ”chaîne hifi” (French for hifi system) has been composed in time by replacing components one by one based on the “weakest link” theory, that, if it ensures a never ending upgrading fever and associated GAS, it does not necessarily help with the coherence of the system.

I currently use a Rotel A11 Tribute amplifier as a pre-amp to drive an Audiophonics MPA-250NC, driving a set of Sonus Faber Lumina I speakers. (think small Parisian apartment setup)

Up the chain is a Bluesound Node connected to a Denafrips Ares II for streaming, and an old Oppo BDP-83 to play the occasional CD.
I also added a small sub (Audioengine S6) to help with the low frequencies lacking in the Luminas.

I am considering replacing the Rotel with a dedicated pre-amp- Schiit Kara, or Denafrips HESTIA, or else, as I assume that the integrated Rotel pre-amp section is not necessarily an ideal match:

Looking at the specs, the Rotel indicates a 1V Pre-out Level.
The Audiophonics MPA-250NC indicates a Input sensitivity of 1.66V RMS for full power.

So my questions would be:

- Is the Rotel preamp section is underpowered for the Audiophonics?

- To make things perhaps worse, I splitted the Rotel pre-out between the Power amp and the subwoofer, so I am concerned that it would lower the voltage available for the power amp. Is my sub crippling my preamp?

- What criterias should I be giving priority in choosing a preamp replacement?

Thanks to anyone who could help me with my questions, and educate me along the way on equipment pairing…

Cheers!

T
 
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T

Tadaoo

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Hi Audiofire

Volume is plenty loud!
I usually set the Rotel volume button on 70, then use the BlueOs app of the Bluesound note volume control to adjust- usual listening volume around 80% on the app.
 

Audiofire

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Volume is plenty loud!
The Rotel is good enough if power was the only concern.
- To make things perhaps worse, I splitted the Rotel pre-out between the Power amp and the subwoofer, so I am concerned that it would lower the voltage available for the power amp. Is my sub crippling my preamp?
No problem, as long as it was split correctly like an RCA adapter. If you split by cutting the cable yourself, then insulation could be missing or there could be a bad connection in the cable.
 

DVDdoug

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Personally, I don't worry too much about the "sound quality" of the electronics as along as I have enough amplifier power that I'm not over-driving it into clipping (distortion). Most electronics is very good and there is usually little or no difference (in a proper, scientific, bind, level matched ABX Test).

On the other hand, every speaker or headphone sounds different.


I splitted the Rotel pre-out between the Power amp and the subwoofer, so I am concerned that it would lower the voltage available for the power amp. Is my sub crippling my preamp?
It shouldn't affect the level... It's an "impedance thing". The preamp's output impedance is low, and the power amp & sub have higher impedance (you don't "match" impedance) and this means whatever you plug-into the preamp doesn't "load" the preamp and drop the voltage. You could probably plug-in 10 amplifiers with little or no effect.

However... Ideally, you should have a crossover to route the bass to the sub while blocking the bass to the main speakers. The most common way of doing that is with an Audio Video Receiver. They have a dedicated line-level sub output and optional* "bass management" (a crossover).

Or, some active subwoofers have crossovers built-in. The line-level signal passes-through and the bass is filtered-out of the signal that goes to the power amp.

Or, you can buy an Active Crossover or some people use a miniDSP as a crossover.



* The crossover/bass management is optional because the "point one" LFE channel in movies goes to the subwoofer and only to the subwoofer (the LFE channel isn't included in the stereo downmix). If your main speakers are full range, you can turn-off the bass management and they can handle the regular bass, with the sub handling the LFE.
 

Roland68

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Hello from Paris, France

This would be my first post on this forum that I have been reading with great interest in the limit of my technical ability…

My question concerns a possible mismatch between my pre-amplification device and my power amp.

My ”chaîne hifi” (French for hifi system) has been composed in time by replacing components one by one based on the “weakest link” theory, that, if it ensures a never ending upgrading fever and associated GAS, it does not necessarily help with the coherence of the system.

I currently use a Rotel A11 Tribute amplifier as a pre-amp to drive an Audiophonics MPA-250NC, driving a set of Sonus Faber Lumina I speakers. (think small Parisian apartment setup)

Up the chain is a Bluesound Node connected to a Denafrips Ares II for streaming, and an old Oppo BDP-83 to play the occasional CD.
I also added a small sub (Audioengine S6) to help with the low frequencies lacking in the Luminas.

I am considering replacing the Rotel with a dedicated pre-amp- Schiit Kara, or Denafrips HESTIA, or else, as I assume that the integrated Rotel pre-amp section is not necessarily an ideal match:

Looking at the specs, the Rotel indicates a 1V Pre-out Level.
The Audiophonics MPA-250NC indicates a Input sensitivity of 1.66V RMS for full power.

So my questions would be:

- Is the Rotel preamp section is underpowered for the Audiophonics?

- To make things perhaps worse, I splitted the Rotel pre-out between the Power amp and the subwoofer, so I am concerned that it would lower the voltage available for the power amp. Is my sub crippling my preamp?

- What criterias should I be giving priority in choosing a preamp replacement?

Thanks to anyone who could help me with my questions, and educate me along the way on equipment pairing…

Cheers!

T
You are making a typical and fundamental mistake.
It doesn't matter what kind of preamplifier you connect to your power amplifier, the voltage required for your combination of power amplifier and speaker to reach a certain volume is always the same.
So if you don't need a higher volume at all, the only thing that will change with a new preamplifier is the position of the volume control. And a higher gain in the preamplifier is not an advantage if the higher gain is not needed.
 

Chagall

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Welcome to ASR!
As @DVDdoug said, you would benefit from crossing over mains and sub. If I understand correctly all your sources, miniDSP Flex is exactly what you need. It would replace your Rotel, Denafrips, and Node and give you crossover for sub and mains.

But if you want to keep the Node (Flex also streams but maybe Node is better in that aspect) <EDIT>Flex isn't a streamer</EDIT> it would look something like this:

Frame 72.jpg


Flex also opens up the possibility for PEQ and Dirac if later you want to do some UMIK measurements.
 
Last edited:
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T

Tadaoo

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The Rotel is good enough if power was the only concern.

No problem, as long as it was split correctly like an RCA adapter. If you split by cutting the cable yourself, then insulation could be missing or there could be a bad connection in the cable.
Thanks for your reply.
Regarding their subwoofer I use RCA splitters so I should be all right.

Regarding the Rotel I feel better regarding the power; however I would be interested to understand what a dedicated pre-amp would bring to the picture;
In other words, I am not sure what to look for (other than ASR reviews of course although my ability to appreciate frequency curves hasn’t improved since high school…) when it will comes to choose a preamp…
Personally, I don't worry too much about the "sound quality" of the electronics as along as I have enough amplifier power that I'm not over-driving it into clipping (distortion). Most electronics is very good and there is usually little or no difference (in a proper, scientific, bind, level matched ABX Test).

On the other hand, every speaker or headphone sounds different.



It shouldn't affect the level... It's an "impedance thing". The preamp's output impedance is low, and the power amp & sub have higher impedance (you don't "match" impedance) and this means whatever you plug-into the preamp doesn't "load" the preamp and drop the voltage. You could probably plug-in 10 amplifiers with little or no effect.

However... Ideally, you should have a crossover to route the bass to the sub while blocking the bass to the main speakers. The most common way of doing that is with an Audio Video Receiver. They have a dedicated line-level sub output and optional* "bass management" (a crossover).

Or, some active subwoofers have crossovers built-in. The line-level signal passes-through and the bass is filtered-out of the signal that goes to the power amp.

Or, you can buy an Active Crossover or some people use a miniDSP as a crossover.



* The crossover/bass management is optional because the "point one" LFE channel in movies goes to the subwoofer and only to the subwoofer (the LFE channel isn't included in the stereo downmix). If your main speakers are full range, you can turn-off the bass management and they can handle the regular bass, with the sub handling the LFE.
Thanks!
I also always wondered how electronics actually affects the sound, but then I’ve always been an electrical ignorant…

I will have to check the impedance with Audiophonics, the ROTEL indicates an output impedance of 470 Ohms.

Usage is mostly Music for the sub so I might not need a bass management.
The sub, however mini has a crossover knob, but only inputs so it cannot filter out the signal I guess.

My tiny speakers are unfortunately not full range (65 Hz à 24 kHz) So bass extension is most welcome.
 
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Tadaoo

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You are making a typical and fundamental mistake.
It doesn't matter what kind of preamplifier you connect to your power amplifier, the voltage required for your combination of power amplifier and speaker to reach a certain volume is always the same.
So if you don't need a higher volume at all, the only thing that will change with a new preamplifier is the position of the volume control. And a higher gain in the preamplifier is not an advantage if the higher gain is not needed.
Thanks for your input; indeed if higher gain only equals to higher volume it is not needed…
Not sure asking questions qualifies as mistake though…;-)
 
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Tadaoo

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Welcome to ASR!
As @DVDdoug said, you would benefit from crossing over mains and sub. If I understand correctly all your sources, miniDSP Flex is exactly what you need. It would replace your Rotel, Denafrips, and Node and give you crossover for sub and mains.

But if you want to keep the Node (Flex also streams but maybe Node is better in that aspect) <EDIT>Flex isn't a streamer</EDIT> it would look something like this:

View attachment 347067

Flex also opens up the possibility for PEQ and Dirac if later you want to do some UMIK measurements.
Thanks for your welcome!

I will look into the miniDSP Flex device which is very new to me but seems like an interesting solution.
I shall keep the Bluesound node as I am using the HDMI Arc for TV (did I mention tiny apartment?)

The Node also has a sub out port with control on the app but never seemed to work so i used the pre-out on the Rotel
 
OP
T

Tadaoo

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Welcome to ASR!
As @DVDdoug said, you would benefit from crossing over mains and sub. If I understand correctly all your sources, miniDSP Flex is exactly what you need. It would replace your Rotel, Denafrips, and Node and give you crossover for sub and mains.

But if you want to keep the Node (Flex also streams but maybe Node is better in that aspect) <EDIT>Flex isn't a streamer</EDIT> it would look something like this:

View attachment 347067

Flex also opens up the possibility for PEQ and Dirac if later you want to do some UMIK measurements.
This is indeed a very interesting device; would it be possible (and make any sense) to keep my Ares II DAC in the chain before the Flex since it has analog inputs and use the Flex only as a preamp with EQ and Dirac functions?
 

Chagall

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This is indeed a very interesting device; would it be possible (and make any sense) to keep my Ares II DAC in the chain before the Flex since it has analog inputs and use the Flex only as a preamp with EQ and Dirac functions?

Sure, but what would be the point? Let's say you put it after Node -> Ares II -> Flex. You will have D/A, A/D, D/A conversion. Flex digitizes analog input.

Another option, if you want to keep Ares is Flex Digital. But then you would need to get one more DAC for the sub.

Frame 73.jpg
 

Chrispy

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Many avrs will quote a nominal pre-out level of 1V when they are capable of more....wouldn't be surprised if the same applies to the Rotel integrated amp....

ps I went looking for a bench test that might reveal actual measurement but the only one I found didn't address it (which is pretty normal for an integrated amp, not much point to one if you need more amplification).
 
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Roland68

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Thanks for your input; indeed if higher gain only equals to higher volume it is not needed…
Not sure asking questions qualifies as mistake though…;-)
Please do not interpret anything personal into my post.
It was intended to be purely informative and factual and should only protect you from unnecessary expenditure of money and new purchases based on incorrect assumptions or information.
 
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Tadaoo

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Please do not interpret anything personal into my post.
It was intended to be purely informative and factual and should only protect you from unnecessary expenditure of money and new purchases based on incorrect assumptions or information.
No hard feelings! I was merely speaking philosophically...
And I do need protection from buying things I don't need with money I don't have...
 
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Tadaoo

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Many avrs will quote a nominal pre-out level of 1V when they are capable of more....wouldn't be surprised if the same applies to the Rotel integrated amp....

ps I went looking for a bench test that might reveal actual measurement but the only one I found didn't address it (which is pretty normal for an integrated amp, not much point to one if you need more amplification).


The only detailed review of the Rotel A11 Tribute I found is from SoundStage Network, and indeed they don't test its preamp performance
https://www.soundstagenetwork.com/i...ts&catid=97:amplifier-measurements&Itemid=154
My inexistent knowledge in acoustics (except guitars) does not allow me to have any opinion on the various curves in the review...

I tested the system without the power amp again to check if there were audible differences with the Rotel A11 alone; I couldn't to proper A/B comparison for obvious reasons (not having 2 sets of everything is actually good for the planet) so I just played the same 4 tracks in both configurations :
- by removing the power amp out of the equation, the overall presentation is more open and airy- makes it seem more detailed - but the highs become very forward with some unpleasant harshness that might come from the speakers and not tamed by the amp
- reconnecting the power amp gives a more balanced sound and kill the harshness, and gives more texture and presence to the bass and mids;

The Sonus Faber Lumina 1 have a low sensitivity (84db) and are rated for 4Ohms Nominal impedance- so I am guessing they appreciate the extra headroom provided by the Audiophonics (250W at 4 Ohms per channel).
They are staying for now, having a good size/performance ratio and I actually enjoy the sound, rich and detailed enough for living room listening (room is 30' wide and 10' deep) in the current configuration.

To go back to my pairing problematic, is there a point getting a dedicated preamp (like Schiit Kara, Denafrips Hestia range) ? Is a preamp more than an input selctor with a volume knob?

Or should I just ditch (sell) the Audiophonics and upgrade the Rotel to a more powerful Integrated Amp in the 1500€ range ? like the Rotel A14 MK2, Musical Fidelity M5Si, Atoll In200, Denon Pma-1700?
 

Audiofire

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- by removing the power amp out of the equation, the overall presentation is more open and airy- makes it seem more detailed - but the highs become very forward with some unpleasant harshness that might come from the speakers and not tamed by the amp
You have heard increased distortion or it was all in the imagination. Distortion in hi-fi = lo-fi.

Is a preamp more than an input selctor with a volume knob?
Not really.
 
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