Matching pre out gain to power amp sensitivity

[ciotime]

With regards to choosing an external amp to power the Denon X3700H I've been told that it's very important to get one with a specific sensitivity that will match the Denon's pre-out voltage gain. I had wanted to get the Rotel RMB1585 to pair with the Denon's.

The output signal from the 3700 in preamp mode is optimal at 1.1 volts and clips at 1.4 volts, meaning that ideally one would want to match it with an amp with an input sensitivity of 1.1 volts, meaning that with 1.1 volts of input is enough to drive the amp to it's full output power. The input sensitivity of the Rotel RB 1585 is 1.9 volts, meaning that it takes 1.9 volts of input signal for it to amplify that signal to it's full rated watts/channel. IF an input voltage to an amp is less than it's rated sensitivity, the amp will not come close to amplifying the signal to it's rated wattage.

Is my conclusion correct?

 

[TLS Guy]

With regards to choosing an external amp to power the Denon X3700H I've been told that it's very important to get one with a specific sensitivity that will match the Denon's pre-out voltage gain. I had wanted to get the Rotel RMB1585 to pair with the Denon's.

The output signal from the 3700 in preamp mode is optimal at 1.1 volts and clips at 1.4 volts, meaning that ideally one would want to match it with an amp with an input sensitivity of 1.1 volts, meaning that with 1.1 volts of input is enough to drive the amp to it's full output power. The input sensitivity of the Rotel RB 1585 is 1.9 volts, meaning that it takes 1.9 volts of input signal for it to amplify that signal to it's full rated watts/channel. IF an input voltage to an amp is less than it's rated sensitivity, the amp will not come close to amplifying the signal to it's rated wattage.

Is my conclusion correct?

You are overthinking this a bit. because the db scale is log, that 0.5 volt discrepancy is not great. So you would in fact be fine.

The real problem is that receivers do not have enough head room on the preouts.

 

[ciotime]

You are overthinking this a bit. because the db scale is log, that 0.5 volt discrepancy is not great. So you would in fact be fine.

The real problem is that receivers do not have enough head room on the preouts.

So do you think the Rotel RMB1585 will work as a power amp to the Denon? I don't wanna end up with the Rotel's and not having to be able to use its max capacity. Ive read a lot of people saying that adding a power amp to their existing AVR's didnt do much improvements.

 

[warnerwh]

Over at ASR they measured a sinad of like 96 or 97db and that's at 2 volts from the pre outs on the 3700. Btw those numbers are of the very best among avr's. You should go there and read the review, it's well done and thorough. You will be fine with the Rotel.

 

[ciotime]

Over at ASR they measured a sinad of like 96 or 97db and that's at 2 volts from the pre outs on the 3700. Btw those numbers are of the very best among avr's. You should go there and read the review, it's well done and thorough. You will be fine with the Rotel.

Thanks...so the Rotels will definitely help? Do you think it'll be a huge or just a minor improvement than just using the Denon's internal amps? I ask coz I just dunno if it's worth the cost.

 

[lovinthehd]

That would perhaps depend on what the external amp is to help with particularly....which is?

 

[PENG]

Thanks...so the Rotels will definitely help? Do you think it'll be a huge or just a minor improvement than just using the Denon's internal amps? I ask coz I just dunno if it's worth the cost.

Whether that will help or not depends on other factors. As for the input sensitivity being 1.9V, it is not going to be an issue for the X3700H especially if you are not going to be using the AVR's built in amps. If you are, then you cannot use the preamp mode, and in that case the pre out would have higher THD+N, about -77 dB, that is 0.014%, still a reasonable to the Rotel amp's 0.03%. Even if you are using the preamp mode, you can still use the amp assign function to disconnect the internal power amps for the front left and right channel and then you will back to the 93 to 101 dB SINAD range from very low output to rated output level.

93 dB SINAD is 0.0022%
101 dB SINAD is 0.00089%

Denon AVR-X3700H AVR Review | Audio Science Review (ASR) Forum

 

[danny.winfield42]

Whether that will help or not depends on other factors. As for the input sensitivity being 1.9V, it is not going to be an issue for the X3700H especially if you are not going to be using the AVR's built in amps. If you are, then you cannot use the preamp mode, and in that case the pre out would have higher THD+N, about -77 dB, that is 0.014%, still a reasonable to the Rotel amp's 0.03%. Even if you are using the preamp mode, you can still use the amp assign function to disconnect the internal power amps for the front left and right channel and then you will back to the 93 to 101 dB SINAD range from very low output to rated output level.

93 dB SINAD is 0.0022%
101 dB SINAD is 0.00089%

Denon AVR-X3700H AVR Review | Audio Science Review (ASR) Forum

View attachment 43700

I'm not sure if your statement is quite correct, although I wish it were.

I dont believe there is any way to disconnect the amp's for the front right and left channels apart from in the pre out only mode which disconnects all channels. I have the 3700 running a 5.1.2 setup currently and am using my Naim separates system for the front left and right via the pre outs. From the options I can see in amp assign, there is no option which has fl and fr as preamp and the rest as amplified.

Sent from my SM-G975F using Tapatalk

 

[ciotime]

I'm not sure if your statement is quite correct, although I wish it were.

I dont believe there is any way to disconnect the amp's for the front right and left channels apart from in the pre out only mode which disconnects all channels. I have the 3700 running a 5.1.2 setup currently and am using my Naim separates system for the front left and right via the pre outs. From the options I can see in amp assign, there is no option which has fl and fr as preamp and the rest as amplified.

Sent from my SM-G975F using Tapatalk

As written below YES one can assign either the 2 Front's or the 2 Height channels on the amp assign mode. Since the X3700H can only power 9 CH but need's an external amp to do 11 CH ( 7.2.4 ) one really need's to add an external amp or use an old AVR ( which is what I've done ). I've connected the FL/FR pre-out from the X3700H to the CD input on my old Denon AVR 3313 using RCA cables. So now the X3700H is powering all the 9 CH while the old AVR is powering the FL/FR CH. I've also decided to get the 4 channel NC252MP from Buckeye to replace the old AVR and eventually use it to power the 3 FRONT CH. From what I understand one can use all the pre-outs even if you don't disconnect all channels on the X3700H. " Note: The above PREOUT = Front setting simply identifies which speaker pre-outs are being used for the "expansion" .... you can externally power as many additional speakers as desired as all the pre-outs are hot (ie. there is no setting to turn them ON) such that you could externally power up to all 11/13 speakers if you prefer".

Expanding the AVR by adding 2Ch amp (X3700H/X4700H/X6700H only)

The only models that can be expanded beyond their on board amp capability are the X3700H/X4700H/X6700H. When expanding the X3700H/X4700H from 9CH --> 11CH and the X6700H from 11CH --> 13CH, the most cost effective solution is to purchase a smaller amp (eg. 50W AudioSource Amp100VS2) or re-purpose an existing AVR that you are replacing to power the Height 2 (Height 3 on the X6700H) speakers. Another option for much higher cost is to purchase a much more powerful amp (eg. 300W Emotiva XPA-2) and power the Front L/R speakers on any of the three models.


If the external amp is used for the Front L/R speakers:

Assign Mode: 11.1 (13.1 on the X6700H)
Floor
- Layout: 5ch & SB (or possibly 5Ch + FW on the X6700H)
Height
– Height Sp: 4ch (or 6Ch on the X6700H)
- Layout: Front Height + Rear Height (or whatever 2 (or 3 on the X6700H) settings are available that you want to use)
- Pre-out: Front

Note: The above PREOUT = Front setting simply identifies which speaker pre-outs are being used for the "expansion" .... you can externally power as many additional speakers as desired as all the pre-outs are hot (ie. there is no setting to turn them ON) such that you could externally power up to all 11/13 speakers if you prefer. Note however, that if you do externally power all speakers (regardless of the number), use AMP ASSIGN = Pre-Amp instead of 11.1/13.1.

 

[ciotime]

Below is Buckeye's response asking whether the X3700H is capable of driving external amp's that have an input sensitivity of +1.4V.

Reading Amirs review for the X3700, one need only worry about matching an amp that has an input sensitivity at or below 1.4v if you are using the amp for any speakers beside the fronts:

"So when selecting an external amplifier for channels beyond fronts, make sure it can output its maximum power at or below 1.4 volts"

That said, the NC252MP modules have a maximum power output when the input signal is 1.66Vrms (sensitivity) so there will be almost no audible impact if they are fed a signal of only 1.4v.

Depending on your speakers impedance, the 252's would give between 140-250w per channel.

1) My understanding from what Amir reported in his testing is that the Denon will output 2V (a standard value) if only using the preouts for the front LCR speakers and some of the internal amplifiers are used for surround speakers. But if you used external amps for all of your speaker and therefore none of the internal amps are being used, then the output voltage will drop to around 1.4.

2) You absolutely DO NOT need an amp that requires 1.4V or less. It's not a brick wall value. If you hooked up an amp that is listed as 2V input sensitivity and the Denon is still putting out 1.4V, the amp will work normally but it will just mean it can't get as loud as expected. And for such a small voltage difference we are talking about maybe 2dB difference.
Simple answer: if you used a Hypex NC252 that is listed as 1.66V and could only get the denon to output 1.4V, the amp would be only 1dB less "loud" at maximize volume compared to if it was being supplied 1.66V

3) So no, you do not need an amplifier with an input sensitivity of 1.4V or lower. The Hypex NC252 would work just fine.

 

[lovinthehd]

Then there's trying to control or even know the pre-output voltage in normal use....(or the input signal level to the Denon for that matter). I doubt there would be any audible issues in typical use, tho.

 

[PENG]

Below is Buckeye's response asking whether the X3700H is capable of driving external amp's that have an input sensitivity of +1.4V.

Reading Amirs review for the X3700, one need only worry about matching an amp that has an input sensitivity at or below 1.4v if you are using the amp for any speakers beside the fronts:

"So when selecting an external amplifier for channels beyond fronts, make sure it can output its maximum power at or below 1.4 volts"

That said, the NC252MP modules have a maximum power output when the input signal is 1.66Vrms (sensitivity) so there will be almost no audible impact if they are fed a signal of only 1.4v.

Depending on your speakers impedance, the 252's would give between 140-250w per channel.

1) My understanding from what Amir reported in his testing is that the Denon will output 2V (a standard value) if only using the preouts for the front LCR speakers and some of the internal amplifiers are used for surround speakers. But if you used external amps for all of your speaker and therefore none of the internal amps are being used, then the output voltage will drop to around 1.4.

2) You absolutely DO NOT need an amp that requires 1.4V or less. It's not a brick wall value. If you hooked up an amp that is listed as 2V input sensitivity and the Denon is still putting out 1.4V, the amp will work normally but it will just mean it can't get as loud as expected. And for such a small voltage difference we are talking about maybe 2dB difference.
Simple answer: if you used a Hypex NC252 that is listed as 1.66V and could only get the denon to output 1.4V, the amp would be only 1dB less "loud" at maximize volume compared to if it was being supplied 1.66V

3) So no, you do not need an amplifier with an input sensitivity of 1.4V or lower. The Hypex NC252 would work just fine.

Just for clarity, the pre out is actually capable of a little over 4 V maximum. Gene mentioned it, and Amir has measured it up to 4 V. The 1.4 V thing is, based on ASR's tests, that's where you can expect the highest SINAD, if the internal amps are connected, it will go higher as you turn the volume up, and/or the input signal increases with the media contents (music, explosions in movies etc..), but distortions will increase, that is SINAD will drop. So again, it is not like the pre out would somehow be limited to 1.4 V, amps connected, or 2 V amps disconnected, but SINAD would increase as the output voltage increase.

Pictures better than a thousand words, so take a look of the graphs below (noted that SINAD is the inverse/reciprocal of THD+N, that's why the two graphs look sort of inverted to each other):

The one posted by Gene:
Denon AVR-X3600H 9.2CH IMAX Enhanced AV Receiver Offers Best In Class Features | Audioholics

The one posted by Amir/ASR:
Denon AVR-X6700H AVR Review (Updated) | Audio Science Review (ASR) Forum

 

[ciotime]

Anyway being a noob do you guys think my decision in getting the 4 channel NC252MP from Buckeye to use as the power amp for the LCR ( X3700H ) was a good one?

 

[PENG]

Anyway being a noob do you guys think my decision in getting the 4 channel NC252MP from Buckeye to use as the power amp for the LCR ( X3700H ) was a good one?

I think it is a good decision only if you promise to post a detailed review complete with photos of the inside/outside after using it for a week or two.

 

[lovinthehd]

Sometimes ya just want an amp.....did you ask Buckeye about a 3ch instead of 4ch version or do you have something in mind for that fourth channell?

 

[PENG]

Sometimes ya just want an amp.....did you ask Buckeye about a 3ch instead of 4ch version or do you have something in mind for that fourth channell?

I thought I suggested that he did, might have mixed up with another person though. Buckeye did not list the 3 channel option, but I would be surprised if he wouldn't do it on request.

 

[lovinthehd]

I thought I suggested that he did, might have mixed up with another person though. Buckeye did not list the 3 channel option, but I would be surprised if he wouldn't do it on request.

I thought you had and since it is a small sort of custom thing to begin with, I'd at least ask. Might help alleviate cost of shipping?

 

[ciotime]

I did ask and below is his reply...I saw the Nord website and they do make them in 3 ch but their price is way more expensive. Dunno why though.

"They come in modules of 1 or 2 channels. I only build with the two channel modules (so all my amps are even numbers, 2 through 8 channel configurations). But there is nothing wrong or performance impacting of leaving one channel unused. In fact for my front LCR speakers I use a 4 channel Hypex build with one channel left unused. Max power per channel, etc are still the same."

 

[PENG]

I did ask and below is his reply...I saw the Nord website and they do make them in 3 ch but their price is way more expensive. Dunno why though.

"They come in modules of 1 or 2 channels. I only build with the two channel modules (so all my amps are even numbers, 2 through 8 channel configurations). But there is nothing wrong or performance impacting of leaving one channel unused. In fact for my front LCR speakers I use a 4 channel Hypex build with one channel left unused. Max power per channel, etc are still the same."

May be you can ask him to use 3 and ship the 1 loose to you. You can then sell it easily, I think.

 

[cheyne barnhouse]

Greetings everybody! I posted this query on an ASR thread too but I was hoping to get some advice here as well on a change that I'm in the process of making to my non-dedicated home theater.

Right now I have a Model 7220 and a Model 5000x from Outlaw powering my 7 base layer spkrs and 4 Atmos spkrs; the input sensitivity for the 7220 is 1.64V and for the 5000x it is 1.2V.

I've had the same trusty Marantz unit at the heart of my setup since 2015 but I recently decided it was time to upgrade my AVR/Processor - it couldn't pass a 4K signal (i used the workaround 2nd HDMI cord option with my Oppo - one to the tv for picture and one to the receiver for audio), and while I can decode Atmos I was missing out on some of the the newer immersive sound codecs like DTS-X, Imax Enhanced, and DTS- X Pro. I've been saving up for the last 4 years or so so I decided to forego the climbing of the 'gradual upgrade tree' and just go all out and buy myself a Trinnov Altitude 16. I believe the Altitude's XLR output voltage is rated at 6.15 vrms.

My curiosity is related to the large difference in voltage/gain - I wanted to know if it would be ok to try and pair my existing amps up with the Trinnov once it arrives. I don't know very much about the subject but I believe that such a large voltage difference could impact the noise floor, I'm just not sure about what kind of pros/cons I'd be looking at with the intended pairing. I definitely don't want to damage anything so I thought it would be wise to cover the bases and get some advice from people that are more technically inclined in this area.

I read up on them a little bit and it appears that the Outlaw amps are very similar to ATI amps - the 7220 was actually made in collaboration w/ ATI, and I think Outlaw amps are made in the same factory. On the various forums that I frequent I've seen people using ATI amps as the power stage for their Trinnovs, so my thinking is that the current Outlaw amps would be a decent match for the Trinnov. When I looked around online, the majority of the people that own a Trinnov use higher end amps, however, my budget won't let me flex enough to get something like the matching Amplitude amps from Trinnov that were actually made for the Altitude... it's just more $ than I can realistically do right now since I'm already stretching my limits to be able to get the Altitude. I looked at other brands like NAD, Bryson, D-Sonic, and ATI, but most of them are also out of my price range since I have 11 channels that I have to power in my setup.

I'm not sure if this information would be helpful for this discussion or not, but I wanted to include it as well to help give some context for my specific situation. I usually listen to movies between -8.5 and -15 dB's (or between -3 and 0 dB for a Disney+ stream, lol), at the MLP I sit between 8 and 6 feet from all of my speakers including the Atmos sprs (ceiling is 7'9"), the speakers that I run for the base layer are: Triton 5 towers as the L/R mains, BRX bookshelves as the C and side surrounds, Aon 3's for the rear surrounds and Atlantic Technology IC-OBA in-ceiling spkrs for the Atmos channels. If more info or pics of the room are needed I can provide those as well.

Cheers everyone, and thanks in advance!