Anthem MRX-740 or Denon 6700h for main channels power amp with 2.71 Vrms input sensitivity?

M

mtrot

Full Audioholic
As my current AVR's front left channel has cratered and it may not be worth it to repair it, I'm looking to get a new AVR. I currently run a 5.1 system. As posted in the title, my Krell power amp for the front main channels has input sensitivity of 2.71 Vrms and 26.4 dB of gain. I drive the other channels with the AVR.

It seems that, from reading reviews of Denon AVRs, their pre-out distortion begins to rise above around 1.2 Vrms. How much so, I do not know, nor do I know whether it would be audible at all. I read Gene's review, in which he praised the pre-out voltage and low distortion of the Anthem 740/1140.

Also, if I understand correctly, I do understand that I can turn off the internal amps on the 6700 for the front L/R channels, but also that you have to turn off ALL the internal amps in order to achieve the lower distortion numbers on the pre-outs that the 6700 is capable of. Is this correct?

Finally, my cratered AVR is a Denon, so I am already more familiar with the brand. Thanks for any advice or suggestions.
 
lovinthehd

lovinthehd

Audioholic Jedi
I'm pretty sure the X8500/A110 models are the only ones currently that you can turn off the individual internal amps with pre-out mode. That gets you closer to 2V before clipping with the Denons IIRC. If the Anthems can output 3V unclipped then that seems a better solution assuming you're keeping the Krell.....
 
Last edited:
M

mtrot

Full Audioholic
I'm pretty sure the X8500/A110 models are the only ones currently that you can turn off the individual internal amps with pre-out mode. That gets you closer to 2V before clipping with the Denons IIRC. If the Anthems can output 3V unclipped then that seems a better solution assuming you're keeping the Krell.....
Thanks, after some reading, it appears that the Denon 3700 and up can be put into pre-amp mode for only the front L/R channels. I don't think it turns off the internal amps for those channels, but perhaps it will keep them from being driven into distortion, by virtue of no signal being sent to them. Is that correct?
 
lovinthehd

lovinthehd

Audioholic Jedi
Thanks, after some reading, it appears that the Denon 3700 and up can be put into pre-amp mode for only the front L/R channels. I don't think it turns off the internal amps for those channels, but perhaps it will keep them from being driven into distortion, by virtue of no signal being sent to them. Is that correct?
Believe that is true of the 3700-6700 models, that they can indeed only turn off internal amps for those two channels if set correctly (vs both being "live"). Does make me wonder if even for those it may be a firmware update away but to keep those price points in line....

The distortion level up to 1.2V isn't a particularly worry, but there is a slight improvement to 2.0V (IIRC, haven't reviewed the measurements made over at ASR) if you can turn off the internal amp for that channel. Or you can use an amp with more reasonable sensitivity (which I've always done).
 
P

PENG

Audioholic Slumlord
As my current AVR's front left channel has cratered and it may not be worth it to repair it, I'm looking to get a new AVR. I currently run a 5.1 system. As posted in the title, my Krell power amp for the front main channels has input sensitivity of 2.71 Vrms and 26.4 dB of gain. I drive the other channels with the AVR.

It seems that, from reading reviews of Denon AVRs, their pre-out distortion begins to rise above around 1.2 Vrms. How much so, I do not know, nor do I know whether it would be audible at all. I read Gene's review, in which he praised the pre-out voltage and low distortion of the Anthem 740/1140.

Also, if I understand correctly, I do understand that I can turn off the internal amps on the 6700 for the front L/R channels, but also that you have to turn off ALL the internal amps in order to achieve the lower distortion numbers on the pre-outs that the 6700 is capable of. Is this correct?

Finally, my cratered AVR is a Denon, so I am already more familiar with the brand. Thanks for any advice or suggestions.
Regarding the preout of the 3700, 4700 through 8500, I have explained that misconception about the 1.2v thing and disconnecting the internal amps a few times on this forum, and also on ASR. Please do a search and find the posts for details. If you can't find them, I can do it tomorrow. Basically you have nothing to worry about, Denon or Anthem..
 
Replicant 7

Replicant 7

Audioholic Samurai
Believe that is true of the 3700-6700 models, that they can indeed only turn off internal amps for those two channels if set correctly (vs both being "live"). Does make me wonder if even for those it may be a firmware update away but to keep those price points in line....

The distortion level up to 1.2V isn't a particularly worry, but there is a slight improvement to 2.0V (IIRC, haven't reviewed the measurements made over at ASR) if you can turn off the internal amp for that channel. Or you can use an amp with more reasonable sensitivity (which I've always done).
"keep those price points"

Turning off the amps, will the heat still be a issue?

@PENG what's your take on switching off amps in a AVR that runs hot. Think heat output will be reduce?
 
P

PENG

Audioholic Slumlord
"keep those price points"

Turning off the amps, will the heat still be a issue?

@PENG what's your take on switching off amps in a AVR that runs hot. Think heat output will be reduce?
Thank you for bring this up, unfortunately no matter how many times we post on this topic, similar questions due to people's misconception or confusing about the related specs keep popping up and people end up worry for nothng.

I'll just do a quick recap as follow:

1) Denon+Marantz AVRs do not turn off the internal amps.
2) D+M AVRs, from the AVR-X3700H and up, newer models included, have a preamp mode.
2a) In preamp mode, D+M AVRs will enable ECO mode automatically (not in the specs, but reported by some reliable sources, including Gene iirc..) so the unit will in fact runner cooler as the bias current for the power amp will be much reduced in preamp mode.
3) In preamp mode, the AVR will disconnect the pre amp output (so called pre-outs) to the power amp inputs.
4) With the internal power amp inputs disconnected from the pre outs, the power amps are still powered, but since there are no signal for them to amplify, they will never clip.
5) Because the power amps will never clip in preamp mode, there will be no distortions due to clipping fed back to the preamp side, as a result the pre outs will have lower distortions at higher output voltage, right up to its clipping point, that according to Gene (Audioholics) and Amir (ASR)'s measurements. That would be in the range of 3 to a little over 4 Volts.
6) The AVR-X3600H, AVR-X4400H, 4500H (not sure about the 4300), SR6011, SR7010 through 7013 do not have preamp mode, but you can use the amp assign function to have the pre outs disconnect from the power amp inputs, just like the preamp mode, but you can only do it to the front left and front right channels. Gene was the first only discovered this and shared with Audioholics, in his review of the AVR-X3600H:
Denon AVR-X3600H 9.2CH IMAX Enhanced AV Receiver Offers Best In Class Features | Audioholics
In that review (actually preview) Gene also commented that:

With the AVR-X3600H configured to reroute the main front L/R internal amplifiers, the preamp is physically disconnected from the power amp. This allows the preamp stage full capability of delivering up to 4Vrms unclipped when connected to external amplification as can be seen in the following output vs distortion plot courtesy of Sound United Engineering.
7) So basically, in 6) above you can only disconnect the FL and FR internal power amp channels whereas in 2) you can do that, or if you use preamp mode, all internal power amp channels will be disconnected from the pre outs.
8) It is important to understand that even if the internal power amps are not disconnected from the pre outs, it is not true that the pre outs will be clipping at 1.2, 1.4 or even 2, 3 volts, the pre outs can still go up to 3.5 to 4.0 V or a little higher. It just mean that from about 1.4 to 1.45 V, it will generally start being affected by the clipped power amp output distortions fed back to the preamp section, thereby causing the pre out distortions to rise rather quickly. That is shown in ASR's measurements, at 2 V, the preout distortion would be about -75 dB, that is 0.018%THD+N, still below the threshold of audibility. At voltages higher than 2 V, say at 3 to 3.5 V, THD+N will have increased further but not by much, because the distortion from the power amp clipping will not affect the pre outs proportionally, at some point it would taper off.

I have spend a lot of time posting some or all of the above on AH, I wish there is a quick way for people to find the answers either from my, or others including Gene posts.
 
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P

PENG

Audioholic Slumlord
Thanks, after some reading, it appears that the Denon 3700 and up can be put into pre-amp mode for only the front L/R channels. I don't think it turns off the internal amps for those channels, but perhaps it will keep them from being driven into distortion, by virtue of no signal being sent to them. Is that correct?
The first part is not correct but your second sentence is sort of correct please read post#7.
 
P

PENG

Audioholic Slumlord
I'm pretty sure the X8500/A110 models are the only ones currently that you can turn off the individual internal amps with pre-out mode. That gets you closer to 2V before clipping with the Denons IIRC. If the Anthems can output 3V unclipped then that seems a better solution assuming you're keeping the Krell.....
Denon and Marantz AVR preouts don't clip at 2 V, won't likely clip until it reaches 4 V. People get confused with the internal power amp clipping, and the resulting higher distortions would affect the preamp section because of the feed back loop. Such bad effects tend to taper off though so distortions would increase more rapidly after 2 V but tend to rise at a gentler way from there, until about 4 V when it would actually start to clip.

In the X3600H preview, Gene included the follow graph, he said was "output vs distortion plot courtesy of Sound United Engineering", note that the Clipping point shown is 4.25V.

1662037882815.png
 
P

PENG

Audioholic Slumlord
As my current AVR's front left channel has cratered and it may not be worth it to repair it, I'm looking to get a new AVR. I currently run a 5.1 system. As posted in the title, my Krell power amp for the front main channels has input sensitivity of 2.71 Vrms and 26.4 dB of gain. I drive the other channels with the AVR.
Gain and input sensitivity specifications are highly related, with additional info you can calculate one from the other. I prefer gain because input sensitivity often confused people. For example, input sensitivity of 2.71 Vrms is not a complete spec, it should also include at the minimum, the power amp output voltage or power at 2.71 V as well as the load impedance.

If your Krell power amp's sensitivity spec is 2.71 Vrms without stating the output voltage/or power, then knowing Krell, my educated guess would be that at 2.71 Vrms input, your power amp will output just about 400 W into 8 ohms or 800 W into 4 ohms (if it doubles down, some Krell amps do but not all).

Now you can do a check by calculation using the gain spec:

Power output = Votage input X 10^(gain in dB/20) = ((2.71X10^(26.4/20))^2)/8 = 400.73 W

So I would assume your Krell amp is rated about 400 W into 8 ohms.

Any of the Denon X3700H and above AVRs should have no trouble driving your power amp. I have tried my buckeyeamp (Hypex) amp and my VTV (Purifi) amp that have 26 dB gain with my AVR-X4400H and have no issues at all with sound quality, that's without disconnected the internal power amps from the pre outs.
 
M

mtrot

Full Audioholic
Gain and input sensitivity specifications are highly related, with additional info you can calculate one from the other. I prefer gain because input sensitivity often confused people. For example, input sensitivity of 2.71 Vrms is not a complete spec, it should also include at the minimum, the power amp output voltage or power at 2.71 V as well as the load impedance.

If your Krell power amp's sensitivity spec is 2.71 Vrms without stating the output voltage/or power, then knowing Krell, my educated guess would be that at 2.71 Vrms input, your power amp will output just about 400 W into 8 ohms or 800 W into 4 ohms (if it doubles down, some Krell amps do but not all).

Now you can do a check by calculation using the gain spec:

Power output = Votage input X 10^(gain in dB/20) = ((2.71X10^(26.4/20))^2)/8 = 400.73 W

So I would assume your Krell amp is rated about 400 W into 8 ohms.

Any of the Denon X3700H and above AVRs should have no trouble driving your power amp. I have tried my buckeyeamp (Hypex) amp and my VTV (Purifi) amp that have 26 dB gain with my AVR-X4400H and have no issues at all with sound quality, that's without disconnected the internal power amps from the pre outs.
Dang, you are good! My amp is the FPB-400cx in this chart:

 
P

PENG

Audioholic Slumlord
Dang, you are good! My amp is the FPB-400cx in this chart:

Wow, that's a great amp to pair with either the Denon or Anthem AVRs, the gain is neither low or high but it is low enough to avoid some of the Yamaha AVRs (the new ones are okay) that did not do well on pre out higher than 1.5 V. You cannot use preamp mode of the X3700H because you have to use its internal amps to drive the other channels, but you can disconnect the FL/FR power amps to drive the stereo FPB-400CX if you want to keep THD+N exceptionally low. If you are in Canada then the MRX-740 could be a good option too.
 
MaxInValrico

MaxInValrico

Full Audioholic
Wow, that's a great amp to pair with either the Denon or Anthem AVRs, the gain is neither low or high but it is low enough to avoid some of the Yamaha AVRs (the new ones are okay) that did not do well on pre out higher than 1.5 V. You cannot use preamp mode of the X3700H because you have to use its internal amps to drive the other channels, but you can disconnect the FL/FR power amps to drive the stereo FPB-400CX if you want to keep THD+N exceptionally low. If you are in Canada then the MRX-740 could be a good option too.
I purchased my Anthem in the US and they have been tested here by Gene.
 
M

mtrot

Full Audioholic
Wow, that's a great amp to pair with either the Denon or Anthem AVRs, the gain is neither low or high but it is low enough to avoid some of the Yamaha AVRs (the new ones are okay) that did not do well on pre out higher than 1.5 V. You cannot use preamp mode of the X3700H because you have to use its internal amps to drive the other channels, but you can disconnect the FL/FR power amps to drive the stereo FPB-400CX if you want to keep THD+N exceptionally low. If you are in Canada then the MRX-740 could be a good option too.
Yes, this Krell seems really good sounding to me, but it is also quite the space heater!

Just curious why you say the MRX-740 could be a good option if I'm in Canada?

At this point, I'm thinking of going with the X4700h or X6700h, since I plan to drive the non-front L/R channels with the AVR and I run tower speakers for surrounds and a big center channel speaker. And I may soon end up with a center speaker that dips to 4 ohms or lower.

In order to actually match the power output of my cratered X5200W(140 wpc), I will need to go with the X6700h.

 
M

mtrot

Full Audioholic
Or, I could go with a nice used X6500 and just not worry about doing the "pre outs disconnect from the power amp" thing for the front L/R channels. I don't have this feature with my X5200W and it seems to work great into the Krell. That would save me around $1000.
 
P

PENG

Audioholic Slumlord
Or, I could go with a nice used X6500 and just not worry about doing the "pre outs disconnect from the power amp" thing for the front L/R channels. I don't have this feature with my X5200W and it seems to work great into the Krell. That would save me around $1000.
Why not the 4700, is 11 channel not enough?
 
M

mtrot

Full Audioholic
Why not the 4700, is 11 channel not enough?
Thanks, it's not the channels. It's that I want to match the power output of my 5200. I know, it's not supposed to be that much difference, but I just want it! :cool:
 
lovinthehd

lovinthehd

Audioholic Jedi
Denon and Marantz AVR preouts don't clip at 2 V, won't likely clip until it reaches 4 V. People get confused with the internal power amp clipping, and the resulting higher distortions would affect the preamp section because of the feed back loop. Such bad effects tend to taper off though so distortions would increase more rapidly after 2 V but tend to rise at a gentler way from there, until about 4 V when it would actually start to clip.

In the X3600H preview, Gene included the follow graph, he said was "output vs distortion plot courtesy of Sound United Engineering", note that the Clipping point shown is 4.25V.

View attachment 57603
I was thinking on some of the x7xx series that Amir tested it was closer to 2V or was that just the optimal point? It's been a while.
 
M

mtrot

Full Audioholic
Why not the 4700, is 11 channel not enough?
I've been doing some more reading and thinking about this, and spoke with a dealer. Perhaps the 4700 and its 125 wpc will be fine for my center speaker and I'll save around $1,000, to boot!
 

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