Monoprice Monolith 7-Channel Amplifier Review

[RichB]

That's a 7X200 WPC amp. If true, and if the circuity and parts are of high enough quality to assure the full benefits (noise and distortions) are realized without any bad tradeoffs, then how can they still make a reasonable profit. Something has to give right?

ATI has enconomies of scale.

It's balanced bridged. In the ATI Morris interview, he states that balanced is to a degree and better performance (S/N) was achieved in their AT4000/AT6000 amps, which are also balanced designs but not bridged. I am not sure if these are industry standard terms or not.

Emotiva recently released their XPA-DR series amps that are their "Differential Reference" starting at $1599. These amps are reated 550/800 WPC into 8 and 4 ohms.

https://emotiva.com/collections/x-series/products/xpa-dr2

- Rich

 

[Irvrobinson]

ATI has enconomies of scale.

It's balanced bridged. In the ATI Morris interview, he states that balanced is to a degree and better performance (S/N) was achieved in their AT4000/AT6000 amps (which are also balanced designs) but not bridged. I am not sure if these are industry standard terms or not.

ATI's own marketing material is quite confusing on the topic:

As in Kessler’s previous top-of-the-line designs, these amplifiers are fully balanced, differential amps, but unlike his earlier balanced designs which were essentially balanced bridged amplifiers, the 6000 series uses only a single input stage with dual-differential output stages. The reason: the advantages of balanced designs are retained and noise is reduced by 50%.

I'm not sure what "a single input stage" means. I think in context it means that the input stage is single-ended, so by definition the amps are not "fully balanced", but "single input stage" is not the typical terminology one would use to describe a single-ended topology. Normally I would read that as a single input gain stage driving the four output stages (dual differential means four parallel gain stages converging to one), and that 1st gain stage could be balanced or not. I'm also confused by the 3db noise reduction claim, as I was always taught that common-mode cancellation in differential designs could reduce noise by 3db, not increase it. Perhaps ATI is implying that the input stage has noise that doesn't cancel. I give up.

I admit, I'm stickler for precision and clarity, and nonsense like ATI's marketing material annoys me, but in the end I doubt it matters at all. While your review didn't include measurements, I suspect Kessler had a good reason for what he did (he could have just reused the AT3000 topology), and I'd bet a week's pay that it performs, measures, and sounds great.

 

[PENG]

ATI has enconomies of scale.

I understand that point, but it will still result in added cost, and wouldn't it be better to spend that added cost on things that may result in more audible benefits (e.g. better/larger power supply, output devices)? Fully balanced could reduced harmonic distortions, but THD+N can be so low that it is inaudible without being fully balanced. As for SN, you don't need fully balanced design to keep it super low either. On everything being equal and money no object basis, of course fully balance is the way to go, that's why my skepticism of the scheme is only on the more budget oriented products such as Emotiva's and the Outlaw you mentioned.

 

[RichB]

ATI's own marketing material is quite confusing on the topic:

As in Kessler’s previous top-of-the-line designs, these amplifiers are fully balanced, differential amps, but unlike his earlier balanced designs which were essentially balanced bridged amplifiers, the 6000 series uses only a single input stage with dual-differential output stages. The reason: the advantages of balanced designs are retained and noise is reduced by 50%.

I'm not sure what "a single input stage" means. I think in context it means that the input stage is single-ended, so by definition the amps are not "fully balanced", but "single input stage" is not the typical terminology one would use to describe a single-ended topology. Normally I would read that as a single input gain stage driving the four output stages (dual differential means four parallel gain stages converging to one), and that 1st gain stage could be balanced or not. I'm also confused by the 3db noise reduction claim, as I was always taught that common-mode cancellation in differential designs could reduce noise by 3db, not increase it. Perhaps ATI is implying that the input stage has noise that doesn't cancel. I give up.

I admit, I'm stickler for precision and clarity, and nonsense like ATI's marketing material annoys me, but in the end I doubt it matters at all. While your review didn't include measurements, I suspect Kessler had a good reason for what he did (he could have just reused the AT3000 topology), and I'd bet a week's pay that it performs, measures, and sounds great.

Here is a description from the HomeTheaterHifi review:

https://hometheaterhifi.com/reviews/amplifier/power-amplifier/ati-at6002-multi-channel-power-amplifier-review/

The ATI6002 is fully complimentary, meaning that every PNP transistor is matched by an NPN transistor for the entire circuit. The voltage gain stage consists of the four input differential core terminated with resistors. The complementary circuit approach is essential since some DC offsets in the core are canceled. The second voltage gain stage is a standard differential pair, one on the positive rail and one on the negative rail. The complimentary collectors of the second stage differential pairs connect through the output stage base spreading circuit (VBE multiplier). The base spreading circuit, which sets the output stage bias current, uses the diodes in the ThermalTrak output devices. The base spreading circuit is also complementary in the AT6002.

My simplistic take on this is: The 2000/3000 amps were more like strapping two amps together and are balanced, so duplicate input stages. Whereas, 4000/6000 have a single stage that that is fully balanced differenlty throughout the circuit. Technically, I am on really thin ice here

- Rich

 

[RichB]

I understand that point, but it will still result in added cost, and wouldn't it be better to spend that added cost on things that may result in more audible benefits (e.g. better/larger power supply, output devices)? Fully balanced could reduced harmonic distortions, but THD+N can be so low that it is inaudible without being fully balanced. As for SN, you don't need fully balanced design to keep it super low either. On everything being equal and money no object basis, of course fully balance is the way to go, that's why my skepticism of the scheme is only on the more budget oriented products such as Emotiva's and the Outlaw you mentioned.

Sticking with ATI under the hood, all options seem to be available from various vendors.

I don't thing we have really good consistent first-watt THD+N data but just looking at SoundAndVision, the AT6000 and AT522NC don't seem the climb the left wall as do many other amps, including the 7700. If that is indicative of noise and distortion where it counts, that is a difference of 10 fold. Audible, it seems like that may be been discussed a few times on a few forums

IMO, some amps perform far less well driving real loads than the measurements would indicate.

- Rich

 

[PENG]

I don't thing we have really good consistent first-watt THD+N data but just looking at SoundAndVision, the AT6000 and AT522NC don't seem the climb the left wall as do many other amps, including the 7700. If that is indicative of noise and distortion where it counts, that is a difference of 10 fold. Audible, it seems like that may be been discussed a few times on a few forums

- Rich

Rich, if you take a look of the comparison below, there isn't a 10 fold difference. I agree they don't show the first watt, but for the first 5-10 W, the AVR-4308CI actually looks marginally better, I would say practically the same.

Just found some low output THD figures for the AVR-4308CI:

Front channels:
0.00418% @ 1.0W
0.00275% @1.2W

Surround channels:
0.00271% @ 1.0W
0.00275% @ 1.2W

That's for 1 kHz into 8 ohms, but at such low output level, I doubt it would be much different for lower or higher frequencies.

I really believe THD is not an issue for most near flag ship AVRs and two channel Class AB amps in the >$1,000 amp rated 100-200 WPC.

 

[gene]

For power amps, it was only the Emotiva XPA-1 I had in mind at the time. ATI's least expensive model cost more but not by much. I know a lot of people would not consider those low cost and they would be right. I did a quick search, and found the TEAC AX-501 integrated amp also claimed fully balanced, but on a closer look, only the preamp section is fully balanced.

After posting I realized I should not have used the "low cost" term that is highly subjective to define. Put it this way, I am skeptical about any >200 WPC X2 and <$3,000 (list price) class AB end to end balanced amps but that's just me.

By the way, I seem to remember you have a very nice article on AH that describes the fully balanced input to output (all stages) configuration, with some sort of block diagrams or simplified schematics. I also remember the Denon pair was used as an example in that article. I wanted to link it but for some reason, could not find it via a key word search. Can you kindly provide a link please?

There are so much info on the internet but I always find those in the AH AV Research are the most informative and reliable ones, I suspect you may have some background in Quality control management, seriously..

I do mention benefits of differential designs in several product reviews like this one:
https://www.audioholics.com/amplifier-reviews/emotiva-xpr1-amplifier

And on cables here:
https://www.audioholics.com/audio-video-cables/balanced-vs-unbalanced-interconnects

But probably need to do a dedicated article regarding amplifiers.

 

[RichB]

QUOTE="PENG, post: 1242386, member: 6097"]Rich, if you take a look of the comparison below, there isn't a 10 fold difference. I agree they don't show the first watt, but for the first 5-10 W, the AVR-4308CI actually looks marginally better, I would say practically the same.
[/quote]

I tend to agree but these tests are far from exhaustive.
Here are some ATI Variants. The distortion numbers are taken from the graphs because I have seen errors in the article text.

AT5200NBC
Max: .05
1 Watt Est: .0015

AT6000
Max: .03
1 Watt Est: .004

Monolith
Max: .3
1 Watt Est: .01

Outlaw 7500
Max: .1
1 Watt Est: .004

I think SV measurements are of limited value.
I have/had the AT6000, AT500NV, and Outlaw 7500 in my system and I don't find them equivalent.

- Rich

 

[PENG]

I do mention benefits of differential designs in several product reviews like this one:
https://www.audioholics.com/amplifier-reviews/emotiva-xpr1-amplifier

And on cables here:
https://www.audioholics.com/audio-video-cables/balanced-vs-unbalanced-interconnects

But probably need to do a dedicated article regarding amplifiers.

That will be great, I did research this topic to the nth degree and couldn't find one single article that offers both good technical and simple layman description of the main fully differential and non fully differential schemes.

By the way, I did find the one that you used the Denon AVP as example. I guess it was hard to find because it was buried in the reviews instead of under AV Research.

Here it is:

https://www.audioholics.com/av-preamp-processor-reviews/denon-avp-a1hdci/design-overview

in which you mentioned something that most others didn't talk about, the doubling of components and the significant reduction in distortions.

The advantages of fully balanced circuit designs include significant reduction in distortion and noise / RFI/EMI pickup. The only disadvantage is cost and complexity in circuit design as you need double the components and occupy more internal real estate.

Dr. Rich (hometheaterhifi.com) has one that mentioned the distortion part but he's all over the place in that article, making it hard to follow.

Now with the two you linked, we can get a pretty good picture. Thanks again!

 

[PENG]

QUOTE="PENG, post: 1242386, member: 6097"]
I think SV measurements are of limited value.
I have/had the AT6000, AT500NV, and Outlaw 7500 in my system and I don't find them equivalent.

- Rich

I feel the same, Gene's on AH are way better, I wish he would do more and be more consistent with his battery of test protocols.

 

[slipperybidness]

That will be great, I did research this topic to the nth degree and couldn't find one single article that offers both good technical and simple layman description of the main fully differential and non fully differential schemes.

By the way, I did find the one that you used the Denon AVP as example. I guess it was hard to find because it was buried in the reviews instead of under AV Research.

Here it is:

https://www.audioholics.com/av-preamp-processor-reviews/denon-avp-a1hdci/design-overview

in which you mentioned something that most others didn't talk about, the doubling of components and the significant reduction in distortions.



Dr. Rich (hometheaterhifi.com) has one that mentioned the distortion part but he's all over the place in that article, making it hard to follow.

Now with the two you linked, we can get a pretty good picture. Thanks again!

Likely best resource is from an actual amp construction and design book. But, these won't be in layman's terms, the will be hard-core technical details.

 

[gene]

I feel the same, Gene's on AH are way better, I wish he would do more and be more consistent with his battery of test protocols.

I wish I had time to measure more amps but my test procedures are pretty consistent from product to product per my standard I use here:
https://www.audioholics.com/audio-amplifier/basic-amplifier-measurement-techniques

 

[PENG]

I wish I had time to measure more amps but my test procedures are pretty consistent from product to product per my standard I use here:
https://www.audioholics.com/audio-amplifier/basic-amplifier-measurement-techniques

I know, and have read the linked article more than once. I actually meant for example you didn't always measure IMD, and I found the SNR section could be made a little clearer, so people (like me) don't have to assume things.

Example:

The RR2150 exhibited a low noise floor. At 1 watt I measured 83dB (A-weighted) and 76dB with no filter engaged. The relatively small difference between A-wt and un-weighed measurements indicates that out of band residual noise residuals are low. At rated power, I measured 103dB (A-wt).

With the receiver in Direct mode bypassing the DSP and 100mVin, and 1 Vrms output, the AVR-X5200W exhibited an excellent SNR of 95dB with the AES17 filter engaged. With no filter, it dropped down to 88dB, which is still an excellent figure. Because of the digital processing and clocks, with DSP engaged, the noise floor went up to 77dB with no filter engaged. Overall, these are very good results. The preamp is quiet when it should be.

The AVR-X3300W preamp output exhibited a low noise floor (90dB) unweighted with 100mV input drive.

So it seems you measured the RR2150 at the power amp output and the Denons at the pre-outs? If so, then I have the following questions:

- For AVRs, did you always measure in Direct mode at the minimum, and with DSP only in some cases?
- Did you always use 100 mV in, or whatever it needs to obtain 1 Vrms at the pre-out?
- In addition to measuring SN or the prepro section, why wouldn't you measure the overall SNR of AVRs from input to speaker output as well, so we can compare SNRs of AVRs (when used as prepro only) to prepros, and also AVR to prepro/power amp combos.

It will be great if, for AVR, receivers and integrated amps, we can see the SNR values for:

- Preamp input to preamp output (e.g. 100 mV in, 1 Vrms out).
- Preamp input to speaker output (e.g. 10mVin, 1 W out, 100mVin, 100 W, or rated output)

Sorry about asking so many questions, I do appreciate the fact that the AH test lab has already gone way over and above anyone else in the business, in providing so much valuable information and making it publicly available, for free. Thanks again for the great work!

 

[M Code]

The amount of THD @ low levels in a Class A-B depends largely upon how the amplifier's output devices bias levels are set..
Some brands tend to keep these down to minimize idle current and heat buildup, other brands tend to increase this so that the output devices are partially turned ON so their power response is smoother @ lower THD.. This difference can be audible if one has quality hi-resolution loudspeakers...

Just my $0.02...

 

[Glenv6]

That will be great, I did research this topic to the nth degree and couldn't find one single article that offers both good technical and simple layman description of the main fully differential and non fully differential schemes.....

There is a ton of stuff out there on differential/balanced circuits - some interesting links I have found are below.

The first link is to an article from 1994 in Stereophile, which is probably the most informative. Maybe you have seen it. In 2018 the value proposition of balanced vs unbalanced remains the same as in 1994. Regardless of how the technology works, or what its real benefits are, I think whether or not you buy into it boils down to two things (as in all things audio): Do you like what you hear, and are you willing to pay for it.

https://www.stereophile.com/features/335/index.html

https://neatcircuits.com/audio/balanced.htm

https://electronics.stackexchange.com/questions/95803/what-makes-a-balanced-audio-signal

https://hometheaterhifi.com/technical/technical-reviews/the-fully-balanced-power-amplifier-advantages-and-design-challenges/

http://www.ti.com/lit/an/sloa054e/sloa054e.pdf

http://www.ti.com/lit/an/slyt737/slyt737.pdf

 

[PENG]

There is a ton of stuff out there on differential/balanced circuits - some interesting links I have found are below.

The first link is to an article from 1994 in Stereophile, which is probably the most informative. Maybe you have seen it. In 2018 the value proposition of balanced vs unbalanced remains the same as in 1994. Regardless of how the technology works, or what its real benefits are, I think whether or not you buy into it boils down to two things (as in all things audio): Do you like what you hear, and are you willing to pay for it.

https://www.stereophile.com/features/335/index.html

https://neatcircuits.com/audio/balanced.htm

https://electronics.stackexchange.com/questions/95803/what-makes-a-balanced-audio-signal

https://hometheaterhifi.com/technical/technical-reviews/the-fully-balanced-power-amplifier-advantages-and-design-challenges/

http://www.ti.com/lit/an/sloa054e/sloa054e.pdf

http://www.ti.com/lit/an/slyt737/slyt737.pdf

I read all but the neatcircuits.com one and found none that tells me clearly the pros and cons of each scheme, but thanks anyway. As I said before, Dr. Rich's one does provide a lot of technical details, but for some reasons he seemed all over the place in that particular presentation, sort of lacking focus. I suppose if I am patient enough to read every single word a few times it may just do the trick for me. As for "buy in to it", there is no need, because the advantages of any of the fully differential schemes I have read about are obvious. Whether I would be willing to pay for it, it depends, as it is more a bang for the buck kind of deal when the complete system (source input to speaker output) is considered as a whole.

 

[RichB]

^ The Stereophile article author finds single-ended amps have a "toe tapping" quality not found in some balanced implementations.

- Rich

 

[Glenv6]

^ The Stereophile article author finds single-ended amps have a "toe tapping" quality not found in some balanced implementations.

- Rich

Is that a discrediting remark?

 

[RichB]

Is that a discrediting remark?

To each their own, but seems a bit out of place in a discussion of amplifier architecture.
This is the first time I have read that balanced amplifier technology negatively impacts pace and rhythm.

- Rich

 

[Glenv6]

I read all but the neatcircuits.com one and found none that tells me clearly the pros and cons of each scheme, but thanks anyway. As I said before, Dr. Rich's one does provide a lot of technical details, but for some reasons he seemed all over the place in that particular presentation, sort of lacking focus. I suppose if I am patient enough to read every single word a few times it may just do the trick for me. As for "buy in to it", there is no need, because the advantages of any of the fully differential schemes I have read about are obvious. Whether I would be willing to pay for it, it depends, as it is more a bang for the buck kind of deal when the complete system (source input to speaker output) is considered as a whole.

Yup, the benefits are definitely there on paper, but as you say you have to consider the complete system. Those benefits are in the ear of the beholder.