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Amp for Polk L800's - NonDifferential

tjcinnamon

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I just purchased the Polk L800's with SDA which have some particular amp requirements. I'm looking for an amp that is 300W @ 4ohm that's 3 channels or more. The impedance on these speakers is 2.8 to 4ohms per Polk

My budget is about $3000. So far the short list is the MonoPrice Monolith 11CH and the Anthem MCA 325. Other brands are welcomed.

https://www.audioholics.com/tower-speaker-reviews/polk-legend-l800
One important set up point is that differential output amplifiers will not work as well with the SDA technology. The SDA feed comes from the positive leg of the speaker inputs. With single-ended amplifiers, that gives all of the difference signal, but with a differential amp, you only get half of the difference signal. We tested both and found better sound with single-ended amplifiers. Most modern Class D amplifiers have differential outputs and won’t work well, such as the Cherry Megachino I tried, the Hypex based amplifiers (including Marantz’s own Reference PM-10), various NAD amplifiers, etc. Most amplifiers in general are single-ended output so finding a good amplifier that works is not a big problem. The best way to tell is to look at the back of the amplifier and see if it notes that the negative terminal of the amplifier cannot be connected to ground or if it is referred to as a balanced output or differential output amplifier. If all else fails, ask the manufacturer.
 
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tjcinnamon

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Bumping this up because I've narrowed down my results. Is the Anthem P2 or MCA325 a fully-differential output?
 

restorer-john

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The audioholics reviewer is gettting himself dreadfully confused with amplifiers that are BTL (bridged tied load) and amplifiers that are ground return for the negative.

He's also getting himself badly confused again, as NAD often (and have done for decades since the 2200 power amplifier in the early 1980s) run one channel in opposite polarity to the other in order to reduce strain on the power supply. It doesn't make the ouput "differential", merely opposite polarity to the other channel. They can be quite successfully used for the SDA, as long as you take the opposite polarity into account.

The Hypex amplifiers such as ones used in the NAD M-22 (NC 400oem) are not "differential ouputs". They are ground referenced and will work fine with the SDA. As will the M-22v2.

It appears that any of the NAD power amplifiers (or integrated) that use an opposite polarity arrangement colour code the terminals where the "cold" is blue, not black.

NAD C-268.
1620424063741.png


Notice the bridge mode connections are one red and one blue? Normally bridge mode is connected to two "hots". It tells me the amplifier normally runs in 2 channel with one channel in opposite polarity and the right channel "cold" (blue) is really a "hot". The right channel red terminal is, in reality, connected to ground. Confused? Combine that with Polk's SDA and people could get themselves in trouble.

Hypex NC-400oem excerpt from M-22 manual, notice the cold is grounded:
1620423362934.png


A DMM on continuity will tell you which terminals are in fact ground referenced for a single ended NAD using this arrangement. You can then take that into account for the SDA cross-feed wires.
 
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tjcinnamon

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The audioholics reviewer is gettting himself dreadfully confused with amplifiers that are BTL (bridged tied load) and amplifiers that are ground return for the negative.

He's also getting himself badly confused again, as NAD often (and have done for decades since the 2200 power amplifier in the early 1980s) run one channel in opposite polarity to the other in order to reduce strain on the power supply. It doesn't make the ouput "differential", merely opposite polarity to the other channel. They can be quite successfully used for the SDA, as long as you take the opposite polarity into account.

The Hypex amplifiers such as ones used in the NAD M-22 (NC 400oem) are not "differential ouputs". They are ground referenced and will work fine with the SDA. As will the M-22v2.

It appears that any of the NAD power amplifiers (or integrated) that use an opposite polarity arrangement colour code the terminals where the "cold" is blue, not black.

NAD C-268.
View attachment 128562

Notice the bridge mode connections are one red and one blue? Normally bridge mode is connected to two "hots". It tells me the amplifier normally runs in 2 channel with one channel in opposite polarity and the right channel "cold" (blue) is really a "hot". The right channel red terminal is, in reality, connected to ground. Confused? Combine that with Polk's SDA and people could get themselves in trouble.

Hypex NC-400oem excerpt from M-22 manual, notice the cold is grounded:
View attachment 128554

A DMM on continuity will tell you which terminals are in fact ground referenced for a single ended NAD using this arrangement. You can then take that into account for the SDA cross-feed wires.
I wish I knew this much!
Would a standard VTV purifi “work” or meet the criteria for the crossover?
also, would the Anthem MCA work with them?
I feel like an idiot even posting these responses... Polk support wasn’t helpful but when I heard these in the store it was mind blowing.
 
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tjcinnamon

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This I got off the Polk site. Some of these look like Class D as well...

Scott Orth was the designer of the crossover

“ Polk's Scott Orth for recommendations and after he consulted with the electronics engineers he replied:

"In general, the requirements for the mating amp/receiver are fairly simple:


1. Not balanced/bridged output. SDA requires this to function at it’s best. A balanced/bridged amp should play, but the dimensional arrays will only get half of the signal they need.
2. Should be able to drive a 4 ohm load. This is most receivers/amps.

The speakers will benefit from higher power and higher quality amplification, just like any other speaker. I would recommend at least 50W and typically no more than about 300W. Of course, the user should exercise the usual caution: if things are distorting, turn it down, etc. You can use higher power, but be careful not to overdrive the speaker. Low output impedance/high damping factor is always a plus in my book.

From our stable of brands, there are several amps and receivers one could use to drive the L800:

Integrated amps:
Marantz PM-KIRuby (200W into 4Ω)
Marantz PM12SE (200W into 4Ω)
Denon PMA A110 (160W into 4Ω)
Marantz Model 30 (200W+200W into 4Ω)
Marantz PM8006 (100W into 4Ω)

A/V receivers/separates:
Marantz MM8077 (180W into 6Ω)
Marantz MM7025 (170W into 6Ω)
Marantz 8000 and 7000 series

Classe Delta Series

There are certainly plenty of amps from other manufacturers that will drive the L800 as has been pointed out in reviews."

Thoughts on this?
 

restorer-john

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I feel like an idiot even posting these responses...

Don't feel that way. Your questions are perfectly valid and the Polk SDA array has been the undoing of more than a few systems in the distant past.

The Anthem MCA range appears to be a conventional design and should work perfectly well with the Polks. I haven't seen one myself, but they sure look very nicely made.

As it is rated on a continuous basis into 2ohms, it really cannot be a bridged/balanced design as if it were, each amplifier would be seeing 1 ohm- no chance.

1620430789882.png


All the amplifiers listed above appear to be well up the range and some a pretty expensive. You should have no problems with the Polk SDAs with such gear.
 

VintageFlanker

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The audioholics reviewer is gettting himself dreadfully confused with amplifiers that are BTL (bridged tied load) and amplifiers that are ground return for the negative.

He's also getting himself badly confused again
"The Audioholics reviewer" is called @Matthew J Poes and is a member here.
 
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tjcinnamon

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Don't feel that way. Your questions are perfectly valid and the Polk SDA array has been the undoing of more than a few systems in the distant past.

The Anthem MCA range appears to be a conventional design and should work perfectly well with the Polks. I haven't seen one myself, but they sure look very nicely made.

As it is rated on a continuous basis into 2ohms, it really cannot be a bridged/balanced design as if it were, each amplifier would be seeing 1 ohm- no chance.

View attachment 128574

All the amplifiers listed above appear to be well up the range and some a pretty expensive. You should have no problems with the Polk SDAs with such gear.
Thanks for the empathy. I’ve got a lead on a super battered statement P2 within my price point or just going new with the MCA 325. I’ve been eyeing purifi since I’ve seen this site and I think they do 400W into 4ohms. They can also hit 2 so by that logic they could work?
 
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tjcinnamon

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Hi All,
I pulled the trigger on an Anthem MCA 325 for the Polk Legend LCR. I’m pretty stoked!
Thanks for all the feedback.

On Friday I put in a call to anthem to validate that nothing changed in the Gen 2’s to make it Bridge-Tied-Load.
 
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tjcinnamon

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Don't feel that way. Your questions are perfectly valid and the Polk SDA array has been the undoing of more than a few systems in the distant past.

The Anthem MCA range appears to be a conventional design and should work perfectly well with the Polks. I haven't seen one myself, but they sure look very nicely made.

As it is rated on a continuous basis into 2ohms, it really cannot be a bridged/balanced design as if it were, each amplifier would be seeing 1 ohm- no chance.

View attachment 128574

All the amplifiers listed above appear to be well up the range and some a pretty expensive. You should have no problems with the Polk SDAs with such gear.

Well I found this on their site: https://www.anthemav.com/support/faq.php
---------------------------------------------------
What about the whole circuit from front to back - is it fully balanced?

No. At some point the signal must become single-ended, or interference can't be cancelled. This is better done sooner rather than later in the signal chain. The purpose of a balanced stage within a circuit is cancelling out nonlinearities arising in the circuit itself, and/or to double the signal level while cancelling out some noise. This is purely a means, not an end. We use a balanced arrangement in specific areas within a circuit where it makes a meaningful difference. Doing this to an entire piece of equipment for the sake of using the catch phrase "fully balanced" may achieve nothing but a significant increase in cost, or worse if the two halves of the circuit aren't matched well.
-----------------------------------------


Not exactly sure what this means? I'm assuming it means that it's single ended but not confident
 

restorer-john

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Well I found this on their site: https://www.anthemav.com/support/faq.php
---------------------------------------------------
What about the whole circuit from front to back - is it fully balanced?

No. At some point the signal must become single-ended, or interference can't be cancelled. This is better done sooner rather than later in the signal chain. The purpose of a balanced stage within a circuit is cancelling out nonlinearities arising in the circuit itself, and/or to double the signal level while cancelling out some noise. This is purely a means, not an end. We use a balanced arrangement in specific areas within a circuit where it makes a meaningful difference. Doing this to an entire piece of equipment for the sake of using the catch phrase "fully balanced" may achieve nothing but a significant increase in cost, or worse if the two halves of the circuit aren't matched well.
-----------------------------------------


Not exactly sure what this means? I'm assuming it means that it's single ended but not confident

It will be fine.
 
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tjcinnamon

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From Anthem

#2.) -I emailed 2 different colleagues, both were heads of their departments,(head of parts and service and the Brand Manager), and they both agreed that our OUTPUT STAGE is exactly what you are looking for, and essentially why we design it like that.

We looked into those New Polk speakers and (very confusingly) they are asking for an open-loop at some point, in the amp's design, which is exactly what we explain on our website.

So, you can buy /test/ use those speakers without any fear,:

All three pins of the XLR connection are part of the circuit, which means it's a real balanced connection.
(If pin 3 is sent to the ground or left open, as is sometimes the case, then an XLR jack is an adapter, not a balanced input.)
The purpose of a balanced connection is to cancel out certain types of interference and ground loops.
 
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