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Multichannel amps for active systems

Burning Sounds

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Since building my Linkwitz LX521s several years ago I've been trying to find a good quality but inexpensive multichannel amp to drive them. As these speakers cost me about £1500 to build I needed something commensurate pricewise and as they are a 4-way that's 8 channels of amplification.

They are not a difficult speaker to drive other than the bass drivers present a 2 ohm load at about 100hz if connected in parallel. The amps that can drive that load are generally out of my price range (ie Bryston etc). The alternative is to use 10 channels of amplification, assigning a separate amp channel to each bass driver.

About 3 years ago I purchased a pair of Nakamichi AVP1 7 channel amps to do just that. At £499 each they were a bargain and I've been very happy with their build quality and reliability. They are built in the same Chinese Winner factory as the earlier Emotiva amps. In fact the AVP1 is very similar to the now discontinued Emotiva UPA-7 - see Audioholics review) but with the addition of balanced inputs. The importer no longer licenses the Nakamich name for the UK and the amp is now called the Iota AVXP1 and costs more than double what I paid. Still not a bad price, but not the bargain it once was.

With more OEM Hypex-based amps at reasonable prices coming on to the market I began to look at other options that might offer a potential improvement in sound quality as well as a smaller form factor. Hypex's specs for these modules are pretty impressive and they are able to drive a 2ohm load.

After considering several brands I settled on the Apollon Audio NCMP8350 as their amps appeared to have a tidy build and a good price. (I initially ordered the NC8200, but there was an issue with the Hypex NC252MP modules, so Apollon offered me a very good deal on the larger NCMP5308 which uses the NC502MP modules.

I've now been listening to this for a couple of weeks and I'm very impressed :). The considerable turn-on surge from those 4 modules has been handled well using what appears to be a pair of start up sequencers. These are right at the front of the amp and do not appear in the images of the NCMP5308 on Apollon's website. The case is an unpretentious, but perfectly adequate pressed steel affair with a nice aluminium front panel. Apollon appear to be one of the few amp companies to offer Speakon connectors instead of banana sockets. I went with the ETI banana sockets, although I am now thinking the Speakons might have been a better option. My LX521s have speakons on the bass units, but banana's on the upper baffle.

The amp runs warmer than I expected (I was probably pre-conditioned by the oft quoted notion that class D amps are cool running). The amp reaches about 35 degrees centigrade at the air vents on the top panel, so well within its operating range, so nothing to worry about there. What is interesting is that all the modules seem to run at the same temperature considering the upper mid drivers and tweeters will only be using a few watts. Only the bass and lower mid channels ever got warm on the Nakamichis. The Apollon is physically absolutely silent. With the deal Apollon gave me mine came in not much above ASR's $500 amp (per stereo pair) price.
 

DonH56

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Cool. Pictures...?

Switch-mode power supplies and amplifiers are generally least efficient at their lowest output power. Note 35 degC is less than average human body temperature (37 degC) so nothing to worry about and I imagine is quite a bit cooler than conventional amplifiers.

Do you know why rated power at 2 ohms is less than at 4 ohms? Just curious... Wondering if it is current-limited or a thermal issue.
 
OP
Burning Sounds

Burning Sounds

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Cool. Pictures...?

Switch-mode power supplies and amplifiers are generally least efficient at their lowest output power. Note 35 degC is less than average human body temperature (37 degC) so nothing to worry about and I imagine is quite a bit cooler than conventional amplifiers.

Do you know why rated power at 2 ohms is less than at 4 ohms? Just curious... Wondering if it is current-limited or a thermal issue.

Here's a pic of the inside of my amp showing what I think are the startup sequencers (please correct me if I am wrong and they have some other function). The amp has twin power cords.

DSC_00201000.jpg


Yes, I'm sure you are right about their efficiency at low output power and that would explain what I'm observing. It was just a surprise that the amp ran warmer than the class AB Nakamichis, but then again the Naks do have much larger heatsinks. As you say, nothing to worry about.

As to the power output at 2 ohms I don't know the answer I'm afraid, but it's still far more power than my bass drivers will ever need. If I remember correctly the SEAS L26ROY bass drivers as used in the LX521 only require about 60 watts to reach their full 28mm linear excursion (they can safely reach 56mm without damage, although distortion has risen at that point of course).

Here it is in my system.....

DSC_00261000.jpg

and the room...the Maggie 2.5Rs swing out from the wall when I want to use them with the Linkwitz bass units.

DSC_00051000.jpg
 

Cosmik

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As one of the official cheapskates in this forum, it all seems so much easier to me...

For one system I use one of these:
0c14c0e4-a0db-48ec-9686-620c2d680e04.jpg


and for another system, one of these:

sony_str_da_1200es_strda1200es_camarossaudio%20(13).JPG


What do they give you?
Beefy power capability; discrete multi-channel mode with 'straight' amplification, a common volume control *and* a separate non-volatile gain trim for each channel; decent construction standard and finish; comprehensive remote control; reasonable confidence they won't go mad and blow up your speakers/burn your house down; silly low price on eBay (possibly $100!).
 
OP
Burning Sounds

Burning Sounds

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As one of the official cheapskates in this forum, it all seems so much easier to me...

I think I mentioned something about driving a 2 ohm load... and the Maggies ribbon presents a 3 ohm load...;) and I can set non-volatile channel trim in the Mytek 8 channel DAC and my remote can access the internet etc etc.....but I get your point...horses for courses I think :D
 

Cosmik

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I think I mentioned something about driving a 2 ohm load... and the Maggies ribbon presents a 3 ohm load...;) and I can set non-volatile channel trim in the Mytek 8 channel DAC and my remote can access the internet etc etc.....but I get your point...horses for courses I think :D
Cheapskateness is an holistic philosophy and lifestyle. The true cheapskate avoids exotic drivers and their demanding loads.
 
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Burning Sounds

Burning Sounds

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@Cosmik is currently our reining cheapskate champion , a much coveted status here at ASR that carry’s major kudos . Frankly the rest of you are eating his dust in this regard .

Thomas, I'm a Yorkshireman. I hear gauntlets being thrown down...:D

At the risk of turning this thread into a one upmanship race to the bottom (pricewise) I have three O2 Jogglers running Squeezeplay around the house - £25 each off ebay.

DSC_00521000.jpg

In my son's bedroom his Joggler outputs to a pair of M-Audio powered speakers (or his headphones). He can access my music, his music, radio, streaming services, all controlled from his phone. £65 all in (give or take a few cheap cables). :)
 

laidick

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Since building my Linkwitz LX521s several years ago I've been trying to find a good quality but inexpensive multichannel amp to drive them. As these speakers cost me about £1500 to build I needed something commensurate pricewise and as they are a 4-way that's 8 channels of amplification.

They are not a difficult speaker to drive other than the bass drivers present a 2 ohm load at about 100hz if connected in parallel. The amps that can drive that load are generally out of my price range (ie Bryston etc). The alternative is to use 10 channels of amplification, assigning a separate amp channel to each bass driver.

About 3 years ago I purchased a pair of Nakamichi AVP1 7 channel amps to do just that. At £499 each they were a bargain and I've been very happy with their build quality and reliability. They are built in the same Chinese Winner factory as the earlier Emotiva amps. In fact the AVP1 is very similar to the now discontinued Emotiva UPA-7 - see Audioholics review) but with the addition of balanced inputs. The importer no longer licenses the Nakamich name for the UK and the amp is now called the Iota AVXP1 and costs more than double what I paid. Still not a bad price, but not the bargain it once was.

With more OEM Hypex-based amps at reasonable prices coming on to the market I began to look at other options that might offer a potential improvement in sound quality as well as a smaller form factor. Hypex's specs for these modules are pretty impressive and they are able to drive a 2ohm load.

After considering several brands I settled on the Apollon Audio NCMP8350 as their amps appeared to have a tidy build and a good price. (I initially ordered the NC8200, but there was an issue with the Hypex NC252MP modules, so Apollon offered me a very good deal on the larger NCMP5308 which uses the NC502MP modules.

I've now been listening to this for a couple of weeks and I'm very impressed :). The considerable turn-on surge from those 4 modules has been handled well using what appears to be a pair of start up sequencers. These are right at the front of the amp and do not appear in the images of the NCMP5308 on Apollon's website. The case is an unpretentious, but perfectly adequate pressed steel affair with a nice aluminium front panel. Apollon appear to be one of the few amp companies to offer Speakon connectors instead of banana sockets. I went with the ETI banana sockets, although I am now thinking the Speakons might have been a better option. My LX521s have speakons on the bass units, but banana's on the upper baffle.

The amp runs warmer than I expected (I was probably pre-conditioned by the oft quoted notion that class D amps are cool running). The amp reaches about 35 degrees centigrade at the air vents on the top panel, so well within its operating range, so nothing to worry about there. What is interesting is that all the modules seem to run at the same temperature considering the upper mid drivers and tweeters will only be using a few watts. Only the bass and lower mid channels ever got warm on the Nakamichis. The Apollon is physically absolutely silent. With the deal Apollon gave me mine came in not much above ASR's $500 amp (per stereo pair) price.


How do you connect the amplifier to power ? Do you use any power strip or directly to wall?
Will there be any difference in sound ?

Thanks.
 
OP
Burning Sounds

Burning Sounds

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The two power cables from the amp are connected directly to the wall - no power strip. The wall sockets are on a standard 16amp breaker. Apollon suggested to me in an email that if I had any issues at turn on to use a 20amp breaker if necessary. My music room is separate from the house and the power to it comes from the main house board via a 32amp breaker. The amp's turn on relays seem to work very well and I've had no issues at all. No lights dimming, which I've had with big class AB power amps in the past.

As to a difference in sound I wouldn't expect any as long as the powerstrip is adequate to handle the turn on.

As to the sound of the amp itself - of course I heard all the things @amirm (and others) have warned about - more detail, better bass, separation of voices, instruments etc ;)

But what I can say for sure is that it is quieter, uses less energy and takes up less space than the two class AB amps it replaced. I'm very happy with it. :)
 

laidick

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It looks like the amp uses low power normally, but only draw a lot when start up, the inrush current.
Is there any way to reduce this inrush current ? I am not good at electronics.

Thanks
 

Wombat

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How do you connect the amplifier to power ? Do you use any power strip or directly to wall?
Will there be any difference in sound ?

Thanks.

I have recently had 4-outlet GPOs installed to replace my twin-outlet GPOs. I did this to reduce the number of power boards supplying my system. All about reducing clutter(fewer powerboards). Good quality GPOs and powerboards are not a problem. Beware the cheap stuff that barely grips the plug and possibly uses inferior alloys for contacts.

GPO = General Power Outlet.
 
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OP
Burning Sounds

Burning Sounds

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It looks like the amp uses low power normally, but only draw a lot when start up, the inrush current.
Is there any way to reduce this inrush current ? I am not good at electronics.

Thanks

As I showed in the pic of the inside of the amp at the top of the thread there appears to be startup sequencers to manage that inrush current.

It's worth noting this from the Hypex datasheet for the NC 502MP - "The NC-MP is an all-in-one module, designed to be applied in a single module configuration and is certified as such. If a multi NC-MP setup is desired, one should take care of EMI, EMC, inrush currents and other related phenomena."

Before I purchased the amp I asked Apollon for some pictures of the internal layout (there were none on their website at the time) as I was aware of potential issues regarding EMI and inrush current. Apollon were very responsive to my questions and their layout looked neat and tidy to me and was part of my decision to go ahead and purchase from them.
 

laidick

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As I showed in the pic of the inside of the amp at the top of the thread there appears to be startup sequencers to manage that inrush current.

It's worth noting this from the Hypex datasheet for the NC 502MP - "The NC-MP is an all-in-one module, designed to be applied in a single module configuration and is certified as such. If a multi NC-MP setup is desired, one should take care of EMI, EMC, inrush currents and other related phenomena."

Before I purchased the amp I asked Apollon for some pictures of the internal layout (there were none on their website at the time) as I was aware of potential issues regarding EMI and inrush current. Apollon were very responsive to my questions and their layout looked neat and tidy to me and was part of my decision to go ahead and purchase from them.


How long did it take for you to receive the amp after you purchase ?
 
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Burning Sounds

Burning Sounds

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It was about 3 weeks, which included a few days delay in shipping as Europe and the UK were experiencing some very heavy snowfall at that time.
 

laidick

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I still have 2 more weeks to wait , sigh...
 

oivavoi

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I got one of these off eBay for 250 USD: https://m.ebay.com/itm/Crown-CTs-82...428517?hash=item33e6acfc25:g:0owAAOSwAghax4wH

Eight channels of 160 w each, can be bridged. Discontinued now, but was fairly expensive before it was discontinued a couple of years ago. Can frequently be found cheap on eBay because of restaurants etc closing down.

Planning to switch out the fans with silent noctua fans and see if it becomes inaudible. Will otherwise resell it. Will use it in bridged mode, with four channels of 350-400 w powering an active two-way system. I would otherwise be very tempted to go down Cosmik's route with an old AVR, but my one concession to audiophilia nevrosa is that I have this idea that amps should be plenty powerful to give sufficient dynamics to the kind of music I'm listening to.

I also am not 100 percent convinced about class d for treble use. That's probably a misconception on my side though.
 
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Burning Sounds

Burning Sounds

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I got one of these off eBay for 250 USD: https://m.ebay.com/itm/Crown-CTs-82...428517?hash=item33e6acfc25:g:0owAAOSwAghax4wH

Eight channels of 160 w each, can be bridged. Discontinued now, but was fairly expensive before it was discontinued a couple of years ago. Can frequently be found cheap on eBay because of restaurants etc closing down.

Planning to switch out the fans with silent noctua fans and see if it becomes inaudible. Will otherwise resell it. Will use it in bridged mode, with four channels of 350-400 w powering an active two-way system. I would otherwise be very tempted to go down Cosmik's route with an old AVR, but my one concession to audiophilia nevrosa is that I have this idea that amps should be plenty powerful to give sufficient dynamics to the kind of music I'm listening to.

I also am not 100 percent convinced about class d for treble use. That's probably a misconception on my side though.

My Mytek 8-channel dac came with a small fan - quite a noisy one at that - it is designed to go in a rack in a studio so I can understand why it has a fan. I put in a Noctua which is for all practical purposes silent. Mytek say that in a domestic environment the fan can be removed and certainly the Noctua doesn't move as much air as the original, but at least it provides some additional cooling. In the past I've also used a larger Noctua in a QSC 1450 and was also impressed with its quietness. Good well-designed products IME.

Sounds like you got a bargain with the amp - regarding class D treble - I can only say that with the Apollon the treble is just fine IMO.
 

DonH56

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I also am not 100 percent convinced about class d for treble use. That's probably a misconception on my side though.

Not necessarily a misconception, but probably out of date. Most of the issues with early class-D amplifiers have been resolved and the treble (and other) early growing pain issues have been (mostly) resolved. There are still cheap amps that have issues IME/IMO, but designs based on standard modules seem to be fine.
 
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