Need Advice on Multi-channel Amp Choices.
@erik_squires - why are you suspicious of multi-channel amps? Is it because of the shared power supply? I would probably not look at the AudioControl amp because it's Class H. They are usually used in pro-audio where it requires a very high power amp with efficient power supply. I had a Crown Class I amp and it sounded good (although it had it's own tube-like signature), but it did not compare to a normal high-current amp with linear power supply. Class H is another way to create In your three choices I would choose the Classe CA-5100 first and I'll tell you why. I took a quick look at the Arcam AV950 and I would guess it's using an opamp based audio stage with no Class A biasing. You can look at the pic below, the power supply is very small with tiny heatsinks for voltage regulators. A processor with a Class A audio stage would use larger heatsinks because it pulls more constant current/power. http://www.hifitest.de/images/testbilder/thumb_slider/arcam-av950p777-av-kombinationen-29280.jpg Each channel of the Classe CA-5100 is biased into Class A for the first 30 watts. This will definitely help give you more body/thickness in the sound from the Arcam. It may also help give you more solid bass/midbass. The shared power supply might give you a little more punch on midbass. The Earthquake would be second choice. It has shared transformer, but individual capacitor banks for each amp channel (only 22,200 uf per channel). Nice for channel separation, but for home theater may lack some meat/punch. If you had a processor that ran in Class A (like a Bryston or Krell), I might recommend the Earthquake. It's a hard call. This next suggestion might be an amplifier older than what you are looking for, but the Krell Theater Amplifier Standard was an exceptional multi-channel amp. The amp output stage is Class AB, but the driver stage is Class A, so you will still get some benefit here, and the power supply is a lot larger than the others. It may be too old for you (probably about 15 years old). |
Multichannel amps are usually compromised some way. From limited power outputs, inter-channel crosstalk, heat generation and disspation and yes, the shared power supplies. Especially if we are talking 7 channel outputs. Otherwise, you get into really mosntrous amps like the Theta Dreadnaughts. Physically huge beasts. The NAD with the nCore amplifier modules is one of the very few I would not be worried about. It’s still limited to 180W continuous, but that’s all 7 channels driven, or 1,200 W continuous. That’s a lot of power in a single relatively small 7 channel chassis and I could fit it on one of my existing shelves. It also does around 600W peaks. That's pretty awesome and useful in a home theater. |
Hi Guys, Thanks for all the responses. Firstly, I do indeed have those speakers and my room has decent treatments, I do have a vaulted celing at 14ft high which certainly comes into play a little bit. I do not tend to listen at reference levels and find myself leaning towards the Classe CA 5100, The class A bias is certainly of interest to me as my prior unit was an Arcam AVR750 which I loved and was hands down the best sounding receiver I have ever owned, its first 20 watts per channel were in Class A. My only concern is that the Monitor Audio Platinum Pl300's are considered to require significant power to get the best from them, they are 4 ohm and recommended amplifier of 100-300w. I like the look of the krell that Auxinput suggested but he correctly reasoned that I was looking for something a little newer. Basicallly will the Ca 5100 drive my speakers adequately? or should I continue looking at higher powered options. Thanks Again! |
@erik_squires - yes, I do agree with all your points on multi-channel amps. It is, basically, a compromise to get 5 or 7 channels into a single device and still perform -somewhat- well. The Monitor Audio speakers are 4 ohm, which will make it more difficult for an amplifier to drive. However, it doesn’t really drop down below 4 ohms like some speakers do, and most of the impedance is readily above 4 ohms: That being said, you will probably lose some midbass punch where the impedance is almost a flat 4 ohms between 100 and 200 Hz. Also, some areas in the deep bass. The Classe amp is probably the best choice out of your 3 because of the "Class A" bias, but it is not really the best choice for the speakers. Yes, nCore and ICE Class D amps can generate more power, but in my experience in research, the frequency response of Class D amps are typically dictated by the speakers impedance curve, meaning that the lower impedance areas will affect how powerful the Class D amp outputs. A Class D amp will probably perform very well on a speaker that is almost a flat 8ohms across the entire frequency range (much like a basic 8 ohm resistor). I don’t know about the newer Class D amps, but this is what I found with earlier Class D. I don’t know if you are taking suggestions, but I have owned the B&K Reference 7 channel before. It’s more power than the Classe (at 200 w/ch). It has a Class A pre-driver and good power supply. The amp had really good power and volume and it was very sweet sounding, but I felt that the sound was too warm for me. At the time, I was running a Bryston SP2 Class A processor, so it was too much Class A in the audio path for me, but I think it could work out for you if you want to consider it. Otherwise, another suggestion is to start buying up used Emotiva XPA-1L monoblock amps and run them in the Class A mode (30 watts). They are typically less than $400 each used, so it is in your budget. The only problem is supplying a separate outlet (or heavy power strip) for each amp. You need space for 5-7 individual amps and they do get hot in Class A - so you will need a good 3" space above for heat ventilation. |
I found your comments about frequency response interesting. That would imply that they have high output impedance (or low damping factor) which they do not, by themselves have. Tube amps of course tend to behave this way. If you can point me to any measurements for the ICEPower or nCore amps which do this I’d love to check them out. Most amps reduce DF (increase output impedance) as F increases, but older class-D amps pretty bad in this respect. If memory serves though, nCore and the later generation ICEPower units solved this quite well. In solid state amps improving (reducing) output impedance is usually a matter of feedback, and in D class amps where the feedback is applied. If memory serves, the feedback on the nCore is at the output stage, instead of before, a good thing. They have ridiculously low output impedance as a result. Any "frequency tracking" of the speaker impedance is not due to the nCore design. I use bare ICEPower 250ASP based monoblocks to drive 4 Ohm speakers (min impedance 4 Ohms through mid bass) and they do superbly. The ICEPower amps replaced a pair of Parasound A23s, which are fairly well biased into Class-A for the first 30 or 40 watts. I could not hear a difference, so I completely converted. I was running the Parasounds in a 4.0 HT configuration, so 1 amp was left, 1 amp was right. Best, Erik |
This was 7-8 years ago when me and my cousin were into Class D amps for a while. ICE and Hypex UCD were the only two. We were using the Channel Island which had the Hypex UCD - we chose that for some reason I can’t remember (it may have been the design of the negative feedback, not sure). What we experienced was that it drove different speakers differently. I had some Focal speakers that were easy to drive. However, when put on a Aerial 10T, it had good midrange body, but we lost all bass punch/impact and the highs were severely rolled off. Others had problems with the Channel Island, such as pairing with B&W Diamond. When we matched the 10T up with an Aragon 8088BB high-current, the problems went away and the sound was significantly better. That being said, the Channel Islands did well with the Focal, but we could tell that it wasn’t perfect. It did have a somewhat forward sound, as some frequencies were pushed and others were not (the high frequency rolloff actually helped the Focal a bit). Moving on to B&W Diamonds. I had a Crown CTS2000 - Class I (variation of Class D). It was decent, but the Crown had weird tube-like overtones and wasn’t exactly neutral/dry. The Channel Islands did much better. But when I put on an Emotiva XPA-1 (high current), it pretty much blew the other two away. There was an article/document I read years ago about Class D - I can’t find it anymore. The guy had worked with Class D amp design a lot. What he said was that the speaker itself must be part of the Class D circuit design and influences the circuit itself. So, in a Class D circuit, the engineer has to make some design decisions on the assumption of what kind of speaker is going to be placed. In a perfect world, a speaker with a flat 8 ohm impedance (across the entire frequency range) would be very good. However, when the impedance starts to go all over the place, it will influence how the Class D circuit responds. (don’t ask more I cannot technical explain more than the bits I have remembered from the artical which I stated above). A linear Class A/AB amp will still be influenced by the speaker impedance curve, but it is much more resistant to this when compared to a Class D circuit. I don’t know how nCore compares as it wasn’t around at that time. It could be something related only to Hypex UCD. |
Thanks for your additional comments, Eric. It may be that the newer ICE and ncore amps work better with difficult speaker loads. I did some quick browsing on ICEpower and nCore. One of the things that stood out was that nCore was designed to remove any coloration on the sound - extremely low distortion. The idea was to reproduce exactly as the sound was input. More searching indicates that this is the nature of these new Class D amps - no coloration. Some have commented that they are lean or a bit bright/cold. I do not have any direct experience with ICE or nCore, but it could be the preamp/source that is dictating this nature. The Wyred 4 Sound amps use ICEpower and I know the general approach from Wyred is to make things as transparent as possible. I'm wondering if the listener experience is dictated by the preamp/source. If they are using an opamp based preamp/source, the nCore may be too transparent and you end up getting a lean/thin sound. When paired with a Class A or tube preamp, the nCore may really shine - as you are putting a limit on how much coloration is going into the audio signal path. The only thing that catches me here is that you could not hear any difference between ICEpower and the Parasound A23, which is very interesting. Don't know. If you pair the nCore NAD M27 amp with the Arcam AV950, you might not get that sweet/full sound - it may be too much transparency. Thoughts? |
I was just looking around and came across this Classe CA-5200. It is twice as much as your budget (around $2k), but it has a shared power supply twice as large as the CA-5100 -- at 200w/ch 8ohm, 375w/ch @ 4ohm. It’s expensive, but if you were liking the idea of Classe brand, you could look at this. It is a beast at 121 lbs (like the Theta Dreadnaught), but I think it will do better because of it’s huge shared power supply - akin to the Krell Theater Amplifier Standard. |
I’m not sure about the nCore, but as for the ICEPower units, I would say that’s true, they really don't add anything to the signal so if you need warmth or liquidity added these are b. .... however.... Using my current reference speakers I could not tell a musical difference between an ICEPower 250ASP and Parasound A23. The A23 is often described as warm, and my system is as well by listeners who do not kwow what the amps are. My sources are a Mytek Brooklyn DAC feeding a Parasound P7. I could see myself trying out a tube preamp here or there to add some liquidity to the top and magic to the midrange, but the sound is most definitely not lean or soul-sucking like I have heard some mass produced processors to sound. I’m pretty happy with what I have, but tubes are tempting. :) I have heard from a couple of users who attempted to use the ICEPower amps directly from PC sources, that did not go very well for them, I'm afraid. :D Certainly for movies I lack nothing. Engagement, dynamic range, dialog intelligibility and transparency across the audible range are excellent. Some of this may have to do with having relatively easy to drive speakers. Min 4 Ohms, and 8-10 in the treble, where I have read at least 1 complaint of the ICEPower units with Maggies. The ribbon tweeter in Maggies becomes inductive, while my speakers use an AMT which remains resistive from the crossover frequency upwards. It may very well be that there is some speaker dependent behavior. On the other hand, the Monitor Audio speakers are fairly straightforward to drive and nCore have an even lower output impedance than the ICEPower units. My surrounds are even easier to drive, remaining around 8 Ohms through the midbass, and min 6 elsewhere. So, to sum it up, if you have reasonably normal speakers without reactive tweeters and your sources have all you need in terms of warmth, tone, etc. I think the current batch of Class-D amps is an excellent choice, and the NAD 7 channel nCore a fabulous bargain. Best, Erik |
Thanks for all the great responses, this forum is always a wealth of information, even though a lot of it goes a bit over my head. Well,I made my choice today and the winner was the Classe CA-5100 which is now hooked up on my rack. Since everyone was so kind in suggesting pros and cons I will explain my choice. Firstly the ones that I did not buy. The Earthquake BR Grand 7 looked great on paper but the prospect of lugging around a 145lb amp and finding a rack that could support it and shipping fees if it was not working etc... just ruled it out for me. The Audiocontrol was an interesting prospect and I could get it at just over half retail new. New is always good for warranty and out of the box experience. However its design seemed to be an update of the old Arcam P1000 albeit with more power. What scared me off the Audiocontrol was again the complete lack of reviews of any kind and also the prospect of it being impossible to sell in the future and the class H topology as I am primarily interested in music, stereo and multi-channel. Now, onto the Classe. The seller was local, original owner and the unit was mint, complete and 6 years old. As Auxinput noted the class A bias on the delta series is likely a nice complementary feature considering my choice of prepro. I reasoned that in the event of upgrade ( Which we always do despite our best efforts not to...) the classe is a far easier resale proposition than the other two. Also I need seven channels so a Ca-2200 would make a nice addition in a year or so. I have the surround rears covered with a NAD which only triggers when I have my bluray input selected. After a quick listen to my got to 5.1 SACD Avalon by Roxy Music , I was instantly put at ease in terms of choice. I have listed to this disc perhaps 300 times and know it from start to finish. The Classe does a wonderful job and the improvement was instantly apparent over the NAD T955 which was serving as a stopgap solution. I only had a small window to test until real life interupted my listening test. Anyway, Thanks a lot for all the advice. |
