Mono vs. stereo vs. multichannel amp builds

[TEK]

Hi

Looking for some input on my amp(s) build.

I'm looking for some input on advantages/disadvantages for different build choices.
I "need" 7 channels of amplificationd. Two to drive my mains, one for the center and 4 for surround channels.
(I will also have some amplification need for sub(s) but that will be in another place in the house and is keept out of the discussion for now).

I see the following alternative setups/solutions:
3 mono blocks + one 4 channel amp
2 monoblocks + one 5 channel amp
1 stereo amp + one 5 channel amp
1 tree channel amp + one 4 channel amp
1 7 channel amp

Monoblock and stereo is most commercialy used amps and will have benefits if there will ever be a option to sell some blocks - but that is a minor.

In practical stereo or three channel amps will require full rack width and will result in some placing issues for me - so because of that it's not to tempting (I will not get 2 amps and the AV8801 in one height in the rack).

So, for me that result in two main options left.
2 monoblocks and a 5 channel amp. The monoblocks will most likely be place close by each speaker and the 5 channel amp in the center of the rack.
One 7 channel amp.

In both cases there will be monoblock construction for the main channels inside the casing.
Space wise as well as cost wise there is no doubt that a 7 channel amp will take lesd room as well as cost less (2 cases++ less).

So the question is: What do I gain by building 2 monoblocks instead of putting all 7 channels into a 7 channel amp? (We do still speak about the same internal build-up)
1) the possibility to have shorter speaker cables
2) possible less heat issues (not expected to be a problem)
3) possible less space issue (not expected to be a problem)

For now these arguments seems a bit weak compared to the space issue (to get the room for to full width amps). However a bit dependent on how mutch effect 1-2m or so with speaker cables do...

[JonMarsh]

One factor is apparent dynamic and low frequency response, which is pretty directly related to power supply loading and energy storage. In this case, there is pretty universal consensus that though you can use two DIY NC400 modules with one DIY SMPS600, they sound better when pushed if there are two SMPS600 modules. A big part of this is rail voltage movement under load.

IMPORTANT POINT:

The Hyepex SMPS has NO load regulation capability other than the primary side AC capacitance - this is equivalent to the output capacitance in a linear power supply. The primary side load capacitance is "refreshed" at 50/60 or 100/120 Hz depending on the doubler or not configuration (European or American input voltage). It sags in between the peak of each AC line, and the amount of sag is a function of the current draw. Two modules at the same output level draw twice as much current, so the sag is twice as great.

In principle, the negative feedback loop in the amplifier compensates for this automatically up until the point you run out of supply voltage. The more feedback, the more compensation. This is true of linear amplifiers, also.

But you see, I did a simple experiment back in the mid 70's- I took a Dynaco 400 kit and hot rodded it in the power supply- increased the bypass capacitance by 5 fold, added substantial polycarbonate film bypass caps, and doubled the number of output transistors and tweaked the bias slightly on the bench. This was back when I was a partner in a high end audio shop in Boulder Colorado, selling Stax class A amplifiers, Luxman, Mark Levinson, Yamaha, and others (B&O, B&W speakers, Quad ESLs, Janis subwoofers, Magneplanar, etc).

The thing is, the dynamic behavior of that power supply was rock solid, and that modified Dyna 400 sounded as relaxed and natural at 250 watts output as it did at 1 watt output. No one who listened to it versus our 150W/ch Stax Class A, or the top Luxman amplifiers, preferred those- the Dyna was a winner if you were pushing the output at all by a clear margin. It just didn't sound electronic; it sounded like the music.

Now, consider the M22- examining the power supply configuration, it has what Hypex would rate at roughly 1800W, compared to the construction of the SMPS1200 or SMPS600. I believe this is the main reason auditioned remark that it is somewhat more authoritative in the bottom end, and more relaxed sounding at high levels. Less power supply modulation, to put it in a word.

Now, for HT, the requirements on each channel are less demanding in most cases. Two or three channels per 1200W is probably just fine for HT. (Note my qualification; I'm a Luddite in the modern world; my GF runs and owns the HT sytsem, other than my contributions like the built sub and amplifier; it's just not a priority to me with all the other things going on. Music is my priority).

If I do some builds with Hypex supplies, they will be mono with the SMPS1200. Overkill? Perhaps. Only audible at the performance extremes? likely. But they follow my personal mantra of some' so good, more is better, and too much is just enough.

Note, the SMPS we're working on for the IR Legacy class D is in the similar voltage class (+/- 75V to 84V), but uses PFC, a regulated bulk buss supply, and a semi-regulated output using multi-resonant LLC converter operating in a restricted frequency range, with synchronous rectification on the output. Please consider this information to be confidential, and do not share with others. The peak power output for this supply before current limiting is a minimum of 2800W, to be used for two channels of amplification. How long this is going to take to complete development is an open question, as we're being required to interleave this effort with other customer support activities. I have a lot of system design done and simulations running, working on some more simulation stuff for third harmonic injection in the PFC to minimize bulk capacitor ripple voltage.

For my own builds, everything will probably be mono, and using the Ghent Audio Chassis, as it's reasonably well designed, and I'm not keen on doing a bunch of metal work (have done that in the past, prefer Parmetal chassis as a starting point, but I have to focus my time- there's always more things to work on than time available! I would sooner rack up mono units side by side on simple shelves than package a multi-channel amp- the latter is a significant design undertaking- look at the NAD M27.

[JonMarsh]

Par-Metal link:

http://www.par-metal.com

[TEK]

Thanks Jon

I'm not sure if I got your point right. You seem to expect that there would be fewer smps when using fewer boxes, and that is negative. I was thinking the same components either way and that the question here just is about one or several boxes.
Reading a bit between the lines, as well as considering what tounhave described before, it seems likely that some extra caps (or something) will be added. Those may of course take up some space and will cause some challenges when it comes to pack a lot into one singel case.

No matter if this is one case or several cases, the two main channels will have separate smps and be fully equipped.
It's just about using one or 3 cases.
Placing the equipment WILL be a design challange, no matter if I go for 5 or 7 channels. And it might of course be that the design challange is to big and that it will not work.

But right now I'm more wondering about other issues, like that having the amps close together may cause disturbtion between them, that short cables run made possible by mono amps are a big advandage and simular stuff.

However, you gave me another idea...
If you were to build the amps as low as possible, then it might be a possibility to build full with 2 channel (2 smps + 2 amps) + 2 channel (1 smps/2 amps) + 3 channel (1 smps/2amps + 1 smps/1amp) stacked on top of each other.

A different alternative would be 1 channel + 1 channel + 2 channel + 3 channel.
The reason for these setups would be that the task of designing a 5 or 7 channel amp is to complex.
I think that any 5 or 7 channel amp must stack modules vertically to get enough amps placed on limited area.
That will also require extra case work/metal work to ensure mounting brackets or something. Perhaps also extra heat handling. It may also be a good idea, or even nessesarly, to have some sort of shielding between the a amp modules.

Jon (or Darrel/Ben), are there technical or soundwise reasond to NOT but all amps in one casing - given the preassumption of the same internal compomemts?
Design challenges is one - have to do some test to know if that one is to big.
Speaker cable length is another one - but how kmportant is that?
Is disturbtion between components a issue?