Sizing an SMPS power supply for an 8 channel amp. - diyAudio
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Old 2nd January 2013, 09:21 PM   #1
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Default Sizing an SMPS power supply for an 8 channel amp.

I have what is likely one of the very few 8 channel tripath amps made, an MC8 x 100 from AudioDigit. Originally it came with a torroidial supply rated at 18-0-18V, 160VA. While the resulting sound was more pleasing than the Sunfire amps it replaced, the power was never there to drive the levels I needed for several musical styles. Many here have replaced there Torroids with a Meanwell SMPS, but with ranges from 100W to 300W and I believe that was just for the 2-channel 2020 chip.

In looking at the 4100 chip specs, it shows that providing 24V to the 4100, the chip should produce ~62W of power @ 4 ohms @ 1%THD, which should be plenty for my requirements since I currently get only ~34W@1%. That's an 80% increase in output, certainly a good starting point.

Now my 8 channels drive 8 individual speakers, 6 of which are currently 8 Ohm and two are Heil AMT's which are ~4 Ohm. So how do I calculate the size of the single Meanwell SMPS supply I need to drive all this load.

One additional item, I'd like to replace the current coupling caps(4) which are Rubycon with something better, but the size of this component(5 x11) is tiny and getting at it is impossible from the top of the board………also the circuit board is a dual layer board and trying to remove them would likely cause a liftoff problem(plus my geriatric status leaves my vision and steady hands at a great disadvantage). Would it be best to just try to run a small bypass wire on the bottom of the board and control the circuits from a tube buffer directly prior to the amp?
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Old 5th January 2013, 05:06 PM   #2
stewin is offline stewin  Kenya
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try offline full bridge lukas smps in this site but in power-supply side. one is up to 1.2kw make four or eight pieces for your amp. the smps is quite simple.
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Old 7th January 2013, 01:50 AM   #3
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Thanks for the reply, but I really wasn't looking for a sales pitch yet, however I could ask for a few more responses from the experienced users here.

So, here is what I've been able to learn so far. The 4100 chip operating at 25V will produce ~65W/Channel and since Amps = Watts/Volts, then 65/25= 2.6A Channel and with 8 Channels(2-4100chips) at Peak draw I'll need an SMPS thats capable of putting out ~21Amps! and producing 65W/channel thats a whopping 520W @ 25VDC. Seems pretty high, am I oversizing this?

One additional question, on the amp board(next to the power inputs) is a Bridge Rectifier(GBU8K). This component's spec sheet reads "Average Rectified Output Current = 8.0A" while the 4100 Spec Sheet lists an Absolute Maximum Ratings of Repetitive Peak Output Current of 12A for a single chip. so 2 chips = 24A. So should this Rectifier chip be removed or bypassed? Since I'm already supplying 25VDC directly to the board? and will need 21Amps@max?
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Old 7th January 2013, 04:49 AM   #4
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Hi.

Quite a bit of over sizing going on here I think.

You say 6 of the 8 channels are 8 Ohm rather than 4 so you need to calculate the actual power output at 8 Ohm for these 6 channels. Even with the (much) lower figure this will generate the total is assuming all channels are fully driven, will that actually be the case?

I'm not sure why you are concerned over the ratings of the on board bridge rectifier. If you are going to supply DC you are going to bypass the BR ?

If you read some of the builders threads here you will find the Connexelectronics power supplies are generally much preferred over the Meanwells and are the ones I'll be using for my coming project (there is a vendor forum for these on this board).

Good luck,
Rob.
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Old 7th January 2013, 01:25 PM   #5
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Actually (after reading your last post properly) and doing a quick sanity check your numbers are pretty reasonable. 6 channels * 24V/8R = 18A plus 2 channels * 24/4R = 12A so that is theoretical max draw of 30A@24V which is 720W.

So if you are going to fully drive all channels (and if the chip is rated for that) you'll need a decent power supply - fortunately 500 or 800W or even several KW is readily available in SMPS. From memory the Connex power supplies have something like 1.3 crest factor so (assuming you are amplifying music and don't have huge amounts of current sucking eq going on and it isn't really driving all the channels at max simultaneously) the 500W model would seem a good fit -but the bigger models are always there if you really want
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Old 7th January 2013, 01:34 PM   #6
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The use of 4 Ohms as a 'basis' for the numbers I generated is due to forward thinking about what may get replaced in the future. Yes 6 speakers are currently 8 Ohms, however, should I replace them with some 4 ohm models I don't want to have to re-do the power component again. So, IF all speakers are 4 ohm, is the use of 520W & 21Amps still oversizing? Should I be sizing for absolute peak power even with the cap buffers on board? If not, where is the acceptable level? I should add that there are 9 2200uF Caps on this board as a buffer. I would like to bypass/remove the BR, however this is one of those dual layer circuit boards and removal of chips without pulling the top circuit off is difficult(for my experience level), would it be easier/safer to just clip the 4 pins off at the base of the chip and then wire over both the (+ ~) and (- ~) legs to accomplish this? Guys, I'm relatively new at this, recently retired and looking to fill my day with projects that are different from my life experience. Any inputs you give are helpful since all is new to me.
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Old 7th January 2013, 01:46 PM   #7
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The use of 4 Ohms as a 'basis' for the numbers I generated is due to forward thinking about what may get replaced in the future. Yes 6 speakers are currently 8 Ohms, however, should I replace them with some 4 ohm models I don't want to have to re-do the power component again. So, IF all speakers are 4 ohm, is the use of 520W & 21Amps still oversizing? Should I be sizing for absolute peak power even with the cap buffers on board? If not, where is the acceptable level? I should add that there are 9 2200uF Caps on this board as a buffer. I would like to bypass/remove the BR, however this is one of those dual layer circuit boards and removal of chips without pulling the top circuit off is difficult(for my experience level), would it be easier/safer to just clip the 4 pins off at the base of the chip and then wire over both the (+ ~) and (- ~) legs to accomplish this? Guys, I'm relatively new at this, recently retired and looking to fill my day with projects that are different from my life experience. Any inputs/direction you give are helpful since all is new to me. Thanks for pointing out the Connexelectronic's PS. I've seen them here but was not sure of their general acceptance. It appears that I would use their SMPS500R along with their Power soft start & speaker protection circuit?...........their physical sizes certainly are acceptable.
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