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Old 21st June 2007, 01:18 PM   #1
pjpoes is offline pjpoes  United States
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Default Chipamp with SMP

I was wondering if anyone has used a switchmode power supply with a chipamp to good effect. Ebay and MPJA and various other sources have decent prices on SMP's that would work just fine. It seems like a decent way to go about making the amplifier as long as you keep the power supply away from the amp modules themselves, or at least well shielded from them. SMD's offer relatively low ripply compared with a standerd power supply, and it seems to me that a few diodes and caps could further reduce that to a minimal amount. The one I'm looking at is 24 volts at 4.5 amps. Line and Load regulation is .5% and ripple is 150mv. The ripple is higher than I like, but I'm sure the ripple my chip amp currently has is much much higher, given that it only has 4700uf's of capacitance per rail. The amps seem to reject ripple pretty well on their own, and thrive on low impedance supplies.
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Old 21st June 2007, 03:39 PM   #2
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May I suggest that you use the search facility here? Or read this !
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Old 21st June 2007, 05:38 PM   #3
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I've used the skynet 8080 as per Decibel Dungeon and it sounds mighty fine.

You have not linked to the SMPS you intend to use. What outputs does it have, and more importantly what amps are available on each?

Reason i ask is that it is very common in SMPS for the negative voltage rail to supply a fraction of the amps that the positive will.

You can get round this by using a pair of the units to gain the power on the negative side of things, but you must mod the smps to disconnect it from earth.

On the Skynet this is an easy job, Just follow NUUK's instructions on his site. I couldn't tell you if other SMPS are as suitable for modding as the skynet.
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Old 21st June 2007, 06:13 PM   #4
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Thankyou, I missed the Decible Dungeon post, and that was very useful. I hadn't heard of the issue yet of needing to disconnect the earth. It never crossed my mind, and I'm sure I would have fried a few.

I haven't picked a power supply yet, but I was thinking of using the MPJA units which have various voltages available. I was thinking of going with the 24 volt units, but after looking at his comments, I'm reconsidering. There are some 15 and 18 volt units I could try I believe, and plenty of 12 volt units. I was not planning on using one, as I'm well aware of the dual rail current issues. I planned to use two 150 watt modules per rail, which really should be more than enough.
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Old 21st June 2007, 06:46 PM   #5
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I didn't mean two SMPS per rail, I meant one per rail, two total, one for each rail. Sorry about that. Anyway, I think a 150 watt power supply should be enough, I have a 320 watt supply on it now, well rather, 320va tranny and then the caps, and its overkill really.
-matt
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Old 22nd June 2007, 04:14 PM   #6
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Quote:
Originally posted by pjpoes
Thankyou, I missed the Decible Dungeon post, and that was very useful. I hadn't heard of the issue yet of needing to disconnect the earth. It never crossed my mind, and I'm sure I would have fried a few.

I haven't picked a power supply yet, but I was thinking of using the MPJA units which have various voltages available. I was thinking of going with the 24 volt units, but after looking at his comments, I'm reconsidering. There are some 15 and 18 volt units I could try I believe, and plenty of 12 volt units. I was not planning on using one, as I'm well aware of the dual rail current issues. I planned to use two 150 watt modules per rail, which really should be more than enough.
I tried 12-0-12v from two smps and though it worked fine, I prefered the sound from 24in my system. I found the 12v sounded brighter, not bad in Jazz, but I wasn't too impressed for other listening. The 24v to my ears sounded quite a bit better, the bottom end sounded more solid and purposeful. NUUK mentions on DD that he would be happier with either the 12v or 24v flavours, in my system I dont think I could enjoy the 12v for very long. 4 12v smps does take up quite a bit of room, but gives results more pleasing top my tastes. Perhaps it's cause my previous amp was a musical fidelity e200 and I had grown used to the tone from it.
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Old 22nd June 2007, 05:15 PM   #7
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When you are using a smaller PSU like a pair of SMPS at 12 volts, the choice of speaker becomes more critical. I think that I qualified my findings with the 12 v SMPS by saying that all my speakers were fairly high efficiency and easy to drive.

This is what I said comapring the two:

Quote:
From the moment that I pressed the play button on the CD remote control, I noticed a difference between the +/-12v and +/-24v supplies! The former was more 'delicate', more intimate, 'airy', very alluring. The latter was slightly darker, heavier, more authoritive. If I am honest, I probably just prefer the 12 volt supply but for certain types of music, eg rock, the 24 volt supply is better. The control that the 24 volt supply has over even difficult and complicated passages is simply stunning.
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Old 22nd June 2007, 06:52 PM   #8
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Thanks for the posts. Because I wasn't planning on using the power supples that Nuuk used, I have a bit more flexibility it choice of voltage and current. Cost is always a factor, but honestly the cost isn't that high. All the units I"m looking at are single rail supplies, so it will just be about making sure they are isolated from ground once I pick one. My speakers are 92db's efficient, though they do dip into the 4 ohm realm. I will probably test on these speakers, but my main amp is actually still being finished, a couple of amp modules from Aussie amps with a CLC power supply I came up with. This amp will probably serve as either an extra set or rear channels or in the long run, a second system amp for my bedroom. Given how affordable they are, I've even thought about making a few channels, say 4-6, and using it for multiroom sound, powering speakers in my kitchen, bedroom, and outside. We shall see, I need to just finish a few projects. It's so much easier to theorize and dream then to actually do. I just hated to waste these amp modules, and thought this might be an easy way to make a working amp, while experimenting with something a little different. I also thought it might be a good way to reduce some hum problems I have, as I find SMPS's to be easier to ground with, for whatever reason. I never really liked the sound of the amp with a 320va tranny and 4700uf's of capacitance per rail per amp.
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Old 23rd June 2007, 09:48 AM   #9
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Quote:
Originally posted by Nuuk
When you are using a smaller PSU like a pair of SMPS at 12 volts, the choice of speaker becomes more critical. I think that I qualified my findings with the 12 v SMPS by saying that all my speakers were fairly high efficiency and easy to drive.
You did indeed say that.

The speakers I tried it on were mision 753's which efficiency wise are pretty high. It was the lighter tone that didn't sit with me.

I should have mentioned my flatmate on a cursary listen prefered the sound from 12v. He felt that the sound at the top end was more natural sounding. No agreement could be reached between us on this one.
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Old 23rd June 2007, 10:11 AM   #10
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I am often referring to the compromises that we have to make with hi-fi. One of those is that one system, or component, will suit a particular genre of music.

I agree with your findings on the SMPS - the 12 volt supply is a lighter, more delicate sound, ideally suited to acoustic music, jazz etc. The 24 volt supply has the clout and authority you need with rock, or orchestral music. Now, if somebody can come up with a workable switching system......
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