Advice for Powering Multiple Amps Please

Discussion in 'The Projects Forum' started by Moejoe, May 6, 2013.

  1. Moejoe

    Thread Starter New Member

    May 6, 2013
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    Basic power supply advice please

    Hello, and thanks for any advice given, first off I'd like to apolagise as I'm sure the answers I'm looking for are right infront of my nose but I have no idea what to search for that doesn't lead me to normal linear power supplies or dual voltage PSU's (i.e computers psu's with 12V/5V output).

    I want to build a sound system for a chair, which will consist of 5 amplifiers. 1 amplifier requires ±36vdc 4A, and the other 4 require 16vdc 3A. I must confess I'm a little confused with the ± supply ( I imagine it as the + voltage pushing, and the - voltage pulling resulting in a net potential voltage of 72V seen by the amplifier, but I imagine alot of things so please correct me).

    I've not done much with power supplies before and I just have no idea what my best options are for powering these from the same source. My essential criteria is price, the speakers and amps are cheap, It's more of a semi-novelty project.

    I cannot use the normal linear power supply, since I most certainly do not want to put 240V straight into a chair (Insert electric chair joke here), so I guess my best option is to use a switching power supply in it's own external house? (Like a large laptop or xbox brick) for example http://www.aliexpress.com/item/Power-36V5A180W-concentrated-power-supply-LED-power/760468133.html .

    Can i use two of these single supplies to produce a ± supply? I've seen brief references to connecting them in series with the positive from one supply to the negative of the other to create a common ground, leaving a positive and negative rail but I have no idea if this is right or safe?

    I have none of the mentioned equipment yet so nothing is set in stone, I would really just like a point in the right direction. At the risk of looking stupid, I have included a quick sketch of how I currently believe I would achieve this, though I'm very unsure. I would rather look stupid and be certain when dealing with power.

    I would really appreciate any advice you could throw my way, Many Thanks.

    Moejoe
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,967
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    yes you can put two 36v supplies together to make a 72v psu centre zero, as long as the psu does not ground one of the supplies already, like an atx does.
     
  3. ScottWang

    Moderator

    Aug 23, 2012
    4,850
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    I don't think that power is appropriate for your amplifiers, because they looks like made of switching mode, that is for industrial used, they have much noise and that will affect the quality of amplifiers, you may choosing some linear powers.

    I don't know much about their related relationship of amplifiers, but using a common power source for five amplifiers that I also don't think that is a good idea, because I'm afraid of them, and they will affect each other when they're working.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Is there a reason you don't just use a home theater receiver? It would solve a lot of problems and add some capabilities.
     
  5. Moejoe

    Thread Starter New Member

    May 6, 2013
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    Hi

    Thanks Dodgydave, the psu i linked only has two outputs (com and V+) would a dual DC supply not need three? (V-, com and V+). This has been one of the things confusing me, I have seen some with (V- , V+) and (com, V+), I thought you would need all three?

    Thank you ScottWang, I am aware of SMPS's introducing noise, Can this not just be filtered out? I am not expecting perfect sound quality from this, however I have seen that SMPS's are being used for audio applications more and more these days.

    A linear supply would be the obvious choice, but I do not want to put the power supply inside the chair with the sound system, as I do not believe it would be wise to plug mains supply into a chair? so a huge linear supply would be impractical to have sitting on the floor and they are surely not the only choice for power supply?.

    And yes i share your concerns over the amplifiers sharing the same supply, but using two supply's as shown in my sketch, wouldn't each supply only be powering 3 amp's? and would some buffer capacitors help with spreading the load?

    And Thanks wayneh, that would certainly be mucn easier but as said above, the idea is to have all of the sound system (5.1 DAC, amps, 6 speakers, a sub and a tactile transducer/bass shaker but not the power supply) contained within the chair. Home theatre recievers are very bulky with many facilities that will be unneeded and most importantly they run off of mains supply. This is essentially a gaming chair, the only functionality that the audio system needs is volume controls, the most important thing is to have the surround directionality (If thats even a word).

    Again thanks for the help, I'm starting to go round in circles and it's giving me a headache
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    Who is going to sit in this chair?
    Do you know what 700W of music power sounds like?
    Enough power to blast the listener off to the moon,
    besides having serious hearing damage.

    "When you lose it, it would come back."

    I think you ought to tone down the power requirements.
     
  7. Moejoe

    Thread Starter New Member

    May 6, 2013
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    I'm sorry but where did you get 700W from? the actual speaker power of the system will be 6x5W RMS + 1x30W RMS (6x10 + 60 = 120 Max) this doesn't include the 30W tactile transducer as this does not make sound. which yes may be high but this is cheap equipment so i guess im compensating? Given that the amplifiers are 30-50% efficient at best plus loss from step-down transformers etc I'm just trying to make sure I can power the system, I would rather have to much than to little and take away.

    I'm not purchasing any equipment untill I have the whole system planned out so I'm very open to change and eager to hear advice on how you would go about it

    Many Thanks
     
  8. tubeguy

    Well-Known Member

    Nov 3, 2012
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    What power amps are you considering. ?
     
  9. Moejoe

    Thread Starter New Member

    May 6, 2013
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    At the moment I am considering aTDA7294 based board for the subwoofer i.e http://www.aliexpress.com/item/HOT-...ever-amplifier-board-kit-parts/831824452.html and 3 x TDA7297 for the satellites i.e http://www.amazon.co.uk/15W-Amplifi...id=1366326736&sr=1-3&keywords=amplifier+board or others similar to them.

    Like I said cheap and cheerful ;) If I can downsize the system though it would make life easier. However I have only seen amps that are 3W and under which i dont believe would be enough, or 10-15W and up, nothing inbetween so I dont see any choice but to have the 6x10W max for the satellites?

    Thanks for the input
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Sooo, why not just call the receiver your power supply? OK, the amps are in it too but so what? I'm sure you could find one that focuses on power and channels more than a bazilion inputs like some have. They're not all so bulky.

    Sorry to beat on this, it's just that so many problems would be solved by buying a commercial product instead of trying to build something. And down the road, you'll still have a receiver.

    FWIW, a typical modern A/V receiver has a SMPS. It's typical that the sum of the individual channel power specs will exceed the power supply rating, and this is justified because real A/V content will never use all 7.1 channels at full power, at the same time.

    BTW, you haven't said anything about the inputs. If it's a gaming rig, HDMI would be an awesome solution and you'd struggle to include this in a DIY.
     
  11. Moejoe

    Thread Starter New Member

    May 6, 2013
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    Doing it this way would mean it is in a single unit so i would either have to put the reciever inside the chair which will then be plugged into the mains, or the unit will be outside which would mean i would have 16 speaker cables, and maybe some other bits going to the chair. Either way it just doesn't seem suitable?

    Beat away, that is why I am here. I've looked at many commercial products from recievers, complete 5.1 systems, you can even get diy 5.1 amps with all the imputs and controls like http://www.aliexpress.com/item/Free...mplifier-Kit-Class-A-Diy-Board/474715562.html, however with all the commercial products I have come accross just dont fit the needs well enough, they would all require modifications, additions and more work so it just seemed logical to put it together myself to match the needs. There is no financial advantage to either way.

    I know i have probably grossly overestimated power requirements, as this would be my first audio project I've just been planning an 'Ideal' situation but at a minimum It would still require atleast 150-180W total DC power which would still require me to use an SMPS or linear supply? Also if the commercial recievers are using SMPS, why cant I? are they that difficult to work with? This is my real issue, the system I have planned I have full confidence in except powering it (I guess i should have started there).

    Sure thing, HDMI would be nice but yes it would be a nightmare DIY scenario. Instead I plan to use this little decoder that has 2 optical inputs, a coax and a 3.5mm jack, It would act as the source selection, It can switch between 5.1/2.1. It also contains the required low/high pass filters, but as with all cheap imports it does require some modifications to improve the overall quality. http://www.ebay.co.uk/itm/Audio-HD-..._Audio_Amplifiers_Preamps&hash=item2ebf83f194

    With this I have two options, I can house it with the amps inside the chair and have an optical cable go into it, Or I was planning to put the decoder in a standalone housing that would sit by the xbox etc and use 3xstereo fm transmitters/recievers. With this the chair would only require a power lead and no other wires (This is also why i ruled out class D amps which would have been useful for their efficiency, but from what I have read they cause alot of radio interferance.)

    Originally I was trying to just keep the system 12V in which case i could have used a spair Xbox power supply (12V 16A). I do not know what kind of power I would need for a 4-5" 'Subwoofer'. It is the focal point, hence why I'm trying to use higher, dual voltage but this is what is hampering me.

    Thanks for your time and input
     
  12. wayneh

    Expert

    Sep 9, 2010
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    You can absolutely use a SMPS, and I wouldn't recommend anything else. At worst, you may need to select or adapt one for better audio performance.

    I think I'd look hard at computer PSU with enough juice on its 12V rating to fit your needs. They're cheap or free and everywhere, and already have built-in all the nice features you want; a fuse, over-temp and over-current shutdown, high efficiency, and so on.

    With a 12V system, you can look to all sorts of automotive gear.
     
  13. Moejoe

    Thread Starter New Member

    May 6, 2013
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    Ok thank you wayneh thats fantastic. Is there any difference between a computer PSU and the SMPS's i proposed at the start? (they also claim sufficient protection and efficiency). Sorry to keep badgering questions, I'm happy to use a 12V system but I'd really like to try and use higher if it is possible to facilitate a tactile transducer and semi-decent sub.
     
  14. wayneh

    Expert

    Sep 9, 2010
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    That's why we're all here, so no problem. Except that I'm not qualified to answer on the relative merits of different power supplied. You can count on somebody here knowing. ;)
     
  15. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Very interesting project !

    I think wayneh's idea of using some surplus PC 12v switching supply(s)
    is great for powering the mid-hi speakers.

    You're going to need some kind of a box anyway, so why not combine that with a normal +/- linear supply for the subwoofer amp. It wouldn't need to be that big :).

    The mid-hi amps you've selected are good because they are bridging type which gives a a decent output even with a 12 volt supply. You do realize that with a bridging amp you don't connect either output to gnd, correct?

    As you realize, the sub is more power hungry, so a separate power supply is good to isolate it from interacting with the power supply for the other amps when you're pushing it.
     
  16. tubeguy

    Well-Known Member

    Nov 3, 2012
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    What speakers are you considering?

    An often ignored spec for speakers is efficiency. This is typically stated as SPL @ 1watt/1meter. The higher the better, especially when trying to get the most from lower power amplifiers.

    Pro speakers can be in the range of 99db or more spl @1w/1m.
    Many home stereo speakers are much less efficient, with specs like 85db @1w/1m

    You have an advantage because if I get what you are doing, the speakers will be very close to the listeners ears. When you double the distance from a speaker you lose 6db, and of course, closer, you gain db's.

    So, look for the most efficient speakers that will fit the space and budget.
     
    Last edited: May 7, 2013
  17. Moejoe

    Thread Starter New Member

    May 6, 2013
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    Thanks for the feedback to both of you

    I was determined not to be convinced to look at linear supplies but that is a very good point. I will definately have a look at one for the subwoofer, it would save me having to step down voltages as well.

    Yes I chose the mid-hi amps for that reason as I'm hoping one of these bridged will be suitable for the tactile transducer, but your right, I have no idea how to wire it, that is something I will need to read up on when the time comes.

    The SPL is whats got me in this pickle in the first place, I found a nice looking 4" 'sub' (sorry I cant really call anything that small a subwoofer) 10wrms 20w max with a good frequency range, which would have meant I could keep the whole system 12V, however it has an SPL of about 82dB which swayed me away from it. My current choice in my price range is between either:
    Monacor SP-60/8, 4", 30Wrms(60Max), 0-8kHz(65Rf) ,90dB SPL
    or Electrovision L022B 5.25" 45Wrms(60Max) 63-20kHz(63Rf)and 92dB SPL.

    Would you recommend either of these based of these figures? Theres not that much choice in the 4-5" range. It's not fair you have all of the nice stuff over there in the USA! I'm really hoping to get a Dayton puck but they only seem available in the US, I cannot find any tactile transducers available in the UK. Have you had any experiance with these 'bass shakers'? I'd never heard of them until I started researching this project.

    Most of the cheap 2.5" speakers dont give you to many figures but as you said 6 of them all with in a close radius of the user, I'm not to worried about SPL.

    Again, many thanks
     
  18. tubeguy

    Well-Known Member

    Nov 3, 2012
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    It's temoting to go with the Electrovision based on the slightly higher sensitivity, but I think the Monacor is a better choice.

    The speakers with the 'extra' cone always look interesting, but the frequency response can be very uneven. The Monacor has a published response curve which is very smooth and likely possible. :)
    (I think the LO22B published response to 20khz may be a bit of wishful thinking)

    The Monacor's look very similar to drivers I have in my own system which also have a very smooth and natural response.
    If you want some extended high frequency, add a tweeter/xover.
     
    Last edited: May 7, 2013
  19. Moejoe

    Thread Starter New Member

    May 6, 2013
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    Ok thanks alot for your responses tubeguy, I'm glad you said the Monacor as this one provideds Vas, Qts etc... I didn't fancy guessing an enclosure size for a first build.

    I appreciate your time and I'm sure I'll be back for :D
     
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