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Old 29th February 2012, 07:08 PM   #1
diyAudio Member
Join Date: Feb 2012
Default +/- voltage query

i'm trying to read as much as possible without asking too many questions, but i am a complete noob to diy amps/psu's and electricity in general. been looking at the components and differences between smps and linear supplies.
search engines can't seem to recognise symbols +/- as search terms. tried wording 'plus minus voltage' etc. but to no avail.
the specs of this smps http://www.connexelectronic.com/documents/SMPS300R.pdf show two varieties. 24, 30, 36, 45 and +/-24, +/-30, +/-36, +/-45 volts. also it shows +/-V's for all variety AUX outputs.

does +/- mean positive OR negative output, does it mean the voltage is slightly variable being sightly above or slightly less, or does it mean something else?

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Old 29th February 2012, 08:23 PM   #2
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Location: N38
The +/- refers to a dual output, so +/-24 would mean it has a +24V and a -24V output.
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Old 29th February 2012, 09:29 PM   #3
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Location: Brisbane
This may make it easier to understand. If you can imagine two batteries connected in series like this and the 0v point is your reference 0v.

Therefore you can see how you can get a positive 1.5V by connecting between the 0V point and the +1.5V point, or you can get -1.5V by connecting between the 0V point and the -1.5V point.

Most amplifiers use this type of power supply configuration as "music" is an AC waveform, and such has both negative and positive values.
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Old 12th March 2012, 01:19 PM   #4
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sorry for the late response, been away. thanks for the replies too.
now i'm more confused! i know what the sine wave looks like, and regulated DC, but i don't get how DC can resemble a sine wave.

the amp i'm looking to buy accepts both AC and DC. are you saying to connect BOTH positive and negative DC to the amp which in effect pumps the + and - waves through the amp, having the same effect as a sine (with the upper and lower portions of the wave)?
wouldn't this double the voltage?
also, are you saying it's better to have regulated AC rather than 'one sided' DC which translates to a more balanced 'music' wave in the amp?
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Old 12th March 2012, 01:37 PM   #5
DF96 is offline DF96  England
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Join Date: May 2007
Who said that DC resembles a sine wave?

For almost all transistor amps, the supply voltage (both +ve and -ve) must exceed the peak AC voltage output. That mean the amplifier needs both + and - DC supplies, so it can output an AC signal without clipping.

Some amps, mainly older ones, use just a single supply and an output capacitor. For these the supply voltage must exceed the peak-peak signal voltage - twice the peak voltage.

Don't worry about differences between SMPS and other PSUs. You first need to understand more about AC and DC, and simple amplifiers.
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Old 12th March 2012, 09:52 PM   #6
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riotpack said that "music" is an AC waveform (which, from what i gather, is a sine wave), so i assumed he meant that by connecting both +ve and -ve from the appropriate DC psu you get a similar/complimentary wave form of that "music" AC (sine) wave form. i know riotpack said that you can connect either +ve OR -ve, but the only way i could picture something complimenting the AC wave he mentions is to connect both +ve and -ve to the amp. that's where i got confused and thought this configuration would 'resemble' a AC (sine) wave. i'm gonna use 'compliment' instead now.
i've seen oscilloscope videos of AC being regulated to DC (the regulated visibly flat line on the +ve half of the screen), and i imagined by connecting both +ve and -ve DC this would compliment the AC. i just can't quite picture how. how does a flat regulated +ve DC line above the base line and another on the opposite -ve compliment the mentioned "music" wave form, which i picture as the typical single curvy line of the sine wave?

i learnt a while back that there are at least 3 types of learning ability in people (some get words/explanations, some are hands on practical learners and some are more based on imagery, many people can be one or a combination of 2 or 3 learning styles), i'm more of a pictoral learner, sorry if my descriptions of confusion are getting worse!! but, that's why i keep trying to 'imagine' what's going on, rather than reading words and getting it.

any way, sod it!! here's the deal...
when it's back in stock i wanna buy this T (D) amp Hifimediy T2 special version 2*100W@4ohm amplifier STA510a (Nichicon KG 10000uf) with MUNDORF MCAP input caps | Hifimediy
and power it using this 36V DC smps (turned down to 34V) Connexelectronic
the psu comes in either single or dual output (see thunbnail). i'm now gonna buy the +/-36V instead of single 36V, is this best?

when i get the items (don't worry too much about answering this, as i can ask retailer at that time), do i connect psu +ve to amp +ve, psu gnd to amp gnd, and psu -ve to amp -ve?
OR, do i just connect both +ve's (amp and psu) and both -ve's (amp and psu)?

really sorry for these questions, i know to many these things would be made clear at school level. i was one of the ones who either wasn't there or messed around (regret that these days). thanks to anyone who even makes it this far reading this post!!
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Old 12th March 2012, 10:14 PM   #7
DF96 is offline DF96  England
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Join Date: May 2007
I think you might mean 'complement' - that which completes something. 'Compliment' is something nice you say about someone. However, 'complement' is not the appropriate way to look at it.

You may be mixing up the AC which gets converted to DC in the power supply, and the AC which is the music signal. I'm not sure, as if you could describe clearly what is confusing you then it would no longer confuse you. The best learning mode to use is the one which matches the things to be learnt.
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Old 12th March 2012, 11:09 PM   #8
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Join Date: Feb 2012
yep, soz, 'complement'
simply, are you guys saying to connect BOTH +ve and -ve DC to the amp?

the psu i'm looking at comes in either single or dual output. by complement, i mean that having dual voltage configured as mentioned above is more complementary (to the AC music signal in the amp) than a single output DC connected to only +ve and gnd of the amp. does that make more sense?
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Old 13th March 2012, 12:08 PM   #9
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
You need to provide the amp with the PSU it requires. Most modern amps need +, - and ground. Some, especially older ones, need just + and ground. A few very old ones might need just - and ground. Find out what your amp needs. Buy the right PSU. Forget all your ideas about 'complementary'; I have no idea what you mean by this in this context.
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Old 13th March 2012, 12:10 PM   #10
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
look up ESP website and learn some basic electrics.
regards Andrew T.
Sent from my desktop computer using a keyboard
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