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6 posts

Wannabe Geek
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# 175004 13-Jun-2015 13:07
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Hello all,

I'm building a vintage inspired sound system for my workshop and for the amplifier I need a dual 12v power supply, three wires: 12v-0-12v.

I ordered a MM-2018 from Jaycar after seeing it recommended for similar kit amps on Trade Me, but it turned out to be 24v-12v-0 (the product picture on their website is misleading and I was in a hurry, so serves me right I suppose). I can't seem to find what I really need on their website and I couldn't make sense of their reply to my inquiry.



So my question is, am I just misunderstanding the labeling and can I still draw dual 12v from this? I suspect not, so can I alternatively split the 24v to get two 12v? I'm not sure if that would be wired in parallel or series.

Any help would be much appreciated, thanks!

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22185 posts

Uber Geek
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  # 1324050 13-Jun-2015 14:11
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Same thing, yes,

Take the middle one as your 0v and put the other 2 into the bridge rectifier. Someone told me there was a difference based on the orders of the windings or somthing between a 12-0-12 and a 0-12-24 but I cant see any difference on the outputs of the ones I have here.




Richard rich.ms



6 posts

Wannabe Geek
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  # 1324060 13-Jun-2015 14:28
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Thanks richms, that's great! I'll use a multimeter on it (with a bit more confidence that I probably won't blow it up now) to be sure. Thank you for your prompt reply.

 
 
 
 


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  # 1324061 13-Jun-2015 14:33
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I found the same thing when I had to get a 15-0-15 transformer for a pre-amp board. Idiot ebay seller sent me a 110v only transformer and wanted me to ship it back to them to get a 230v one sent..




Richard rich.ms

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Uber Geek
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  # 1324091 13-Jun-2015 15:41
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Like Rich says, go for it.

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Uber Geek
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  # 1324138 13-Jun-2015 18:08
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You say it is for the amp.  Pre-amp or power amp?  If power amp, then you are doing only about 1W per channel?




You can never have enough Volvos!




6 posts

Wannabe Geek
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  # 1324191 13-Jun-2015 20:08
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richms: I found the same thing when I had to get a 15-0-15 transformer for a pre-amp board. Idiot ebay seller sent me a 110v only transformer and wanted me to ship it back to them to get a 230v one sent..

 


I suppose that's one of the troubles with ordering online, especially from overseas. There are so many variables to keep on top of!

 



linw: Like Rich says, go for it.

 


Thank you, yes I'm a bit more confident now.

 



Niel: You say it is for the amp.  Pre-amp or power amp?  If power amp, then you are doing only about 1W per channel?

 


It's a small 'TDA2030A' power amplifier kit I bought from AliExpress (but you can get them on ebay etc too of course). It's designed so you can make it up either in stereo mode (OCL) or in mono mode (BTL or bridge). I'm using bridge mode because I only need mono (I'm mounting a small speaker in a gramophone horn and using it's acoustic amplification qualities, it won't be hi-fi but it'll have a certain charm) and having some extra output power probably can't hurt. Details are a little sketchy but I believe it will output 18w per channel in stereo mode, and 36w in mono bridged mode. Actually on reflection said more power may hurt after all and prove problematic trying to find a small enough speaker with that wattage... but we'll see. Worse comes to worse I use this for another project and write it off as a learning exercise ha!

These are the kits here:
http://www.aliexpress.com/item/New-Style-Audio-Power-Amplifier-DIY-Kit-Components-OCL-18W-x-2-BTL-36W-TDA2030A/32298286272.html

And there's a very good guide and explanation of them here:
http://atoomnet.net/tda2030a-amplifier-diy-kit-schematic-and-soldering-howto/



 

Again, thank you all!

 


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Uber Geek
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  # 1324196 13-Jun-2015 20:35
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That kit looks like it needs 12-0-12 ac which you'll get from that transformer but it won't have enough current , probably need 1.5a or thereabouts. Might be enough to get it going, but at 150ma it will clip badly at a very low volume.

 
 
 
 


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Uber Geek
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  # 1324208 13-Jun-2015 21:17
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I know the TDA2030A very well, I've built some about 20-25 years ago...  Your problem is the transformer is rated only 150mA, so you can get barely 5W out of the transformer to power the amp.  (24V x 1.414 when rectified to DC, x 0.15A current rating)

Start with the speakers and how loud you want to drive them, typical OEM car radios are around 10-20W per channel (or they used to be).  Say you want 2 channels at 15W each, then you need 30W from the transformer which is about 2.5A.  The transformer you bought is intended for pre-amp circuits etc.




You can never have enough Volvos!


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Uber Geek
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  # 1324209 13-Jun-2015 21:20
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I should add that my calculation is how much the transformer can deliver, but it will not all be transferred to the speaker as the speaker is say 8 Ohm so max 0.15 x 0.15 x 8 = 0.18W.




You can never have enough Volvos!


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Uber Geek
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Vocus

  # 1324214 13-Jun-2015 21:28
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Yeah that transformer is not going to drive a power amplifier, the power output is far too small.  Take it back before you butcher it.

Why not go for a class D amp? You can power those off switching laptop power supplies, no need for dual-rail nonsense.

But if you're sticking with the TDA2030 then you want a transformer more like this one : http://www.jaycar.co.nz/Power-Products-Electrical/Power-Conversion-%26-Transformation/AC-AC-Transformers/12V---30V%2C-100VA%2C-6A-Multi-tap-Type-2170-Transformer/p/MM2015 and don't forget you will need a rectifier bridge, and some big capacitors.

You could maybe use this one: http://www.jaycar.co.nz/Power-Products-Electrical/Power-Conversion-%26-Transformation/AC-AC-Transformers/15-30V%2C-30VA%2C-1A-Multi-Tapped/p/MM2008 in a pinch.

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Uber Geek
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Vocus

  # 1324245 13-Jun-2015 21:52
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It may be cheaper, and easier, to instead go for one of these: http://www.aliexpress.com/item/TPA3123-Class-D-Hi-Fi-Mini-Digital-Stereo-Amplifier-25Wx2-DC-10-25V/1605056007.html?spm=2114.32010308.4.11.aJBJvy

a
nd track down an old laptop power supply :) they are typically around 18v and 5A which is ample for one of these, Class-D amps are very efficient, and don't mind switched power supply.

edit: found an even cheaper one, good for 50W a channel @26v: http://www.aliexpress.com/item/TDA7492-D-Class-High-Power-Digital-Amplifier-Board-2x50W-AMP-Board-with-Radiator/32348292767.html?spm=2114.32010308.4.61.GHss3u


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Uber Geek
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  # 1324279 13-Jun-2015 22:49
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If you dont need that level of power, there are even cheaper ones that take only 5V and I think give you 2 watts of output, which is actually quite a bit since its not linear. I got one to use with a couple of 4" car speakers on my arcade cabinet and its enough for games. Not music tho.




Richard rich.ms



6 posts

Wannabe Geek
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  # 1324962 15-Jun-2015 13:27
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Gosh, thank you all for your replies! Really helpful, and I greatly appreciate you all taking the time to explain things and look for solutions for me! I'm incredibly impressed with the community here.

Anyway, as I think several of you may have suspected the transformer wasn't able to supply enough current, the sound would come on for half a second and then very quickly ramp out. Never mind, I'll get another transformer at a later date.

I've decided, since I've realized this power amp is too powerful for what I need (and to get it going I'll just have to throw more money at it) I'm going to put it aside for the moment and go back to a tiny 5w amp I've been playing around with. I think they might be similar to what richms mentioned. With the addition of acoustic amplification (from the gramophone horn I'm using) they're not too bad.One of these: http://www.ebay.com/itm/1x-PAM8403-5V-DC-Audio-Amplifier-Board-3W-2-Volume-Control-USB-Power-2-Channel-/371244375061?pt=LH_DefaultDomain_0&hash=item566fe39c15

I might upgrade to something slightly more robust later, like the ones ubergeeknz suggested, if I find the 5w amps I've got aren't quite cutting it.
Obviously I'm a bit new to a lot of this! I think I only went with the original amplifier I posted about because I knew I only wanted mono, and I found a guide to using them which made them sound quite good (although it neglected to talk about the power supply of course). Also the whole project has been one of those 'pick up bits here and there' sort of affairs. Clearly more planning needed haha! But you live and you learn.

Thank you all again!

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Uber Geek
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Vocus

  # 1325004 15-Jun-2015 14:20
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Best way to learn!  It's not a DIY electronics project until you've sent at least one thing up in smoke ;)

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Uber Geek
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  # 1325026 15-Jun-2015 14:44
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Yep, keep at it.

And, yes, there are a lot of VERY skilled and helpful people here. GZ is a wonderful resource.

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