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my build + amplifier upgrade sense-check

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alexxxor View Drop Down
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    Posted: 13 May 2013 at 12:16pm
Hey guys!

My esky build has come along magnificently! here's a pic for ya



In the slightly beer addled construction process, I blew up my little ta2020 amp and I'm stuck at a bit of a crossroads...

We had possibly the last sunny day until october, so I wasn't going to let a blown amp ruin the last park session of summer. To replace the 2020, I borrowed a 150w car amp off a mate (75+75 bridged) and kept it low on two 7.2 ah SLAs. It was a-ok for about 5 hours of run time off the two batteries including a half hour or so of 'we still have lots of juice, let's crank it and walk around the park'.

Shit it goes loud! I doubt it was even running at much more that 30w, but it gave a nice satisfying thump and a good clean sound through the whole range. there is a bump at around 100hz that can get a bit rough at high volume and it's quite loud around 1000hz too. I think it would benefit from porting to extend the bass a little, but that's for another day.

when we got home, we decided to hook it up to a power supply and let loose. flicked on a 12db boost on the bass, put a HP filter on at 50hz to save it falling to pieces and cranked it. It makes a splendid PA speaker and will surely be powering a few house parties in the future!

Righto, here's my amp dilemma:

One of my main criteria when building this was being able to dj from it and the 2020, while amazingly impressive for a $20 amp couldn't quite cut the mustard. I thought about building it into a half boominator, but I'm not sure that will fit the bill for dj'ing due to the fact that it will make it slightly difficult to monitor if I have full sound blasting at me.

So I've decided to keep it mono and go for an amp upgrade. I'm going to buy another 2020 for festivals and camping where I'll be wanting days of runtime but for a 6 hour park session, I'm happy to sacrifice a bit of efficiency for a bit of thump. as it stands, this is going to be my order:

LM3886TF 1-Channel 68W Amplifier Module Board - Black + Blue
http://dx.com//p/202165 

150W DC 10~32V to DC 12~35V Adjustable Step-Up Mobile Power Supply Module for Laptop 
http://dx.com//p/150610

and some controls with:
DC 12V LM1036n LM1036 HiFi Stereo Audio Amplifier Bass / Treble / Balance / Volume Control Board
http://dx.com//p/206288


the dc step up is purely for tinkering, I'll probably just use the two SLAs if efficiency becomes a major concern. It would also come in handy for running it from a 12v power supply or car battery as backup...

I figure that because this is only going to cost me $40 all up it's worth a shot, if nothing else, just to learn a bit more about electronics in general..

Any thoughts/advice??

thanks! Smile
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lost eden View Drop Down
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Joined: 04 April 2011
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lost eden Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2013 at 1:50pm
Your order won't work.

LM3886 needs +ve & -ve power supply rails (eg +38v GND -38v) which is usually achieved by using a centre-tap toroid & a diode bridge regulator. You can't run it from a single battery. In theory you might be able to power it from 2x sets of batteries (one set to provide the +ve rail & the other to provide the -ve rail) but that would be far from ideal. Also, even if you give it +24v/-24v rails you won't even get 40W into an 8 ohm load (the lower limit for the power supply is +/-20v). They're also nowhere near as efficient as class D amps.

Don't get me wrong, they're wonderful amps & I run a pair at home for my hifi, but that's mains powered with toroids that give nearly +/-40v after rectification & have 8000uF of capacitance per rail!


Edited by lost eden - 13 May 2013 at 1:53pm
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alexxxor View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote alexxxor Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2013 at 2:09pm
thanks for the reply!

I'm new to this whole bizzo, so that's saved me some heartacheSmile. for some reason I had it in my head that the lm3886 was a class d. It didn't click with the +/- either...
back to the drawing board.

I'm pretty impressed with the t-amps, so I think i'll look into it more.

the ta2020 seemed a bit weak on the bass side compared to a beefier class-d, even at similar volume levels. I put it down to the car amp being geared toward bass more (even though the "bass boost" was at 0db) Would bigger caps on a ta2020 improve the response?

maybe this would be a better choice
http://dx.com/p/2-x-50w-class-d-tda7492-audio-amplifier-board-black-dc-14-27v-203772
i'm not sure how the tda7492 would go on efficiency though...

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lost eden View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lost eden Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2013 at 2:24pm
I learned about the whole +/- power supply thing the hard way, when I bought a cheap TDA8920BTH amp for a boombox & only noticed when I received it & tried to attach the battery that there was an extra power input...

That TDA7492 is a Sure Electronics board, which I would recommend buying direct from Sure themselves if you decide to go for it (they have a website & an ebay store). The ones of DealExtreme may be exactly the same, but they may be fakes or use (more) fake components. I actually have one of those 2x 50W boards somewhere but haven't done anything with it. IIRC the chat about it over on diyaudio pointed to it being one of the poorer class D implementations that Sure have come out with (nothing like their earlier marvellous TC2000/TP2050 boards).

The 41Hz AMP11 might be worth a look.
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Saturnus View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2013 at 3:19pm
The problem with the TA2020 is that on a single 8 ohm speaker it outputs under 8W. That's not a lot of juice.

So if you have a HP10W for example with an average sensitivity around 95dB, it's only gong to be about 106dB in peaks. Doubling up on speakers means the can now output 8W into each and there's 2 drivers to share the load, so peaks are now 112dB.

Might only be 6dB difference but the sound is a world apart. 
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alexxxor View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote alexxxor Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2013 at 4:01pm
I hear you saturnus. you're spot on. that's been what's been keeping me awake at night... Smile

the only other problem that I didn't mention before is weight. I want to keep it under 10kg. that being said, if I go for 2 batteries, that's the weight of an extra hp10w. for most sunny afternoons, the 2020 and one battery will be fine. there is also an aesthetic consideration due to the hideously wonderful pattern on the esky itself...

the amp11-lv is exactly what i want, I'm not game to solder it up myself though. bugger!

at this stage I think i'll go for the sure.
I'd advise against getting anything from sure's website at the moment, it looks like wherever the ads are coming from is trying to insert malicious php code into the site. not too dodgy, but hey ebay.

i'm just tossing up between the 100w tripath sta508 or the 50w TDA7492 now

there are a couple of hifimediy ones that don't look too bad on paper. has anyone had any experience with them?

choices, choices...

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Old Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote login4 Quote  Post ReplyReply Direct Link To This Post Posted: 14 May 2013 at 7:28pm
iv got the  hifimediy T2 (designed for 4 ohms) (T1 for 8 ohms) 

there great, very powerful, efficient, and push some good power out.

i have mine in a little alloy box with a buck converter which steps it upto 28v from 12v

handy  
CELTIC SUBSONIC SOUND SYSTEMS
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