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Old 6th February 2013, 02:13 PM   #1
NeoY2k is offline NeoY2k  France
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Default 8ch cheap (chip) amplifier for sound art

Hello,

I'm looking to build an 8 channels amplifier for sound art (installations, theatre...) and would appreciate some input as to best suited design. The goal is to have an ultra inexpensive and small multichannel amplifier.

Inexpensive is easily achieved stacking 20-30$ used hifi amplifier, but that's not fun to carry around. 4ch Behringer amps for around 350$ would work but multiply that by 2 and it's not cheap enough, especially as I plan to upgrade to 16 ch (make a second unit) within a year.

Requirements are:
-mid low power (50W-80W RMS 8R @ 0,1% THD)
-reasonable peak power, ability to have higher output for a couple seconds.
-driving all sort of loads, tactile transducers, small hifi speakers, computer speakers...
- some sort of OL/short/whatnot protection
- decent noise floor
- As cheap as possible.
- Reliable
- Compact/light

My first thought is buying a handful of LM3886 PCBs off ebay for dirt cheap, and stuff them on a large heatsink. Power them with a Meanwell SMPS. Would love to find a way to stuff them in a small 1u rack, and would absolutely love to have passive cooling (goes against light, I know).

But I'm concerned by the lack of balanced input and gain adjustment (strapping a pot on the input resistor is calling for high noise floor at lower gains), I'm worried that I won't find suitable symmetrical SMPS (and I would need to make my own PCB for single rail it would seem). I might want a tad more power.

So, would there be a better solution?

I had a look at the 6*100W Sure Electronics boards, but reliability seems a concern, with overheating. So, not suited. I also like the fact that the LM3886 are mono amps: stuff as many as needed, if one fries, easily replaced/repaired. I won't be treating the amp nicely xD.

Note: I can design PCBs and have them made, but Olimex is not taking orders anymore and it was the cheapest I could find. And I would have had trouble making them for <10$ per channel anyway. So this probably will be a too expensive route.

Thanks,
Nicolas
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Old 7th February 2013, 12:37 AM   #2
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Look at DRV134 and DRV135 chips. They are a single ended input to balanced output drivers.
Complementary chips are INA134 and INA137. These are balanced input receivers with single end output.

BOM is in each case the chip itself and a couple of caps.
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Old 7th February 2013, 01:01 AM   #3
jcx is offline jcx  United States
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Default DIY seldom competes on cost with mass market products

even with free labor you likely can't beat Behringer or other mass marketed PA - simply can't buy the raw parts in small quantity for the delivered amp cost
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Old 7th February 2013, 12:29 PM   #4
bcmbob is offline bcmbob  United States
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You will have to add several components for a bull build, but these amps are an incredible value. The sound quality is amazing for the price and four kits is still ~ $100. Might be a solution with the properly sized transformer and PS.
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Old 29th March 2013, 03:51 PM   #5
samp78 is offline samp78  United Kingdom
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Hi Guys, This is the most appropriate forum I think for what I am looking for... I am looking at building a home cinema system so 5.1 or 7.1 haven't decided yet... I was going to use LM3886 for the 5-7 channels and a bridged LM3886 for the sub. My question is what skinda power will this draw i.e. what VA transformer will i require? looking at running +-30V rails
Thanks in advance
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Old 29th March 2013, 04:01 PM   #6
bcmbob is offline bcmbob  United States
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Let me suggest you take a look at the power requirements of the speakers you will be using and take your lead from that information (working backwards). It has been my experience and understanding the Class D amps are better suited to subs. My multiple LM3886 amps improve their ability to handle 4 ohm drivers but don't necessarily create more power/SPL.
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Old 29th March 2013, 04:52 PM   #7
samp78 is offline samp78  United Kingdom
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Okay well it will be a mono sub only 10" not after moving massive amounts of air more like bass reinforcement that sub-woofing, but it is 8 ohm, I do have 2 to hand though so could parallel them to make 4 ohms? was contemplating Class D but I can get hold of LM3886's cheaper and more readily... and the satellites will be 6 Ohm Sony surround speakers I have managed to get my mits on not very good at the power side of electronics, i know the basics but some things just confuse me... Thanks
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Old 30th March 2013, 11:14 AM   #8
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I built this 8ch gain lone cheap

8-Channel Gainclone Amplifier


And even cheaper with class d

Class-D 8-channel amplifier build - DIY Audio & Electronics - StereoNET Australia
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Old 30th March 2013, 01:32 PM   #9
samp78 is offline samp78  United Kingdom
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So if I was to use these amps would that be better in your opinion? Thanks for the help
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Old 30th March 2013, 04:28 PM   #10
samp78 is offline samp78  United Kingdom
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Hi Guys, just a quick question can the LM4780 run a 4 ohm load at rail voltages of around 32V?
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