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Class D Switching Power Amplifiers and Power D/A conversion

Aux input for TPA3116 bluetooth amp
Aux input for TPA3116 bluetooth amp
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Old 13th October 2016, 01:49 AM   #1
tallnutt is offline tallnutt  Australia
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Join Date: Oct 2016
Default Aux input for TPA3116 bluetooth amp

Hi,

I've built an amp based on this module from ebay
New TPA3116 Class D Amplifier Board Bluetooth 2.1 Amplifier Board 100W+2*50W | eBay
Quite happy with the sound, I have it driving two Kenwood 4ohm coax units and an 8ohm 5x7inch woofer, although the bass seems a bit weak maybe because its supposed to be a proper subwoofer and the Kenwoods are a bit tinny, and too much high end so have to keep the 'treble' control on the unit right down.
My question is, does anyone know how to tap an auxiliary input into it? I have tried all the output pins of the Bluetooth module and the volume pot pins but get nothing. I'm a bit of a noob but have some electronics experience. I guess I'm missing something obvious.

Thanks for any help.

Theo
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Old 13th October 2016, 07:28 AM   #2
Dreamcazman is offline Dreamcazman  Australia
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I have it's bigger brother, the 4.1 board but it comes with an AUX analog input so I'm sure it's possible as long as you find the correct points. If I get a chance, I'll check mine to see if the AUX input connects to any of the BT pins or how it's wired in general.

I surprised your board doesn't have one.
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Old 14th October 2016, 11:31 PM   #3
tallnutt is offline tallnutt  Australia
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Thanks very much, that'd be great. Yes I only noticed the 'bluetooth only' warning after I bought it. I think there is a lowpass filter on tge stereo channels and the bass is very deep so it sounds like its missing the mid-bass range. I need to get a diagram of the position of the components to change.

Thanks,

Theo
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Old 18th October 2016, 07:04 AM   #4
tallnutt is offline tallnutt  Australia
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I located the output lines from the bt module, but wherever I tap into them I get no input. Could there be some protection on it? I notice the L and R channels have separate grounds, my input jack joins them, perhaps that's the problem? Not sure of how to solve it.

Thanks.
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Old 19th October 2016, 06:30 AM   #5
gec is offline gec  United States
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Not sure if adding a line in is going to work out but if its going to work at all I think you need to tap in after the SGM358 op amp, just before the main volume control where the left and right signals pass through the two 1K resistors. Not sure where to pick up the ground lead, but it should be easy enough to figure out. The ground is common for L&R at that point.

Have you noticed a background noise when the volume is low? I like this 2.1 amplifier except for that annoyance. I believe the subwoofer channel crossover point is at 150hz and the stereo channels run full range. What size and type of enclosures are your drivers mounted in? Those being car audio speakers they are likely designed for infinite baffle use (in other words, relatively large enclosures). Also, I think this amp does best with at least a 19v 4a power supply. I'm using this amp to drive a ported 4.5" woofer and two sealed 3" full range with great results (except for the background noise!).
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Old 19th October 2016, 07:09 AM   #6
tallnutt is offline tallnutt  Australia
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Reading another thread it looks like you are right, after the opamp but the lines need to be switched off from the opamp by the input jack. I will try that next.

My enclosure is quite big, 40cm deep by 50 high with a baffle between bass and car speakers and two 3cm vents at the back. My bass speaker is a 7x9 unit. I think for me the 150hz crossover is too low.. would like to try raising that if I can find the filter. Mine is a portable, with two 12V 4Ah batteries in series.

There is some noise for sure but only very high hiss that I think comes from the Bluetooth. Hoping it'll go away with an line in.
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Old 19th October 2016, 11:37 AM   #7
Dreamcazman is offline Dreamcazman  Australia
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Sorry, haven't had a chance to check my amp yet, been busy with work. Will try to get around to it soon.
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Old 19th October 2016, 03:03 PM   #8
gec is offline gec  United States
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Do you have the thiele/small parameters for the woofer? Without those or some enclosure design guidance from the speaker manufacturer it will be difficult to come up with an optimum enclosure type, internal volume, and port size and length if doing bass reflex. If your woofer is a 5x7, 6x8 or 6x9 car audio speaker it was likely optimized for using the car trunk as an enclosure.

Last edited by gec; 19th October 2016 at 03:08 PM.
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Old 19th October 2016, 11:14 PM   #9
tallnutt is offline tallnutt  Australia
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No, sadly no info on the speaker, but it is from a similar portable PA system. It was a coaxial but the midrange was fried from a previous unit's crossover shorting so I took out the mid and tweeter and I am just using the woofer (yes probably 6x9). The only info on it is 'Chiayo 8ohm'. I don't think its the enclosure because it also sounded too tinny before the speakers were enclosed. The stereo channels are on these: Kenwood 5x7" 3 Way Speakers KFC-PS5795C - Supercheap Auto
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Old 20th October 2016, 10:58 AM   #10
tallnutt is offline tallnutt  Australia
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So this is weird... cut the lines from the opamp output from the BT module, connected a jack, and when its turned on it plays for about a second then cuts out. Tried a 10k resistor and a 100uf cap, and both, but get same thing.
????
Must be some protection switch on the amp to cut off if the bt is not connected? How to defeat that?
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