Left channel plays louder on DTA3116S – how to solve it ? - diyAudio
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Old 27th April 2017, 07:24 PM   #1
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Default Left channel plays louder on DTA3116S – how to solve it ?

Well hello there – I have no knowledge of amplifiers or electronics in in the diy/repair sense but I was hoping there may be some chance I can work this one out with some help from people who are much more knowledgeable than me.

My almost new DTA3116S amplifier from Dayton Audio (yes the smallest one in the known universe) is 100% what I wanted but there is a slight problem – the left channel plays louder and I’m afraid there is not going to be any returns/warranty thing because the shop I bought it from (PartsExpresss) is located on another continent… and I don’t really have everything that came in the box anymore.

Details:
Amplifier is connected to 220 volts/Europe (with another cable, but the same power source).
I have done tests with signal coming from my computer which as it turns out has an extra 0.2-0.3 db output / left channel (connected out to in and measured in Soundforge).
I measured voltage at the output of the amplifier with speakers connected:
4000 hz tone at 250 millivolts – right channel was at minus 5.6%
4000 hz tone at 1000 millivolts – right channel was at minus 3.2%
4000 hz tone at 2000 millivolts – right channel was at minus 2.3%
4000 hz tone at 3000 millivolts – right channel was at minus 2.35%
I also measured the voltage without any speakers connected (just one measurement) – 4000hz tone, Left ch = 1704 millivolts / R chanel = 1671 millivolts – that is a 1.93% difference.
I also connected to amp to the line in of the computer and I discovered a 1.1 db difference between the channels – and I even tried to increase the volume but something in the amp cut the power or something – output signal was gone and replaced with single strong impulses (rare ones)… not going to try this one again it was weird and a warning for not doing things that I don’t really know if they are ok or not; the amp was not damaged.
I also discover while testing that one of the speakers (these are full range) sounded weaker than the other and I had them swapped so that they balance the 2 discrepancies.

Can I hear the difference ? yes … however after the swapping took place it’s more of a “I’m not sure” on most recordings but on white noise it’s still clear that the left channel is louder.

I honestly don’t know how to solve this one maybe it’s just a question of adding some cable length for left channel… I really don’t know. I’m planning to fix the speaker loudness difference (probably replace speakers/enclosure) and after that it’s going to be more of a problem (replace or not) but I would really really like to have this one 100% functional as it should.
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Old 27th April 2017, 09:17 PM   #2
irribeo is offline irribeo  Netherlands
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PE data doesn't match picture of ampboard, picture shows gain is 36dB. It seems you mention the computer has a small difference in left right output, that difference will be amplified ~60 times if picture is correct. Next there is a volume pot that will have unbalance especially in lower part and if gain is 36dB you might never get out of lower part of volume pot, I don't know.
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Old 28th April 2017, 06:54 AM   #3
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I don't know what "picture" of ampboard we are talking about.
Yes there is a 0.2 db louder left channel from the computer I'm using but the difference in sound is there indifferent of the source connected. I use headphones about as much as speakers and I have never noticed that 0.2 db difference.
Volume knob is at 35-50% the rest is done from the coomputer.
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Old 28th April 2017, 07:43 AM   #4
irribeo is offline irribeo  Netherlands
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PE shows picture of ampboard. The gainresistors shown in that picture are for ~60 times amplification. The output difference divided by ~60 should be the input difference.
Differences are not very high btw, but if annoying you could lower gain or see if you can adjust balance computersound.
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Old 28th April 2017, 09:13 AM   #5
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To be honest I don't understand everything you said but if I'm correct you are saying the difference of 2-3% is in the neglectable area? and that these might be due to the 0.2 db difference at the input???
Adjusting the balance is not a solution because I regularly use headphones.
I should do another test to see if there is no db difference at the amp input if I still get the imbalance.
I attached an image with the inside of the amp (mine) just in case it helps.
Attached Images
File Type: jpg Amp inside.JPG (567.4 KB, 55 views)
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Old 28th April 2017, 10:19 AM   #6
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OOPS! I should have checked this before posting, but since I don't know these things I thought that a 0.2-0.3 db difference at the source it's not big enough to matter; I replaced the source with a laptop and i got a 0% difference at 404 milivolts, as voltage increased to 1500 milivolts the error got to 1.5% but the left channel was the one that was quieter this time.
I think this is not a problem in the amp at all but one from the source greatly amplified initially by the fact that one of the speakers had a weaker nominal SPL.

So that makes average sound cards not exactly left-right balanced? - correct me if I'm wrong.
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Old 28th April 2017, 10:53 AM   #7
irribeo is offline irribeo  Netherlands
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Most unbalanced part would be the volumepot, normally. I can't read second gainsetting resistor. Below/next to c12 you see a 104 (100k) resistor, that makes 40-20-10 times, next to that 104 is the resistor that determines that.
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Old 28th April 2017, 11:03 AM   #8
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And what would your conclusion be? I don't see anything wrong the amp, it's the source that I see as the problem because once I replaced it the imbalance turned the other way (right channel became louder by a different margin).
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Old 28th April 2017, 12:33 PM   #9
irribeo is offline irribeo  Netherlands
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Yes.
And if you want to decrease the difference at the speakers, you could lower amplifier gain. It isn't 60, but still 40 or 20 times, to get it to 10 times you remove the 104 resistor. That might have other benefits, but only you know how much room there is in both volumecontrols you use. If you end up with an amplifier that can not play loud enough to your taste, you should not do it. Amplifier volume pot position you mentioned suggests you use less than 1/3rd of current gain, but if computer volume now is all the time or often at max, lowering gain might not be convenient.
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Old 28th April 2017, 01:35 PM   #10
Eva is offline Eva  Spain
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Datasheet of TPA3116 chip specifies +/-1dB gain setting error, although it does not specify if this is absolute or mismatch. Anyway, since common quality resistors are 1% and gain setting depends on 2 resistors, amplifier gain mismatch up to 2% is normal, unless trimming or 0.1% resistors, which are not common in consumer equipment. This is usually better than common dual gang potentiometers with 5% or 10% mismatch (plus more with aging). +/- 1dB is approx. +/-10%. This is hearable. +/-1% is about +/-0.1dB and is on the threshold of human audibility.
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