Dual TPA6120A2 headphone design to eliminate crosstalk - diyAudio
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Old 4th August 2013, 06:11 AM   #1
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Default Dual TPA6120A2 headphone design to eliminate crosstalk

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According to the TI datasheet, using one TPA6120A for each channel can reduces crosstalk but there seems no design exist like this.

Crosstalk is very annoying and it is very easy to check by a ear.
Shorting one output channel with a 32ohm resistor(simulate a headphone load), turning the volume to highest of that channel but mute the other channel in the computer. Then, uses headphone listen the muted channel. There should be no sound heard, but most system suffer from a different level of crosstalk. due to ground layout problem, inter chip crosstalk etc.

I just done a quick design of a dual tpa6120a2 and compare to the Texas TPA6120A2 Evaluation Module using one tpa6120a2 for two channel with the same source. The conclusion is All tpa6120a2 single chip design are suffer from different level of interchip crosstalk. The right channel sound will be coming out from left channel and vice-versa
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Last edited by diyinhk; 4th August 2013 at 07:25 AM.
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Old 4th August 2013, 09:01 AM   #2
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From the datasheet you quoted, it means using separate power supply for left and right channel can reduce crosstalk, but mention nothing about using oneTPA6120 for each channel.
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Old 4th August 2013, 11:15 AM   #3
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Quote:
Originally Posted by endy View Post
From the datasheet you quoted, it means using separate power supply for left and right channel can reduce crosstalk, but mention nothing about using oneTPA6120 for each channel.
Yes! separate power supply for left and right channel should reduce crosstalk, it apply to other design too.
And the datasheet also mention "leave one of the amplifier off"
The compare test result is already very positive with only one power supply for two tpa6120, the crosstalk is very low or un-listenable,
The crosstalk of using one tpa6120a2 for two channel is listenable.
I have tested many design in the market(not only tpa6120) with the above mentioned simple test method and many are suffer from different level of listenable crosstalk.
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Old 5th August 2013, 03:32 AM   #4
jcx is offline jcx  United States
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linear crosstalk is usually considered very benign - $k phonograph cartridges often only spec a vague >30 dB - which is considered fine with music - the cutting lathe doesn't do too much better

and the bass of course is mixed to mono on vinyl LP

stereo speakers in typical home listening rooms obviously have huge natural crosstalk

a mastering studio pro opinion - http://www.moultonlabs.com/more/prin...ntom_image/P1/
Quote:
and when the dust finally settled I had found out something quite interesting: that as long as the difference between channels is less than 3 decibels, the phantom image hovers pretty much in the middle point between the two speakers. I promptly ran this down to my buddies at the local loudspeaker factory and we tried it in the anechoic chamber with blindfolds and people pointing at the imaginary phantom, and it still remained true: with up to 3 dB difference between channels (that’s half-power, remember!) the image didn’t move much, maybe five degrees. With between 3 and 6 decibels difference in levels, the phantom quickly and without much stability migrated to the louder speaker, hovering just inboard of that speaker, and once the difference was greater than 7 decibels, the phantom was for all intents and purposes coming from the louder speaker.
headphones do give more opportunity to listen for crosstalk - but there's still no reson to believe its important with music

most full size audiophile headphones are open back and also have a good amount of natural crosstalk

crossfeed processing is a desirable feature for headphone listening - especially with some 60's recordings with different instruments simply hard panned to R, L channels

and of course the TPA6120 itself has very good crosstalk numbers over audio - you get much more crosstalk from the TRS connector single point contact common gnd with low Z headphones - can be 10 milliOhms for 1/4", 10x higher for 1/8" TRS


and multiloop topology is really the way to go for absurd performance numbers – use 2 singles as input op amps, each looping of the TPA as its respective output buffer, separately sub regulate each of the input op amp's supplies and you can easily add another 40 dB to the TPA6120's 90 dB typical crosstalk rejection figures

you really are just pretending unless you you re-terminate the headphone cable with 4-pin multipoint contact lower R connectors (“balanced” headphone cable – but doesn't require a bridged/balanced output to obtain the advantage of eliminating the TRS common gnd contact resistance coupling)

Last edited by jcx; 5th August 2013 at 03:42 AM.
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Old 14th October 2013, 11:20 AM   #5
xslavic is offline xslavic  Moldova
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can you post schematic/circuit for that dual tpa6120a2 board?
how its made? is one channel left unconnected ?
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Old 15th October 2013, 02:21 AM   #6
jcx is offline jcx  United States
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Default -30 dB crosstalk with real music signal is fine - but if you insist

I don't know why CFA with gain inside another “good audio” op amp feedback loop isn't better represented in diy projects

certainly “Jung Multiloop” had a run in the long dead Headwize forum, a little bit in head-fi diy sub forum

but mostly those were unity gain buffer output stages some integrated, some discrete

despite Scott Wurcer and Walt Jung both showing CFA like the AD811 with its own local feedback providing V gain inside the input op amp feedback loop

you can easily find Jung's articles on his website, his “Op Amp Applications” book, audio line driver circuits in free pdf downloads form Analog Devices



to repeat:


you can use both the op amps in one TPA6120 chip, one in each channel with no problems - the basic TPA chip crosstalk specs are only excellent, inaudible @ -90 dB into 32 Ohms at 1 kHz – and should be pretty flat for all audio frequencies

by wrapping the feedback loops of separate input op amps around each of the TPA output/buffer op ams amps, each input op amp corrects for any measured error – including crosstalk – by the amount of loop gain provided by the input op amp
easily another 40 dB for a combined -130 dB crosstalk number due to active parts – you do need to take extreme measures in layout, signal routing to near the potential

Last edited by jcx; 15th October 2013 at 02:31 AM.
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Old 15th October 2013, 05:47 AM   #7
xslavic is offline xslavic  Moldova
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can you show us what do you mean?
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Old 15th October 2013, 06:30 PM   #8
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Quote:
Originally Posted by xslavic View Post
can you post schematic/circuit for that dual tpa6120a2 board?
how its made? is one channel left unconnected ?
the schematic/circuit is designed and printed on the pcb directly, it follows the datasheet available in the official Texas Instruments website
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Old 15th October 2013, 06:36 PM   #9
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Quote:
Originally Posted by jcx View Post
I don't know why CFA with gain inside another “good audio” op amp feedback loop isn't better represented in diy projects

certainly “Jung Multiloop” had a run in the long dead Headwize forum, a little bit in head-fi diy sub forum

but mostly those were unity gain buffer output stages some integrated, some discrete

despite Scott Wurcer and Walt Jung both showing CFA like the AD811 with its own local feedback providing V gain inside the input op amp feedback loop

you can easily find Jung's articles on his website, his “Op Amp Applications” book, audio line driver circuits in free pdf downloads form Analog Devices



to repeat:


you can use both the op amps in one TPA6120 chip, one in each channel with no problems - the basic TPA chip crosstalk specs are only excellent, inaudible @ -90 dB into 32 Ohms at 1 kHz – and should be pretty flat for all audio frequencies

by wrapping the feedback loops of separate input op amps around each of the TPA output/buffer op ams amps, each input op amp corrects for any measured error – including crosstalk – by the amount of loop gain provided by the input op amp
easily another 40 dB for a combined -130 dB crosstalk number due to active parts – you do need to take extreme measures in layout, signal routing to near the potential
sorry, my english is not good enough,
but do you mean that crosstalk is good?
mono is better than stereo?
and it is enough(-90 dB) for audiophile?
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Old 15th October 2013, 10:11 PM   #10
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The chip features separate LVCC- RVCC- LVCC+ RVCC+.
But the EVM features a single positive and negative rail.
Bypass caps C1,C2,C3,C4 0.1uF offer some separation.
I can see why that might not be enough to satisfy.

Just saying I see plenty good reason why this might be
less than ideal layout, and maybe not the chip at fault.

http://www.ti.com/lit/ug/slou169/slou169.pdf
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