My reference amp design TPA6120
Dec 11, 2007 at 11:42 AM Thread Starter Post #1 of 14

Dave_M

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I have designed a new amp based on the TPA6120 chip. Seeing the price for headphone amps like the graham slee solo is one of the reason I got into DIY (no one told me DIY was so expensive :p). I thought I could do a better job and this is what I came up with. I call it reference amp because it should be pretty neutral and transparent (aka straight wire with gain).

imgp2506lf9.jpg


TPA6120 has a monstorous 1300 V/µs Slew Rate and should have no problems driving any normal headphone. There are amps that use this chip out there already, but they have some draw backs to them such as using an opamp input buffer and inverted output. My amp does not. I have also kept capacitors out of the signal path, it uses a DC servo instead to zero the offset.

I had a prototype board made at batch PCB, it came back and looks great. But when I was ordering parts I got everything I needed apart from the TPA6120! I tried to get free samples from TI but they wont send them to me. That was a few months ago. I don't think I will get round to finnishing the amp for quite some time (I don't even need a headphone amp right now). I wanted to post it here and see what people make of it (possible group buy?). I also designed a PSU for it, more details on that later maybe.

Feel free to ask me questions. But bare in mind I am no electronics expert.
 
Dec 11, 2007 at 11:46 AM Post #2 of 14

balou

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schematics plz
smily_headphones1.gif


I'd really like to hear this amp - monolithic chip amps don't have a superb reputation around here, but the pure technical specs of this amp are quite interesting. but.. um... I first have to build my B^3 amp and a pimeta board which has been lying around for about half a year now
 
Dec 11, 2007 at 11:58 AM Post #4 of 14

TzeYang

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Quote:

Originally Posted by balou /img/forum/go_quote.gif
schematics plz
smily_headphones1.gif


I'd really like to hear this amp - monolithic chip amps don't have a superb reputation around here, but the pure technical specs of this amp are quite interesting. but.. um... I first have to build my B^3 amp and a pimeta board which has been lying around for about half a year now



lol, considering how popular amps like xins and rsas, i'd say monolithic chip amps are VERY VERY popular and they have superb reputation.

Anyway, nice TPA6102 design. I like current feedbacks :lol: but their super fast speed and instability always scare me.

And no input ground resistors? Should the pot wiper ever lifts, it's going to be an offset nightmare.

EDIT: It'll be good for a reference "portable" if you can make it that way
smily_headphones1.gif
. Also, why not wider holes for bigger caps?
 
Dec 11, 2007 at 12:15 PM Post #5 of 14

Dave_M

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Quote:

Originally Posted by TzeYang /img/forum/go_quote.gif
Anyway, nice TPA6102 design. I like current feedbacks :lol: but their super fast speed and instability always scare me.


I was very carefull with the layout. I did everything the datasheet said you should do to avoid instability. So it should be ok.

Quote:

Originally Posted by TzeYang /img/forum/go_quote.gif
And no input ground resistors? Should the pot wiper ever lifts, it's going to be an offset nightmare.


My inexperiance is showing already. I did not think of that.


Quote:

Originally Posted by TzeYang /img/forum/go_quote.gif
EDIT: It'll be good for a reference "portable" if you can make it that way
smily_headphones1.gif
. Also, why not wider holes for bigger caps?



Portable yes. But it will not be so good running off batteries. It will drain them quickly.

I do not see the need for such big capacitors. The TPA6120 has 100u and 100n for PSU decoupling for both channels and both power rails. Big capacitors I would use in the PSU before the regulators. Also with big capacitors it would not be so small and sexy :lol:
 
Dec 11, 2007 at 1:33 PM Post #6 of 14

balou

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TzeYang, I think I was a bit unclear, I meant monolithic all-in-one chip amplifiers, not opamps. altough upon closer inspection, the tpa6120 looks much more like a dual opamp than your average chip amplifier - the latter usually require DC blocking caps at the output, and their max, output is often specified at 10% THD - while the TPA6120 looks more like an opamp with an integrated buffer


edit: Dave, have you made any current draw measurements? Looking at the datasheet, it shouldn't draw much more power than a mini^3
 
Dec 12, 2007 at 4:29 PM Post #8 of 14

Dave_M

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Quote:

Originally Posted by balou /img/forum/go_quote.gif
Dave, have you made any current draw measurements? Looking at the datasheet, it shouldn't draw much more power than a mini^3


The TPA6120 has to be heatsinked to the copper ground plane because it can dissipate a lot of heat. Maybe with slightly lower voltage and only driving headphones it will not be that bad.

Quote:

Originally Posted by Shopper /img/forum/go_quote.gif
Also, not sure that I wouldn't use an input opamp, leaving out the DC servo. What's wrong with that?


Using an input opamp with lower specs than TPA6120 seems to me to 'waste' the potential of this chip. Like the slew rate would be limited by the opamp. Also, by design I like the audio path to be kept simple. I wouldn't like to run the signal through many different opamps if the goal is to create somthing with high end performance. Would still need a DC servo or capacitors on the input to protect from DC offset from the source as well.


Nisbeth, YGPM
smily_headphones1.gif
 
Dec 13, 2007 at 11:05 AM Post #9 of 14

majkel

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I agree, buffering TPA6120 inputs with another op-amp is a waste of sound quality. DC servo is a better idea to get rid of input currents influence on output DC. Actually, many months ago on another forum guys drew the same schematic (high current op-amps + DC servo) but used 2x LT1210 instead of TPA6120, and they claim it sounds very good. When my friend finishes the box for the amplifier, I will borrow it from him in order to audition.
 
Dec 18, 2007 at 4:42 AM Post #10 of 14

suzyj

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I've just finished building a TPA6120 amp myself. I used a board from Per-Anders Sjostrom, called the QRV07. I used a pair of OPA134s as input buffers, and an Alps volume pot.

I'm extremely happy with it - I distortion levels are unmeasurable with my test setup (a Tektronix SG505 oscillator, and AA501A distortion analyser, with a floor around 0.008%), and it sounds great. Totally clean and transparent.

Here's a photo of the partially-completed amp:

2112480370_ffc0818a7d.jpg


Yeah, it's an awesome chip. Highly recommended. Per-Ander's board is pretty cool, too.
 
Dec 18, 2007 at 10:08 AM Post #11 of 14

majkel

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OPA134 + TPA6120 is a good old duo, being sold in Poland for a couple of years under a brand name. SQ-wise, it's easy to be beaten. In the other words, it's normally the first headphone amp circuit DIYers clone, or something around LT1210, TPA6120 + servo. From my experience - IC amps with local NFB loops in L/R channels sound bad. For a first time try it's big improvement compared to no amp but honestly, OPA134 sounds poor: tubby bass, veiled midrange, below average detail and soundstage. And then comes the TPA6120 which isn't transparent either. Guys report it sounds "dry" alone and LT1210 is SQ-wise better, but a LT1210 pair will be much more expensive. Regarding slew rate - 1000V/us is much over what you need. Old chips dedicated for headphone outputs had slew rate of 3-20V/us.
As the beginning of tweaking the OPA1134/TPA6120 circuit I recommend using other op-amps like OP275, AD8620, OPA2107, LM6172, LM4562, OPA2228 and hear the differences. After that it should be obvious that the OPA2134 is only good in being easily applied. Good luck!
smily_headphones1.gif
 
Dec 18, 2007 at 10:11 AM Post #12 of 14

00940

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There might be a matter of taste and pairing with sources and headphones... The AD8610 and the OPA2228 don't sound better than the opa134 to my ears, quite the contrary.

What I'm trying to say is that there's nothing wrong with the opa134, after all Headroom uses it on most of its amps line.
 
Dec 18, 2007 at 11:47 AM Post #13 of 14

majkel

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OK but let's don't turn this thread into another op-amp related.
wink.gif
The best ever
is ADA4841-1 single and ADA4841-2 dual because it's ultra-linear (max nonlinearity: 4uV in 1-4V output region), -105dBc THD @ 100kHz. I'm talking about this chip only because of sonic impressions. All other op-amps are crap compared to this one, save OPA1632 if you know how to wire it single-ended (I do, and wrote it once here). And better learn wiring OPA1632 because ADA4841-x are 12V max. supplied. :|
 
Jul 11, 2009 at 9:08 AM Post #14 of 14

bearmann

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Hummm... any news about this nice little amp, Dave?! Looks more than tempting...

*Resurrection*

best regards,
bearmann
 

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