tpa6120a2 headphone amplifier

[steeve]

My first post in this forum.

You know, i read posts here for a long time and i appreciate the knowledge of some of the members.

Regarding the post title, i have just COMPLETED my headphone amp based on the tremendous tpa6120a2 chip from TI.

This is my second try, on a more effective layout with care on positioning components, as my first try ended up with lot of oscillation, excessive dc offset and many other problems.

Currently, my built amp is truly monoblock, with one chip per channel with activated only the left channel.

Gain is 3V/V with 0.1 % ONEOHM resistor on the feedback loop, while topology is non-inverting. No series DC blocking capacitor in the signal path.

Power supply is also monoblock, with two cascaded 317 / 337 regulators, two 10000 ìF AEROVOX in the main bank and a 160 VA talema trafo, all these per channel.

This overkill PSU was initially built for my 627 based preamp, but i included the option of a PSU out for future try outs, as happened!

The amp board was installed into an empty box previously housing the circuitry of black box phono stage. The connection with the pre's PSU is via a mogami 2534 run.

Regarding the chip's power pad, i ' ve read a lot for the difficulty of soldering to the ground plane. This was not a problem. I installed the chip flipped over, cut all 15 pins (out of 20), cut a thin layer of copper, fixing it on the board's pad and soldering the exposed power pad on the copper. Perfect solution for me!

Total cost? 0 Euros (!!!), as the chips were TI samples, while the rest of components were in stock from other DIY projects.

The amp is driven from a passive controller based on a hand-selected black beauty ALPS 10kohm.

Currently, offset is stable at 4-5 mV (always) and no oscillations are observed at any case (may be the better component layout?).

For history, i have made lots of headamps, with any kind of configuration, specially with opamps. Never tried tubes, but in the future this is possible.

OK, what about the sound? My headphones is hd-650 Senns (300 ohm). The negative first (has only ONE !): a slight lack of "weight" in the lowest registers, compared to the direct drive from my monoblock 3886 GC.

Now the positives: NEVER have i listened such a natural sound from a headamp. Voices, three-dimensionality, bass definition, highs, harmonical structure are IMHO first class.

The most characteristic feature is the desire to listen to music disk-after-disk, concentrating on the songs theirselves without wanting to criticize anything (and believe me, i am criticizing everything!).

For the end, this amp is a perfect line preamp, surpassing also my 627 preamp especially in the dynamics field and in the naturalness!

I'll give more details on another post.

Nice to meet you all.

Steeve,

Athens, Greece.

[DaKi][er]

the tpa6120 is a nice chip to use in a headphone amp, i done a circuit board for one and got a few boards manufactured up for it

http://www.mypage.tsn.cc/dakiller/tpapages/

and some finished pics - http://www.mypage.tsn.cc/dakiller/dtpablack/

i really do enjoy the sound, much better than the opamps with buf634 inside the feedback loop that i've done in the past

[steeve]

I now enjoy the sound from my TPA6120 amp!

It has a very natural sound and is NEVER boring .



The amp is configured as a passive one as i told you.

The only problem i encounter is a slight increase in output offset (from around 5 mV to 30 mV) depending on the pot's position.

This from what i know is not really important.

In the first version of the amp thigs were way worst. I had audible oscillations even when moving around. Some times, even when touching the headphone cord, i had hum problems.

Now fortunately these problems disappeared, but what annoys me is the variations of the output offset.

Can anyone elaborate for the physical explanation of what really annoys this chip, independently of the layout?

Anyway, the sound of this amp is something someone must experience to estimate. Because of this, i want to end up this project with a perfect amp without any problem (i.e. no offesets, no oscillations, no nothing).

I have to mention that i have no caps in the signal path, as i believe that a cap is unnecessary.

For the end, i have to mention that the amp was very easy to build. I'd like to hear opinions from other builders (concerning sound impressions).

[Fixup]

As you found, these high speed, current-feedback DSL/vedio opamps were very easy to go instable. Extremely good specs, sound natural but not so musical to some people.

[peranders]

Fixup, your are right but a good pcb helps.

I like also the TPA6120

My amp look like this and this.

Steeve , do you have a picture of your amp?

[stry]

P-A,

soon will upload photos !!! I have to re-loan the camera.

Regarding musicality, i have never listened to a more musical headamp.

Especially the high extension is extension-less and very very pure !!

Only problem the slight lack of weight in the lo registers. But the others,



Will keep you all informed. Greetings

[Fixup]

This article studied the THS6012, tpa6120's elder brother:

http://sound.westhost.com/highspeed.htm

Some key words in this article:

"I could not measure the distortion.

Quite frankly, I was disappointed. There was absolutely nothing that sounded of 'amplifier' - this is probably as close to a straight wire with gain as you are likely to find."

While some people like such hi-fi sound, more people like musical sound - some color from an amp such as a tube amp.

[stry]

I need to limit the (large) bandwidth of the TPA headamp, as my dac (CS4390-based) has minimal 1st order analog filter.

Due to ultra-sonic content at the output of the dac, the TPA oscillates (DC offset, excessive warming, etc.) at specific gain settings of the passive preamp (10k log).

Does anybody knows how to implement a filter at the input of the TPA for cutting the CS4390’s residual 5.6 MHz signal (= 128 x Fs) that so much annoys the TPA’s performance ?

Thanks.

[peranders]

How about making a proper filter after the DAC? Are you sure you have got oscillations of the reasons you claim? How does your pcb look like?

[stry]

P-A,

I'm sure for the oscillations because only this source (dac) presents this kind of problem. With the remaining (phono, dvd player and analog out from my cd player) no problem at all.

The dac is a modified one but presents a 5.6 MHz output at -42 dB, as defined by the 1st order analog filter. So no component or pcb layout problems here.

This that bothers me is the extremely wide BW of TPA that may be triggered by HF signal even at moderate levels.

Sorry, no photos at the moment. Soon, will upload photos of the pcb when available.

Thanks.