Itsy Bitsy TPA6120 Amp - Page 3

Before you send awy the gerber files it may be a good idea to import them into som gerber viewer. Can't you use Altium for this?

It definitely is a nice little headphone amp, the TPA6120A2. I like the sound as well. It's utilized in my DAC/headphone combo.

I think it likes higher voltages though, higher than the OPA690 can handle.

Have you actually tried it at different voltages and found a better sound at higher voltage? What's the supply in your DAC? Can't you please describe the sound of it and what you compared it to. How do you handle the DC offset?

I've seen the graphs in the data sheet, and the spec's are better at higer voltage, especially with a low impedance load. You could be right. Maybe I should use the 7812 to the OPA690 only and use 2 x 9 V to the TPA. I've tried it with 9 and 12 V and there's no audible difference unless driven to distortion. I use a 300 Ohm HD650 and I never listen at crazy levels.

The problem is portability. I've almost decided to use AAA's. With a higher supply it will be a huge amp.

I've noticed an instability problem with low impedance load and with the braided SPC cables I use. There's probably oscillation above the audible frequencies. The current draw raises to 80 mA. With a cheap shielded cable to the Senn's, the current draw returns to normal. I have some beads lying around, think I'm going to add them to the output. I wonder if its the OPA or the TPA that's oscillating.

I haven't done extensive listening with it at different voltages, that's why I said I think.

My DAC is a DAC 301 (which is a bit problematic IMO), and I got tired of tweaking it. I have tried 14V and I currently run it at 24V. I have an external regulated supply based on the Twisted Pear board, it's similar to dual TREADs or STEPs.

The sound seems a bit crisper, and more cleanly defined at 24V, but it's subtle, nothing earth shaking. I have about 10 headphones I used, ranging from 32 ohm (AKG K81DJ, Beyer DT660) to 250 ohm (Beyer DT990) and a few others in between like the AKG 271s. The sound is heavily influenced by the opamp used for I/V, which is where I spent most of my time tweaking.

I compared it to itself at the different voltages, but again only briefly. Compared to my X-Fi to CK2III or Mini3, it doesn't quite hold up because of background noise (not totally black). Since it's an integrated device, it's hard to pull out just the TPA6120A2 contributions. However, I've not used it in a 3 channel configuration and the CK2III is a 2-channel discrete configuration.

DC offset of 30mV is nothing to concern yourself with. Your HD650 won't even flinch at that. My situation was different, I had to balance the voltages coming out of the I/V stage by better matching resistors (going from 1% to 0.1%) of the differential outputs of the DAC. The TPA6120A2 was used for gain (2) and differential to single ended conversion to drive headphones. I believe mine is at 14mV now, due to the tolerance of the opamps and the TPA6120A2.

When you're measuring DC offset, try shorting the inputs to input ground. You may be picking up some stray stuff on an unconnected input.

See if you can account for the DC offset by looking at the measuring resistance of your resistors * gain.

I added a ferrite bead to the OPA690's output, and now the amp is totally stable with the braided cable and HD650. Thank you amb for inspiration and wisdom.

It's funny to notice that a very serious electrical error like this doesn't affect the sound at all. The amp sounds the same.

Thank you for your reply Holland. I'm going to try to short the imput when measureing DC offset in the future. Right now DC is no issue thanks to the servo circuit.

Nice work guys! Love to see SMD projects like this.

Boxed

I went the long-play, but cheap and ugly, way and boxed it in a mint tin, with a trickle charger. Theoretically I should have about 30 h of playing time. I'm charging it now, and I will burn it in for a while. The impressions are still that this amp is detailed and almost neutral. There is some kind of shiny or silky coloration. Like I said before, exciting and fast without being harsh and sibilant. What more could one ask for? A tad meatier (or for me a veggier) sound, it lacks some body compared to e.g. JISBOS. It's still not as exciting and detailed and lacks that fabulous sound stage compared to Analog opamp based amps like my LISAIII clone and AD8599/AD825 amp.

I've read about Channel Island VHP-1 and 2 that use TPA6120. The impressions of it seem to be about the same. This should be better though with an active ground channel and no coupling caps (or how do they handle the DC-offset, it looks like caps), but with a DC-servo that could mess up the sound, but I don't think it sounds worse since I applied the servo. The voltage supply is lower in this amp. I can't really tell tell how important the supply is since OPA690 can't be used above 12 V. There's no audible difference between 9 and 12 V. But most important of all, this is portable.

Another Itsy Bitsy TPA6120 Amp lives

I, finally, got around to putting my amp together. Sounds great. I will have to give it a serious listen. I will compare it against my Mini^3. My first impressions are that it is very neutral and pleasant to listen to. It isn't harsh.

Thanks for the fun project.

Pictures?