TPA6120+OPA headphone amp info needed

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abraxalito

abraxalito

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Joined 2007
If you have valuable headphones I'd definitely use an output capacitor to protect them against a fault condition. An input cap isn't necessary.

If you're concerned about how the thing sounds then I'd pay attention to supply decoupling and have extra PSU filtering for the input opamp so its not directly exposed to the classB hash generated by the TPA.
 
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enton

Member
Joined 2016
abraxalito said:
If you have valuable headphones I'd definitely use an output capacitor to protect them against a fault condition. An input cap isn't necessary.

If you're concerned about how the thing sounds then I'd pay attention to supply decoupling and have extra PSU filtering for the input opamp so its not directly exposed to the classB hash generated by the TPA.
Click to expand...

Thanks for the answer. What will be the best type, and will 1uF do?
 
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enton

Member
Joined 2016
abraxalito said:
1uF will do almost nothing at all. I'd use the lowest ESR electrolytic I could get my hands on. To my knowledge that's a Nichicon HZ series - 1000uF/16V is not exorbitantly priced. If you want to splash the cash you could explore polymers (OSCONs).
Click to expand...

I saw the oscons, aren't those caps that are used in motherboards and gpu cards? My work is around them so I'm pretty sure I've seen them. Usually, they are Panasonic if you search them by "code". (small aluminium ones, very hard to remove from pcb :)))
 
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Idiosyncrasy

Member
Joined 2015
enton said:
I saw the oscons, aren't those caps that are used in motherboards and gpu cards? My work is around them so I'm pretty sure I've seen them. Usually, they are Panasonic if you search them by "code". (small aluminium ones, very hard to remove from pcb :)))
Click to expand...
Yeah, that's right, these are often used in computing hardware. They're a bit more expensive (like a few bucks a pop), but not prohibitively so, as you'll only need a few. The Panasonics you mentioned are good, but the other Japanese suppliers are fine as well and don't charge the Oscon brand name premium. Have a look over here: Aluminium Organic Polymer Capacitors | Mouser Europe
 
00940

00940

Member
Joined 2003
A few things:

- I'd skip an output cap but an input cap should be added unless you are certain the sources used will always have an output cap.
- r109/209 are on the low side at 22k, especially with a jfet input opamp. If you add a 10k pot in front of the amp, consider going up to 100k.
- With 10R output resistors, it's not an amp for low impedance headphones, unless their impedance vs frequency curve is very flat. You could replace r107/207 by a lower value resistor and an inductor/ferrite but beware of oscillations. iirc, jcx also suggested to have the 10r isolation resistor inside the opa134 feedback loop (but not in the tpa's) and then having a coil/ferrite to isolate the output.
- despite what the designer says on his website, don't experiment with any opamp at the input, especially not very fast ones. The opa134 is great here because it's kinda slow compared to the output buffer.
- Be careful with the caps after the lm317. You don't want the lowest esr possible here or you'll get oscillation. If you use an RC filter then it's a bit different.
 
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enton

Member
Joined 2016
Thanks for the answers everyone!

Now more questions about the amp
I won't be able to find uPC1237 where I live, and also if I purchase it from ebay it will take too long to arrive. Can this be replaced with simple transistor driven relay to delay the output turn on?
I will be using 32ohm headphones, for those, how much should be the resistor value or inductor(if needed) at the output? I've seen this, and just to make sure we are talking about the same. It's output strapped with resistor and inductor connected in parallel right?
 
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