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TPA6120+OPA headphone amp info needed
TPA6120+OPA headphone amp info needed
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Old 30th October 2017, 12:07 PM   #1
enton is offline enton
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Question TPA6120+OPA headphone amp info needed

Hello everyone
I came across this headphone amp circuit and before I start building it I wanted a second opinion...

I currently have the TPA6120A2 and couple of OPA2134/4134 that I want to use with it.

Here is the schematic:
http://audioworkshop.org/downloads/comp_tpa6120.pdf

The website:
TPA6120 Headphone Amplifier - COMPOSITE TOPOLOGY - DIY AUDIO BLOG, AUDIO WORKSHOP
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Old 1st November 2017, 09:56 PM   #2
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Also another thing to mention. I didn't see any caps at the input nor output of the amplifier. Should I add any? Or they are omitted purposely?
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Old 2nd November 2017, 01:16 AM   #3
abraxalito is offline abraxalito  United Kingdom
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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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Old 2nd November 2017, 11:24 AM   #4
enton is offline enton
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Quote:
Originally Posted by abraxalito View Post
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.
Thanks for the answer. What will be the best type, and will 1uF do?
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Old 2nd November 2017, 12:40 PM   #5
abraxalito is offline abraxalito  United Kingdom
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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).
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Old 4th November 2017, 05:48 PM   #6
enton is offline enton
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Quote:
Originally Posted by abraxalito View Post
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).
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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Old 5th November 2017, 08:24 AM   #7
Idiosyncrasy is offline Idiosyncrasy  Netherlands
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TPA6120+OPA headphone amp info needed
Quote:
Originally Posted by enton View Post
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 ))
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
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Old 5th November 2017, 08:57 AM   #8
Samsara is offline Samsara  France
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Hello.
Using caps is nonsense.
This IC don't need it ,but if security is needed you could use relays.
Here a complete board with DIP 8 support and uPC1237 controller to prevent output offset with relay Aiyima TPA6120A2 Hi Fi Headphone Amplifier Fever Audio Earphone Amp Diy Kit-in Headphone Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
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Old 5th November 2017, 09:26 AM   #9
00940 is online now 00940  Belgium
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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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Old 5th November 2017, 05:32 PM   #10
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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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