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Headphone Systems Everything to do with Headphones

Heaphone amp inside power amp
Heaphone amp inside power amp
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Old 8th July 2017, 09:42 AM   #1
Niila is offline Niila  Finland
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Default Heaphone amp inside power amp

I'm planning to build an integrated amplifier that also has a decent headphone driving capability. The signal line is as follows: Input selector, relay based attenuator, impedance raising buffer, and the power amp. The question is what would be the way to implement the headphone amplifier to the rest of the system?

I want to make use of my headphone jacks switching capability, so that no other switches has to be used when I want to use headphones. I also want to use dedicated amplifier for the headphones instead of fiddling with the power amp outputs, so the switching has to happen at the buffer stage. But from here, I'm not quite sure how to proceed.

I was thinking about using a relay after the zero gain buffer to redirect the signal to the headphone driver instead of power amp. Is my thinking overly complicated here?

I'm tempted in using a TPA6120 board from Ebay because of its size and ease, but I'm open to suggestions.
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Old 8th July 2017, 10:35 AM   #2
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by Niila View Post

I want to make use of my headphone jacks switching capability, so that no other switches has to be used when I want to use headphones.

I was thinking about using a relay after the zero gain buffer to redirect the signal to the headphone driver instead of power amp.
Hi, relays for signal switching are a good option. Not sure whether you mean to use your switched headphone socket to accomplish this though.

You could also power up/down respectively the amps if they have separate supplies
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Old 8th July 2017, 10:41 AM   #3
Mooly is offline Mooly  United Kingdom
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Heaphone amp inside power amp
You can use the headphone switch to operate a relay/s. Unless you really want a separate headphone amp then I would use the main amp output padded down as here (the fact this was for a bridged amp s irrelevant). You may not need to AC couple as that is amp dependent.

http://www.diyaudio.com/forums/headp...ml#post5111842
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Old 8th July 2017, 11:23 AM   #4
Niila is offline Niila  Finland
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Quote:
Originally Posted by scottjoplin View Post
Hi, relays for signal switching are a good option. Not sure whether you mean to use your switched headphone socket to accomplish this though.

You could also power up/down respectively the amps if they have separate supplies
Yes, the ideal is that the socket makes the switch. Is there any advantage in using a relay instead of splitting the signal to both amps? I'm worried that I damage the headphone amp (TPA6120 propably) if I run it without load connected.
Unfortunately I have to share the power supply between the buffer and the headphone amp.
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Old 8th July 2017, 11:31 AM   #5
Niila is offline Niila  Finland
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Quote:
Originally Posted by Mooly View Post
You can use the headphone switch to operate a relay/s. Unless you really want a separate headphone amp then I would use the main amp output padded down as here (the fact this was for a bridged amp s irrelevant). You may not need to AC couple as that is amp dependent.

http://www.diyaudio.com/forums/headp...ml#post5111842
Thanks, I just don't feel comfortable using the main amp for driving my headphones, seems a bit crude, although it works.
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Old 8th July 2017, 02:10 PM   #6
Mooly is offline Mooly  United Kingdom
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Heaphone amp inside power amp
If the main amp is OK quality wise then there should be no issues. The heavy attenuation provided by the resistive divider also attenuates any hum and noise present.
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Old 8th July 2017, 03:09 PM   #7
Fast Eddie D is offline Fast Eddie D  United States
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Driving the headphones from the main amplifier through resistors is exactly how virtually all the receivers/amplifiers from yesteryear were configured. The headphones were typically 600 ohms so this worked well. Modern headphones are usually 32 ohms give or take, and designed to be run directly from a headphone amplifier with no resistor.

Modern gain structure that I've seen in consumer "hi-fis" has the headphones driven before the power amp. In other words, the preamp does double duty as a driver for the power amp and a driver for the headphones. The switched jack simply disconnects the input to the power amplifier stage.

Maybe this will work for you.
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Old 8th July 2017, 04:44 PM   #8
OlegSh is offline OlegSh
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Heaphone amp inside power amp
+1

Just make a buffer powerful enough that it can easily drive headphones.
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Old 9th July 2017, 05:33 AM   #9
PRR is offline PRR  United States
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> worried that I damage the headphone amp ...if I run it without load connected.

I have *never* seen a headphone amp which would be hurt by lack of load. Headphones unplug easily; if the amp died, that would be a real annoyance.

> (TPA6120 propably)

Especially that one (really any "chip"). Few transistor power amps "need" a load. The chip-makers work very hard to self-protect against nearly "any" failure in the hands of users. TI maybe sells a few thousand of these, and if they had thousands of unhappy buyers demanding money back it would be A Problem at TI. But this chip is really sold by the millions, under another number, slightly different specs, for telephone line and other long-distance wire transmission. Phone wires get broken. Phone companies do not want to replace the wire AND the chip in the box every time a tree branch falls, or a weed-wacker eats the wire on the house, etc etc.
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Old 17th July 2017, 10:41 AM   #10
sgrossklass is offline sgrossklass  Germany
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Sorry if I'm a bit late, but I haven't been around here in a while...

Branching off to a headphone amp stage (gain 1-5 depending on needs) after the buffer should be fine. Tapping off after the power amp carries the disadvantage of limiting output level and reducing SNR to whatever the power amp will do.

What I would put some thought into is what to do switching-wise. Ideally I'd want to mute the power amp and turn off power to it as well when headphones are plugged in, assuming you can get rid of power-on/off pop noise. For this to work out best, the power amp should have a dedicated transformer, with another (with lower static loss) powering the buffer and headphone amp circuitry. A decently powerful integrated amp easily consumes 30-40 W in idle, which seems a bit excessive if all you want to do is drive some cans.
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