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Chip Amps Amplifiers based on integrated circuits

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Old 1st July 2011, 12:54 PM   #11
sreten is offline sreten  United Kingdom
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Hi,

The output from the chip cannot drive headphones, minimum load is 10Kohm.

You could send this to the socket but you'd then need a headphone amplifier.

rgds, sreten.
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Old 1st July 2011, 01:17 PM   #12
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Quote:
Originally Posted by sreten View Post
Hi,

The output from the chip cannot drive headphones, minimum load is 10Kohm.

You could send this to the socket but you'd then need a headphone amplifier.

rgds, sreten.
Aha, i hoped, but hopes went pufff...

Well, i could use a small headphone amp (i did one before, it was easy), but now the question is how to route everything so when i connect the phones the speakers are disconnected mechanically. For this the headphone amp (basically, a audio freq op amp) must be before the socket and that means the headphone amp output will go to the chipamp input when headphones are not connected. Is it okay for the chip amp? I really don't know the output voltage range from the sound processor. If the voltage is fine and the problem only is the current limit on the sound processor output then op amp unity gain buffer will do fine, but if the the output is very very small then the gain must be >1 and then the chip amp might choke on that.
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Old 1st July 2011, 02:27 PM   #13
sreten is offline sreten  United Kingdom
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Hi,

I would assume the level is fine for driving headphones so all you need is a unity buffer.
This should cause no problems when it drives the current power amplifier inputs.

rgds, sreten.
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Old 1st July 2011, 03:09 PM   #14
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Do you think it will be okay if i use usual opamp (not specialized audio) like lm358 ?
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Old 1st July 2011, 03:43 PM   #15
sreten is offline sreten  United Kingdom
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Hi,

No, it will not be OK. Modern phones are around 15 ohm to 60 ohm impedance.

I don't know why you need the basic features of that preamp. You can
find far better PC plug-ins for all sorts of heaphone processing effects.

The simplest in this case is I think the best, connect them to the input.
This will work with no power applied to the speakers, or them turned off,
so you wouldn't really need the socket switching arrangements.

rgds, sreten.
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Old 1st July 2011, 04:09 PM   #16
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I simply want to have volume control at one point for both devices.
For imput connection i already have a sultion with a manual switch:
http://www.artem.ru/cgi-bin/news?c=v&id=757
(it can route audio to one of the outputs with a switch).
But i'd really want to have volume control in one point, so, when i switch back to the speaker
i will not have to adjust the volume in two places. I prefer to keep PC colume at one level all the time.

But, i want to clarify why simple opamp will not work. Well, okay, headphones at from 15 to 60 ohms. Why is it bad for a usual unity gain buffer? What will go wrong. I am missing theory here.

Last edited by ArtemKuchin; 1st July 2011 at 04:30 PM.
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Old 1st July 2011, 04:31 PM   #17
sreten is offline sreten  United Kingdom
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Hi, a basic op-amp cannot drive anything lower than around 2Kohm, rgds, sreten.
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Old 1st July 2011, 04:33 PM   #18
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Obviously! Stupid me. Thank you!
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Old 1st July 2011, 05:02 PM   #19
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Umm. Maybe you happen to know any cheap single-supply audio op amp? Most of them need +- supply. I now remember, when i did my phone amp i did supply splitter, but here it is too much trouble.
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Old 2nd July 2011, 12:24 AM   #20
sreten is offline sreten  United Kingdom
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Hi,

The basic problem is the quite a few ~ 12V single rail low powered power
amplifier chips have significant gain not easily adljusted for this case.

As it is its likely you will have to adjust volume as you switch speakers/headphones.

IMO your best bet is to gut some some cheap USB powered
speakers. Ones with a volume knob and a headphone socket.
Note here I also mean USB sound, some use USB for power.

You will then have to select the output device within windows.

rgds, sreten.
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Last edited by sreten; 2nd July 2011 at 12:32 AM.
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