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What Opamp for iems?

post #1 of 17
5/5/11 at 10:40am
Thread Starter 
Hey Guys,
i've been looking around for building an amplifer for my REZEROs. I am actually looking for a change in signature a better soundstage, wanting transparency and brightness with two different Opamps. I have decided on a very small CMoy.
But while reading around, i read that iems need more current gain than voltage gain, and that an Opamp like the OPA2132PA, won't be very good here. What should i be going for guys?
Thanks
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post #2 of 17
5/5/11 at 1:07pm

no thru-hole "audio" DIP op that runs from a single 9 V battery is suited to the current demands of this 16 Ohm 100 db/mW iem

 

you'll need to use a surface mount part - AD8397 as used in the Mini^3 could work except you basically want no V gain and the chip isn't that "unity gain stable" nor does it have full Vsupply input common mode range

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post #3 of 17
5/5/11 at 2:25pm
Thread Starter 

So basically, what u mean is, at a gain of unity, preferred for IEMs, the suitable AD8397 isnt very stable.

plus it doesnt support the common voltage range.

how then, do the iem amplifiers made at iBasso, like the T3 and the T4 accomplish the same using OPamps and a 3.7V supply?

if i use those as in the T3 and the T4, would the amplifier be worth it?

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post #4 of 17
5/5/11 at 2:48pm

Does IEMs require more current gain over voltage gain because that would decrease the output impedance?  Which makes sense because if output impedance is greater than headphone impedance, that would limit the total current through the output passive components, but if output impedance is less or ideally 0, the headphones are getting more current or maximum current as output impedance tends to 0.  Thats my explaination.

 

Also by common mode, are you talking about noise rejection?

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post #5 of 17
5/7/11 at 7:14am
Thread Starter 
Guys,
not drifting away from the topic, what opamp should i go for?
I have batteries rated 3.7 volts and the space limit would let me use only two in series, that gives a max of 7.4 volts.would this voltage, plus a gain of 2, be enough for the AD8397?i want this amp for my RE-ZEROs and RE0s.what other opamps would be suitable?am ok working with SMD.
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post #6 of 17
5/7/11 at 7:39am

OPA690

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post #7 of 17
5/7/11 at 11:04am
Thread Starter 
Thanks Avro_arrow, please keep the suggestions coming.and is this opamp cmoy compatible?i read it is a single opamp.also, somebody in another thread suggested a rail to rail output (don't quite understand what it is) but the OPA690's datasheet never said anything about rail to rail or anything like that, and the AD8937 does say that it has the rail to rail thng.
Am on my cell, thats why i couldn't do my homework about these opamps quite well.
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post #8 of 17
5/7/11 at 12:19pm

The OPA690 is not a rail to rail op amp but it does like low voltage

and it has lots of output current. You can often find it in the Mini^3.

You will need two (or three) to make a Cmoy.

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post #9 of 17
5/7/11 at 1:49pm
Thread Starter 
Thanks avro_arrow.
Two OPA690s, i understand as for right and left channel. Third one for a buffered ground right?where can i find the schematic to a cmoy using 3 opamps?
Also, when its 3 opamps in the cmoy,would the 7.4v supply still be ok/good?
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post #10 of 17
5/7/11 at 4:58pm

Check out the schematic for the Mini^3, linked above.

Yes, the OPA690 will work down to 5 volts (+-2.5 volts).

There is even a three channel version of the OPA690 called

the OPA3690.

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post #11 of 17
5/7/11 at 10:11pm
Thread Starter 
Hey,
i am also building the Mini^3 amp. Saw the schematic linked above, but i just couldn't figure out how a three channel OPA3690 would be used.also, how would this be integrated into a cmoy?is that possible?
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post #12 of 17
5/7/11 at 10:58pm

Ignoring the crappy results part....

Would you care to guess what you would get if you install an OPA2690ID in the U5 position on a Mini3 board? wink_face.gif

 

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post #13 of 17
5/7/11 at 11:16pm
Thread Starter 
That would also work as an amp, right?but why crappy results?
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post #14 of 17
5/8/11 at 5:29am

Brain Fart

 

Quote:
Originally Posted by psgarcha92 View Post

That would also work as an amp, right?but why crappy results?


 


Edited by Avro_Arrow - 5/8/11 at 6:31pm
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post #15 of 17
5/8/11 at 10:43am
Thread Starter 

I dont understand,

what do i have to do here?

i am not an electronic engineer guys, please help.

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