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advice with a low voltage cmoy for low impedance headphones

post #1 of 11
9/9/10 at 1:15am
Thread Starter 

hello!

after a couple of basic cmoys with a opa2134...at last i have the chance to get some better parts...someone on head-fi is disposed to send me some...as in my country i can't find...and i want your opinion..wanna know what to buy

 

my opa2134 cmoy was pretty basic except i was using  2 x 9v battery, gain of 5.7, 470mF for the power supply and 1mf input caps and r5 of 47 ohm as i used it with low impedance headphones...i liked how it sound...but want un upgrade and use it with lower voltage battery

 

here's what i wanna do...

i wanna keep al the settings before the gaine/the capacitors value but with a ad8397 as opamp and a buf634 and a tle2426 instead of 220k resistors shown here :                             but with only one 9v battery

buffer.png 

how will it work ?...i wanna use it with low impedance headphones as audio technica m50...grados sr80...etc

or should i just use a tle2426 and a ad825(it works well with low voltages) in a basic cmoy ?

or could u sugest something else beside making other amp like pimeta/mini3 )

advanced thx

cheers

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post #2 of 11
9/9/10 at 1:24am

Grado SR80?

 

Do you mean low impedance as in abnormally low as in likely to have special current considerations, or do you mean low impedance as in normal modern consumer-grade headphone impedance as in "not high impedance"?

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post #3 of 11
9/9/10 at 1:30am
Thread Starter 
Quote:
Originally Posted by gimble View Post

Grado SR80?

 

Do you mean low impedance as in abnormally low as in likely to have special current considerations, or do you mean low impedance as in normal modern consumer-grade headphone impedance as in "not high impedance"?


i mean for 32/40/60 ohm/consumer-grade headphones...i heard that for them i need i higher output opamp...but don't need high voltage as 300 ohm headphones

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post #4 of 11
9/9/10 at 1:56am

Have a look at

 

http://www.sgheadphones.net/index.php?showtopic=3220&hl=virtual+ground

 

I'm sure the boards are not available, but it was a great design uses a buffered ground and buffered signal channels, I made a couple on home made boards, very nice sound, worth a look and a good read

 

cheers

FRED 

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post #5 of 11
9/9/10 at 6:59am

Assuming your op amps will remain stable go with lower gain. Voltage gain of 5.7 is pretty high for low impedance headphones. Low impedance headphones dont need much voltage swing to play at scary volume levels. Try gain in the 1.5-2 range - if nothing else you get more spin out of the pot, which gets you into a section that is almost certainly better matched. 

 

If you are going for opamp + buffers I would lean towards the Pimeta. Multiloop feedback has soooo much cool going for it that its hard to describe. You can always disable the multiloop on the Pimeta too. The fact that 99% of what you are describing is on a PCB makes it very attractive though.

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post #6 of 11
9/9/10 at 7:08am

You might want to consider dropping the 9 volt battery in favour of AA cells.

The typical 9 volt Alkaline battery does not have much current and are

expensive. Four AA cells will give you more current and more run time

while costing you less.

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post #7 of 11
9/9/10 at 7:54am

What exactly is the point of R5 ? No voltage accross it, no Ohm's law to play with

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post #8 of 11
9/9/10 at 8:03am

 

Quote:
Originally Posted by bidoux View Post

What exactly is the point of R5 ? No voltage accross it, no Ohm's law to play with


In the Pimeta V2 its part of the multiloop feedback thing.

 

IIRC it is there to set the "local" feedback around the op amp to a high value, and then it multi-loops through the buffer to set the total system gain. I could be wrong. If you go to the part selection page Tangent links to the jung multiloop article. 


Edited by nikongod - 9/9/10 at 8:06am
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post #9 of 11
9/9/10 at 8:07am

I'm sorry, I was talking about the 10ohm resistor. Here.


Edited by bidoux - 9/9/10 at 8:12am
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post #10 of 11
9/9/10 at 8:30am

 

Quote:
Originally Posted by bidoux View Post

I'm sorry, I was talking about the 10ohm resistor. Here.


R5 "sort of" bypasses the second stage so that the gain op amp helps to drive the load. It is similar to what is done in the CHA-47, but with smaller resistor values.  

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post #11 of 11
9/9/10 at 8:43am

The 10 ohm resistor acts as a summing resistor like in a Apheard 47.

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