[stoneshadow]

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
 
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

 

[gimble]

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"?

 

[stoneshadow]

Quote:

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

 

[Fred_fred2004]

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 

 

[nikongod]

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.

 

[Avro_Arrow]

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.

 

[bidoux]

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

 

[nikongod]

 
Quote:

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. 

 

[bidoux]

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

 

[nikongod]

 
Quote:

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.  

 

[Avro_Arrow]

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