[A3rd.Zero]

I am looking to build a truly balanced (unbalanced in to balanced xlr out) headamp/preamp. Cost is an object, I am happy to use opamps, discrete is fine too.

Suggestions?

Milo

 

[jefemeister]

How can't have a "truly" balanced amp without balanced inputs.

 

[DaKi][er]

Nearly every headphone amp can be made ballanced, you just need to build 2 of them usually

Not that much point unless you have ballanced inputs though, but converting unballanced to ballanced for your input isnt that hard, Garbs on here has had some very good success in doing that

 

[A3rd.Zero]

Basically I need to drive a balanced amplifier over a distance, so I need to send it a balanced feed. The input doesn't matter because its right next to the preamp. I understand that its not totally balanced if the inputs aren't balanced but in this case it matters far less then the 25' of unbalanced that I am currently running to the amp.

I know the theory behind balanced sends, and the ESP project 51 is very basic but workable. I am interested however in successful implementations of the idea so that I can check some of my assumptions. So if anyone has seen a schematic, or a finished project that has balanced outputs then I would love a link.

Thanks for the help.

Milo

 

[rickcr42]

Quote:

Basically I need to drive a balanced amplifier over a distance, so I need to send it a balanced feed. The input doesn't matter because its right next to the preamp. I understand that its not totally balanced if the inputs aren't balanced but in this case it matters far less then the 25' of unbalanced that I am currently running to the amp.

the assumption was you wanted a balanced headphone amp but what you really are looking for is a simple SE/BAL converter so the quesion now is how far do you need to drive the lines and do you need gain also ?

Rather than get crazy trying to come up with and optimize a brand new design my thought is far easier (and in the end better ?) would be to use one of the chips already specifically designed to do just that :

ADI Version :

http://www.analog.com/UploadedFiles/...443ssm2142.pdf
http://www.analog.com/en/prod/0,2877,SSM2142,00.html

TI/BB Version :

http://www-s.ti.com/sc/ds/drv134.pdf

http://focus.ti.com/docs/prod/folders/print/drv134.html

You can use three opamps and precision matched resistor to make your own but this a far better/easier/more cost effective way to go IMO.

for some good background info

http://www.jensen-transformers.com/an/an003.pdf

 

[A3rd.Zero]

mmmmm. I like the DRV134, and that jensen pdf has been my friend these last three years at least (I would rather avoid transformers, but the document is the best out there).

Thanks for pointing that device out to me, I was looking at some differentials, and they didn't really do what I wanted (opa1632).

Thanks again.

Milo

 

[rickcr42]

Quote:

Thanks for pointing that device out to me, I was looking at some differentials, and they didn't really do what I wanted (opa1632).

why ? You said you needed a "single ended to balanced" device which both the TI and ADI chips are designed for-true balanced driver amps.
Both also offer balanced receiver chips to match up at the other end so better (IMO) than an all inclusive single package (=comprimised) "fully differential amp" such as the TI you mention (designaed for driving a balanced ADC input from a balanced signal)

The transformer option would be the ultimate though I did not suggest this for reasons of cost.Combined with a buffer at the driving side (Discrete,VT,IC)and an opamp ( discrete,vacuum tube,IC) at the end of the cable would be hard pressed to better it.

 

[A3rd.Zero]

Our two boats just passed in the night.

I was saying that the OPA1632 I had looked at originally didn't seem suitable so I wrote off an "all in one" solution. I like the DRV134 and may in fact use it.

Should have said, "I was looking at some OTHER differentials"

Milo

 

[rickcr42]

Quote:

Our two boats just passed in the night.

one of those "can't see the forest man,too many damn trees !" things

Quote:

Should have said, "I was looking at some OTHER differentials"

Well there is this but I can not vouch for the sound.The fact that it is meant for DSL meaningless :

http://focus.ti.com/lit/ds/symlink/drv1100.pdf

specs out good for audio use,available in either PDIP or SOIC,gobs of driving current.........

 

[A3rd.Zero]

Cool thanks. I still like the DRV134 so maybe I'll use that. Thanks again

Milo

 

[rickcr42]

Another option and one I will be checking out soon is this puppy here :

http://www.thatcorp.com/1420desc.html

http://www.thatcorp.com/datashts/1420data.pdf

So far I have used the TI and ADI chips plus others that "pretended" to compete though did not with the above looking to be another major player in the single chip audio line driving/receiving area (though even here adding a line level 1:1 trafos would only help

).

Otherwise I go straight to opamp/buffer/trafos if I need gain or buffer/trafos if not with full discrete if the app critical.Lotta choices out there and the only hard part picking one

BTW-In the "good a place as any to park this" department on the other end these babies are looking mighty good for an IC based design :

http://www.thatcorp.com/1200desc.html

Even better a "virtual transformer" designed by Mr Audio Transformer himself :

http://www.thatcorp.com/1200desc.html

http://www.thatcorp.com/datashts/1200data.pdf

THAT is very impressive (pun intended

)

 

[Garbz]

Everything you wanted to know Plus more is in http://www6.head-fi.org/forums/showthread.php?t=134816 this thread. At the top I posted links to threads where the DRV134 and several transformers were discussed.

The DRV134 worked well, but it did muddy things a bit.

 

[A3rd.Zero]

Wow thanks for all the data.

Milo