[TrevorNetwork]

Hi all,

I have given it some thought, and I would like to make a balanced CMOY. What I am curious about however is what hurdles I may encounter while making it. I suspect someone has attempted if not succeeded in making one.

Cheers!

Trevor

 

[rickcr42]

you mean balanced In ? Out ? both ?

balanced in is easy.Just use both the "+" and"-" inputs of the opamp and use matched resistors networks for both inputs.

Balanced output can be done with two but should be done with three opamp stages : Input stage.positive amp stage,negative amp stage.

Balanced input AND output is best done with one of the new TI chips that has both a balanced input AND balanced out (cant remember the # TH something.Mine is not at hand to look at).If not enough current for your application just hang a buffer on ther ouput "open loop" and you should be fine.

for the headphone/balanced amp hookup diagram and ideas look to kevin gilmores dynamic headphone amp project at the headwize project library

 

[MisterX]

For a amp that had balanced input's check out Tangent's personal montior.

http://www.tangentsoft.net/audio/tpm/misc/tpm11-sch.pdf

There is a parts list and other stuff on his site but I assume it's not linked from the Audiologica page for a reason so you will have to figure the link out yourself.

 

[amb]

The cmoy-style amp (using simple opamps with no output buffering) is not a good candidate for balanced output operation if you have lo-Z phones. Remember, the load impedance as seen by each of the opamps' outputs is effectively half of the actual impedance of the phone. Most of the "audio-grade" opamps are already a bit strained with such loads in unbalanced use. For high-Z phones it is ok. You must re-wire your headphones to separate the "ground" lines of the two stereo channels so that you have a dual-mono (4-wire) configuration.

On the input side, no additional opamp is necessary to support either balanced or unbalanced operation. Just wire them up as shown in one of the two configurations below (note that the resistor numbers don't match the headwize cmoy's schematic):

In the second case, "Rb" should have the same value as R22 and R55, and "Ra" can be just a few hundred ohms for a FET opamp.

Note that you can easily wire-in a regular dual-gang volume control pot at the input of the second diagram, but you need a four-gang unit with good tracking characteristics for the first diagram (that is, if you want a single knob to control the volume for both channels).

 

[Wodgy]

Rickcr42's suggestion about using a balanced output (aka. fully-differential) op-amp is a good one. With one of these, you'd only need a single op-amp per channel, which is more in keeping with the CMOY spirit. The OPA1632 is probably the part you want. It's designed for audio, has very low distortion, and delivers a good amount of current for an op-amp.

 

[amb]

Quote:

Originally Posted by Wodgy The OPA1632 is probably the part you want. It's designed for audio, has very low distortion, and delivers a good amount of current for an op-amp.

Yes, that's a pretty cool chip. However there is no dual version so you'll need two for stereo, and that's not much different (in terms of parts count) than using two OPA2132 dual opamps. Note that the OPA1632's quiescent supply current is 14mA each. Compare this to the OPA2132 which is 8mA (4mA per amplifier). The balanced output doubles the current consumption for both, so if it's to be powered by a 9V batteries, expect the battery life to be shorter.

If anyone has actually built a headphone amp based on the OPA1632, I'd like to hear your opinions about its sonics compared to the usual favorites.