[AffeX]

Don't want to hijack thread, but I have a question for Ti related to this.
I find the SE/balanced input switching very interesting, but I am puzzled though.
As I understood, in the 3 channel active ground setup, the ground amp board has slightly different config. Now using a normally configured amp board as active ground, one for each channel. Can you explain it for me Ti?
Also would a 5 board not make more sense then?

 

[amb]

Affex, when the switch is set to unbalanced, the "cold" channel amps do indeed act a bit like the ground channel in a 3-channel setup, except it isn't a 3-channel amp -- the 4 channels are still driving balanced headphones, each side with a separate return. If an unbalanced TRS headphone jack is present, its sleeve ground return goes to the PSU's ground (passive ground), or to a 5th channel which would be configured the same as the ground channel amp in a 3-channel setup.

In a 3-channel active ground amp, the ground channel runs at a lower gain than the left and right channels for the lowest amount of noise. In a 4-channel balanced setup, all four amps must have the same gain. Since it is unwieldy to switch the gain of a β22, we simply don't do it. In practice it still works very well because the amp's inherent noise floor is low.

 

[AffeX]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Affex, when the switch is set to unbalanced, the "cold" channel amps do indeed act a bit like the ground channel in a 3-channel setup, except it isn't a 3-channel amp -- the 4 channels are still driving balanced headphones, each side with a separate return. If an unbalanced TRS headphone jack is present, its sleeve ground return goes to the PSU's ground (passive ground), or to a 5th channel which would be configured the same as the ground channel amp in a 3-channel setup. In a 3-channel active ground amp, the ground channel runs at a lower gain than the left and right channels for the lowest amount of noise. In a 4-channel balanced setup, all four amps must have the same gain. Since it is unwieldy to switch the gain of a β22, we simply don't do it. In practice it still works very well because the amp's inherent noise floor is low.

Good reply - I understand it all now. Thank you, Ti !

 

[DoYouRight]

In my case it is not so much a need for help from balanced vs unbalance source. But having things like HF-2 SE since I dont want to mangle them with a reterm. So if using a balanced source, with 4 boards and the switch I could get SE headphones to run in a seemingly active ground?

 

[digger945]

The switch is used for unbalanced source and HP's with balanced termination.
According to AMB in post #47 above, you would need a 3rd or 5th board configured for active ground to be used with unbalanced HP's, as the ground channel runs at a lower gain than the amp channels.

 

[Hottuna_]

Quote:

Originally Posted by amb /img/forum/go_quote.gif In a 3-channel active ground amp, the ground channel runs at a lower gain than the left and right channels for the lowest amount of noise. In a 4-channel balanced setup, all four amps must have the same gain. Since it is unwieldy to switch the gain of a β22, we simply don't do it. In practice it still works very well because the amp's inherent noise floor is low.

Just to throw a spanner into the works...
If i do make a 4 board balanced β22 and have a switch to go unbalanced with 2 boards being signal and 1 board being active ground all having the same gain....
Would it work?
Will it have too much noise this way?

 

[amb]

Quote:

Originally Posted by Hottuna_ /img/forum/go_quote.gif If i do make a 4 board balanced β22 and have a switch to go unbalanced with 2 boards being signal and 1 board being active ground all having the same gain.... Would it work?

Yes, it would. But it won't be as quiet as a proper ground channel (assuming that your gain is >2).

Quote:

Will it have too much noise this way?

Depends on how much gain there is. Much of an amp's noise comes from its input stage, which is then amplified by the gain. It's no different in the ground channel.