Switch signal to power amp before or after JISBOS Buffer?
Oct 9, 2009 at 6:07 AM Thread Starter Post #1 of 5

Zaubertuba

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I'm preparing to build a Balanced JISBOS-with-gain headphone amp. I need to be able to switch my source to drive either the headphone stage or send a line-level out to my amp for my speakers. I would like to have a front-panel switch so my wife can switch back from the headphone output to the speaker output to the amp (actually a receiver, but I'm using the term "amp" so as not to confuse with a balanced receiver circuit, which I may need to implement) at will. Currently my 1212m is driving my headphone amp, and the onboard Realtek chip is driving the power amp. She has to switch between the 1212m and the onboard sound card in the computer settings, which is a pain, and I'd rather not use the onboard sound anyway.

The way I see it, I could implement it like this:

1212m--->Switch--->Bal. Receiver--->Unbalanced Line Out
|--->JISBOS Boards--->Bal. Headphone Out
...or like this:

1212m--->JISBOS Boards w/gain switch--->Switch--->Bal. Receiver--->Unbal. Line Out
Are either of these options practical, or is there another better option to accomplish the same thing?
 
Oct 9, 2009 at 7:23 AM Post #3 of 5

Zaubertuba

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The 1212m only has one set of analog outputs, that can operate *either* in balanced or unbalanced mode--but not both.

The two end uses are:

1.) Balanced Headphone Amplifier
2.) Unbalanced Line Output to

So I need to be able to switch the signal to an unbalanced line out at some point.

The receiver would be something like this:

p51-f2.gif


...a TL071 (or equivalent) balanced-to-unbalanced converter.

My idea behind switching is that the whole point in my building a balanced amp is being able to go double-ended all the way from source-to-headphones. I want to be able to maintain that signal scheme, but have the flexibility to send my signal elsewhere to drive an unbalanced amp.

*OR*

Could I just take the output from say, just the R+ and L+ of the JISBOS boards and send them to a switched line-out? If this would work, I'd probably air-wire the potential divider to the JISBOS boards and make it switchable, so I could switch from 4x to no-gain for line out (and lower-impedance phones).
 
Oct 9, 2009 at 3:52 PM Post #5 of 5

Zaubertuba

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Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif
Didn't think that the 1212 had a headphone amp, was quite sure that it was a balanced line output.


Methinks you didn't have much sleep last night--where did I say the 1212 had a headphone out?
tongue.gif
...Or maybe I'm not being clear enough. I excel at that.
rolleyes.gif


Quote:

I'd say wire the amps (balanced and unbalanced) in parallel. No extra circuits, no conversions, nothing extra.


So, I'd just wire the balanced +&- input jacks to the 4 input poles on the switch, and then on the output poles to the unbalanced output, I'd short the - wires to ground?

Or are you saying I don't even need a switch. Wouldn't that be, umm, dangerous?
 

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