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Ok to plug unbalanced 1/4 plug into the balanced outputs of a Audiobox USB96

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Ok to plug unbalanced 1/4 plug into the balanced outputs of a Audiobox USB96

Postby petercu » Fri May 22, 2020 10:50 am

I have plugged unbalanced 1/4 plugs into the output of my usb96, can this damage the unit?
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Re: Ok to plug unbalanced 1/4 plug into the balanced outputs of a Audiobox USB96

Postby Sam Spoons » Fri May 22, 2020 11:12 am

No, it'll be fine.
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Re: Ok to plug unbalanced 1/4 plug into the balanced outputs of a Audiobox USB96

Postby ef37a » Fri May 22, 2020 11:46 am

Sam Spoons wrote:No, it'll be fine.

Agreed, whilst the USB 96 has a balanced line output it is almost certainly of the 'impedance' balanced form and so there is no signal on the ring connection and shorting it to sleeve will cause no problem. Where a line out uses two amplifiers of opposite polarity, shorting the 'cold' side is not recommended. There is very little danger of damage with modern op amps but it does mean one side is driving a very low resistance, could be as low as 47 Ohms and way lower than the IC's specification. Since the output IC is almost certain to be a dual chip, this could put spiky clipping int to the hot side.

The use of impedance balance seems now to be fairly universal since few people need the +26dbu or so headroom the dual amps give, especially us home bods! This not only gives S/C protection but makes it impossible to run with a cable wired wrong polarity.

Beware however of 'modern' headphone outlets! There is a fashion now to design them with a very low source resistance, less than one Ohm in some cases. I am not sure how kindly those amplifiers will take to a short?

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Re: Ok to plug unbalanced 1/4 plug into the balanced outputs of a Audiobox USB96

Postby Sam Spoons » Fri May 22, 2020 1:59 pm

In a strange 'cherry picking' of data Presonus say the OP impedance is 51 ohms balanced but give no further detail. I agree Dave, the chances of them being anything other than impedance balanced outputs is vanishingly small.

The manual is no more forthcoming (more than half of it is concerned with the bundled Studio One software) and while the spec refers to TRS Female Balanced outputs the hook up diagram does not specify TRS cables for connecting the interface to the speakers so they don't seem concerned that TS cables will cause a problem.
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