Balanced Output Gain

[4pyros]

I need to up the gain of the output from a Gemini CDMP-1400 Player. It came with XLR outputs that should supply +4dbV, but uses the same level as a Unbalanced output -10dbV. I think all I need to change is one resistor but what would the right value be?

 

[ericgibbs]

I need to up the gain of the output from a Gemini CDMP-1400 Player. It came with XLR outputs that should supply +4dbV, but uses the same level as a Unbalanced output -10dbV. I think all I need to change is one resistor but what would the right value be?

hi,
The gain of the 1st stage non inverting is *2 and the 2nd buffer inverting stage is *-1.
If you increased the marked 10K to say 20k, this would give a gain of *3.

The gain for a non inverting stage is G= 1 + [Rf/Rin]

 

[4pyros]

If you increased the marked 10K to say 20k, this would give a gain of *3.

Thats what I thought and I should not have to do anything with the 2nd stage, right?

 

[Nigel Goodwin]

Thats what I thought and I should not have to do anything with the 2nd stage, right?

No, just ignore it - however, the single ended output shouldn't be much lower than the balanced output, and certainly not only -10dB.

It should work perfectly fine without needed any modification.

 

[4pyros]

however, the single ended output shouldn't be much lower than the balanced output, and certainly not only -10dB.

Sorry Nigel; you lost me on this one. Did you mean the input to the output stage?

 

[Nigel Goodwin]

Sorry Nigel; you lost me on this one. Did you mean the input to the output stage?

You said in the first post that the balanced output was +4dB, and using it as unbalanced was -10dB, this shouldn't be so, the unbalanced output should be close enough not to require any modification - it only loses 6dB (giving -2dB).

 

[4pyros]

You said in the first post that the balanced output was +4dB

No I said it should be +4dbV.

and using it as unbalanced was -10dB

No the balanced output is only -10dBV. This output will not fully drive the input to a Behringer dcx2496. It needs to be +4dbV.

the single ended output shouldn't be much lower than the balanced output, and certainly not only -10dB

The two outputs are at the same level -10dBV. It is not shown in the diagram but the unbalanced output is taken off the output from the 1st op amp.
Hope that explains it. Andy

 

[Nigel Goodwin]

No I said it should be +4dbV.

No the balanced output is only -10dBV. This output will not fully drive the input to a Behringer dcx2496. It needs to be +4dbV.

The two outputs are at the same level -10dBV. It is not shown in the diagram but the unbalanced output is taken off the output from the 1st op amp.
Hope that explains it. Andy

The spec on the Behringer doesn't give the sensitivity, only a maximum of +22dB - however, it does say that all inputs and outputs are balanced, as you would expect.

So why the problem?.

But if you want to increase the output, increase the marked resistor - try something like a 56K for a start.

 

[4pyros]

So why the problem?.

An input of only -10dBV to the DCX will only drive the input to about 1/3 of max at the most.
You should have at least 3/4 of max input on the DCX so as not to loose bits in the A to D convershoin.
Andy

 

[4pyros]

I will try and change the resistor today. I will srart with a pot and then put in a fixed resistor.

 

[ericgibbs]

I will try and change the resistor today. I will srart with a pot and then put in a fixed resistor.

If you must use a pot, keep the fixed 10k in circuit at one end and connect the pot in series with the 10K

 

[4pyros]

If you must use a pot, keep the fixed 10k in circuit at one end and connect the pot in series with the 10K

Thanks I will do that.

 

[4pyros]

But if you want to increase the output, increase the marked resistor - try something like a 56K for a start.

56K worked perfectly. Thanks All Andy