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Unbalanced outputs to balanced inputs

mandryka

mandryka

pfm Member
I'm using a Quad 520f, a studio amp which expects balanced inputs. My preamp is a Quad 404, which does not have balanced outputs, with the predictable result that the volume / sensitivity of everything have to be turned way up high.

Are there any undesirable consequences from having the amp and preamp controls near to maximum? Is there anything else I can do apart from changing the kit?

I have just one music source - plugged into CD for no reason really. Sounds great!

Short cable runs. Speakers are ESL 63s
 
There advantages to having the controls right up in fact.. or you could remove the balanced input modules from the 520F which is it seems straightforward but I can't tell you how to do it... This should also increase the sound quality as you are removing both a transformer and an op amp from the signal path.
 
Do you have the unused terminal grounded? It usually works better and often gives you more gain depending on the circuit
 
mandryka said:
I'm using a Quad 520f, a studio amp which expects balanced inputs. My preamp is a Quad 404, which does not have balanced outputs, with the predictable result that the volume / sensitivity of everything have to be turned way up high.
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The difference should only be 6 dB.
 
Arkless Repairs said:
There advantages to having the controls right up in fact..
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Indeed.

you could remove the balanced input modules from the 520F which is it seems straightforward but I can't tell you how to do it... This should also increase the sound quality as you are removing both a transformer and an op amp from the signal path.
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That is likely to cause a lower gain - making the problem worse. Do you know the turn ratio on the transformer and the gain of the opamp?
 
Julf said:
Indeed.



That is likely to cause a lower gain - making the problem worse. Do you know the turn ratio on the transformer and the gain of the opamp?
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...or a higher gain... no I don't know the spec for the balanced module. It's not in the manual and there is insufficient info to work it out. It doesn't give a different gain figure for balanced so it may well be the same 35dB as the unbalanced.
It is truly floating with no centre tap so either + or - will need to be grounded.
 
Arkless Repairs said:
It is truly floating with no centre tap so either + or - will need to be grounded.
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Why? The whole point with a truly floating / differential input is that the ground can be kept completely separate from the signal. If the source is unbalanced, "-" will of course be connected to the *source* earth/ground.
 
Julf said:
Why? The whole point with a truly floating / differential input is that the ground can be kept completely separate from the signal. If the source is unbalanced, "-" will of course be connected to the *source* earth/ground.
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Because it would be open circuit otherwise! It's transformer input followed by an op amp.
 
Thanks for all this discussion, a lot of it is more technical than I can appreciate, but you've reassured me about keeping the controls turned up high.
 
Arkless Repairs said:
No! The input TX is not centre tapped.
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What has that to do with it? What you have is basically this situation:

n110fig2.png
 
If you use pin 1 and pin 3 for the input or pin 1 and pin 2 (changes absolute phase of course) no current can flow in the TX unless you also connect whichever of the unused pins, 2 or 3 to ground. If the TX had a grounded centre tap it would not matter.
 
Arkless Repairs said:
If you use pin 1 and pin 3 for the input or pin 1 and pin 2 (changes absolute phase of course) no current can flow in the TX unless you also connect whichever of the unused pins, 2 or 3 to ground. If the TX had a grounded centre tap it would not matter.
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But you don't. The input pins are pins 2 and 3. 1 is ground/chassis. So your cable should, at the (unbalanced) source end, connect "hot" to pin 2 and "neutral" to pin 3 (or the other way around if you want reverse phase).
 
If wired like that then yes but often people will use ground and ether - or + leaving the other open circuit. In this case this would not work. That is what I'm getting at..
 
Arkless Repairs said:
If wired like that then yes but often people will use ground and ether - or + leaving the other open circuit. In this case this would not work. That is what I'm getting at..
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OK, happy to agree that if people connect up their gear wrong, it won't work. :)
 
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