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Old 22nd July 2010, 09:32 AM   #1
teleman is offline teleman  Norway
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Default Active balanced line output

Hi All,
I came across this old Neve 1272 active balanced balanced output schematic and would appreciate if anyone/someone could answer the following:

1.What should be the resistor values for +/-12v dc?

2.How are these resistor values calculated?

3.What would be the gain of this circuit?

4.Would changing any Cap. values improve it's performance or specification?

I didn't quite understand the topology, so any help/advice to educate myself & improve my knowledge would be of immense help to me!

Thanks.
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Last edited by teleman; 22nd July 2010 at 09:54 AM.
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Old 22nd July 2010, 09:45 AM   #2
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Quote:
Originally Posted by teleman View Post
so any help/advice to educate myself & improve my knowledge would be of immense help to me!



This is all basic textbook stuff. Have you considered opening a book and getting the answers on your own? It will probably take 20-30 min but in the long term is a much better idea than getting pre-digested replies on forums.
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Old 22nd July 2010, 09:52 AM   #3
teleman is offline teleman  Norway
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Oops!

Last edited by teleman; 22nd July 2010 at 09:56 AM.
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Old 22nd July 2010, 10:00 AM   #4
AndrewT is offline AndrewT  Scotland
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I will add one comment.
Notice the proliferation of 5k1

Now a question: would changing all the resistors to 10k make any difference?
Now change all the resistors to 100r. Does that change make any difference?

Finally, are all the 5k1 the same measured value?
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Old 22nd July 2010, 11:01 AM   #5
teleman is offline teleman  Norway
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Well,I don't know what this schematic configuration is called..that's my confusion!

AndrewT It doesn't say if it's measured or actual values.Here's the link to the whole article:

Neve 1272 Preamp

Last edited by teleman; 22nd July 2010 at 11:11 AM.
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Old 22nd July 2010, 11:57 AM   #6
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Originally Posted by teleman View Post
Well,I don't know what this schematic configuration is called..that's my confusion!


A basic opamp differential amp x 2
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Old 22nd July 2010, 05:36 PM   #7
AndrewT is offline AndrewT  Scotland
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you have a lot of homework:

D.Self
ESP
Rane
Jensen

for starters.
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Old 22nd July 2010, 05:59 PM   #8
teleman is offline teleman  Norway
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Thank you Sir,hope I'll pass the test with flying colours when I come back in autumn!
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Old 22nd July 2010, 09:55 PM   #9
DF96 is offline DF96  England
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Most of the resistor values probably were not calculated, they just need to be the same. Any error reduces balance - unlike a transformer. If 1% resistors are used and you are unlucky, then the output balance could be out by up to 8%. The description of this circuit confuses balance with gain - it has a gain of 6dB because it is a x2 amplifier, not because it has a balanced output.

In order to 'improve' this circuit you would need to decide what aspects of its performance you wanted to change, which might depend on what you were intending to use it for.
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Old 22nd July 2010, 11:04 PM   #10
teleman is offline teleman  Norway
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Thank you indeed DF96, for the invaluable piece of info & advice!

It is for an acoustic guitar blender preamp. I've already constructed a unit with the a balanced output derived from single-ended output with a resistor/capacitor divider network as described in the Jensen pages. However,I cannot use both outs at the same time due to the nature of this particular circuit.That is why I've opted for this differential circuit instead.

I don't need much gain as not to create feedback,noise etc, besides + 6dB from this balanced config; is more than adequate for my needs. I just need a good balanced signal to drive long cables & clean,undistorted sound to the mixer or similar for live & recording.

Would very closely matched 1% metal film res.still result in such a large discrepancy in balance?

Taking AndrewT's cue I've already started reading on the subject,but most of the designs are variations on this one...I'll just have to keep reading !

Thanks!

Last edited by teleman; 22nd July 2010 at 11:09 PM.
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