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.
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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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.
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?
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?
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
AndrewT It doesn't say if it's measured or actual values.Here's the link to the whole article:
Neve 1272 Preamp
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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.
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.
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!
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!
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Wow! so many interesting projects!, but why have you chosen LF411 JFETs over BJT devices?,especially on an output stage! Any special reason?
I understand,JFETs especially, TL0xx,LF411,LFxx series are not suitable for driving capacitive loads,as they become very unstable!
Comparing just 3 parameters of both LF411 & NE5532:
LF411 NE5532
SR 15 8
GBW 4 10
en 25nV! 8nV
It's apparent that the NE5532 is a far better candidate than LF411! or any other JFET device for this particular job.The very high noise figure of the LF411 alone would render it unsuitable for any high quality audio, I would imagine.
NE5532 on the other hand can drive reasonably low loads in addition to it's
rather musical & clean sound!
It appears,that on these differential balanced line output circuits, the R values have some relationship to the supply voltage as well. ie: higher the voltage higher the R ?
Is there any other specific reason for choosing these R values?
I understand,JFETs especially, TL0xx,LF411,LFxx series are not suitable for driving capacitive loads,as they become very unstable!
Comparing just 3 parameters of both LF411 & NE5532:
LF411 NE5532
SR 15 8
GBW 4 10
en 25nV! 8nV
It's apparent that the NE5532 is a far better candidate than LF411! or any other JFET device for this particular job.The very high noise figure of the LF411 alone would render it unsuitable for any high quality audio, I would imagine.
NE5532 on the other hand can drive reasonably low loads in addition to it's
rather musical & clean sound!
It appears,that on these differential balanced line output circuits, the R values have some relationship to the supply voltage as well. ie: higher the voltage higher the R ?
Is there any other specific reason for choosing these R values?
Why make this so complicated?
You can find one stop shopping here:
http://focus.ti.com/lit/ds/symlink/drv134.pdf
-Charlie
You can find one stop shopping here:
http://focus.ti.com/lit/ds/symlink/drv134.pdf
-Charlie
Still reluctant to open a book, hey?
Had a second look at your circuit and it appears to have been drawn wrongly: positive and negative opamp inputs are interchanged.
As for the resistor values, they bear almost no relationship to supply voltage. The resistors on the input are responsible for input impedance and cannot be too low for the sake of the previous stage. The resistors at output/feedback load the output of the opamp and similarly should not be too low in value depending on the current capabilities of the opamp. All resistors should not be too high in value as they contribute to noise.
As for the LF411, it used to be popular in servos in the eighties but today there are much better performing opamps even in this position. I don't see any reason to use it anywhere in audio.
Sorry, I miscalculated. 1% resistors could cause up to 6% imbalance, not 8%. It probably won't be this bad if all the resistors come from the same batch, and I believe that input balance is more important than output balance for reducing noise and interference on long cable runs. Actually, the inputs to this circuit are more-or-less balanced too even though the diagram describes them as unbalanced.
resistor matching isn't important. The usual 1% will do fine, as there is no common mode signal to suppress and a slight +/- line imbalance is of no consequence.
The transformer like behaviour of sophisticated circuits is not always needed and not provided by that "Neve 1272 active balanced balanced output schematic" anyway.
regards
me would use a simple combination of inverting and noninverting circuit to convert a unbalanced to balanced signal.
The transformer like behaviour of sophisticated circuits is not always needed and not provided by that "Neve 1272 active balanced balanced output schematic" anyway.
regards
Given how much stuff Jung has written I think you will need to be a little more specific! In any case, it's not my circuit; I am merely trying to be helpful.
Thanks for the nice comments.
Ignore the LF411, that's just the model that was in the simulation software. I recommend the use of OPA2134 devices. I must update the schematic and component layout.
The value of R's is not at all related to the supply voltage, it is purely to set the designers chosen input impedance and gain.
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