Adding DRV134 balanced circuit to the preamp. - diyAudio
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Old 30th December 2014, 01:05 PM   #1
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Default Adding DRV134 balanced circuit to the preamp.

Hey guys so recently I have completed my build on the ina217 preamp.
I am now considering adding a unbalance to balance circuit using a DRV134 chip.

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However I am not sure if there are anything good on doing this. From what I understand a fully balanced preamp. The hot and cold signal should be amplify by different opamp. Obviously INA217 have converted the mic signal into a unbalanced one. It is too stupid to convert it back into balanced signal using DRV134? Will it consider to be a 'fake balanced" signal?

If not. Will the quality of the sound increase if balanced circuit is added?
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Old 30th December 2014, 01:57 PM   #2
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Quote:
Originally Posted by nguitar12 View Post
Obviously INA217 have converted the mic signal into a unbalanced one. It is too stupid to convert it back into balanced signal using DRV134? Will it consider to be a 'fake balanced" signal?
I wouldn't call it "fake" as practically all pro audio gear works like this. The I/O is balanced, but the internal signal path is single-ended. To me it makes more sense than the high-end hifi practice of keeping the signal path balanced throughout, using twice the amount of electronics.

The DRV134 will help break ground loops and drive long cables, but it will introduce a tiny bit of distortion that is probably not audible. It may also give you another 6dB of headroom if you are driving another piece of pro equipment with a balanced input.
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Old 30th December 2014, 02:31 PM   #3
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Originally Posted by scopeboy View Post
I wouldn't call it "fake" as practically all pro audio gear works like this. The I/O is balanced, but the internal signal path is single-ended. To me it makes more sense than the high-end hifi practice of keeping the signal path balanced throughout, using twice the amount of electronics.

The DRV134 will help break ground loops and drive long cables, but it will introduce a tiny bit of distortion that is probably not audible. It may also give you another 6dB of headroom if you are driving another piece of pro equipment with a balanced input.
I am not sure because generating a balanced signal from unbalanced one just feel like encoding a 320kps mp3 from a 128kps one. Will it be a good comparison?

And yes I am using this preamp on a recorder with balanced XLR input. However the length will not be too long probably 2-3m in total. Do you recommend adding a balanced circuit? Will the sound quality increase or decrease?

Last edited by nguitar12; 30th December 2014 at 02:40 PM.
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Old 30th December 2014, 03:25 PM   #4
sangram is offline sangram  India
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Quote:
Originally Posted by nguitar12 View Post
I am not sure because generating a balanced signal from unbalanced one just feel like encoding a 320kps mp3 from a 128kps one. Will it be a good comparison?
No. You imply that unbalanced in lower quality than balanced, which is not necessarily true. You do get 6dB extra SNR, but that is 'free' when you double the signal.

Balanced is designed for long cable runs and not really a requirement for electronics within the equipment. If your signal path and layout is properly designed there is no need to stay balanced internally.

If you're feeling squeamish you can design a fully balanced discrete stage....

And if you do need a balanced output you can try the cheap trick using 1R+1C to ground on the cold output.

The DRV does not break ground loops, AFAIK. It needs a supply voltage and if that is shared with the source, the original loop still exists unless you do not use pin 1 at the receiver end.

For your purpose staying balanced will help consistency of cabling etc, so if you do later replace preamps there would be no need to change cables. That might be a more important consideration for studio than sound 'quality'. I am assuming this is a professional or semi-pro setup?
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Old 30th December 2014, 03:55 PM   #5
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OK, the DRV134 doesn't break ground loops. What I should have said is that the balanced connection rejects hum from ground loops because the cable shield is no longer part of the signal path. You can connect pin 1 at both ends (directly to the chassis- google pin 1 problem) and still not be bothered by ground loops.
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Last edited by scopeboy; 30th December 2014 at 03:58 PM.
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Old 30th December 2014, 04:07 PM   #6
AndrewT is offline AndrewT  Scotland
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or use a chip that has IN and OUT that are balanced.

Where is your gain? Is it inside the ina217?
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Old 31st December 2014, 01:44 AM   #7
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Quote:
Originally Posted by sangram View Post
No. You imply that unbalanced in lower quality than balanced, which is not necessarily true. You do get 6dB extra SNR, but that is 'free' when you double the signal.

Balanced is designed for long cable runs and not really a requirement for electronics within the equipment. If your signal path and layout is properly designed there is no need to stay balanced internally.

If you're feeling squeamish you can design a fully balanced discrete stage....

And if you do need a balanced output you can try the cheap trick using 1R+1C to ground on the cold output.

The DRV does not break ground loops, AFAIK. It needs a supply voltage and if that is shared with the source, the original loop still exists unless you do not use pin 1 at the receiver end.

For your purpose staying balanced will help consistency of cabling etc, so if you do later replace preamps there would be no need to change cables. That might be a more important consideration for studio than sound 'quality'. I am assuming this is a professional or semi-pro setup?
Changing a cable is not a big deal. I don't have a studio with complicated setup. I would rather keep the signal as original as possible.
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Old 31st December 2014, 01:45 AM   #8
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Quote:
Originally Posted by scopeboy View Post
OK, the DRV134 doesn't break ground loops. What I should have said is that the balanced connection rejects hum from ground loops because the cable shield is no longer part of the signal path. You can connect pin 1 at both ends (directly to the chassis- google pin 1 problem) and still not be bothered by ground loops.
Sorry I am not a professional in this but what do you mean by the ground loops? So adding a balanced connection is good in this case?
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Old 31st December 2014, 01:47 AM   #9
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Originally Posted by AndrewT View Post
or use a chip that has IN and OUT that are balanced.

Where is your gain? Is it inside the ina217?
I wonder if this chip is exist. The gain controlled by a resistor across pin 1 and 8. Which doesn't show in the schematic.
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Old 31st December 2014, 02:37 AM   #10
sangram is offline sangram  India
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Quote:
Originally Posted by scopeboy View Post
You can connect pin 1 at both ends (directly to the chassis- google pin 1 problem) and still not be bothered by ground loops.
Some equipment with XLR input connectors do not have actively balanced receiving circuitry and connect Pin 1 to audio ground as a reference for the input signal. This severely impacts performance and could actually be worse than running unbalanced.

That is what I meant by 'using' pin 1.

Quote:
I would rather keep the signal as original as possible.
The use the pseudo-balanced arrangement shown on the ESP site and other places. It uses no active circuitry, and creates a properly balanced signal.

Last edited by sangram; 31st December 2014 at 02:41 AM.
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