Hello guys, I am currently trying to learn to design audio electronics.. only been at it for a few months so go easy xD
At this moment I am trying to design a simpel Single Ended(SE from now on) to Balanced(BAL from now on)/SE converter with adjustable gain. I understand the basic theory and how it works, but I need some clarification on the specific terminology used in analog line level in order to get my silkscreen and resistor values for the gain correct...
Sorry for this stupid question.. I have tried to google my way to this simple answer, but I got very confused and need someone who knows what they are talking about to tell me if I got it right.
At this moment I am trying to design a simpel Single Ended(SE from now on) to Balanced(BAL from now on)/SE converter with adjustable gain. I understand the basic theory and how it works, but I need some clarification on the specific terminology used in analog line level in order to get my silkscreen and resistor values for the gain correct...
- When looking at a SE signal with a RMS voltage of 2.1Vrms (output of my PCM5102) this equals 5.9Vp-p, meaning I would measure from +2.97V to -2.97V on the signal line with respect to signal GND correct?
I used this calculator/formula: https://www.omnicalculator.com/physics/rms-voltage - If looking at a BAL signal with a RMS voltage of 2.1Vrms would this mean that each signal line is 2.1Vrms/5.9Vp-p as with the SE and after a summing opamp I will have a SE signal of 4.2Vrms/11.8Vp-p?
Or will each line have half the voltage swing of 1.05Vrms/2.97Vp-p to end up as a 2.1Vrms/5.9Vp-p single ended signal after a summing opamp?
Sorry for this stupid question.. I have tried to google my way to this simple answer, but I got very confused and need someone who knows what they are talking about to tell me if I got it right.
1. Yes. Vpp = 2 x sqrt2 xVrms.
2. Balanced 2.1V is 1.05V if referred to ground for each side. (both having same units)
2. Balanced 2.1V is 1.05V if referred to ground for each side. (both having same units)
1/ Correct. You multiply the the rms value by root 2 (1.414) to get the peak level.
2/ I believe it is measured between hot and cold rather than ground referenced, which is the opposite of what Rayma thinks 🙂 I think you would see half the voltage as measured between ground and hot and ground and cold.
2/ I believe it is measured between hot and cold rather than ground referenced, which is the opposite of what Rayma thinks 🙂 I think you would see half the voltage as measured between ground and hot and ground and cold.
Thanks guys!
Okay so if I look at each line of the balanced they individuallly swing 2.97Vp-p. but when one is fully positive the other is fully negative giving a total of 5.9Vp-p?
Okay so if I look at each line of the balanced they individuallly swing 2.97Vp-p. but when one is fully positive the other is fully negative giving a total of 5.9Vp-p?
Yes they do 🙂 and there is no room for error with that but I was thinking about a spec that reads say '2 volts rms balanced output'. I would take that to mean 2 volts rms between the signal leads and without reference to ground. Measured from ground you would see 1v rms on each line with a 180 degree phase shift between the two.
... for a sine wave. And some other waveforms too, but not for every waveform.
1.0 V RMS is one volt root-mean-squared. 1 V RMS single-ended is one volt RMS. 1 V RMS balanced is one volt RMS. There's nothing magic about it. 1 V = 1 V.
A 1 V single-ended sine wave will have an amplitude of 1.41 (= 1 * sqrt(2)) volt, peak. That's 2.82 V = 2 * 1 * sqrt(2) volt peak-to-peak.
A 1 V differential or balanced sine wave will have an amplitude of 1.41 (= 1 * sqrt(2)) volt, peak. That's 2.82 V = 2 * 1 * sqrt(2) volt peak-to-peak.
A 1 V (peak) amplitude, single-ended square wave with a duty cycle of 25 % will have an RMS value of 1*sqrt(0.25) = 0.5 V RMS.
A 1 V (peak) amplitude, balanced square wave with a duty cycle of 25 % will have an RMS value of 1*sqrt(0.25) = 0.5 V RMS.
I think the confusion arises because a common way of generating a balanced output is to invert a single-ended output and using the single-ended output as V+ and the inverted output as V-. That sets up a gain of 2 V/V (= 6 dB). This does not mean that all balanced outputs do this.
Tom
Here's a good summary of the RMS value for various waveforms: https://web.eecs.utk.edu/~dcostine/ECE482/materials/AppendixA.pdf
Tom
Tom
Thanks guys! Then I did understand it correctly. Good to get that straight.
Next question. I use a OPA1632 to convert the SE signal to balanced by grounding the negative input and inputting the SE signal on the positive input. Both positive and negative outpouts are connected back to opposite input with gain resistors as pr datasheet.
Given a SE signal of 2Vrms (5,6Vp-p) applied to the positive input I would expect both of the outputs of the opa1632 to output a voltage swing of 5.6Vp-p as to keep inputs and outputs equal (with a gain of 1 of course). Is this corect? It would result in a 4Vrms BAL output then?
Alternatively if the opa1632 is givien a BAL input of 4Vrms(5.6Vp-p on eqach line) instead of the SE input. Then the output of the OPA1632 will still be 5.6Vp-p on each line maintaining the 4Vrms outout?
Or does the OPA1632 take the difference of the inputs and thus only outputs half the voltage for SE input?
Bonus question: For the SE input the negative input is GND, so why would the positive output (connected with feedback) be anything else than GND? I asume the opa1632 just works a bit different than a classic opamp?
Thanks again!
Next question. I use a OPA1632 to convert the SE signal to balanced by grounding the negative input and inputting the SE signal on the positive input. Both positive and negative outpouts are connected back to opposite input with gain resistors as pr datasheet.
Given a SE signal of 2Vrms (5,6Vp-p) applied to the positive input I would expect both of the outputs of the opa1632 to output a voltage swing of 5.6Vp-p as to keep inputs and outputs equal (with a gain of 1 of course). Is this corect? It would result in a 4Vrms BAL output then?
Alternatively if the opa1632 is givien a BAL input of 4Vrms(5.6Vp-p on eqach line) instead of the SE input. Then the output of the OPA1632 will still be 5.6Vp-p on each line maintaining the 4Vrms outout?
Or does the OPA1632 take the difference of the inputs and thus only outputs half the voltage for SE input?
Bonus question: For the SE input the negative input is GND, so why would the positive output (connected with feedback) be anything else than GND? I asume the opa1632 just works a bit different than a classic opamp?
Thanks again!
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Hi,
no: in a symetrical drive ( balanced is a misnomer, it is related to balanced impedance to ground, which is not mandatory achieved through symmetrical drive and is related to noise in the relation between line driver and receiver, see bill Whitlock articles related to this at Jensen-Transformers site if you want to go deeper ) the resulting ouput voltage is from the difference between both side ( +/-) not relative to ground as in an asymetrical drive ( 'SE').
As such you have same voltage out as asymetrical ('SE') in both side of a symetrical drive ('bal' +/-), and so the resulting difference is equal to 2x the value of an asymetrical drive.
EG:
_asymetrical +2vrms
_symetrical (+2vrms) - (-2vrms) = 4vrms
All other things being equal, symmetrical drive is +6db louder ( or have +6db more headroom) than an asymetrical drive.
no: in a symetrical drive ( balanced is a misnomer, it is related to balanced impedance to ground, which is not mandatory achieved through symmetrical drive and is related to noise in the relation between line driver and receiver, see bill Whitlock articles related to this at Jensen-Transformers site if you want to go deeper ) the resulting ouput voltage is from the difference between both side ( +/-) not relative to ground as in an asymetrical drive ( 'SE').
As such you have same voltage out as asymetrical ('SE') in both side of a symetrical drive ('bal' +/-), and so the resulting difference is equal to 2x the value of an asymetrical drive.
EG:
_asymetrical +2vrms
_symetrical (+2vrms) - (-2vrms) = 4vrms
All other things being equal, symmetrical drive is +6db louder ( or have +6db more headroom) than an asymetrical drive.
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2 V RMS = 2 V RMS. It doesn't matter if it's measured with respect to ground (as for single-ended) or from V+ to V- in a differential pair.
Unity gain is exactly that. Unity gain. A gain of 1 V/V or 0 dB. One volt in -> one volt out. So if you put one volt into the OPA1632 and have it set up for unity gain you will get one volt out. If you put two volt in you'll get two volt out.
You can convince yourself pretty easily of this by running a simulation.
Tom
No it is not.
You're right that a balanced drive will have 6 dB higher headroom but a balanced transmitter with unity gain will output 1 V RMS if you put 1 V RMS into it. In that scenario you will measure 0.5 V RMS from V+ to ground and V- to ground in the differential pair.
Tom
What you were asking at the beginning is effectively what you would expect to see based on a written specification. If you measure 2v rms then of course it is 2v rms. Its an absolute measurement. You may or may not have expected that result though.
If I say this balanced audio output puts out 2v rms then without measuring we can say it means it puts out 2vrms as would be measured between the hot and cold lines and you would then see 1v rms between ground and hot and also 1v rms between ground and cold.
If I say this balanced audio output puts out 2v rms then without measuring we can say it means it puts out 2vrms as would be measured between the hot and cold lines and you would then see 1v rms between ground and hot and also 1v rms between ground and cold.
Damn, you are right, i made same shortcut as Rayma it seems... 🙂
@DannerD3H , please don't use 'balanced' for symmetrical... this will only confuse you in the long term and others too.
The confusion in the terminology doesn't help. Here's how I have come to understand it:
Differential: The signal is between a signal PAIR that could be floating at any voltage. All we care about is the difference between the two conductors in the pair. All fine and good, except reality gets in the way. Differential receivers have common-mode requirements. This is true even for transformers. Their dielectric only goes so high. So the signal pair can't float at any voltage, but it can float within the common-mode voltage range of the receiver.
Balanced: This really refers to balanced impedances. A differential source will also be a balanced source, but the inverse is not always true. For example, you could create a balanced output simply by connecting VP (or 'hot') to a single-ended output with, say, 50 Ω output impedance and connecting VN (or 'cold') to ground through a 50 Ω impedance. Then you'll have a balanced output. It still won't be differential, but it will be balanced.
Single-ended: The output is referenced to ground, so it's the voltage between the signal conductor and ground that a single-ended receiver cares about.
Unbalanced: To me, this is synonymous with single-ended. Though, I suppose it could also refer to a differential connection with unequal impedances in VP and VN. The only time I've seen a deliberate imbalance between impedances like that is for CMRR testing where an imbalance of a few tens of ohm is often introduced.
It doesn't help that everybody, including me, uses the terminology willy-nilly. Audio Precision, for example, uses 'balanced' and 'unbalanced' for their differential XLR output and single-ended BNC output on their analyzers. It gets even more fun on the digital side where they use the term 'digital unbalanced' to mean the BNC S/PDIF output even though I bet it's actually a balanced output (transformer-coupled).
Just one of them things. 🙂
Tom
Differential: The signal is between a signal PAIR that could be floating at any voltage. All we care about is the difference between the two conductors in the pair. All fine and good, except reality gets in the way. Differential receivers have common-mode requirements. This is true even for transformers. Their dielectric only goes so high. So the signal pair can't float at any voltage, but it can float within the common-mode voltage range of the receiver.
Balanced: This really refers to balanced impedances. A differential source will also be a balanced source, but the inverse is not always true. For example, you could create a balanced output simply by connecting VP (or 'hot') to a single-ended output with, say, 50 Ω output impedance and connecting VN (or 'cold') to ground through a 50 Ω impedance. Then you'll have a balanced output. It still won't be differential, but it will be balanced.
Single-ended: The output is referenced to ground, so it's the voltage between the signal conductor and ground that a single-ended receiver cares about.
Unbalanced: To me, this is synonymous with single-ended. Though, I suppose it could also refer to a differential connection with unequal impedances in VP and VN. The only time I've seen a deliberate imbalance between impedances like that is for CMRR testing where an imbalance of a few tens of ohm is often introduced.
It doesn't help that everybody, including me, uses the terminology willy-nilly. Audio Precision, for example, uses 'balanced' and 'unbalanced' for their differential XLR output and single-ended BNC output on their analyzers. It gets even more fun on the digital side where they use the term 'digital unbalanced' to mean the BNC S/PDIF output even though I bet it's actually a balanced output (transformer-coupled).
Just one of them things. 🙂
Tom