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Regarding Balanced Signals and the THX AAA 789 + Other Questions

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#1
I asked on Reddit and received somewhat of an answer but I want to cover all of my bases so that I can learn more by asking the question here as well.

From what the user on Reddit posted digital signals cannot be balanced, so we'll start with the DAC. Let's assume the following setup. Computer > Optical connection > Balanced DAC > Balanced connection > Balanced AMP > Balanced connection to cans. At what point in this chain does the balanced signal need to originate? At the DAC? Is the optical signal coming from the computer sufficient enough for the DAC to create a balanced signal all the way to your headphones, assuming the Amp is also balanced.

I'm looking to purchase the THX AAA 789 and combine it with the OL DAC from JDS Labs. I understand the OL DAC is not balanced, but it's a cheap starting point from which I can upgrade from. I also want to purchase western made products and that is why I am not getting something like a Topping or SMSL. My next question regards the THX AAA 789. I've seen mention of it not being fully balanced, what exactly does that mean and does it negatively affect the performance of that Amp?

One more thing, the JDS Labs OL DAC says it uses TOSLINK. I understand TOSLINK is the physical connector, similar to say an RJ45 connector for Ethernet. What isn't stated on their website is what digital audio interconnect the OL DAC uses. Is it S/PDIF? If it doesn't use that particular method of communication what does it use and is it inferior?

Edit: Almost forgot. Does the signal coming from the DAC have to be balanced for me to use the balanced headphone connection on the front of the THX 789 Amp. For example: Computer > Optical Signal > OL DAC > SE Connection > THX AAA 789 > Balanced Connection > Cans. Is this possible? The reason I would want to do this is I understand balanced headphone connection has a much higher power ceiling compared to the SE connections on the front of the Amp.

Thanks in advance!
 
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BoosedElephant
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Thread Starter #2
At the risk of sounding desperate, does no one have an answer? Or can I be pointed in right direction? This thread has over 50 views and no replies.
 

MRC01

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#3
From what the user on Reddit posted digital signals cannot be balanced ...
Many DAC chips (like the WM8741) have separate dedicated pins to provide the reconstructed analog wave as a balanced signal. So you can make a DAC that taps these pins and is balanced all the way through. Or you can make it unbalanced.

... At what point in this chain does the balanced signal need to originate? ...
The balanced signal can originate anywhere. If you're going balanced it's best to do it right off the pins on the DAC chip and keep it balanced through the amp and to the headphones because then there's no conversion. But you can convert unbalanced to balanced and vice versa. I can't think of a good reason to do that. Get high quality gear, use whatever connections they provide and don't worry about it.

My advice is not to put too much emphasis on balanced. It's essential for microphones which have low level signals with long cables traveling through EMF rich environments. It makes less of a different in consumer audio, which has higher level signals and shorter cables.

PS: well engineered DACs show little or no difference in performance with coax, toslink or USB. So just use whatever is convenient to carry the digital signal and don't worry about it.

PPS: if you're worried about headphone amplifier max power output, consider that noise related hearing loss is a real thing. Most amps have more than enough power to drive most headphones to levels that will damage hearing. Balanced theoretically gives you 4x power but not with all amps, and do you really want to use that power? Unless you have some super inefficient headphone like the HiFiMan HE-6, you don't.
 
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BoosedElephant
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Thread Starter #4
PPS: if you're worried about headphone amplifier max power output, consider that noise related hearing loss is a real thing. Most amps have more than enough power to drive most headphones to levels that will damage hearing. Balanced theoretically gives you 4x power but not with all amps, and do you really want to use that power? Unless you have some super inefficient headphone like the HiFiMan HE-6, you don't.
I'll be attaching the THX AAA 789 to a pair of Sennheiser HD600's that I already own. I'm not sure how inefficient they are, I just know they have 300 ohms of resistance. Right now they're connected to a crappy set of Logitech desktop speakers I intend on replacing with Vanatoo T0's using the SE pass-through on the THX 789 AAA. But right now the JDS OL DAC and THX 789 are my next purchase.
 

amirm

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#5
From what the user on Reddit posted digital signals cannot be balanced, so we'll start with the DAC. Let's assume the following setup. Computer > Optical connection > Balanced DAC > Balanced connection > Balanced AMP > Balanced connection to cans. At what point in this chain does the balanced signal need to originate? At the DAC? Is the optical signal coming from the computer sufficient enough for the DAC to create a balanced signal all the way to your headphones, assuming the Amp is also balanced.
I want to make sure a distinction is made:

1. Balanced headphone connection has nothing to do with it being "balanced." All headphone connections are balanced since one end of your headphone is not connected to ground. Balanced option on a headphone amp can simply be thought of providing more power and that is it. If you don't need its extra power, you can use its 1/4 inch or 3.5mm output and be just as well.

2. Balanced input into a headphone amplifier helps break ground loops. These can be nasty and cause problems that are hard to resolve. So if you can, build a balanced system from DAC on.

Note that none of this requires that the electronics inside a device be "balanced."

So answering your question, yes, having optical input a DAC breaks the ground currents from travelling into the DAC. I would do this though if USB creates audible problems, worst of which is hearing the computer activity through your headphones. From there, it does make sense to go XLR balanced connection into THX 789. Whether you use balanced from there to your headphone cans, is up to you. For most headphones and uses, you don't need the extra power but it is there if you need it.
 

amirm

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#6
I'll be attaching the THX AAA 789 to a pair of Sennheiser HD600's that I already own. I'm not sure how inefficient they are, I just know they have 300 ohms of resistance.
I test with the HD-650 and there is plenty of power available using 1/4 cable (i.e. "unbalanced"). So you are good there.
 

amirm

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Edit: Almost forgot. Does the signal coming from the DAC have to be balanced for me to use the balanced headphone connection on the front of the THX 789 Amp. For example: Computer > Optical Signal > OL DAC > SE Connection > THX AAA 789 > Balanced Connection > Cans. Is this possible? The reason I would want to do this is I understand balanced headphone connection has a much higher power ceiling compared to the SE connections on the front of the Amp.
No. The headphone amp creates "differential" outputs which people call balanced from either input.
 
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BoosedElephant
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Thread Starter #8
So answering your question, yes, having optical input a DAC breaks the ground currents from travelling into the DAC. I would do this though if USB creates audible problems, worst of which is hearing the computer activity through your headphones. From there, it does make sense to go XLR balanced connection into THX 789. Whether you use balanced from there to your headphone cans, is up to you. For most headphones and uses, you don't need the extra power but it is there if you need it.
While I have you here, what software type does the OL DAC use to communicate? Is it inferior to, say, S/PDIF? I know certain connection interfaces are limited and can't transmit as high as other types. For instance the OL DAC USB tops out at 96kHz and the optical connections tops out at 192kHz. Is 192kHz sufficient?

Basically, should I at all be concerned about how the OL DAC connects to my PC, are there any concerns with compatibility, etc.
 

amirm

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#9
While I have you here, what software type does the OL DAC use to communicate? Is it inferior to, say, S/PDIF? I know certain connection interfaces are limited and can't transmit as high as other types. For instance the OL DAC USB tops out at 96kHz and the optical connections tops out at 192kHz. Is 192kHz sufficient?
Toslink can indeed be limited to 96 kHz on most devices. That is why I said use USB unless you have a noise issue.
 

amirm

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#10
Basically, should I at all be concerned about how the OL DAC connects to my PC, are there any concerns with compatibility, etc.
Almost all new DACs over USB use Windows built-in "class driver" and should work as is. If you do have an incompatibility and toslink works, then use that.
 

MRC01

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#11
.... Balanced headphone connection has nothing to do with it being "balanced." All headphone connections are balanced since one end of your headphone is not connected to ground. ...
The balanced output is different in that the neg terminal carries a signal that is the inverse mirror image of the pos. Unbalanced neg terminal doesn't carry a signal. Either way, the headphone simply responds to the difference between pos and neg which is twice as big with balanced.
 
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BoosedElephant
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Thread Starter #12
The balanced output is different in that the neg terminal carries a signal that is the inverse mirror image of the pos. Unbalanced neg terminal doesn't carry a signal. Either way, the headphone simply responds to the difference between pos and neg which is twice as big with balanced.
Corpse Cable makes a $60.00 balanced headphone cable for the Sennheiser HD 600. Do you know? If it's a good cable. I don't want to spend The 200 or so dollars Sennheiser charges for their cable.
 

amirm

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#13
The balanced output is different in that the neg terminal carries a signal that is the inverse mirror image of the pos.
The right term is then differential signalling, not balanced. The headphones themselves are never ground referenced in either scenario so they are always balanced in that regard.
 

MRC01

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#14
That's true. Balanced and differential signaling are different things but In audio they are often conflated. Balanced headphone amp outputs are differentially signalled.
 

MRC01

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#15
Corpse Cable makes a $60.00 balanced headphone cable for the Sennheiser HD 600. Do you know? If it's a good cable. I don't want to spend The 200 or so dollars Sennheiser charges for their cable.
My amp is balanced and I use this cable for my HD-580, which use the same pads and cables as your HD-600.
https://www.amazon.com/gp/product/B07M8Z89FJ
You can leave the balanced cable connected all the time, then use this adapter when you need to plug into an unbalanced output
https://www.amazon.com/gp/product/B00KQRN306
Note: this doesn't work the opposite way.
PS: to clarify why this only works 1 way. When the headphone has a balanced cable, the (-) terminals for L and R can be connected to each other and to ground. It doesn't hurt anything because an unbalanced output (-) carries no signal. Now consider the opposite way: a headphone with an unbalanced cable. This cable wires the L and R (-) wires to each other and to the signal ground. A balanced output carries signal on both (+) and (-) terminals. So you can't connect the (-) to ground, else you'll short the amplifier.
So if you have a headphone that you want to use with any amp, whether balanced or not, it's best to wire that headphone with a balanced cable, and have an adapter to connect it to unbalanced amps.
 
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