Balanced Line Output from MiniDSP 2x4HD (help!)

[aasearles]

Having a problem with my first balanced set-up and could use some advice from the more experienced folks.

I have a Loxjie P20 headphone amp, which features balanced XLR 3-pin inputs and balanced 4-pin output. I'd like to feed the balanced inputs by fabbing a custom cable and driving with a MiniDSP 2x4HD that I'm told can be configured for balanced output.

Essentially, the MiniDSP's 4 RCA outputs would be configured this way (#1 and #3 are inverted):
#1 Out: Left channel (-) cold
#2 Out: Left channel (+) hot
#3 Out: Right channel (-) cold
#4 Out: Right channel (+) hot

MiniDSP development team says the configuration (and wiring below) should work.

My custom cable consists of 4 RCA plugs from the MiniDSP outs to 2 XLR 3-pin connectors, like this:

I've triple checked the wiring for both cables is as described above. I think this should be correct, but this is my first adventure in balanced cabling.

The problem is, when I switch the Loxjie P20 to balanced input mode, it's acting (in my opinion) as single-ended. Here are the symptoms:

For either L/R channel, if I pull either of the "cold" RCA plugs (#1 or #3) there this no audible change. It's as if they're not contributing to the input.

In the MiniDSP configuration, if I mute, non-invert, or change levels for the same plugs #1 or #3, there is no audible change.

Have verified the MiniDSP is outputting signal from both the #1 and #3 RCAs.

Conversely, if I mute, invert, change levels, or pull plugs for either if the "hot" RCA outputs (#2 or #4), I can hear the expected audible results.

If I pull all RCA plugs (leaving input XLRs connected), touching either of the hot RCA plugs creates hum. Touching the cold RCA plugs makes no sound.

It's as if the amp is operating in single-ended mode using the balanced inputs.

Trying to decide if the amp has a fault, or is my wiring the problem?

Is there a way to easily test the balanced inputs are working?

Thanks in advance for any help.

 

[DanielT]

I see you haven't received an answer yet. Some tips/links. Please note this is general information only. Hopefully someone will help you with your concrete thoughts, regarding your case. Your specific thoughts on how to connect your things:

Balanced and unbalanced circuits can be interfaced by the use of a balun, often through a DI unit (also called a "DI box" or "direct box").

As a last resort a balanced audio line can be fed into an unbalanced input and vice versa as long as the electronic design used for the output stage is known. In the case of balanced output to unbalanced input, the negative output can be tied to ground, but in certain cases the negative output should be left disconnected.[4]

Balanced audio - Wikipedia

en.wikipedia.org

A DI unit (direct input or direct inject) is an electronic device typically used in recording studios and in sound reinforcement systems to connect a high-output impedance, line level, unbalanced output signal to a low-impedance, microphone level, balanced input, usually via an XLR connector and XLR cable. DIs are frequently used to connect an electric guitar or electric bass to a mixing console's microphone input jack. The DI performs level matching, balancing, and either active buffering or passive impedance matching/impedance bridging to minimize unwanted noise, distortion, and ground loops. DI units are typically metal boxes with input and output jacks and, for more expensive units, “ground lift” and attenuator switches.

DI unit - Wikipedia

en.wikipedia.org

A balun /ˈbælʌn/ (from "balanced to unbalanced", originally, but now dated from "balancing unit")[1] is an electrical device that allows balanced and unbalanced lines to be interfaced without disturbing the impedance arrangement of either line.[2] A balun can take many forms and may include devices that also transform impedances but need not do so. Sometimes, in the case of transformer baluns, they use magnetic coupling but need not do so. Common-mode chokes are also used as baluns and work by eliminating, rather than rejecting, common mode signals.

Balun - Wikipedia

en.wikipedia.org

What’s the Difference Between Balanced and Unbalanced? : Aviom Blog

www.aviom.com

 

[DanielT]

Hm, so the wiring diagram is this and:

The MiniDSP development team says the configuration (and wiring below) should work.

should...not that it will work? Have you asked the people at Loxjie if they think it will, should, work?

Nothing wrong with the cables?Faulty contacts, bad soldering or something like that? Are you able to check that, perhaps measure with a multimeter?
Or test the cables on some other gadgets and see if they work properly?

 

[antcollinet]

Hi

Your testing for noise by touching the RCA certainly suggests the amp is not using the cold input.

Are you listening from the balanced or unbalanced output of the amp? If the unbalanced, is it possible that only hot signal of the balanced input is sent to the unbalanced output?

IE do the balanced inputs only work balanced for the balanced output?

 

[Sokel]

Can we see the miniDSP configuration?Are all channels mapped properly?

 

[solderdude]

The P20 may only be balanced in when using balanced outputs (so 4 separate amplifiers).
In that case, when using SE out only the RCA inputs (or + inputs of balanced inputs) are used and - input could be ignored (only goes to - out of balanced out)

If not then balanced would be made SE inside the amp and become balanced out both with SE and balanced in.

Maybe this is the case (not seen a schematic)

 

[DanielT]

Balanced within PA. Lots of gadgets, long cable lengths. Totally reasonable.
Unbalanced for home HiFi. In any case, it was like that not so long ago, but now when various gadgets have to be plugged into the audio chain, DACs, DSPs, several different amplifiers to drive different speaker elements and so on.

This with balanced for home HiFi seems to be unclear. I myself am confused. It's not an end in itself to run balanced for home HiFi, is it?

Mixing unbalanced and balanced, isn't that asking for trouble? Or? I could be wrong.

 

[sam_adams]

@aasearles, have you tried simply switching the output cables of the MiniDSP: 1-to-2 and 2-to-1, to see what happens?

 

[antcollinet]

I've just noticed we are answering a question from more than a year ago.

OP hasn't been on the site since May.

I think we are wasting our time here

 

[DanielT]

I've just noticed we are answering a question from more than a year ago.

OP hasn't been on the site since May.

I think we are wasting our time here

Ooops. Sorry, excuse me! OP wrote 2021! Missed that. In any case, others who are curious may have read this thread by now.

Create this now, 2022, today's date:

Mixing unbalanced and balanced, isn't that asking for trouble?

Or? Considering this thread: https://audiosciencereview.com/forum/index.php?threads/balanced-line-output-from-minidsp-2x4hd-help.24439/ To the overall, general questions: When, how and why mix balanced with unbalanced? In general, what should you think about when are you going ( if are you...

audiosciencereview.com

 

[aasearles]

Thank you DanielT for reviving this thread, and to the others who've replied - I sincerely appreciate it! Now I'll work through and give some responses.

Balanced and unbalanced circuits can be interfaced by the use of a balun, often through a DI unit (also called a "DI box" or "direct box").

Thanks for this info. If I can't achieve balanced (differential) output through the use of this miniDSP unit on it's own, I might look into one of these options to isolate the RCA outputs before sending to the P20 amp.

As a last resort a balanced audio line can be fed into an unbalanced input and vice versa as long as the electronic design used for the output stage is known. In the case of balanced output to unbalanced input, the negative output can be tied to ground, but in certain cases the negative output should be left disconnected.

Maybe this is a good time to mention balanced vs. differential topologies. I don't know for sure if my Loxjie P20 amp has true balanced operation, or if it's the differential type. My hunch is differential, based on this finding from an article by Headphonesty, citing a quite from Moon Audio:

"As explained earlier, the term “balanced amplifier” is something of a misnomer. Balanced and unbalanced are types of interconnections between devices; these terms do not refer to specific amplifier architectures. Usually when you see the phrase “balanced amplifier” it is referring to a differential amplifier without shared grounds and balanced outputs.

“A true Balanced amplifier will be balanced from input all the way through to the output. Opamp splitters are often used to convert the input and output from single-ended to balanced. There are plusses and minuses to this method. This is cheaper to produce but it is not a true balanced circuit and it may not sound as good as if the entire chain would have been balanced.” -- Moon Audio

Source: https://www.headphonesty.com/2019/05/balanced-vs-unbalanced-audio-connections/

I am going for differential topology, balanced or un. Here is the basic concept of the differential signal that I'm trying to achieve with the MiniDSP:

To sum up, I don't need to convert SE to true balanced. The P20 has SE inputs that work just fine. I could just use them! I'm more interested in using the MiniDSP to send differential line outs that will work with the P20's 'balanced' inputs.

All of this is my understanding based on reading a few articles and watching YouTube reviews. If I'm off, please someone educate me; set me straight on the topic.

The MiniDSP development team says the configuration (and wiring below) should work.
should...not that it will work? Have you asked the people at Loxjie if they think it will, should, work?

Here is the actual response from MiniDSP:
"From what we can tell from your plugin and diagram, everything looks pretty good. Maybe try to double-check if you have got all the soldering right on the XLR end?

DevTeam"

I haven't yet reached out to Loxjie. I'd just rather not burden them with this complicated experiment right now. Maybe after I have better understanding from discussions like this one, and if still no result, I will ask them.

Nothing wrong with the cables?Faulty contacts, bad soldering or something like that? Are you able to check that, perhaps measure with a multimeter?
Or test the cables on some other gadgets and see if they work properly?

I agree to suspect the new, unproven element in the system, i.e. custom built cables. MiniDSP zeroed in on this as well. To rule out the cables as a possibility, I conducted this continuity test 3 times. Here are the results (it confirms the above cable diagram is legit):

Hi
Your testing for noise by touching the RCA certainly suggests the amp is not using the cold input.
Are you listening from the balanced or unbalanced output of the amp? If the unbalanced, is it possible that only hot signal of the balanced input is sent to the unbalanced output?
IE do the balanced inputs only work balanced for the balanced output?

Thanks for the feedback, Tony. I'm almost sure I tried listening from both the XLR and SE output settings, and noticed no change in results between them. When I made these observations, I know for sure I was listening through the XLR output using 'balanced' cables to my Sennheisers.

It's a good theory, though. If I can't figure this out through more experimenting, I'll revisit this and report back.

Can we see the miniDSP configuration?Are all channels mapped properly?

Sure, sorry I didn't post this earlier. Here is the output map (if the problem lies here, would be an easy fix!):

The P20 may only be balanced in when using balanced outputs (so 4 separate amplifiers).
In that case, when using SE out only the RCA inputs (or + inputs of balanced inputs) are used and - input could be ignored (only goes to - out of balanced out)

If not then balanced would be made SE inside the amp and become balanced out both with SE and balanced in.

Maybe this is the case (not seen a schematic)

Interesting theory that I am only partially able to grasp. I guess we can't know for sure unless I ask Loxjie how their amp is wired. I think you're saying the P20 may be differential only, not true balanced?

As mentioned above, I'm okay with differential only. My understanding is a stereo differential output can be made by configuring 4 SE outputs (2 for each channel) to send an inverted and non-inverted signal (for each channel) to be summed by a differential receiver at the input of the amp.

So far as I know, that should be what I'm doing with the MiniDSP, unless somehow I'm not.

This with balanced for home HiFi seems to be unclear. I myself am confused. It's not an end in itself to run balanced for home HiFi, is it?
Mixing unbalanced and balanced, isn't that asking for trouble? Or? I could be wrong.

I think your concern is similar to mine, with 'balanced' being used as a buzzword to describe the differential topology. Not all 'balanced' is actually balanced. Or maybe you mean something else. Whatever the case, I agree it is confusing.

have you tried simply switching the output cables of the MiniDSP: 1-to-2 and 2-to-1, to see what happens?

Yes, I'm sure I did, but this was over a year ago. If memory serves, the behavior of cable #1 remained the same (null) when swapped with #2.

I've just noticed we are answering a question from more than a year ago.
OP hasn't been on the site since May.
I think we are wasting our time here

Nope, not at all. I follow threads for decades, lol. After some time I shelved this project, but fully intended to try again on a rainy day...
I'm using a Schiit Valhalla now, which got me the headroom I needed with SE with 150 ohm Senns, but I'm still curious to hear what the hybrid P20 can do with differential ins/outs!

PS - to rule out the P20 amp as defective, I own 2 units and they both react in the same way to the input fed from the MiniDSP.

Thanks again for all of your ideas. I'm now motivated to pull out the P20 and figure this out.

 

[solderdude]

Interesting theory that I am only partially able to grasp. I guess we can't know for sure unless I ask Loxjie how their amp is wired. I think you're saying the P20 may be differential only, not true balanced?

As mentioned above, I'm okay with differential only. My understanding is a stereo differential output can be made by configuring 4 SE outputs (2 for each channel) to send an inverted and non-inverted signal (for each channel) to be summed by a differential receiver at the input of the amp.

So far as I know, that should be what I'm doing with the MiniDSP, unless somehow I'm not.

The question is whether or not you are using the balanced out or using the TRS out of the amp.

When you are using TRS output and the amp is indeed wires as I described then connecting the - input of balanced in will make no difference.
You then have no benefits from balanced either. It is just SE all the way even if you go in truly balanced. It would explain your findings.

 

[aasearles]

Thx for the reply. To your question, yes, I'm using the XLR output (#4 below) from the P20 amp to drive my headphones.

Per the manual's instruction, I've set the output mode to "ou1" for the balanced port.

PS - solderdude, I visited your country last month and enjoyed it very much (not quite enough). I would like to return again someday!

 

[DanielT]

Thank you DanielT for reviving this thread, and to the others who've replied - I sincerely appreciate it! Now I'll work through and give some responses.


Thanks for this info. If I can't achieve balanced (differential) output through the use of this miniDSP unit on it's own, I might look into one of these options to isolate the RCA outputs before sending to the P20 amp.


Maybe this is a good time to mention balanced vs. differential topologies. I don't know for sure if my Loxjie P20 amp has true balanced operation, or if it's the differential type. My hunch is differential, based on this finding from an article by Headphonesty, citing a quite from Moon Audio:

"As explained earlier, the term “balanced amplifier” is something of a misnomer. Balanced and unbalanced are types of interconnections between devices; these terms do not refer to specific amplifier architectures. Usually when you see the phrase “balanced amplifier” it is referring to a differential amplifier without shared grounds and balanced outputs.

“A true Balanced amplifier will be balanced from input all the way through to the output. Opamp splitters are often used to convert the input and output from single-ended to balanced. There are plusses and minuses to this method. This is cheaper to produce but it is not a true balanced circuit and it may not sound as good as if the entire chain would have been balanced.” -- Moon Audio

Source: https://www.headphonesty.com/2019/05/balanced-vs-unbalanced-audio-connections/

I am going for differential topology, balanced or un. Here is the basic concept of the differential signal that I'm trying to achieve with the MiniDSP:

To sum up, I don't need to convert SE to true balanced. The P20 has SE inputs that work just fine. I could just use them! I'm more interested in using the MiniDSP to send differential line outs that will work with the P20's 'balanced' inputs.

All of this is my understanding based on reading a few articles and watching YouTube reviews. If I'm off, please someone educate me; set me straight on the topic.


Here is the actual response from MiniDSP:
"From what we can tell from your plugin and diagram, everything looks pretty good. Maybe try to double-check if you have got all the soldering right on the XLR end?

DevTeam"

I haven't yet reached out to Loxjie. I'd just rather not burden them with this complicated experiment right now. Maybe after I have better understanding from discussions like this one, and if still no result, I will ask them.


I agree to suspect the new, unproven element in the system, i.e. custom built cables. MiniDSP zeroed in on this as well. To rule out the cables as a possibility, I conducted this continuity test 3 times. Here are the results (it confirms the above cable diagram is legit):

Thanks for the feedback, Tony. I'm almost sure I tried listening from both the XLR and SE output settings, and noticed no change in results between them. When I made these observations, I know for sure I was listening through the XLR output using 'balanced' cables to my Sennheisers.

It's a good theory, though. If I can't figure this out through more experimenting, I'll revisit this and report back.


Sure, sorry I didn't post this earlier. Here is the output map (if the problem lies here, would be an easy fix!):

Interesting theory that I am only partially able to grasp. I guess we can't know for sure unless I ask Loxjie how their amp is wired. I think you're saying the P20 may be differential only, not true balanced?

As mentioned above, I'm okay with differential only. My understanding is a stereo differential output can be made by configuring 4 SE outputs (2 for each channel) to send an inverted and non-inverted signal (for each channel) to be summed by a differential receiver at the input of the amp.

So far as I know, that should be what I'm doing with the MiniDSP, unless somehow I'm not.


I think your concern is similar to mine, with 'balanced' being used as a buzzword to describe the differential topology. Not all 'balanced' is actually balanced. Or maybe you mean something else. Whatever the case, I agree it is confusing.


Yes, I'm sure I did, but this was over a year ago. If memory serves, the behavior of cable #1 remained the same (null) when swapped with #2.


Nope, not at all. I follow threads for decades, lol. After some time I shelved this project, but fully intended to try again on a rainy day...
I'm using a Schiit Valhalla now, which got me the headroom I needed with SE with 150 ohm Senns, but I'm still curious to hear what the hybrid P20 can do with differential ins/outs!

PS - to rule out the P20 amp as defective, I own 2 units and they both react in the same way to the input fed from the MiniDSP.

Thanks again for all of your ideas. I'm now motivated to pull out the P20 and figure this out.

Aha, but if I got it all right now, you don't use the combination Loxjie P20 + MiniDSP 2x4HD but Schiit Valhalla and MiniDSP 2x4HD?
But the Schiit Valhalla has, from what I can see, unbalanced inputs and outputs so in that regard, your question for the thread you are on the same point, or? Do you wear headphones? Do you hear any noise? If not why bother? Then it seems to work.

What you are thinking about in your specific I leave it to more knowledgeable people to help you. What I pasted in see it as general information. Whether that in itself helps you, whether it works in your case, I don't know.

Here, however, I can give you some advice, you say:

I haven't yet reached out to Loxjie. I'd just rather not burden them with this complicated experiment right now. Maybe after I have better understanding from discussions like this one, and if still no result, I will ask them.

Complicated experiment for you but maybe Loxjie may not think it's complicated. In addition, you are their customer, have bought their stuff, of course you should contact them and ask. It is part of a service-minded company to help its customers.

If you listen to streamed music via the mentioned system with headphones and if you want to EQ why not use a player for example?:

Neutron Music Player | Advanced sound and DSP

Neutron Music Player - The only true audiophile music player with Hi-Fi audio rendering and DSP engine.

neutroncode.com

Schiit Valhalla:

Edit:
Fixing the EQ with headphones. Check with those who are "headphone guys" (or girls) here at ASR. There are probably a lot of threads on how to optimize that.

How about EQ with headphones?

You who do EQ with headphones . EQ setting,it's based on subjective, liking and taste in terms of sound, right? Subjectively because frequency curves and headphones are pretty pointless (how measure?) to start with because our ears look different, right? Or what do I know there may be special...

audiosciencereview.com

How to EQ my headphones.

Hey guys, so for the longest time ever, I was a firm believer that eq destroys music because I always found that whenever I tried to EQ my headphones they sounded really distorted. This was until I got my Sennheiser HD58x, Topping E30, and JDS Atom. With much better equipment, I found eq-ing to...

audiosciencereview.com

 

[aasearles]

Aha, but if I got it all right now, you don't use the combination Loxjie P20 + MiniDSP 2x4HD but Schiit Valhalla and MiniDSP 2x4HD?
But the Schiit Valhalla has, from what I can see, unbalanced inputs and outputs so in that regard, your question for the thread you are on the same point, or? Do you wear headphones? Do you hear any noise? If not why bother? Then it seems to work.

What I meant in mentioning the Valhalla, it's a great zero-feedback SE amp that works with higher impedance phones, but I'd still like to get this P20 working through its balanced inputs, for using with a pair 32 ohm AKGs. The Valhalla isn't so good with the lower impedance loads. Sorry to confuse there.

I can use the MiniDSP with either amplifier, it's just a matter of swapping the DSP profile. But most likely I'd keep the MiniDSP on the Loxjie P20 full time if I can get the balanced output to work. The Valhalla is currently being fed by a PC, which has DSP software (no need for MiniDSP).

Complicated experiment for you but maybe Loxjie may not think it's complicated. In addition, you are their customer, have bought their stuff, of course you should contact them and ask. It is part of a service-minded company to help its customers.

You make a good point here. They may choose to help me out. I will reach out to get their angle!

 

[aasearles]

If you listen to streamed music via the mentioned system with headphones and if you want to EQ why not use a player for example?:

I don't stream music normally. My music is mostly MP3/AAC/WAV, MiniDisc, and occasionally analog (LP, Cassette).
MiniDSP's analog/digital inputs gives me connectivity with many formats + DA conversion + PEQ, and it works standalone if I want to use it offline.

Fixing the EQ with headphones. Check with those who are "headphone guys" (or girls) here at ASR. There are probably a lot of threads on how to optimize that.

I have a make-shift measurement rig that measures decent response up to about 1kHz. Above that point I rely on Amir's review of my 58x and K371 phones.
His PEQ values sound good to my ears, but I prefer a more aggressive ramp in the deep bass, so it's a custom blend to get the sound I want.
MiniDSP's user interface is another reason I use it. I have another unit on the home theater, and another one in my car. Invaluable for the kind of tuning I like to do.

I'll check your links though and maybe learn some more. Thanks!

 

[DanielT]

I don't stream music normally. My music is mostly MP3/AAC/WAV, MiniDisc, and occasionally analog (LP, Cassette).
MiniDSP's analog/digital inputs gives me connectivity with many formats + DA conversion + PEQ, and it works standalone if I want to use it offline.

I have a make-shift measurement rig that measures decent response up to about 1kHz. Above that point I rely on Amir's review of my 58x and K371 phones.
His PEQ values sound good to my ears, but I prefer a more aggressive ramp in the deep bass, so it's a custom blend to get the sound I want.
MiniDSP's user interface is another reason I use it. I have another unit on the home theater, and another one in my car. Invaluable for the kind of tuning I like to do.

I'll check your links though and maybe learn some more. Thanks!

Now I got curious. So signal source: MP3/AAC/WAV, MiniDisc, and occasionally analog (LP, Cassette).

But if we take record players. What does your set up look like then? Do you only listen to headphones?

If you hear noise how do you know it's not coming from the turntable? If you hear any noise that is. Is what you describe in the thread a theoretical problem or something that you practically experience, hear with your ears?

 

[antcollinet]

Thx for the reply. To your question, yes, I'm using the XLR output (#4 below) from the P20 amp to drive my headphones.

View attachment 224704


Per the manual's instruction, I've set the output mode to "ou1" for the balanced port.

View attachment 224705

PS - solderdude, I visited your country last month and enjoyed it very much (not quite enough). I would like to return again someday!

Is the full cable to headphone cable to headphones all balanced (Do the headphones have a balanced connector - or are you going from XLR to headphones via a balanced to unbalanced converter).

 

[solderdude]

Thx for the reply. To your question, yes, I'm using the XLR output (#4 below) from the P20 amp to drive my headphones.

View attachment 224704


Per the manual's instruction, I've set the output mode to "ou1" for the balanced port.

View attachment 224705

PS - solderdude, I visited your country last month and enjoyed it very much (not quite enough). I would like to return again someday!

This could suggest that in SE input mode you can still have balanced output drive.
It could also suggest that in SE output mode balanced input can be used but it could also not be the case.

 

[aasearles]

Now I got curious. So signal source: MP3/AAC/WAV, MiniDisc, and occasionally analog (LP, Cassette).

But if we take record players. What does your set up look like then? Do you only listen to headphones?

Set-up at my office desk is modular components. Mostly listen w/headphones. This is where I enjoy tweaking the sound, experimenting. I
I have a Denon DMD-M10 Minidisc recorder feeding toslink to the MiniDSP, which is connected USB to a MacBook Pro - this is my main music player w/remote.
Occasionally I will feed cassette tape to the MiniDSP through one of two Walkman players. One of them sounds okay for cassette!

I haven't actually connected my turntable to the office desk system, but I could do so. My LPs are listened to in the main living area, a simple 30W 2.0 system. Phono preamp sends the signal to a pair of Audioengine HD3s. Apple TV audio feeds to another MiniDSP unit with output to the same speakers. A '60s Panasonic FM table radio waits to connected to the system!

If you hear noise how do you know it's not coming from the turntable? If you hear any noise that is. Is what you describe in the thread a theoretical problem or something that you practically experience, hear with your ears?

The experiment with the MiniDSP and P20 amp was controlled, only fed signal from the MacBook Pro.
I don't recall reporting any instance of noise in the thread, but if it were turntable generated, it would be quite unique and identifiable as such.