Amp/Preamp Asylum

Looking for a new Amp or Preamp? If you're after tubes, post over here.

Return to Amp/Preamp Asylum

Message Sort: Post Order or Asylum Reverse Threaded

Balanced/Unbalanced Simultaneously

76.25.33.99
Posted on September 28, 2015 at 23:20:30
jsr
Audiophile

Posts: 2865
Location: Heart of the Rockies
Joined: March 1, 2001
 Haven't found this addressed anywhere: I am running a Thule PR100 preamp into a Thule PA100 power amp. The pre has both unbalanced and balanced outputs. No switch to choose which you're running as the output.

The amp has balanced/unbalanced inputs. There is a selector switch where you have to choose whether you're using the balanced or unbalanced inputs.

I am running the balanced outputs from the preamp to the amp. I am also running the unbalanced RCA outputs of the preamp to a separate sub.

The amp came used without a manual. I had a manual for the preamp, but I lost it. Best I can recall, the preamp manual didn't say anything about using or not using both sets of outputs simultaneously. It was just silent on that.

Any idea if I'm screwing up the signal and/or the preamp by using both outputs at the same time? I don't see any harm to the amp, because it's getting only the balanced signal, and it hasn't complained.

 

Hide full thread outline!
    ...
RE: Balanced/Unbalanced Simultaneously, posted on September 29, 2015 at 03:55:31
John Elison
Audiophile

Posts: 23900
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 You can check to see if the two outputs are buffered by turning off and unplugging the preamp and using an ohmmeter to check the resistance between the RCA center pin and the XLR pins 2 or 3. If you get a reading of zero ohms or thereabouts, this indicates they are not buffered and should not be used simultaneously.

I have a Pass Labs X1 preamp with the same output configuration and it states in my manual that the two outputs are buffered and can be used simultaneously. Therefore, I'm doing exactly what you are doing.

It would be a shame if your preamp doesn't have buffered outputs. However, if it doesn't, then you are screwing up the signal to the power amplifier, but it shouldn't do any harm. You can always remove the cables to the sub and see if you notice any difference in sound quality to the main speakers. The sub would be placing an unbalanced load on the balanced output.

Good luck,
John Elison

 

You started correctly... but... , posted on September 29, 2015 at 08:03:35
Victor Khomenko
Manufacturer

Posts: 55317
Joined: April 5, 2000
 You described a good test, but your conclusion is incorrect.

In most cases it is perfectly fine to use both outputs simultaneously, even if they are not buffered. Typical inputs are purely resistive, so you just need to make sure the total load is not below minimum recommended for that preamp.

There is one small caveat - some solid state amp inputs might become non-linear when the unit is powered down. Whether this is or is not a problem for you is another question. But this is a small concern.


 

RE: You started correctly... but... , posted on September 29, 2015 at 08:18:11
John Elison
Audiophile

Posts: 23900
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 I disagree with you. First of all, I didn't say it would hurt anything to connect both components simultaneously. I said it would create an unbalanced load on the preamplifier. Furthermore, it would be more than a restive load because the unbalanced cables to the sub have capacitance and if they happen to be 25-feet long like the cables to my sub, this presents significant capacitance. I like my sub to be placed on a rear wall behind my listening position. At any rate, placing different loads on each leg of a balanced connection kind of defeats the purpose of a balanced connection. It basically negates the word "balanced." ;-)

Best regards,
John Elison

 

RE: Balanced/Unbalanced Simultaneously, posted on September 29, 2015 at 09:34:59
jsr
Audiophile

Posts: 2865
Location: Heart of the Rockies
Joined: March 1, 2001
 Thanks! Unfortunately, my meter's in storage.

I will say that the sound quality seems the same, but I will try what you suggest. Is there anything I could physically observe inside the preamp that would tell me they're buffered or not?

Thanks again.

 

RE: You started correctly... but... , posted on September 29, 2015 at 09:36:51
jsr
Audiophile

Posts: 2865
Location: Heart of the Rockies
Joined: March 1, 2001
 Thanks, Victor.

 

RE: You started correctly... but... , posted on September 29, 2015 at 09:38:22
jsr
Audiophile

Posts: 2865
Location: Heart of the Rockies
Joined: March 1, 2001
 My sub cables aren't particularly high end (though I could dig out some that are probably of better design/manufacture, like Canare), but the run is only about 8'.

 

What is the effect of those cables capacitance on a typical preamp output?, posted on September 29, 2015 at 09:44:53
Victor Khomenko
Manufacturer

Posts: 55317
Joined: April 5, 2000
 Figure, 100 Ohm output resistance.


 

RE: Balanced/Unbalanced Simultaneously, posted on September 29, 2015 at 09:45:26
John Elison
Audiophile

Posts: 23900
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 Just buy another meter or else take yours out of storage; then you will be certain. It might be difficult to trace the connection when looking inside. Then, again, it might be quite apparent. Take a look and see.

Good luck,
John Elison

 

RE: What is the effect of those cables capacitance on a typical preamp output?, posted on September 29, 2015 at 09:52:45
John Elison
Audiophile

Posts: 23900
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 It doesn't matter what the output resistance is for the preamp; you no longer have a balanced connection because you no longer have a balanced load. That may or may not make an audible difference, but it is definitely not ideal. The two outputs should be buffered if you intend to use them simultaneously. On the other hand, if you can't hear any difference, it might not matter to you. It just depends. I, personally, wouldn't be happy with such a configuration.

Best regards,
John Elison

 

RE: Balanced/Unbalanced Simultaneously - Thanks! (NT), posted on September 29, 2015 at 09:59:56
jsr
Audiophile

Posts: 2865
Location: Heart of the Rockies
Joined: March 1, 2001
 Thanks!

 

OK, so now it "doesn't matter", posted on September 29, 2015 at 10:18:40
Victor Khomenko
Manufacturer

Posts: 55317
Joined: April 5, 2000
 But you just wrote earlier:

" Furthermore, it would be more than a restive load because the unbalanced cables to the sub have capacitance and if they happen to be 25-feet long like the cables to my sub, this presents significant capacitance."

After which I asked you to describe their effect. You then stated, totally incorrectly, that the output resistance does not matter.

OK... I am out of this discussion.




 

RE: OK, so now it "doesn't matter", posted on September 29, 2015 at 10:40:48
John Elison
Audiophile

Posts: 23900
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 You stated that the imbalance from the load of the sub was purely resistive and I was pointing out that it also had a reactive component due to cable capacitance. Regardless of whether the load is purely resistive or partially reactive, it constitutes an imbalance to a supposedly balanced connection. The reactive component will create phase shift to the audio signal on one of the supposedly balanced legs. My point is that I, personally, would not be happy with that situation in my audio system.

> OK... I am out of this discussion.

Well, it's about time!

Good luck,
John Elison

 

RE: Balanced/Unbalanced Simultaneously - One thing I should have mentioned, posted on September 29, 2015 at 11:23:47
jsr
Audiophile

Posts: 2865
Location: Heart of the Rockies
Joined: March 1, 2001
 One thing I didn't get into is probably important. When I run the system using both preamp outputs (balanced and unbalanced), the sub puts out much less volume than normal. For instance, if the preamp runs unbalanced to the sub, and then unbalanced from the sub to the amp, the sub is happy with the sub's volume set around 9-11 o'clock. When the balanced outputs are used direct to the amp, and the unbalanced to the sub, then the sub doesn't get happy until the sub's volume is set to almost 3 o'clock. Strangely, the balanced output seems to remain the same (louder than the unbalanced, naturally).

I really like the balanced sound - it is not only louder (which is meaningless as to fidelity), but much, much clearer and with superior resolution, because the noise of an unbalanced connection is gone. I have always liked this in the few truly balanced systems I've had in the past - I don't care what anyone says, truly balanced has always sounded better than unbalanced in every way. No comparison.

Don't know if this info means anything or not.

 

RE: Balanced/Unbalanced Simultaneously - One thing I should have mentioned, posted on September 29, 2015 at 12:10:05
John Elison
Audiophile

Posts: 23900
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 Balanced outputs are often 6-dB louder than unbalanced outputs. The reason is that each leg of the balanced output is the same level as the unbalanced output but 180-degrees out of phase with each other. The difference between the two legs is therefore 6-dB louder than either of the individual legs to ground.

I know what you mean by the lack of noise in a fully balanced system. I've noticed the same thing in my system.

Best regards,
John Elison

 

RE: Balanced/Unbalanced Simultaneously, posted on September 29, 2015 at 14:27:11
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 Not much of a manual but here it is:
Thule PR100 Manual



"Our head is round in order to allow our thoughts to change direction." Francis Picabia

 

RE: Balanced/Unbalanced Simultaneously, posted on September 29, 2015 at 18:51:12
jsr
Audiophile

Posts: 2865
Location: Heart of the Rockies
Joined: March 1, 2001
 Yup, that's it. Almost uniquely uninformative.

But thanks for this! These things are rarer than the preamps themselves. They did come out with a similar pre that had balanced inputs, as well. I'd like to get my hands on that, but they are hard to find. Apparently, the power amps had problems as well, but mine's been hanging in there.

Thanks again!

 

probably doesn't matter, posted on September 29, 2015 at 23:53:48
madisonears
Audiophile

Posts: 1587
Location: midwest
Joined: September 6, 2006
 There are no balanced inputs. Therefore, the preamp is deriving a balanced output signal from its own circuitry. This most likely involves a chip or opamp to split the phase. That would essentially isolate the balanced output from the SE output. Connecting them simultaneously will have no effect.

However, there is little sonic benefit, and possibly a slight detriment due to the extra circuitry, to such an arrangement unless you use very long IC's. All you are getting is 6db of gain, which you could get just as easily by turning the volume control. The XLR connectors might be better than SE types, and some balanced cabling is higher quality. Any improvement you hear is likely your own bias influencing you, or simply the system playing louder, which is always perceived as sounding better.

Balanced operation is truly beneficial when source (CD player or DAC, phono preamp) and the rest of the signal chain are balanced. Equipment that derives a balanced signal is not necessarily better, and possibly worse, than SE.

Peace,
Tom E
berate is 8 and benign is 9

 

It is all implementation dependent, posted on September 30, 2015 at 07:20:36
Victor Khomenko
Manufacturer

Posts: 55317
Joined: April 5, 2000
 I will take a small issue with the sonic degradation due to "extra circuitry" - in reality, none is required, if things are done right. In fact, I would have exactly the same internal circuit, if my job was to design a single-ended preamp. Many well-designed classic single-ended preamps contain differential gain stages inside, so it is just the matter of putting the proper connectors. There are sizable advantages to using symmetrical differential gain stages, no matter what interface.

As far as using both outputs at the same time - we certainly do not put any such limitation on our products, the only one being the resistance issue. Many people in fact do so with very good results. Running a sub is one such case.


 

RE: It is all implementation dependent, posted on September 30, 2015 at 11:02:05
jsr
Audiophile

Posts: 2865
Location: Heart of the Rockies
Joined: March 1, 2001
 Victor, I understand that I can be fooled psychologically, but I certainly understand that one can compare volume levels, equalize them, and then determine (subjectively at this point) if there's a difference.

Thule, when it was in operation, boasted of many strides in balanced circuitry. Some of these strides postdate the models I have, some don't. So I still believe that the operation between preamp and amp is "balanced," with the proviso that the source isn't. (Sadly, my DAC is balanced - it's a pro audio piece, but I don't have balanced inputs on the pre, so for now I'm making do with what I have.

Am I understanding you correctly, that there is a balanced operation between the two components? (I realize you don't have any schematics or diagrams to consult.) BTW, the balanced interconnects are 3' in length, and are basic Canare retail interconnects. I have little patience for cable woo.

Thanks for generously giving me the time you have thus far.

 

RE: It is all implementation dependent, posted on September 30, 2015 at 11:56:03
Victor Khomenko
Manufacturer

Posts: 55317
Joined: April 5, 2000
 Without having the schematic, I can presume that you indeed have balanced interface to power amp. It is not hard to generate good balanced signal out of single-ended one, so if your incoming signal is good, there will be less chance of degrading it from that point on.

Now, that can be done many different ways, with various degrees of imperfection. If one's goal is to achieve perfect symmetry, then he will likely resort to some solid state inverter/splitter - either discrete, or an IC. It can also be done with a more "purist" approach, for instance, a simple long tailed pair, either tube, or solid state. Looks like your preamp is solid state.

Going whole hog after the ultimate signal symmetry will most likely result in sonic degradation, due to the use of IC's - all, of course, IMHO.

A tube phase splitter, while being less perfect, might provide better sound. That is why we usually try to strike the right balance between the perfection and sound. Audio interface is not designed the same way the electronic instrumentation is done.

All this is academic, because you are not changing anything internally, so this is purely for the sake of general idea.

Many people believe, that even less than perfect balanced signal will beat the single-ended one. I certainly do.

For this reason I suggested earlier, that it might be perfectly fine to use both outputs at the same time, provided your load is not a heavy one. I would try to find out the input resistance of your power amp, and your sub. If both happen to be in the 20-47K range, then I would sit back and let your ears guide you. If below, say, 10K, then I would still sit back, but do a more careful comparison.

One test you could do would be as follows:

Move the sub out of your room, but have enough cable to connect it to your preamp. Listen to your main amp, with the sub plugged in, and unplugged. Hopefully there will be no noticeable difference.

If moving the sub out is too cumbersome for whatever reason, do it with its volume set at zero.


 

RE: It is all implementation dependent, posted on September 30, 2015 at 12:15:56
jsr
Audiophile

Posts: 2865
Location: Heart of the Rockies
Joined: March 1, 2001
 Well, thank you again Victor for your time and expertise.

I tried a version of the test you suggest, but I will try your version, as its obviously better.

If I hit the Lotto tonight, I'll be buying a full kit of your stuff. Soooo, it looks like I'll have to make do with what I have for now.

Again, my deepest thanks.

 

RE: It is all implementation dependent, posted on September 30, 2015 at 12:28:48
Victor Khomenko
Manufacturer

Posts: 55317
Joined: April 5, 2000
 You are welcome, and I suspect you will be happy with the dual connection.


 

Please get your information straight, posted on September 30, 2015 at 15:44:35
madisonears
Audiophile

Posts: 1587
Location: midwest
Joined: September 6, 2006
 Victor, nice to see you posting here.

First of all, I owned BAT equipment (VK200, VK30, VK60 monoblocks) for many years because I was intensely interested in having properly implemented balanced circuitry throughout my system from source to amp. I admire your capabilities and execution, enough to spend lots of my money in obtaining your products.

Your response to my post about degradation of the signal due to deriving balanced signal from SE source is in conflict with what you posted here. Please clarify.

I maintain that, unless there are extraordinary system requirements, a SE connection throughout will usually sound better than deriving a balanced signal from a SE source. I've heard it myself on some equipment. Perhaps BAT gear is an exception of excellence, but, typically, the only thing to be gained is 6db gain and possibly some modest CMR with long IC's. I agree that a true balanced source will make a balanced system sound better than SE.

I agree that your test is an obvious method to determine whether there is, in this specific case, any sonic degradation. I wouldn't even bother with moving the sub and using crazy long cables which may introduce their own negative effects. Simply turn down the sub volume (not quite at zero) and play the mains with the sub plugged and unplugged. What could be easier and more definitive?

As you wrote, I would expect negative effects only if load impedance gets too small. Probably not an issue with properly designed SS amps.

Peace,
Tom E
berate is 8 and benign is 9

 

RE: Please get your information straight, posted on September 30, 2015 at 18:05:18
Victor Khomenko
Manufacturer

Posts: 55317
Joined: April 5, 2000
 Thank you for your kind words!

Regarding the subject, I think we should start with your statement:

"and possibly a slight detriment due to the extra circuitry,"

I have been long maintaining that there is no extra circuitry or complexity in balanced INTERNAL implementation (there's some in its connectors and cables, but that is another story).

Sure enough, one can build a very simple one-triode single-ended gain stage, and such things exist. But the question is - would this be the ideal way of implementing a gain stage? To me the answer is a NO... as such a stage would be suffering from many ills.

Very long ago... longer, than I care to remember, one of my first mentors taught me the beauty of balanced gain stages. We were designing "serious" electronics back then, and pretty much all our linear tracts were done using balanced gain stages. The reason was their unquestionable superiority in terms of signal integrity, stability, linearity, predictability, etc.

So many years later, when I decided to build some audio circuit, I didn't have to think twice, I simply started with what I thought... or knew... was best.

This situation is not unique to me - you should ask yourself: why did some great designers of the past use balanced gain stages long before the word even appeared on the audio horizon. The answer is - because that made things better... OK... in their minds.

Not just the gain stage itself is much more accurate, but also the way it interacts with the power supply is much less demanding. We all know that the power supply is in the signal path... well, in the balanced circuit it is substantially removed from it, so in essence its quality is multiplied manifold.

When moving onto the interface issue, we need to realize that in "serious" electronics the signal return is never combined with the chassis ground, for many good reasons.

The reason these two totally alien to each other functions were combined into single ground had nothing to do with quality, and everything with cost, so it seems only logical to leave that bad heritage behind and do things the way they should be done... hence - a symmetrical signal drive.

So the next question then is: given the single-ended signal, how should you handle it? In my view, the sooner you convert it into balanced, the better you are, because you will avoid many degradation mechanisms down the road.

Of course I am somewhat sympathetic to the idea of using as few components as possible - it has some merit, but Einstein was smart when he said: "Make things as simple as possible, but not simpler".

Every design is balancing act - there is that word again... :) I am presenting a bit of our philosophy, but the proof is, as usual in the pudding. :) What I am describing does not guarantee the superiority of every balanced component over every single ended one - in both worlds there is plenty of room for mistakes.

So I don't know if this answers all your questions, but this is how I tend to approach it.



 

Now I get it, posted on September 30, 2015 at 20:29:21
madisonears
Audiophile

Posts: 1587
Location: midwest
Joined: September 6, 2006
 Thanks. You mean that the sooner the signal is balanced (differential), the better. The amplification, or gain, is accomplished more accurately in differential mode than SE.

A true, not derived, balanced source such as DAC or CD or phono stage would be the best way to maximize those advantages without additional circuitry. Yes, simple as needed, but not simpler.

I am perplexed that more CD players do not have balanced outputs, as a balanced signal is easily obtained from the DAC. Making it SE is simpler than needed.

I also agree that transmission of ground on top of one leg of the signal can be a significant compromise. One should evaluate whether a SE to balanced stage is worth avoiding that compromise. You maintain a design and corporate philosophy, but not every company is so adept at implementation. If you ever adopted the SE industry standard for any equipment you manufactured, you would need to change your name to BAT/SEAT. That might not fly!

Peace,
Tom E
berate is 8 and benign is 9

 

If the unit is balanced, posted on October 6, 2015 at 12:37:32
Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002
 Then running a single-ended output at the same time should not be possible, unless the unit either has a buffered single-ended output or does not support the balanced line standard (AES file 48).

Now if it supposed to be balanced and does not support the standard, then the issue is that the balanced outputs are referenced to ground. One side is then going to be loaded harder than the other and this will unbalance the signal to the balanced amp.

The degradation might be slight, depending on the the CMRR (common mode rejection ratio) at the input of the amp, but could be audible.

 

Page processed in 0.030 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]