Using dual outputs


#1

I’d like to use a subwoofer to supplement my powered speakers for nearfield listening. I am using the balanced out into my Focal Solo6 Be’s and I would like to use the unbalanced out into a powered subwoofer. I can use the gain control on the sub to correct the difference between the gain on the two outputs. I just want to make sure I am not hurting anything on the DS DAC in doing this.

Please confirm if this is okay.

Thanks.


#2

There are several threads about this (e.g. mine confused )

The single ended outputs has a lower level than the balanced one, because the SE ouput is tapped between the trafo center point and one of the winding extremeties. Since the DS output impedance is low and the load impedance is high it will work without dropping the signal however you need to count in the differences in level. If you have a volume control on your sub this should work, however the calibration procedure could be slightly challenging.


#3

Welcome, ksalno

Short answer, you will not hurt anything.

There is a 6dB difference between the single ended and balanced outputs of the DS. The only downsides are that once you use both, you lose common mode noise rejection - the biggest advantage to a balanced system - and more capacitance.

The additional capacitance exists when you have both balanced and unbalanced interconnects connected at the same time you have more capacitance on that one leg. Typically this is not an issue, but it can be if you have long interconnects and/or a system which is sensitive to this.

Adjusting the level of the subwooferis will be no trickier than usual, but you will need to increase the gain by 6dB more than you would otherwise.

In any event, I prefer driving a sub off of the speaker outputs of the main amp if the sub allows for a high level input. This integrates the sub much better with the sound of the main speakers as the characteristics of the amp are passed on to the sub.

Happy experimenting.


#4
Elk said
In any event, I prefer driving a sub off of the speaker outputs of the main amp if the sub allows for a high level input. This integrates the sub much better with the sound of the main speakers as the characteristics of the amp are passed on to the sub.
Unfortunately, that isn't possible for two reasons. One the Focals are powered speakers, so there is no main amp. I run balanced out from the DS DAC directly to the speakers. Also, the sub I'm using has an active crossover, so I need a line level input, not speaker level. There is plenty of gain control, so I don't think calibration will be any issue.

Thanks for the help.


#5

Please take a look at this thread (my nick is ‘Distinctive’ over at the CA forum):

http://www.computeraudiophile.com/f12-headphones-and-speakers/ok-last-resort-subwoofer-tuning-21921/

My impression of the calibration process is that on paper it is easy, but I ran into problems while doing it in practice due to some unexpected results.

Maybe there is an easier way…

@Elk:

We had a discussion on the CMRR topic here:

http://www.psaudio.com/forum/directstream-all-about-it/ds-dac-questions-and-concerns/page-3/#p26918

From what I could see the ‘CMRR degradation’ is debatable when you have high-impedance loads connected and do not have problems with noise and long IC leads in general. It might be that I reconnect my Jensen trafo in the loop for the galvanic isolation purpose.

PS:

My sub supplier (pun intended) recommend NOT to use the high level inputs, because there will be some negative impacts due to regenerated effects propagating into the main speakers vice versa. In your (ksalno) case this is not an issue.

I encourage PS Audio to look into how this issue could be satisfactory solved in the future. If you go direct from DS DAC to power amps (omitting a preamp with both line out and pre out), quite a few setups will suffer when subs are brought into the loop. Surprisingly, no other manufacturers seem to recognize this either. This could mean a competitive edge, however also an impact on cost (but then again if you could avoid spending a preamp…).


#6

Integrating a sub is always tricky and must ultimately be done by ear.

All subs have different gain v. the main speakers, etc. One must always adjust the volume of the sub to integrate with the main speakers and then tune the setup to taste. This is the same regardless of the voltage input into the sub.

This issue remains even when both the main amp and the sub receive exactly the same level input. The adjustment is no more tricky when there is a 6dB voltage difference between the two. Regardless of the signal level the sub receives you need to turn the volume of the sub up or down to compensate for the different gain structure of the sub amp v. the main amp, output efficiency of the main speakers to amp, etc. This is why subs have volume controls. :)

As I stated, the additional capacitance is typically not an issue. Loss of common mode noise rejection will similarly be of little concern in a typical home setup. But the potential problems exist. As always, try it and see.

While it is theoretically possible there can be “back voltage” hooking up an amp to a sub, amps are designed to deal with exactly this issue as this is something all speakers produce. This is the amp’s damping ability. The high level inputs of a sub are a non-issue however as the inputs are very high impedance and no signal wants to come back down the line (the amp is, of course , very low impedance). Your sub may be designed differently so that it is unhappy receiving a high level input or does send junk back down the connection.

Ksalno, it sounds like you are all set! Please report back and let us know how it all works out.


#7

Ok, but I guess we can all agree that using a SPL meter is difficult when calibrating sub and mains at the same time, so you have to trust your ears during the adjustment process. At least this is my experience outlined in my thread.


#8

No question; using an SPL meter is going to be exceedingly difficult - regardless if you are playing the sub at the same time as the mains or singly. This will somewhat work only if you graph the response for the requisite 1Hz resolution, move the sub/adjust volume, and repeat nearly indefinitely. Ouch.

A big problem still exists however; by measuring fixed frequencies you are setting up standing waves, and you will both hit and miss troughs and valleys if you use less than 1Hz resolution, such as the typical 1/3 octave of test CDs. It is a crude procedure.

If you want to use software to assist, you need a program that sweeps from 20Hz to 200Hz or so, with a repeat and hold function. You take a measurement, adjust, measure again, and optimize placement and volume settings. This is the same process as above, but humanly possible. :slight_smile: Another option is a real time analyzer. (Free room acoustics measurement software is here.)

It makes zero sense to attempt to adjust/place a sub without the mains on at the same time. The main speakers interact with the subs and this will be how you listen. Adjusting a sub alone makes sense only if you are using a high pass filter on your mains, and the sub is exclusively reproducing the lower frequencies.


#9

I originally had dual balanced outputs on my pre, one set for my M60’s and one set to drive my Sub225’s directly ( through a parametric eq for bass management )

Going direct from the DS via the balanced out left me with little choice but to connect the Sub225’s directly via speaker level.

I lost my active bass management, but was able to realign and dial things back in to a point where the bass management was no longer needed.

Ultimately this was for the better sonically.

One of the items that I was considering to solve my single balanced output dilemma was the MSB Technology Sub Isolator.

It is a " Y " output connector that provides a dual output from a single balanced output.

One output half is straight out, the other output provides an isolated output for a sub connection.

This was a last resort option for me due to the listed price of $995.00, each I think.

But this may be the solution to your problem.

You may want to look into this item.


#10

Yes, I have seen this before.

Insanely priced, though.


#11

Another instrument I find convenient for this kind of work is the Phonic PAA3: http://www.phonic.com/en/paa3.html

It’s interface is a little weird until you get used to it, but among other things it does a 31-band real time spectrum analysis, you can watch the spectrum change as you adjust your sub… I typically play white noise from a CD instead of using it’s audio output, both work fine.

I should say that I’ve had mine for more than a decade and I have no idea if they or someone else makes a better or more convenient version. (It’s probably a phone app these days :) )


#12
Ted Smith said (It's probably a phone app these days :) )
On my iPad, I have Audio Tools from Studio Six Digital. I'm not enough of a techie to know if their stuff is as accurate as something like the Phonic, but it seems pretty good to me; certainly worth a look if you already own an iPad.

#13

The real issue is how good is the mic - the application is relatively simple but a good mic isn’t cheap.


#14

I hooked up the DS directly to my amp while my preamp is at the factory for gain matching. I noticed that when using the balanced output towards the amps while at the same time hooking up my subs to the single ended outputs, the DS output level appeared attenuated. This is as expected given the fact that the high level balanced mode is broken by the RCA connection (load on one side of the trafo winding).

However what was noticed also was that my sound was less distinct than before. It was slightly more muffled and less focused. Any comments on the latter? Should this be expected?

My hope is that a PS DAC would be the first unit that could drive a sub line level while at the same time feed a signal to the main amps without any sound degradation. All nice talk about ‘no preamp is like no preamp’ and associated cost savings means nothing to us sub owners. We are left with the option to buy a preamp with both line out and pre out (splitters and high level connection is not an option for me). Such a remedy would be a helluva added value for the owner and a marketing statement that will separate it from the crowd.


#15

If I used opamp drivers instead of a passive filter with a transformer it could have been done without much more circuitry or cost. But to do that properly with the current design would almost double the circuitry on the analog card. If that were a design goal I could have saved somewhat over doubling, but at the cost of sound quality for everyone else.

No matter how good your system as a whole is (e.g. so there’s not a big difference between balanced and unbalanced interconnects), you still essentially double the capacitance on one leg of the balanced output with both a balanced cable and an unbalanced cable attached at the same time. With any kind of passive output that will filter one side of the balanced connector differently - whether this is audible depends on the cables and the rest of your system.


#16

Thanks.

I appreciate that it is not straight forward to solve this with the current design, but a preamp normally fixes this problem without con’s, so it actualizes arguments in favor of a preamp in the loop.

When you say others will suffer, isn’t it possible to use a dummy load (RCA plug) for those who do not use this option? In this case I reckon also the interconnects predicted capacitance must be included.

I have been looking at this one, but the price is extreme: Sub isolator


#17

That’s the problem - cables are all over the map re. capacitance. I have sympathy for the issue, but at some point in system’s complexity a preamp is just what the doctor ordered.


#18

I think I have an alternative solution to the problem.

I run the optical out from the source feeding the DS to this one: Antimode 2.0

Then I connect the subs to the line out from this processor of mine. I can adjust the volume on the sub.

One issue is if this may bring some latency problems into the mix, but I think this is minor.

I will report back if this produce better results, however the limitation is 96kHz and PCM only.