Single Ended vs XLR Bass Extension Differences


#1

Just curious if someone might be able to explain this odd phenomenon I’m experiencing with my Directstream. For whatever reason it almost sounds like there’s a low pass filter, if you will, that cuts off sub bass frequencies when using the XLR output. When I switch back over to the single ended RCA output, I notice far deeper more extended bass. I don’t have anything to measure, but it’s as if anything under ~40hz doesn’t end up being sent out if I’m using the XLR output.

I’ve tested this two ways. I have two different speaker set ups. I’ll only explain how my desktop PC audio set up is, as I believe it reveals more about the issue. The Direcstream normally feeds a Parasound A21 via XLR, which powers a pair of Bowers & Wilkins PM1s. On the back of the A21 there is a “loop out” RCA connector if you wanted to send a single ended signal to another amp or, how it’s set up in my case, it’s feeding a pair of Bowers & Wilkins PV1D subwoofers (one for each channel). I simply set a low pass filter on the DSP of each sub to take over where the PM1s roll off. If I’m using the XLR output to feed the A21 I notice there’s a lack of sub bass. If I switch over to the RCA outs on the Directstream to the A21 things work as they should with full frequency output and deep bass extension. Alternatively, instead of using the loop out connectors on the back of the A21, I can use the RCA outs to feed the subs directly from the Directstream and use concurrently the XLR outs to feed the A21 for my PM1 speakers. Same results as if I were using the loop outs; nice deep extended bass as it should be.

It just seems like the smoking gun here is the XLR outs causing some sort of issue. Does anyone have an explanation? Has anyone else experienced the same issue?


#2

The XLR and RCA analog output connectors of the DS are in parallel. (Well the RCA is in parallel to 1/2 the XLR) There’s no chance that there’s something that acts like a filter between them inside the DS. I’d check that the DS and your amp assume the same pinouts on the XLR: the DS is pin 2 + (or hot), pin 3 -, and pin 1 gnd. The center of the RCA is wired to the XLR pin 2 and the shield of the RCA is wired to gnd as is pin 1 of the XLR.


#3

If it is indeed a pin out issue that would mean I’d need a crossover cable of some sort? I’ll have to email Richard Schram of Parasound to see about the XLR pin out. I’m also wondering if I should just stick with RCA cables? Do you think there’s a sonic loss using RCA single ended if XLR is available?


#4

All of these things can be system specific. There are definitely some amps, preamps, dacs, etc. that sound better one way or the other. If the RCA is functioning well for you I wouldn’t worry about it.

All other things being equal balanced has the chance to sound better since common mode noise can be eliminated easier. But many people have great single ended systems.


#5

Interestingly enough, it seems like the XLR inputs function as they should:

<img src=“http://i.imgur.com/QdU1u8s.png” width=“1091” alt=“QdU1u8s.png” " />

Maybe it’s my XLR cables? That’s the only thing I can think of because the RCA outs fed direct to my subwoofers have no problems.


#6

Hi,

Quick question in relation to this - I am going to try hooking up my Velodyne DD 15s into my setup (Directstream into BHK 300s into Sopra 3s). I posted on another PS audio thread and the recommendation was to go speaker level out -which I can do and will try today.

So if I wanted to go line level in to the subs, could I use the RCA outs off the Directstream as per Seegs108 above while still driving the BHKs through the existing XLR inputs? These are in parallel so there would be an impedance impact - except that the subs would likely draw very little I suppose.

Reason I ask is that the Directstream manual says (in bold) that it is not recommended to use both the RCA and XLR outputs at the same time. Is that because of impedance issues or that the level out is different? Will it damage the Directstream or amps to run both out that way?

Thanks,

Jay Daniels


#7

The issue with using both on the Directstream is on unbalances the XLR output by simultaneously using the RCA. This does not hurt anything, but removes the ability of the balanced output to reject common mode noise. In the vast majority of circumstances there is insufficient common mode noise for this to be any issue whatsoever.


#8
Seegs108 said

Maybe it’s my XLR cables? That’s the only thing I can think of because the RCA outs fed direct to my subwoofers have no problems.


In the illustration you posted, there is a toggle switch in the middle between the two XLR connectors that toggles between Balanced (XLR/Up) and Unbalanced (RCA/Down). Just checking to see that you didn’t miss the switch setting when using the XLR cables.

#9
bstanwick said

In the illustration you posted, there is a toggle switch in the middle between the two XLR connectors that toggles between Balanced (XLR/Up) and Unbalanced (RCA/Down). Just checking to see that you didn’t miss the switch setting when using the XLR cables.


Yes, I have the switch set to Balanced when I have the XLR cables going to and from my Directstream. Still have this odd issue. I have some new AudioQuest single ended cables on their way to me. If I don’t notice any decreases in audio quality using them, I’ll probably just end up using them instead of the XLRs.

#10

Ted Smith has told us that inside the DirectStream the phono (RCA) output is wired in parallel with pins 2 (+ ‘hot’) and 1 (ground) of the XLR. So another way of wiring both a power amp and a subwoofer to the DirectStream is to use a conventional, unbalanced interconnect (phono -to- phono) to connect the power amp and a special balanced to unbalanced (XLR pin 2 -to- phono centre pin) interconnect to connect the subwoofer. (Using them the opposite way—phono > sub and XLR > amp would be electrically equivalent.)

Why would you want to do this? Well, like me, you might have a power amp and a sub both of which have only phono inputs.

Balanced to unbalanced interconnect? Before anybody asks I have no idea whether these are available from stock from any suppliers. (Fortunately I myself can solder and make things up.)

Peter


#11

Cardas sells over-priced XLR to RCA adapters. There are many suppliers of XLR to RCA cables. One can also order bespoke cables from any pro cable shop, such as Redco Audio and Pro Audio LA.

Or like Peter and me, it is easy to make your own. :slight_smile:


#12

Example: https://benchmarkmedia.com/products/benchmark-rca-to-xlrm-adapter-cable

IMG_1606.PNG


#13

So I need to ask … there seems to be some confusion on the xlr pin out on my sunfire amp. Let’s suppose 2 was cold / 3 was hot…is that just an out of phase signal and could it be flipped back in phase by setting the phase on the DS to ‘out’?


#14

Yippers. Or reversing the speaker leads.

Carver used to run pin 3 hot, but I assume he switched over to the standard pin arrangement by now. Then again, he enjoys being an iconoclast.


#15

Thanks elk. I was obsessing. I will be moving to new speakers shortly and want to use the balanced connections.


#16

For a really good balance cable try MOGAMI gold mic cables. BH photo or Sam ash or guitar center has them . I did have an issue with 25 foot SE , I then changed to the above its same as SE if just 3 feet.