I have a question related to direct connection of the DS, which I am currently exploring;
I am struggling to connect my stereo subs at the same time as the power amps when the pre out of my preamp cannot be used. I do not like the idea of using a splitter.
So the only viable option I am left with is to use the RCA outputs of the DS. Now, it says in the owners manual that you should not use the RCA and the XLR output at the same time, but this warning is linked to the fact that the single ended output is having 6dB less gain which in my case won’t pose a problem because there are individual gain control on the sub itself. The warning was not addressing possible impedance mismatch and possibly contamination of the balanced principle as Elk was elaborating on.
I have no measurement on Rin on my sub plate amp (has to be measured) but at least I know that the Rin on my iso trafo is nominal 47kOhm. This is not as high as my power amps (200kOhm).
I would like PS Audio to comment on this. Will this degrade the SQ?
Ted and I may have differing opinions on this and I hope he has time to chime in.
The output of DS is a transformer. Transformers like to be balanced in their impedance delivery as much as possible. When you connect a single ended input to your preamp or amp to DS, the output transformer handles it nicely, although it is now technically unbalanced in that one leg of its secondary has a small load on it while the unused leg has nothing. Given the higher input impedances, like 47k Ohm, I can’t see this as being a problem.
Adding a balanced input on top of the the single ended one definitely unbalances the whole affair, the unused leg now used and loaded, the single ended original leg has half the impedance it formerly did. How much this affects the output is debatable. For my money, if all the inputs are kept high impedance as you suggest, I don’t think it’s problematic.
Ted is welcome to point out the error in my thinking. He’s never proven to be shy in the past.
Paul McGowan said
Ted and I may have differing opinions on this and I hope he has time to chime in.
The output of DS is a transformer. Transformers like to be balanced in their impedance delivery as much as possible. When you connect a single ended input to your preamp or amp to DS, the output transformer handles it nicely, although it is now technically unbalanced in that one leg of its secondary has a small load on it while the unused leg has nothing. Given the higher input impedances, like 47k Ohm, I can’t see this as being a problem.
Adding a balanced input on top of the the single ended one definitely unbalances the whole affair, the unused leg now used and loaded, the single ended original leg has half the impedance it formerly did. How much this affects the output is debatable. For my money, if all the inputs are kept high impedance as you suggest, I don’t think it’s problematic.
Ted is welcome to point out the error in my thinking. He’s never proven to be shy in the past.
I am with you on this one, Paul.
I also get a feeling that I have not that much volume to regulate on my power amp (sensitivity = 1V RMS), so I am probably 6dB short from ideal (ie. balanced).
But this ‘unbalancing act’ means that both the XLR and RCA gives off the same level from the DAC meaning that any volume adjustment on the sub to compensate is no longer an issue.
Elk said
I take it your sub does not have a high level input?
Good thinking, but my sub supplier claims that regenerated currents from the main speakers makes this solution questionable wrt. SQ.
I have an additional 8Ohm speaker binding post on my power amp, but I reckon it is not intended to use this one together with the 4Ohm one for my main speakers.
A lot is going to depend on your sub, I found with my older RCA velodyne that to make up the loss of gain for both the XLR cable vs RCA, and the gain of the both amps, I had to turn up the sub so much it hummed. If you are running two channel audio and 5.1 is a possible add in later (xlr or RCA) the best option would be to look into REL. Use the HFE inputs for 2 channel (connect to amp outputs), and RCA/xlr for the HT .1 output. There is independent volume control for each circuit.
if you have HFE inputs that is good, but some subs use the as a crossover between your amps and main. I’d avoid those, they really limit your options for future changes IMO.
canto4me said
A lot is going to depend on your sub, I found with my older RCA velodyne that to make up the loss of gain for both the XLR cable vs RCA, and the gain of the both amps, I had to turn up the sub so much it hummed. If you are running two channel audio and 5.1 is a possible add in later (xlr or RCA) the best option would be to look into REL. Use the HFE inputs for 2 channel (connect to amp outputs), and RCA/xlr for the HT .1 output. There is independent volume control for each circuit.
if you have HFE inputs that is good, but some subs use the as a crossover between your amps and main. I’d avoid those, they really limit your options for future changes IMO.
$ard
Thanks,
I am using a separete sub for the LFE channel. REL is not an option.
With Pre out (in addition to Line out) on my Preamp this is a non-existing problem…
Definitely just try it before you invest in any remediations.
The theoretical problem of unbalancing the legs of the balanced cnnection mostly revolve around greatly reducing the natural common mode noise rejection of the balanced connection. If you don’t have a lot of common mode noise (in particular hum) then that’s not as much of an issue.
Another possible problem is that if your cables are highly capacitive or very long you might affect the frequency response. Once again the best thing is to try it.
BTW I have some of the Jensen Isomax devices (e.g. for S-Video once upon a time) and they are well done.
Definitely just try it before you invest in any remediations.
The theoretical problem of unbalancing the legs of the balanced cnnection mostly revolve around greatly reducing the natural common mode noise rejection of the balanced connection. If you don’t have a lot of common mode noise (in particular hum) then that’s not as much of an issue.
Another possible problem is that if your cables are highly capacitive or very long you might affect the frequency response. Once again the best thing is to try it.
BTW I have some of the Jensen Isomax devices (e.g. for S-Video once upon a time) and they are well done.
Thanks, Ted.
My IC’s are of very good quality (top of the line Chord, Crystal cable and Wireworld)) and they are of short length.
The background noise is dead silent, so this seems ok.
I am actually uncertain if the isotrafo in fact is required, but at least any ground loops should be addressed. If the input impedance of the sub plate amp is greater than 47kOhm I might omit it.
Do you agree that a level compensation locally on the sub is not required, because when unbalancing the XLR side the single ended output will have the same level?
Do you agree that a level compensation locally on the sub is not required, because when unbalancing the XLR side the single ended output will have the same level?
Actually I’m not quite posive which way you expect it to be or want it to be. The balanced output is double the voltage of the single ended output. That doubling is sometimes shorted out when people naively use XLR to Coax adapters that sometimes short out 1/2 of the output. That isn’t the case with direct connections to two difference devices from the DS, they will 6dB different.
Frode said
Do you agree that a level compensation locally on the sub is not required, because when unbalancing the XLR side the single ended output will have the same level?
Actually I’m not quite posive which way you expect it to be or want it to be. The balanced output is double the voltage of the single ended output. That doubling is sometimes shorted out when people naively use XLR to Coax adapters that sometimes short out 1/2 of the output. That isn’t the case with direct connections to two difference devices from the DS, they will 6dB different.
Well perhaps I misunderstood your original question. I’m too used to people asking about using the balance and unbalanced outputs at the same time to two different devices.
Frode said
Do you agree that a level compensation locally on the sub is not required, because when unbalancing the XLR side the single ended output will have the same level?
Actually I’m not quite posive which way you expect it to be or want it to be. The balanced output is double the voltage of the single ended output. That doubling is sometimes shorted out when people naively use XLR to Coax adapters that sometimes short out 1/2 of the output. That isn’t the case with direct connections to two difference devices from the DS, they will 6dB different.
Well perhaps I misunderstood your original question. I’m too used to people asking about using the balance and unbalanced outputs at the same time to two different devices.
My comment was based on a logical assumption derived trom the fact that when the RCA output also is connected it unbalances the XLR output and by doing this the +6dB gain is cancelled out as a direct consequence of this. It seems that Elk got this one correct.
Elk said
I'm assuming simultaneously to two different devices using the typical shorting adapter.
The DS single ended output sees the input impedance of the isotrafo (47kOhm) opposed to an open circuit.
The XLR goes direct from the DS to the power amp.
There are no shorting devices, only single ended and differential.
The trouble is that the balanced circuit sees the load on the single ended output and thereby is coupled if my understanding is correct.
In the first post you say that Elk got it right, then you say he didn’t
Without weird adapters the balanced will be about double the voltage of the unbalanced no matter whether one, the other or both are connected. At the next level of detail impedance output level issues are almost moot till you get down below, say 1k. Capacitance issues can affect FR. Balance issues can affect hum.
The balanced output is connected to a transformer with the center tap of the xformer connected to ground. The single ended output is also connected to the positive output of the transformer and ground - i.e. in parallel with the positive half of the balanced output.
Elk said
I'm assuming simultaneously to two different devices using the typical shorting adapter.
The DS single ended output sees the input impedance of the isotrafo (47kOhm) opposed to an open circuit.
The XLR goes direct from the DS to the power amp.
There are no shorting devices, only single ended and differential.
The trouble is that the balanced circuit sees the load on the single ended output and thereby is coupled if my understanding is correct.
In the first post you say that Elk got it right, then you say he didn’t
Without weird adapters the balanced will be about double the voltage of the unbalanced no matter whether one, the other or both are connected. At the next level of detail impedance output level issues are almost moot till you get down below, say 1k. Capacitance issues can affect FR. Balance issues can affect hum.
The balanced output is connected to a transformer with the center tap of the xformer connected to ground. The single ended output is also connected to the positive output of the transformer and ground - i.e. in parallel with the positive half of the balanced output.
Elk got it right, until I saw the shorting adapter question (I thought)
OK, so if a the shorting device is not in place, the XLR is +6dB still if ground is common for SE and Diff.?
Meaning that the hot side on diff will not be pulled down with SE in parallel as long as the SE load is not below 1k?
Frode said
Elk got it right, until I saw the shorting adapter question (I thought)
OK, so if a the shorting device is not in place, the XLR is +6dB still if ground is common for SE and Diff.?
Meaning that the hot side on diff will not be pulled down with SE in parallel as long as the SE load is not below 1k?
Yep, that’s correct. The 1k figure is just a guideline - the 20dB attenuator loads it by a lot more than that, but somewhere the load gets too low to not affect the level or FR noticeably.
Frode said
Elk got it right, until I saw the shorting adapter question (I thought)
OK, so if a the shorting device is not in place, the XLR is +6dB still if ground is common for SE and Diff.?
Meaning that the hot side on diff will not be pulled down with SE in parallel as long as the SE load is not below 1k?
Yep, that's correct. The 1k figure is just a guideline - the 20dB attenuator loads it by a lot more than that, but somewhere the load gets too low to not affect the level or FR noticeably.
Thx.
I see that the DS Rout (secondary side of trafo winding) is just 200Ohms.
I know what to do now. The sub volume is currently set at 0dB so I will input pink noise with power amps off and measure the level at the sweet spot with a dB meter (dB c-weight). Then I will adjust the sub volume until it reads 6dB higher value. Instead of pink noise I guess I can use a sine wave well below the 50Hz xo point for the low pass (eg. 30-40Hz due to graceful roll-off).
Actually, when I come to think of it it might be that I have to adjust my subs to less than 6dB, because I would expect a higher SPL when 2ea. 12’’ woofers is brought into action (stereo subs). As it happens I am not sure if I actually need to power off my amps (ie. main speakers) when doing this exercise.
means that both the XLR and RCA gives off the same level from the DAC meaning that any volume adjustment on the sub to compensate is no longer an issue.