There seems to be no one right answer to this as it depends on the circuitry of my interface. I have a Tascam US-1800 and it has 2 balanced TRS jacks for Monitor left + right. I want to use a Stereo receiver amplifer for the monitor and it only has unbalanced RCA inputs. What I can't figure out is which of these adapters I should buy.

These ones, mono(TS) to RCA
Metal 6.35mm (1/4 Inch) Mono Plug to RCA Jack Adaptor - Gold Plated at PrimeCables Canada

Or these ones, stereo(TRS) to RCA
Metal 6.35mm (1/4 Inch) Stereo Plug to RCA Jack Adaptor - Gold Plated at PrimeCables Canada

I know I want to convert it to an unbalanced signal, do I want to connect the cold (-) and ground together with a TS connector? Does the other connector do the same thing? How does the second connector merge 3 signals into 2
Thanks for your time if you know the answer

The US-1800 has impedance balanced line-level outputs. That means an unbalanced output should be connected via the TRS tip only. The first TS to RCA adapter (labeled "mono") is the correct one to use. The Ring will be grounded by the TS adapter, but that does not matter and with an impedance balanced output, the signal will be the same with either a grounded or open ring connection. There is no signal on the Ring.

The second "stereo" adapter is an unknown. It may be designed as an adapter to send a mono RCA signal to both stereo channels of a stereo TRS input. In that case the tip and ring would be connected together. If it's wired that way it won't work as a mono TRS to RCA adapter when connected to a balanced output. It may be wired with the Ring open. If so it will work as well as as TS adapter when connected to a impedance balanced output, but not at all if connected to a transformer balanced output.

Only fully-floating, transformer-balanced outputs require that the ring terminal is grounded when driving an unbalanced input. Impedance balanced or electronically balanced outputs do not. Your US-1800 is not transformer-balanced.

Use the first "mono" adapter or better yet use a proper pair of TS to RCA cables to eliminate the extra set of unneeded contacts in the adapter.

from 1/4" tie ring and sleeve together -> ring of RCA
1/4" tip -> tip of RCA

That should do it.

I this true for all PC audio devices? My device just says "1/4” Phone Jack. Ground sensing design" (Konnekt 24D)

There are a number of different balanced and pseudo or quasi-balanced ("pseudo" and "quasi" being fancy words for "not really") output schemes and each device may use any one of them. You're lucky your device specifies which one it is, many don't. To connect a ground sensing output to an unbalanced input, for absolutely best noise performance use a balanced cable (2 wires + shield) and connect the cold wire to ground at the receiving end. If you don't use very long cables nor do you have serious EMI problems in your studio, using an unbalanced cable and grounding the cold pin at the output of the device will work just as well.

what is a very long cable? is 5m long?

what is the diference between conecting cold a and ground at the the source and conecting them at the recieving end?

Good question. This is a very long cable and no, I wouldn't say 5m is very long, but I couldn't tell you where the "threshold" between not very long and very long is, because there isn't one... It's just a matter of likelihood that the cable will pick up noise from e.g. mains wiring (never a good idea to lay a signal cable alongside a mains one!). Signal level matters too, obviously the very weak signal from a microphone is more succeptible to noise than a line level signal. But it all depends on the particulars of your setup and studio, of course (1).

I can't explain it better than Douglas Self in the link above, go to fig. 5a and the paragraph below it, but basically connecting it at the source and using an unbalanced cable simply turns the output into an unbalanced one, while using a balanced cable and connecting it at the receiving end can still cancel out noise picked up by the cable shield, if any (2).

Given (1) and (2), the only way to know whether you actually *need* to use a balanced cable or not is to try and see, or you could just play it safe, use a balanced cable and be done with it. We're talking about 10m here so the difference in cost between one and the other is going to be peanuts, plus if later down the line you upgrade your receiving equipment to something with balanced inputs, you'll be glad you already have a balanced cable.

Inverting an active DI is not possible right? cause I have an old unused Behringer DI-100 with unbalanced inputs and balanced outputs

No and even if it was possible, there's no point in using any sort of balanced - unbalanced converter here since you don't really have a balanced output, as "ground sensing" falls into the quasi / pseudo / not really-balanced category. An active balanced - unbalanced circuit takes the cold signal, inverts it and adds it to the hot, but here you don't have any cold signal: as explained in the link above, the cold pin is actually an *input* used for cancelling ground noise, so even the best converter in the world can only degrade your signal or at best do nothing to it.

after reading the Douglas-Self page and trying to find out more about "ground-sensing" I actualy interpret my output as a quasi-floating one. Doesn't the "ground-sensing" mean that it senses when hot or cold are grounded? if it was ground-canceling they would call it as such.

I send a support message to Tc-Electronic but I don't realy expect an answer as they don't seam to suport my interface anymore

It's the same thing, it's also called ground-sensing because it senses the ground voltage (through the cold pin). The quasi-floating one isn't very common in low cost devices like yours, as it requires two vs. one opamp section and a trimmer that has to be adjusted in each output of each unit. In any case it's easy to find out if you have it: connect shield to shield and hot to hot, leaving cold unconnected, and note the signal level you get; now connect cold to ground (for the purpose of this test it doesn't matter if you do it at the output or receiving end) and, if you have a quasi-floating output, the signal level will increase by 6 dB.

ok, found out an easy "trick". I just pluged in a headphone and indeed it only had output on the right side

now I am still confused since many sites say it is ok to use a simple TS>RCA for this while Douglas-Self says "shorting it locally to ground merely converts the output to a standard unbalanced type".
and in section 6, case 5 he doesn't specify the best cable for it

It is ok, there's nothing wrong with an unbalanced connection, it's just that there will be no ground noise cancellation, but you may not have any significant ground noise to cancel anyway. Section 6 case 5 corresponds to fig. 5a, where he shows a balanced cable, which is what you would use if you need the ground noise cancellation feature. Otherwise, a TS > RCA unbalanced cable will indeed work perfectly ok.

Hello, sorry for side questioning under resolved post!

I have ns-10m with home consumer amplifier with only RCA inputs (unbalanced), I connected it with TS-RCA cable from RME UFX ii (balanced outputs only).. and right side phase is inverted.. any other cable i can try..? or should I swap the wiring from black and red on right side?

Sorry I am noob about balanced / unbalanced connection and wish I could connect it right!

(*with my turntable connection, ns-10m sounded fine)

thanks in advance! and sorry again!

The two connections are obviously the same so if one is out of phase and one is in this is nothing to so with it being a balanced/unbalanced connection....you might have a cable that's incorrectly wired or you're doing something else wrong that you're not telling us about.

Are you 100% sure it's an out of phase issue? How have you established that it's the right channel? Have you swapped cables around to see if the issue travels with the cable?

Hello, thanks for chiming in! I think? I have figured it out. So, I narrowed it down,

1. Tried 2 separate TS-RCA cables, each white side only, connected one white to left rca in, other white to right rca in (I have two ts-rca cables) and still right side phase was inverted

2. I tried, phone to rca cable with my mobile phone, still gave me one side phase inverted

You are right! I am totally confused, it could be either one phase inverted haha... so, I think my Rotel budget ra-820 amp is not the issue (I highly do not think so)

But, my NS-10m, the crossover wiring input panel looks different. Even though it says NS-10m 25w and 50w maxx info is there. So I think? I highly suspect that one side crossover part has been repaired and probably swapped by other technician years ago..? So, which means, its phase has been inverted and repaired that way?

Otherwise, it does not have any other way. So, if I phase invert either side on my TotalMix mixer app, sound is coming out fine, I tested with my fav songs on youtube.

Could this be a common issue/a thing?

So, I guess my test with my cheap turntable was done wrong, I thought it was in phase but it wasn't... I think one side of my ns-10m is wired inverted. (TS-RCA cables I have is just normal standard ones)

If it is so, can I then simply swap the wiring of ns-10m and just move on with it? or could it damage it?

If you want to be absolutely sure, take the tape outs from the rotel and connect to the RME inputs and record something (don't monitor or you'll get feedback).
Then you can check the waveform in the DAW.
Assuming these are in phase then you know the NS10 are definitely the issue.
You could simply swap the speaker cables over in that case, but in theory you should be fine rewiring the connectors for a permanent fix.

It seems odd that someone would have repaired them incorrectly like this though.

Thank you stella645 so much! I narrowed it down and turned out, it was the speaker. I simply swapped the wire on the rear. Now it is simple and good for good. Tweeter and woofer both sound ok thank you so much! Great historic speaker for a/bing application