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Balanced TRS outputs to RCA Phono (again)

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Balanced TRS outputs to RCA Phono (again)

Postby andrew_a » Wed Jun 10, 2020 6:27 pm

Hello

Firstly, I know that this topic has been discussed on the forum several times, but I have a question I've not been able to answer from my reading.

I have an Audient ID14 interface that has balanced TRS L/R outputs.
I have a Rotel amp with RCA phono inputs.

I've read around to understand why a balanced signal is used (summing the positive/negative at the other end cancels the noise) but in my situation I can't use the balanced signal from the ID14.

I currently have a pair of TS to phono cables. I believe the effect of using these cables is either 6db loss of volume, or no effect (if the ID14 has impedance-balanced outputs - which I don't known if it has or not). Is that correct?

My question is, what benefit might be gained of using Pseudo Balanced RCA Phono to TRS Jack Leads (like these https://www.designacable.com/audio-visual/pseudo-balanced/pseudo-balanced-rca-phono-to-trs-jack-lead-pair-van-damme-starquad-cable.html), which have the following wiring: "On these leads we have left the screen connected at the TRS end. This eliminates the risk of induced hum and noise (ground loops) from the screen. The unused Ring inside the TRS Jack is wired to the screen inside the RCA/Jack, this reduces unwanted noise and signal degradation."?

I'm not currently aware of any hum using my current leads.

Thanks in advance
-Andrew
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Re: Balanced TRS outputs to RCA Phono (again)

Postby ef37a » Wed Jun 10, 2020 6:56 pm

Hi Andrew, you only get the 6dB lift if the input is balanced irrespective of whether the AI's output is 'two amps' or impedance balanced.

You just need TRS to RCA phono and ignore the 'cold' ring connection. Tip is hot, sleeve to RCA outer.

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Re: Balanced TRS outputs to RCA Phono (again)

Postby Hugh Robjohns » Wed Jun 10, 2020 8:09 pm

andrew_a wrote:I have an Audient ID14 interface that has balanced TRS L/R outputs.
I have a Rotel amp with RCA phono inputs.

If you want to connect the ID14 speaker outputs to the amp's line inputs, ordinary quarter-inch TS plug to RCA-phono cables will be fine. But you'll need to be careful with the volume comtrol as the Audient is capable of generating a rather bigger signal than the amp will expect.

I've read around to understand why a balanced signal is used...

Balanced interfaces offer greater rejection of interference and, as they do not require a ground reference, they don't suffer ground-loop noises as easily as unbalanced connections..

I currently have a pair of TS to phono cables. I believe the effect of using these cables is either 6db loss of volume, or no effect (if the ID14 has impedance-balanced outputs - which I don't known if it has or not). Is that correct?

The ID14 does have impedance-balanced outputs (stated on page 14 of the manual), so your standard TS-phono cables will be absolutely fine... And there will be no 6dB loss of level because all of the signal is carried on the hot side, rather than half on the hot and half on the cold.

My question is, what benefit might be gained of using Pseudo Balanced RCA Phono to TRS Jack Leads

Probably not much!

The idea (and advantage) of a pseudo-balanced cable only works when connecting an unbalanced source into a balanced input, and the benefit is that the connection can be made without tying the source and destination device grounds directly together, thus avoiding a ground-loop and any groundloop noises.

But you are trying to connect a balanced output to an unbalanced input, so the pseudo-balanced cable isnt really appropriate.

However, if you find you have ground-loop problems then you can use this kind of cable backwards with impedance-balanced outputs where it will help to minimise the unwanted noises by linking the grounds of the two devices via the cold side's matching output impedance.

I'm not currently aware of any hum using my current leads.

Then there would be no benefit, and I would stick with what you're currently using. Its all fine!
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Re: Balanced TRS outputs to RCA Phono (again)

Postby andrew_a » Wed Jun 10, 2020 9:08 pm

Many thanks for the replies.

Thank you Hugh for the reassuring words (crazy how much anxiety a lack of knowledge can cause) and for pointing out the detail in the manual ( :headbang: ).

From reading other posts, I had the feeling that my situation didn't fit the use-case for pseudo-balanced cables, so thank you for the confirmation.

All the best.
-Andrew
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Re: Balanced TRS outputs to RCA Phono (again)

Postby andrew_a » Fri Sep 11, 2020 9:15 pm

Hi

I'm just coming back this thread - specifically the comment Hugh made, i.e.

But you'll need to be careful with the volume control as the Audient is capable of generating a rather bigger signal than the amp will expect.

My amp recently failed (hot signal from the Audient may or may not have been a factor) and I've just got in back from repair.

I want to do my best to keep the output of the Audient at a level that is conformable for the amp.

I've tried to look into the topic myself. I have come up with the notion that -30 dBFS output on the Audient might be equivalent to consumer line level, but to be safe I should keep to a ceiling of -50 dBFS (which is -12 on the led meters of the interface).

I would very much welcome your thoughts on this.

Thanks
-Andrew
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Re: Balanced TRS outputs to RCA Phono (again)

Postby ef37a » Sat Sep 12, 2020 12:09 pm

The specc' for the iD14 gives max output (0 dB fs) as +12dBu or a tad over 3 volts and I would not have thought 3V would have hurt the input of a decent hi fi amp? It will however make the volume control a bit skittish.

The solution is a simple* resistive attenuator at the amplifier end. If we take 'hi fi' consumer level as 150mV then you would seem to need, on the face of it, a 26dB attenuator. In practice that would I think be too much and 10-12dB more like it because you will want to have gain in hand for low level signals.

*Simple for me to say but where you GET a stereo, inline attenuator I do not know! I am sure Orchid would make you one but as a one off be quite expensive? If you can solder and drill metal boxes, give me a PM and I will draw you something up. BTW I would not use fixed resistors but a couple of 10k Ohm presets. Lets you 'calibrate' things.

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Re: Balanced TRS outputs to RCA Phono (again)

Postby James Perrett » Sat Sep 12, 2020 2:13 pm

ef37a wrote:*Simple for me to say but where you GET a stereo, inline attenuator I do not know! I am sure Orchid would make you one but as a one off be quite expensive? If you can solder and drill metal boxes, give me a PM and I will draw you something up. BTW I would not use fixed resistors but a couple of 10k Ohm presets. Lets you 'calibrate' things.

Mike Stranks posted a very useful link to Fentronix a few days ago who make these...

https://www.ebay.co.uk/itm/Stereo-Atten ... Swm8VUsvO0

but there are also plenty of inline phono attenuators like these...

https://www.ebay.co.uk/itm/IMG-Stagelin ... SwWZVdxBfU
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Re: Balanced TRS outputs to RCA Phono (again)

Postby ef37a » Sat Sep 12, 2020 3:31 pm

Woah! Pricey James.

These: https://www.canford.co.uk/Products/20-9 ... ono-in-out look better value but still 30quid for stereo, They are at least about the right level of attenuation, 14dB.

Just thought, for the price of the 50quid ones OP could buy a solder station and all the kit needed to roll his own!

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Re: Balanced TRS outputs to RCA Phono (again)

Postby Mike Stranks » Sat Sep 12, 2020 3:56 pm

C'mon Dave... £11.50 plus postage isn't that bad!

And I can vouch for the quality of the Fentronix gizmos. Neat and well-made.
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Re: Balanced TRS outputs to RCA Phono (again)

Postby ef37a » Sat Sep 12, 2020 5:08 pm

Mike Stranks wrote:C'mon Dave... £11.50 plus postage isn't that bad!

And I can vouch for the quality of the Fentronix gizmos. Neat and well-made.

No, 11 and 'arf ain't bad but I did not see any for that? In any case most of them seemed to be 25dB and I think that will be to much chop.

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Re: Balanced TRS outputs to RCA Phono (again)

Postby James Perrett » Sat Sep 12, 2020 9:23 pm

ef37a wrote:Woah! Pricey James.

These: https://www.canford.co.uk/Products/20-9 ... ono-in-out look better value but still 30quid for stereo, They are at least about the right level of attenuation, 14dB.

Just thought, for the price of the 50quid ones OP could buy a solder station and all the kit needed to roll his own!

Dave.

I must admit that I saw two in the picture and assumed that the price was for both. I'm sure I've seen the same thing much cheaper - that was just the first Ebay listing in the search. I used to use something that looks identical with my Behringer UCA222.

Looks like the car audio enthusiasts use something that might work...

https://www.ebay.co.uk/itm/Universal-Ca ... 0677.m4598
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Re: Balanced TRS outputs to RCA Phono (again)

Postby ef37a » Sun Sep 13, 2020 9:29 am

Yes, a nifty for two but then those audiophools will pay through the nose for anything if you give them some spin and bit o bling!

Yes, those car-people pots look just the bizz, will get one and pull it apart...But!

WHAT is a man of YOUR audio cal-Y-bre James doing with a Behringer UCA222? A handy little box for some purposes I grant you, had 3 over the years but surprised you use one!

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Re: Balanced TRS outputs to RCA Phono (again)

Postby James Perrett » Sun Sep 13, 2020 3:00 pm

ef37a wrote:WHAT is a man of YOUR audio cal-Y-bre James doing with a Behringer UCA222? A handy little box for some purposes I grant you, had 3 over the years but surprised you use one!

I wanted something better than the built-in sound on my laptop and a friend of mine had used a similar looking box from Phonic successfully for a few years so I thought it had to be worth a try. As I've mentioned in other threads, it wasn't really up to the job so I now use a Zoom U44, either with its internal convertors or with a Sonifex RB-ADDA doing the conversion.
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Re: Balanced TRS outputs to RCA Phono (again)

Postby andrew_a » Sun Sep 13, 2020 6:32 pm

Thanks so much for the replies and suggestions - it is much appreciated.

I have no capabilities when it comes to soldering, so I will look to purchase one of the suggested attenuators to deliver a c. 10-12 dB cut in gain (as suggested by Dave).

All the best
-Andrew
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