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Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Sun Jun 09, 2024 1:25 am
by James Steele
So... I found my very old FMR (RNC) Audio Really Nice Compressor the other day and just for giggles thought of hooking it up to an analog pair of ins and outs on my 828es just to have another compressor option (for fun) until such time as I might get something else.
Only thing is that this unit was designed to be connected with the weird Tip Ring Sleeve scheme where one jack would serve as both send and return... like on the old Mackie Board.
The manual does state that you can connect up to other equipment but you must use Tip/Sleeve unbalanced cables... but I'm not sure if connecting Tip/Sleeve cables to TRS balanced ins/outs on 828es will work. Here's pertinent section from the manual:
HOOK-UP
The RNC is designed to interface with unbalanced audio gear (nominal operating level = 0dBu) two distinct ways:
1) TRS Inserts — The RNC can be hooked into Tip-Ring-Sleeve (TRS) insert points found on many consoles where: TIP = Console insert out, RING = Console insert in, SLEEVE = Ground reference. This means that each channel of the RNC can be hooked to a each channel of a TRS console insert with a single TRS cable. For example, on my Mackie 1604VLZ, the main out has left and right insert points so that my RNC can be put in the main out insert (Left and right) with only two TRS cables!
20 All Other Equipment — Hooking up the RNC to gear other than TRS inserts must be done with a pair of TS (Tip-Sleeve) jacks for each RNC channel. Thus, the full ste- reo hook-up of an RNC must be done with four TS 1/4'' cables.
NOTE — Hooking up the RNC to balanced lines with TRS 1/4'' plugs will not work! If the equipment you are connecting the RNC to is balanced, you must first unbalance it and only connect into the RNC with TS 1/4'' plugs.
Re: Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Sun Jun 09, 2024 1:45 am
by James Steele
Hmmm... just found this on Page 46 of the 828es manual:
TRS quarter-inch analog inputs and outputs
Quarter-inch analog inputs and outputs are balanced (TRS) connectors that can also accept an unbalanced plug. The outputs are DC-coupled, so they can be used for CV control output.
☛ Quarter-inch analog outputs are not cross-coupled. Therefore, when connecting them to an unbalanced input, use a TRS plug with the ring disconnected. Not floating the negative terminal will short it to the sleeve ground and cause distortion.
So if I read that correct, I should be able to connect the RNC outputs to 828es inputs with 1/4" TS>TS cable. But need to connect 828es output to RNC input with a 1/4" TRS>TRS with the ring disconnected/unused?
Hmmm... all of this further complicated if I wish to get my 1/4" TRS patchbay involved. Hmmmm
Re: Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Sun Jun 09, 2024 4:33 am
by Phil O
There's always the transformer route, if you're so inclined:
https://www.jensen-transformers.com/wp- ... /an003.pdf
Go to section 3 - Balanced to unbalanced interfaces.
Your friendly neighborhood Phil
Re: Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Sun Jun 09, 2024 6:52 am
by stubbsonic
I have an FMR RNC1773 always on for my Zoom meeting input.
An aux send from my mixer sends to the input of the RNC via unbalanced TS patch cable, and out of the RNC into an input on my FF800 also via unbalanced TS cable. works fine.
That the 828ES is cool with unbal/TS and so is the RNC, I think you have your answer.
[My RNC is old, and it recently]stopped working, only passing noise. I swapped out some caps and was back in action. Easy fix.]
Re: Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Sun Jun 09, 2024 2:24 pm
by James Steele
stubbsonic wrote: ↑Sun Jun 09, 2024 6:52 amThat the 828ES is cool with unbal/TS and so is the RNC, I think you have your answer.
Yeah... the only thing that caused me some concern was this little bit that I got directly from the 828es manual:
☛ Quarter-inch analog outputs are not cross-coupled. Therefore, when connecting them to an unbalanced input, use a TRS plug with the ring disconnected. Not floating the negative terminal will short it to the sleeve ground and cause distortion.
I guess I should just try hooking it up with two unbalanced 1/4" cables and see if I get distortion... I don't think it's possible to fry my 828es.
Re: Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Sun Jun 09, 2024 3:05 pm
by HCMarkus
Best would be your initial approach, or TRS with floated ring to TS for 828 output into RNC.
Re: Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Sun Jun 09, 2024 5:39 pm
by James Steele
HCMarkus wrote: ↑Sun Jun 09, 2024 3:05 pm
Best would be your initial approach, or TRS with floated ring to TS for 828 output into RNC.
Now I'm confused. LOL. What was my initial approach again?
Re: Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Sun Jun 09, 2024 9:59 pm
by stubbsonic
They don't bother to define "cross-coupled" because clearly everyone knows exactly what that means.
It's also weird that most gear I've ever used that has balanced inputs, accepts TS cables with no issues. But there it clearly says something different. Oh poo.
Can you ask one of the nerds over at MOTU?
Re: Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Mon Jun 10, 2024 8:18 am
by Phil O
stubbsonic wrote: ↑Sun Jun 09, 2024 9:59 pmIt's also weird that most gear I've ever used that has balanced inputs, accepts TS cables with no issues. But there it clearly says something different.
It's only the outputs that have this issue. If you look at the link I posted in my reply to James, at the beginning of the paper is a section called "Typical balanced output and the description begins with, "This output circuit provides two equal amplitude but opposite polarity (symmetrical) signals and equal output (source) impedances to the lines."
If you look at the schematic the output connected to pin 3 of the XLR jack would be shorted to ground if the output were a TRS jack (instead of an XLR)and a TS cable was plugged in. This would short the output of the inverting (lower) amplifier, which depending on the amplifier design could cause distortion. In general, balanced outputs are not meant to be used in this configuration but in some cases you can get away with it.
Your friendly neighborhood Phil
Re: Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Mon Jun 10, 2024 8:38 am
by stubbsonic
If ring is shorted to ground, does that essentially increases the signal level (i.e., voltage across Tip & Sleeve)? In that case, is the subsequent input expecting a particular signal strength and just getting more than it bargained for? And, in this case, would a 6 dB pad be the solution?
I know it sounds like I'm bending over backwards to form these as questions, but I have to admit, I SHOULD know this stuff by now, but I don't. I will study that PDF.
Re: Connecting Unbalanced FMC RNC Compressor to 828es?
Posted: Mon Jun 10, 2024 8:46 am
by Phil O
I think that depends on the circuit configuration. The sample circuit in the Jensen paper I believe would do the opposite. The amplitude would be halved with the inverting amp shorted. The distortion, if any, would be due to load on the lower amp.