Line balancing and when to convert -10 dBv to +4 dBm

[howlback]

As I fumble through the analog domain, I’ve noticed that my 388 and many consoles like it are unbalanced after the input. Since much of my outboard gear expects a balanced +4 dBm signal, I found myself with several questions: do I need to convert all my unbalanced signals to ensure outboard processors work correctly? Is it possible to connect the unbalanced signals (inserts, sends, pgm outs) to balanced patchbays? Should I focus on using -10 dBv compatible processors? These questions led me down a rabbit hole.

While I’m still undecided about the optimal wiring setup for my studio, I’ve made some progress. I’ve acquired several Tascam Patchbays, which seem to be a more manageable solution for my small studio. In instances where I’ll be using hardware that requires a balanced +4 dBm signal, I can utilize a balancing amp. My microphone lines, console inputs, and balanced outboard processors will connect to a balanced TT patchbay (PB-664, 704H/N), while my inserts, programs outs and monitoring will plug into unbalanced TS or RCA patchbays (PB-32P/H/R/W). When necessary, I can use an LA-40 to create a bridge between the two.

I’m posting this in hopes of finding someone who has faced a similar dilemma and would be willing to share their experiences.

 

[Slouching Raymond]

Every orifice on my SSL XL-Desk is balanced. A lot of my signal sources are balanced too, but some are unbalanced.
To help here, I got a dual DI box, which I have yet to use. I may buy more.
Apparently, you can get Reverse DI Boxes.

 

[ecc83]

As I fumble through the analog domain, I’ve noticed that my 388 and many consoles like it are unbalanced after the input. Since much of my outboard gear expects a balanced +4 dBm signal, I found myself with several questions: do I need to convert all my unbalanced signals to ensure outboard processors work correctly? Is it possible to connect the unbalanced signals (inserts, sends, pgm outs) to balanced patchbays? Should I focus on using -10 dBv compatible processors? These questions led me down a rabbit hole.

While I’m still undecided about the optimal wiring setup for my studio, I’ve made some progress. I’ve acquired several Tascam Patchbays, which seem to be a more manageable solution for my small studio. In instances where I’ll be using hardware that requires a balanced +4 dBm signal, I can utilize a balancing amp. My microphone lines, console inputs, and balanced outboard processors will connect to a balanced TT patchbay (PB-664, 704H/N), while my inserts, programs outs and monitoring will plug into unbalanced TS or RCA patchbays (PB-32P/H/R/W). When necessary, I can use an LA-40 to create a bridge between the two.

I’m posting this in hopes of finding someone who has faced a similar dilemma and would be willing to share their experiences.

Fork in H! This is a complex subject and one moreover that raises issues peculiar to each individual setup. Deep intake!
First of all there is the concept of "unity gain and connector standard". This means every line input and output works at the same nominal level, uses the same connector and is balanced because mixing bal and unbal is a nightmare.
The usual reason for balanced working is the rejection of external noise, mostly hum. Very often it is claimed that balanced operation eliminates Ground Loops? It certainly can but is not a total fix in every situation.

N very B! Keep microphone circuits separate and on XLRs not LEAST because of the presence of phantom power!!

For a very simple rig, a small mixer say and a stereo tape recorder, there is little to be gained from converting to balanced operation even over quite long lines provided that the output resistances of the gear is low and it will be from most mixers, of the order of <200 Ohms and could be as low as 100R. That low value will both keep hum at bay and preserve HF from being shunted by cable capacitance. Tape machines can have higher OP Zs but rarely more than 1k and that is generally acceptable. It is handy that most semi-pro tape machines are earth free such as my Teac A 3440h.

You can convert an unbal output to balanced with a single resistor, so called "impedance" balanced where R goes to the source ground then the ring of a TRS jack and is equal to the OP resistance of the source. You can only get truly balanced signals an active unit such as https://www.fruugo.co.uk/amplifier-...RLusbeqzxBtsXaWhT09RTw-BjxgmWXrQaAi4AEALw_wcB

or a transformer the latter having the extra advantage of GL isolation. Note, a disadvantage of balanced op' is the ever present danger of a polarity flip. Make a tester! Impedance balancing has the advantage that a flipped cable delivers FA audio!

There is no such cheap way to get a balanced INPUT. You either need an active device or a special "10k+10k" line input transformer. All decent traffs are expensive, bulky and can pickup hum.

As to OP level? Most tape decks run at neg ten and it is easier and cheaper to attenuate than amplify plus you don't run the risk of signal degradation. Where cable runs are short, no more than about 10m say, -10dBV will be fine.

Lots of paper, diagrams and thought needed!

Dave.

 

[howlback]

Thanks for the reply. My first encounter with this all was using a 436-style Varimu compressor on an unbalanced insert. The compressor input and output were rated for a balanced +4 dBm signal, and since the threshold on a 436-style compressor is determined by driving the input, providing the correct signal level was necessary. Outside of this sort of use case, I’ll likely avoid the cost and possible introduction of added noise associated with converting the signal.