Handling Unbalanced Signals with the Model 12

[whynot]

Hi all,

(This is my first post on the forum—glad to be here!)

I’m currently researching the Model 12 before buying and trying to wrap my head around the TRS balanced inputs and outputs. On my current mixer and soundcard, I can use TRS or TS cables interchangeably without issues (per the manuals).

After checking with the very helpful team at Tascam support, they confirmed that it's important to convert a TS unbalanced signal to TRS balanced before using the channel. They mentioned:

"Using a TS jack could result in damage to the input op-amps, as one leg of the balanced input will be shorted."

Their recommendation is to use a DI box, such as the ART DualZDirect.

I have a couple of unbalanced line-out instruments:

• Novation BassStation Mk1
• Behringer TD-3

And a couple of effects:

• Delay pedal (between Aux and channel in)
• Korg Kaoss Pad (between Sub and channel in)

I’m curious—what solutions have others come up with for handling unbalanced signals with the Model 12?


Any insight would be greatly appreciated! Thanks in advance.


(BTW, I might be a little slow to reply sometimes.)

​

 

[Mark Richards]

Welcome to the forum, @whynot.
I'm not an owner of a Model 12, but here's the relevant pages of the Model 12 OM showing a typical connection setup. If you don't yet have it, the OM pdf is on the TASCAM website under the "Support" section.

 

[Max Relic]

Using a TS jack could result in damage to the input op-amps, as one leg of the balanced input will be shorted.

Hi @whynot , I would rate that sentence more misleading than helpful.

For a line level signal input, shorting one input leg of a differential op-amp (Operational Amplifier) to ground should be considered not harmful, in that it consists in no signal reaching one side of the amp stage (while the other side still works).
Shorting the output of any amplifying device can be harmful or even dangerous depending on voltage and current rating involved.
For a phantom-powered microphone input stage there could be the risk of burning a fuse or some component (likely in the power supply board) because of voltage/current circulation.

From a signal quality perspective, balanced connection should be adopted whenever equipment is connected to the mixer with long cables and/or signal level is weak (i.e.mic level); a full-balanced line (from instrument output to mixer input) grants lesser noise and better Signal to Noise Ratio than unbalanced line.
That said, in my Model 12 I use indifferently balanced and unbalanced connections depending on the gear. No input op-amp were harmed in the last 40 years.

I suggest reading some Mackie mixer owner's manual to learn some useful notions about connections, they are well written and funny to read.

 

[whynot]

Hi @Mark Richards, thanks for your reply! The manual is actually what got me thinking, as it seems to specify TRS balanced for line inputs. The keyboard and guitar in the connection diagram are using TS, but I assume that’s for high-impedance instrument level? (From what I understand, when ‘Inst’ is enabled, the inputs become unbalanced?)


Hi @Max Relic, that’s really interesting! So you’re saying TS and line-level unbalanced signals aren’t an issue? From my limited experience, that does usually seem to be the case. I’m just curious why Tascam is advising otherwise. This is a big purchase for me, so I really want to make sure I get it right.


Really appreciate the input—thanks again!

 

[Max Relic]

The example picture on page 22 shows a keyboard and an effect processor connected to line-level balanced inputs with TS (aka unbalanced or mono) cables: these kind of equipment never need hi-impedance input stage, which otherwise must be used when connecting non-preamplified electric bass or guitar to the mixer.
Hope it makes sense.

 

[shredd]

Hey @whynot - Resident dumazz here, with my $0.02:

I'm no rocket surgeon, certainly not a studio-electronix tech...nor did I read the sections @Mark Richards posted, as I don't have a M12 (and wouldn't, unless I had a gun to my head). BUT:

Would it be possible that the designation of the input as "TRS" means they support TRS connections (are capable of properly connecting such a source) - but not REQUIRING it?
I say this because I imagine something like 98-1/2% of instrument sources that are not XLR, but use 1/" plugs (git'rs/basses, synth outputs - even stereo) are TS 1/4"...even outputs from outboard FX's, processors, etc, are split between TS and TRS type connections.

I can hardly imagine why the M12's inputs wouldn't safely accommodate 1/" TS plugs...it's my perception that the Tascam tech that answered your question must've somehow misunderstood exactly what you were asking...or perhaps it was late on a Friday and he was well into his weekend meth-loadup???

Dunno. But surely merits further exploring...I do NOT see why a standard channel input wouldn't safely accommodate a 1/4" TS....

 

[Mark Richards]

Shorting the output of any amplifying device can be harmful or even dangerous depending on voltage and current rating involved...

For a line level signal input, shorting one input leg of a differential op-amp (Operational Amplifier) to ground should be considered not harmful, in that it consists in no signal reaching one side of the amp stage (while the other side still works)...

From a signal quality perspective, balanced connection should be adopted whenever equipment is connected to the mixer with long cables and/or signal level is weak...

@whynot, to expand a bit on what Max wrote in posts #3 and #5:

I agree with Max on all points:

*For example, keeping a monophonic TS headphone plug inserted into a TRS stereo headphone output jack will eventually fry the headphone circuit.

*A TS line level output to a TRS line level input should not cause any harm.

*Generally, the purpose of TRS (balanced) mic and line inputs is to accomodate cable runs in excess of about 12 meters that otherwise, using only TS (unbalanced) cable, would pass unwanted line noise to the input's op-amp.

The keyboard and guitar in the connection diagram are using TS, but I assume that’s for high-impedance instrument level? (From what I understand, when ‘Inst’ is enabled, the inputs become unbalanced?)

Line level inputs are always high impedance whether TS or TRS. Looking at the Specification page of the OM, on the Model 12, the line level input's impedance is 22 kOhm, which is appropriate for keyboards, FX processors, etc. (i.e., anything that outputs at line level).

However, the pickups of electric and bass guitars without an on-board pre-amp are typically in the 40 kOhm range. Again looking at the Specification page of the OM, we see that when the "INST" button is engaged, the line level circuit's impedance changes from 22 kOhm to 1 MOhm to accommodate the much greater impedance of guitars without an on-board pre-amp.

"INST" should not be engaged for guitars that have an on-board pre-amp, which will have the correct ouput impedance match for the Model 12 line level input's 22 kOhm impedance; nor should it be engaged for any typical line level gear or instruments.