Pseudo-Balanced . . . Adaptor Plugs?

[n o i s e f l e ur]

Pseudo-balanced, it's all the rage! All the cool kids are doing it. Or not.

It's been on the first page at least once aside from my own enquiries in the last week though and therefore apart from whatever circumstances that prompted me to be thinking about the subject in the first place - having spotted another topic vaguely along the same lines sems to have tickled my tiny brain and prompted my question.

Does the, or rather CAN the concept as applied in the SoS implementation be, ahhhhh, implemented (my old English teacher turns in her grave!) in an adaptor? My gut says yes, but my gut knows as much about these things as the rest of me, which isn't a lot really.

I think it may have been Hugh's exhortation to learn to solder with, among other benefits accrueing, right-length cables. So what about already-bloody-have-length cables? Or even this-would-be-easier-to-recable-if-I-only-had-to-rewire-one-bloody-side type situations?

Yep, I hear ya. DI box.

Shut-up-you-muppet-and-just-get-some-DI-boxes even.

Still though, is it a completely terrible idea? I think it would probably be a hellishy ambitious thing to tool up as a compact adaptor plug as normally seen, but perhaps as a short PB cable length with a male / female arrangement? If it's not technically illiterate, ie: concept works in adaptor form then I think it would be a way for people to hew to whichever side of the connection they wish to float (not actually just float, but let's use that for simplicity).

I await my continuing education with absolutely nothing like bated breath, because it's late and I'm off to me pit!

[ef37a]

First of all, those things that are generally called "Direct Injection" boxes take a middling impedance source, typically passive e guitar and transform it down to an ill defined but much lower impedance at mic level and the output is both balanced and almost always optionally earth isolated from the source, i.e. a Ground Lift Switch.
That is MY definition of a DI box and I wish people would stick to it!

But they don't and lazily call anything that "matches" or/and balances a signal a DI box.
What they mean is a transformer earth isolation box. These use 1:1 audio transformers instead of the 10 or 12:1 of "guitar" DI boxes. The unity ratio means the transformers can have a much better performance (at a given price point and size) than high ratio types.

Much better but not perfect and even if the audio response and distortion was beyond reproach there is still the problem of induced hum. Very expensive transformers with dual "mu metal" screens can be almost perfect but even a stereo pair is a decent wedge and mulitples get silly. On the other hand a piece of cable can be considered as having no discernable effect on the audio quality despite the mad ramblings of the Russ Andrews brigade. (yes, cable capacitance can attenuate HF but unlikely for line applications and even long cables)

Then, it is not always appreciated that there are two very different basic sorts of 1:1 audio transformers. Those designed as "output" transformers which need to be driven from a low, lower the better, source resistance and "input" transformers which must be loaded by a higher impedance, typically greater than 10k. The two types are not interchangeable if best performance is sought. The various "iso" boxes that are marketed must I think use some form of compromise between the two types. Personally I would treat all such devices as best connected to low Z outputs, i.e. put them close to the line out jacks not the remote input end.

In difficult situations, where there is a high level of external electrical noise, hum, RF etc, the use of a good quality output traff (often called "600 Ohms") at the source and an input traff (aka "10k+10k bridging") can deliver a massive reduction in noise pickup and with minimal impact on audio quality. Costalot mind!

For the real dope hunt up papers from the Jensen transformer Co.

Dave.

[Hugh Robjohns]

CAN the concept as applied in the SoS implementation be, ... implemented ... in an adaptor?

Yes, of course it can. And I do have some XLR barrel adaptors that perform a broadly similar (but slightly different) function.

The problem though, is that the adaptor would need to go at the instrument end, and its weight combined with that of the output cable will tend to strain the instrument's jack socket... which really isn't a good idea IMHO.

... perhaps as a short PB cable length with a male / female arrangement?

If you're going to make up a short pseudo-balanced cable and then extend it, why not just make one long enough to get the job done in one hit, and avoid the extra weight, expense, and potential reliability complications of extended cables?

H

[Drew Stephenson]

To me, the obvious advantage of a short pseudo-balanced cable would be that it's immediately obvious that it's a different cable and not just a standard balanced job. Ease of identification. Actual cost of manufacture would obviously just be the meters of cable difference.
That was a horrible sentence but you know what I mean.
I guess it would all depend on how frequently you're likely to mixing up your cabling or whether things will be semi-permanent installs.

[Hugh Robjohns]

To me, the obvious advantage of a short pseudo-balanced cable would be that it's immediately obvious that it's a different cable and not just a standard balanced job. Ease of identification.

I take the point... but the SOS special cables are already easily identified by the printed sleeving that states 'SOS pseudo-balanced' in big friendly letters...



H

[John Willett]

Why not run properly balanced and then use a balanceed to unbalanced transformer at the unbalanced end?

Canford Audio do them.

[Hugh Robjohns]

Mainly because a transformer isn't necessary and a special cable is a heck of a lot cheaper...

H

[ef37a]

John! Did you not read my waffle?

Mortified.

Actually John some years ago our interface was a 2496 fed from an A&H ZED10. The mixer was some distance away and fed two (Maplin) 5 mtr XLR mic cables terminating close to the PC in a box containing two OEP Z3002E 10k:10k transformers kindly sent me as samples!

The noise floor of the whole system, mixer on but output fader at minimum, was a satifactory -93dB fs.

Dave.

[n o i s e f l e ur]

Yes, of course it can. And I do have some XLR barrel adaptors that perform a broadly similar (but slightly different) function.

The problem though, is that the adaptor would need to go at the instrument end, and its weight combined with that of the output cable will tend to strain the instrument's jack socket... which really isn't a good idea IMHO.

The instrument end? Oh . . . I thought it would go at the input end, so as to negate the unbalanced cable shield acting as an antenna on the receiving device (think converters / AI). The added weight wouldn't be much, just whatever a jack weighs. One could easily rig some mechanical relief but sure, it's something to be considered definitely.

If you're going to make up a short pseudo-balanced cable and then extend it, why not just make one long enough to get the job done in one hit, and avoid the extra weight, expense, and potential reliability complications of extended cables?

H

As I mentioned, to continue using existing cables, and in many situations to leave existing cabling in situ and to just perform the re-cabling at just one end.

For my own situation it would be semi / permanent so basically mechanical reliability wouldn't be much of an issue once the connection was established and tested as working. Clearly other people will have different needs and should act accordingly.

I should stress that I originally envisaged something like the XLR barrel adaptor you mention Hugh, and it was concern about so much weight / length of metal sticking directly out of the back of the device that led me to think of the jack>short cable>jackplug arrangement.

Anyway, I have my answer. Thanks all.

ETA: Anyone else notice the forum is running an hour ahead?

[Hugh Robjohns]

I originally envisaged something like the XLR barrel adaptor you mention Hugh, and it was concern about so much weight / length of metal sticking directly out of the back of the device that led me to think of the jack>short cable>jackplug arrangement.

Yes, weight and length -- and the resulting leverage acting on the quarter-inch socket contact springs -- would be the major concern against using a barrel adaptor. But a potential secondary issue might be the relatively broad diameter which might well prevent access to adjacent sockets for other audio outputs/foot switches/pedals etc.

H

[ef37a]

With regard to "weighty things" straining connectors? If you have a particularly tasty and expensive piece of kit it is worth considering making up some "sacrificial" adaptors?
(not that expensive but things like cable tester conns' get a hard life as well)

These are short, XLR-XLR say leads that take the day to day pluggerating stress off the sockets in the £1000+ interface. Same goes for TRS but you would need the Neutrik locking free socket as every other brand I have found to be unreliable (NEVER use them for speaker lines!) I also favour breakout boxes screwed to walls or benches.

At the network factory there was a £40,000 analyser and the front connectors were £1000 a pop (and who knows the labour/re calibration cost?) so THEY were rarely undone!

Dave.

[Bucky Lastard]

I have personally tested these leads and or adaptors as a little experiment: Result = junk input and even more junk output: Just my two cents:

[n o i s e f l e ur]

I have personally tested these leads and or adaptors as a little experiment: Result = junk input and even more junk output: Just my two cents:

Oh? That's quite interesting, could you tell us how you put your experiment together so we might learn from your experience?