Balanced line receiver/transmitter, are these circuits going to do the job?

[Skruffyhound]

http://sound.westhost.com/project51.htm

I'm assuming these two modules are intended to be used at each their end of a long XLR cable. What I want to know is can I use them successfully in another way i.e. ;


            PA⬅Mixer⟽⬅⟽XLR⬅([Balanced line Transmitter][other switching and effects stuff][Balanced line receiver])⬅XLR⬅Mic

In other words, can I use them in a kind of stomp box with effects and other unbalanced stuff going on in the middle.
Another question would be; is there something simpler? This will require making a bipolar power supply, which I can do, but would rather not. (transformer schemes are out due to price restrictions).
I will run them at +/- 12v because I have chips that can just about handle that (IIRC) and because I want 12v to power a Subcaster. Apart from less headroom, that should be fine right?
Am I heading in the right direction or barking up the wrong tree?
Thanks
          Aston

[Mike Burgundy]

Okay, took me a few takes, I expected the signal flow to be L>R ;P
Mic into unbalanced effects into balanced mixer again, okay. Yes, that will work, but there are considerations.
Stompboxes are designed for a different signal level from microphones, these linedrivers were designed for an audio setup which operates at line level, which is another level yet again. Mics provide less output than PU's, line level is highest. Mic typically at a couple of mV to several tens of mV, line up to 1V, guitar in between.
You'll want a mic preamp with adjustable gain in front, have that put out unbalanced into effects, and after the effects you could go balanced again. However, if you keep your interconnects short and tidy, you might not need the line driver/DI stage at all. The main function of balanced lines is to prevent interference when running long lines. Using unbalanced signals should be no problem with short connections, so if you're right next to the mixer it should be ok.
The difference between +/-15V and +/- 12V is trivial in this case.

[Skruffyhound]

I understand your confusion Mike, but since I got into stomps signal goes from right to left, like the boxes themselves.

I have another thread running here http://www.diystompboxes.com/smfforum/index.php?topic=100442.msg884050#msg884050, but thought I might get more success asking a simple question in the title for this issue.

The box will be a Subcaster followed by effects loop all of which will be bypassable plus an on off switch for the mic. The mic is for my friends blues harp, so the sound is probably fine if it's fairly low tech.

Last I saw him he had about 35 feet of cable, so he could get out in the crowd.

I'll likely let the signal from the receiver run straight into the Subcaster so I'll have a volume pot to attenuate the result before it goes through the effects loop.

I'm still fishing for something simpler so I don't have to build the bipolar power supply, but if it is necessary I really should find out how to make the Subcaster run bipolar, the extra clean headroom would be useful. 

Thanks Mike.
Other suggestions still welcome.

[ashcat_lt]

You can usually "psuedo-balance" the run to the mixer.  Build the pedal with normal TS output.  Make a shortish adapter cable with TS on one end and XLR on the other.  Use two-conductor plus shield cable.  Connect the shield on the XLR where it would normally go (always forget which pin that is) and leave it unconnected on the TS side.  Connect T and S via the inside conductors to the two other XLR pins.  Gives most of the benefits of balanced and quite a bit simpler than a balanced output stage.

[Skruffyhound]

That is a very creative solution ashcat.

As I've been reading around I've found constant mention of leaving one end of the shield un-connected (same as shielding in our high gain pedals) but how does that work with standard XLR cables, are they all shield un-connected in one end and if so what is the convention? Perhaps I don't need to worry about that now (for this pedal). Thanks

Any further suggestions still welcome, I won't build this until tomorrow.

[ashcat_lt]

Usually the shield is connected on both ends in balanced cable.  Sometimes lifting the shield on the source end can break ground loops, but I consider it a last resort.  That's opposed to lifting the AC safety ground, which is NEVER an option.

In this case, though, there's just no place to connect the shield on the TS side.

[Skruffyhound]

Thanks for that. Makes sense.
Yeah I don't reckon I'll lift the AC ground anywhere since he effectively has one end of the cable in his mouth

[PRR]

> will require making a bipolar power supply

Why??

Do the usual changes from +/- power to Vref power. Input and output caps, DC bias to half the supply.

> transformer schemes are out due to price restrictions

The pocket radio trannies are under $2.

[PRR]

> Balanced line receiver])?XLR?Mic

You work right-left like early Mesa-Boogie?

That "Balanced line receiver" is NOT a terrific Mike Amp. The Noise (hiss) Resistance is like 30K, somewhat(!) larger than the mike's 200 ohm inpedance. Hiss is about 12 times higher than the mike's own hiss. This type "line receiver" is meant to go *after* at least 1:12 of mike preamp gain.

You may get away with it in the frenzy of live performance. OTOH I used a similar circuit with only 2K of noise resistance and found the idle-hiss annoying any time the kids were not playing.

Rod has proper mike-amps elsewhere on his site.

[Skruffyhound]

Great info as usual Paul,Thanks.

Do the usual changes from +/- power to Vref power. Input and output caps, DC bias to half the supply.

That hadn't occurred to me.

The pocket radio trannies are under $2.

Everywhere on the interwebs people are talking big bucks for 1:1 trannies (600ohm isn't it?) also on Rod's site. Although why that should be the case I don't know.

You work right-left like early Mesa-Boogie?

It was counter-intuitive to start with but I now think of my signal chain from right to left because that's how it is if you connect a bunch of pedals together on the floor              (output-input)⬅(output-input)⬅(output-input)
Circuits still run from left to right because they go in the box with solder side up to the back of the pots and follow the input/output convention.

That "Balanced line receiver" is NOT a terrific Mike Amp

Thanks, that has just saved me some effort.

Well by a process of attrition this thing is starting to shape up  

[greaser_au]

You work right-left like early Mesa-Boogie?

It was counter-intuitive to start with but I now think of my signal chain from right to left because that's how it is if you connect a bunch of pedals together on the floor              (output-input)⬅(output-input)⬅(output-input)
Circuits still run from left to right because they go in the box with solder side up to the back of the pots and follow the input/output convention.

Hey now,  THERE'S AN IDEA!   The boutique/customshop guys could make a killing on the lefty guitar market by making effects that go left (input) to  right (output)...! Contact me for my licensing arrangements 

david

[Skruffyhound]

Brilliant, no more treading on your cable while stomping for the lefty's 

[Skruffyhound]

Paul (PRR),
                would I be right in assuming that the balanced line transmitter here is good enough to send from my box to the mixer. I've built one Ron's mic pre's for the input to the box.

                Thanks.