Adding DI output to stompbox

[bal704]

I'm getting ready to build one of the amp simulations from ROG, namely the Supreaux:

http://runoffgroove.com/supreaux.html

I'd like to add an XLR output to plug into our mixer, similar to what you see on most bass amps and a few guitar amps.  I'm assuming I'll need an audio transformer.  Would the Mouser TM018 work, and is it as simple as plugging the instrument signal into one side, and taking the transformed signal off the other side?

http://www.mouser.com/search/ProductDetail.aspx?R=42TM018virtualkey21980000

I don't see much discussion about DI outputs on the forum.  Is that becasue they're trivial to build, or because they're a real nut-buster?

[Gilles C]

You could use the Red Box as the inspiration to build one without a transformer.

http://www.diystompboxes.com/smfforum/index.php?topic=44939.msg328136#msg328136

Or you could check Jensen site for their schematics

I built one but still have to connect the circuit to an XLR connector to try it as a balanced output. But it works well as an isolated unbalanced output.

http://www.diystompboxes.com/smfforum/index.php?topic=45817.msg336434#msg336434

http://www.diystompboxes.com/smfforum/index.php?topic=45996.msg337246#msg337246

I used a 42TM018 as the isolation transformer.

Gilles

[bal704]

Thanks.  I thought that using the TM108 would be a quick, dirty way to do the job.  Put the input signal in, get the transformed signal out.  Looking at the links you provided, it's apparently not that simple.  Thanks for the info.

[Gilles C]

Well,  may have misleaded you a bit. I just remembered that you wanted to add a balanced output to an amp simulator from ROG. So forget about the extras from the schems I gave you. All you need is indeed a transformer, and an inverter for the (-) output to make the output balanced i.e. (+) and (-) output of the same signal.

That was they did for the Red Pro.

Gilles

[BrianJ]

You might also try the Burr brown DRV134 chip.  One input yeilds complementary balanced outs. I think it can run on a single 9v supply.  It will certainly be higher sonic quality than your average transformer, for less $ than many average transformers.

[Gilles C]

Still thinking about it, I tried to find if a transformer could just be used, and my thinking is that the output of the circuit must be able to drive it, because a transformer is low impedance, espacially when the other balanced side is connected to a low impedance input.

This application note gives some info about how to do it.

http://www.jensen-transformers.com/an/an003.pdf#search=%22balanced%20output%20%22

I like the "Typical Balanced Output" schematic, which I would use with a 5532 opamp. I should try that some day with the 42TM018 for an unbalanced to a balanced output adapter.

Still more info:

http://www.herby.kielce.pl/~piter/konstr/cabsims/schem/Engl_LineOut.GIF

And check Fig.4

http://sound.westhost.com/project87.htm



Gilles

[RaceDriver205]

Use the Marshall Speaker Sim - works awesome as a DI

[Gilles C]

But it doesn't have a balanced output.

This is another circuit that could be used, at least as the inspiration for a project.

http://www.jensen-transformers.com/as/as022.pdf

Indeed, there are many distortions and the likes on the forum, but no DI box to be used as a separate project. It's giving me ideas...

Gilles

[Morocotopo]

How about this?

It´s from a japanese circuits book at experimentalists anonymous. Looks simple, interesting...
Bal, remember that to get an authentic tone, you need a speaker simulator besides a pedal (for example the condor cab sim at Runoffgroove).

Morocotopo

[bal704]

Thanks for the schematic.  I notice the xfmr they call out is a 50k:600.  I don't see an exact match for that XFMR at mouser.  Which of the values is more important, the 50K or 600?.  I see a mouser TM109 at 10K:600, and I see a mouser TM117 at 50k:1k.  Would either of these work in it's place?

[Pushtone]

DI output is like a mic - low impedance.
The transformers output should be 200-600 ohms.

The transformer is doing three things,
1. balancening the signal
2. converting the impedance to low-Z
3. converting the level to mic level.

The transformer does all this.
the opamp is only nessasary if you need gain.
And it helps with loading when spliting the signal for the 1/4" parrallel

Passive DIs work with and buffer amp or power for that matter.