DI vs buffer for direct to mixer...

[ACS]

So, I've got a nice little home recording setup, where I run my guitar and bass into a SHO, then direct into my mixer. Mixer then goes to USB interface at line level (RCa fwiw) for pc input.

So this works pretty well - certainly /much/ better than just running the guitar direct into the desk. But I'm wondering if i can do better?

Would an active DI make an appreciable difference to (particularly) noise levels? I ask as this setup does seem noise prone, even with humbuckers.  If a DI is a better option, can anyone point me towards a good DIY (active and phantom powered) solution? Google was not my friend when I tried...

Thanks all

[Hides-His-Eyes]

DI might well give better noise behaviour, although NOTHING will prevent your monitor from making a noise in your pickups if you're sat close to the computer. Check it's not that first.

Otherwise, yeah, I think step one is a passive DI (but you might lose some treble due to the impedance; if so you'd have to see if SHO=>DI caused appreciable extra noise or not)

[familyortiz]

A balanced signal from an active DI box will do a better job at reducing any noise that is common to all cable conductors, because of the way it works, assuming that your board has balanced inputs. For your requirement of both DI and phantom power, the Audio Buddy is a good, inexpensive and simple 2 channel device but I'm sure there are others.

[ACS]

Thanks guys, sounds like the DI is definitely worth a crack then.

Anyone know of a good schematic for an active DI?  I've had a reasonable search on Google and can't come up with anything useful...

[jkokura]

I would use a Passive DI over the active. And I'd also recommend you buy one rather than build one.

My top recommendation for DI's is the stuff from Radial. I have both a ProDI and a JDI (passive DI boxes) and they are stellar. Better than anything I've used in the last 15 years. I've also used a J48 DI from Radial, which runs on phantom power and is active, and it sounds just as good but requires phantom power. I don't like using phantom power because I play in a variety of places that may or may not have phantom power on their board.

If you are considering building a DI, check out the Jensen Transformer. It's the same that's used in the Radial JDI and J48. It's 85 bucks I think, available at Smallbear. Jensen has application documents at their website, and you can google them if you want. They basically look exactly like the ProDI and JDI, but in schematic form.

Jacob

[Gus]

Here is something I drew up for a question at another forum.  A DI that uses a 9VDC supply and one transistor.  It is a simple design the outputs are inverted to each other and is limited compared to other better DI designs

http://www.aronnelson.com/gallery/main.php/v/gus/NPNDI.GIF.html

For some reason the img is not working for me today that is why I have the link posted

active design you can search for "Bo Hansen di"

[Earthscum]

Here is something I drew up for a question at another forum.  A DI that uses a 9VDC supply and one transistor.  It is a simple design the outputs are inverted to each other

http://www.aronnelson.com/gallery/main.php/v/gus/NPNDI.GIF.html

That's pretty slick. 5089 should work in place of MPSA18, right? I'm gonna have to try this to run between my pre-amp and board. Right now I use a Behringer DI20, and it kinda sucks, the passive DI's suck the bass, and I'm not completely happy with the IC based DI's. Although I have yet to try one of the quiet OP's, I see this as being a bit more tune-able... like an old carb compared to 80's fuel injection. (new FI rocks... nothing bad to say about it, now that it's tunable). 

That looks more like what I've been wanting to use for a small mixer board I've been mulling around in my head. I want to make a 2 channel mixer module that's more akin to the old Japanese mixers (no IC's), but the impedance converters I was coming across were all IC based, or "I found this schem in the attic". Think anything would need changed to run off a 12V supply?

[a soBer Newt]

stumbled across this the other day looks like it may be right for the job http://fivefish.net/diy/balanced/default.htm

[ACS]

Topp stuff, thanks guys. Might try breadboarding both of those and see how they go.

Jacob, I did definitely look at the transformer based ones first up and decided against them for a couple of reasons. Cost was definitely one of those reasons, but the other was a lot of references to coloring of the sound. Would be interested to hear your opinion on this...

[Mike Burgundy]

Also nice:
http://sound.westhost.com/project35.htm
Google something like "balanced line driver"
I think RG has some stuff up on GEO too.
I used to prefer passive DI's, but when I got into 5-string bass I quickly found that really low freqeuncies need really big, heavy and expensive iron. In most cases active now has my preference.
hih.
That 1-transistor driver is interesting, Gus!

[edvard]

I was gonna suggest something like Gus's one-transistor thingy, but he beat me to it... 

For better input impedance (probably not necessary if it's coming AFTER and effect), you can use a JFET in the same manner, but with 2-5k resistors at source and drain.

One more transistor, but from what I gather, the classic "complementary" AKA "differential pair" AKA "long-tail" circuit has great common-mode rejection; which is what I think you're looking for in your DI quest.
Here's an example using FETs on the input of a simple solid-state guitar amp:
http://www.hawestv.com/amp_projects/amp_solid_tube/compl_output1.htm
BJT version here:
http://www.ecircuitcenter.com/Circuits/BJT_Diffamp1/BJT_Diffamp1.htm

There's also an interesting phantom-powered gadget described at the bottom here:
http://www.ethanwiner.com/gadgets.html

Ooh... Looky here:
http://www.epanorama.net/links/audiocircuits.html#dibox