opamp ( presumed) vs transistor in real world AB test.

[joegagan]

i know this subject has been discussed a lot here and elsewhere, just thought i would share my 2 person firsthand eartest of two systems.

my brother has a high end equipped recording studio, his employer required a low noise floor compatible with sony records standards, a leftover criteria from their ten record deal.

he was using a radial engineering direct box ( sorry, cannot recall which model), we AB tested it against one of my very simple bipolar trans buffers in an AB box. the desired use was sending a guitar signal through the patch bay to a tube guitar amp in the recording room, in order for the guitarist to track while sitting ni the control room instead of the main room.

we used the same guitar and amp (tele and 65 deluxe), same cords, same riff played as similarly as humanly possib le. each test was tracked in protools to allow instant AB testing and repeated listenings without the distraction of playing the guitar in my case.

i cannot knock the radial device. impressively built, looks and feels like you could drive a mack truck over it and it would still work. really nice.
i assume it has an opamp inside it, it was a swiss army knife direct box, but one of the listed/recommended uses was exactly  as we were using it. we followed the directions in the manual for setup.

my AB box had a simple 2n3904 emitter buffer, and presumably less wiring and components overall.

my box had more punch, clarity, and high end, as heard in our careful listening. jon and i both agreed. he bought it from me, by the way.

not making any claims, just a test some of you might be interested in.

[DougH]

Stupid question: is the radial DI box passive or active? Most typical DI boxes are passive and just use a transformer.

[joegagan]

it used a battery. it was more deluxe than a lower line DI. my bro still has it. i will get the scoop and report back.

[DougH]

Get the model # so we can get an idea what's in it.

[JDoyle]

Well...that "punch, clarity, and high end" could simply be a result of the added distortion from a simple BJT buffer rather than anything else.

That doesn't mean that it sounds any better, or worse, than the DI - just that it might not reproduce the signal as accurately.

- Jay Doyle

[DougH]

My reason for getting to the bottom of what's exactly in the DI is that a typical passive DI is the wrong tool for driving a long cable in the first place. A passive transformer-based DI is for matching impedance only- guitar to console input or console output to guitar amp for "reamping" (ostensibly) for example. If you are just driving a long cable through a patch bay into another room and through nothing active (presumably), you need a buffer that drives current- not a passive DI box. His DI box is active but without really knowing the circuitry, who knows? It may just be a matter of using the wrong tool for the job.

As buffers go- you can drive a lot more current with an op amp than you will ever hope to with a BJT (or FET) transistor. And you can do it with sufficient Zin to not load the guitar pup, whereas you really can't with a simple single BJT emitter follower. Higher Zin means more clarity. More current out means more clarity. Op amps can drive loads down in the low 100's of ohms easily. I have compared JFET or BJT buffers to op amp buffers on the breadboard and op amps had much more clarity in general, sometimes too much, depending on what I was doing.

[joegagan]

Man, did I screw this up. I talked to my bro today, corroborated the whole story except. For one major detail. The device was a countryman active DI. I will be at the studio Sunday so i will get the model number before further embarrassing myself any further. Furtheringly yours, jg.

Btw, he does own a radial REAMP, but that wasn't what we were comparing that day.