Tapco/Mackie DB-1a

[km6xz]

Hi Guys, I have a little Tapco DI box that seems simple enough but there is a problem that does not make sense so I am asking if anyone has a schematic for this unit.
Thanks in advance

[Jazz P Bass]

I contacted Mackie & was informed that there are not any schematics available.
This is all there is: http://www.mackie.com/products/disco...o/DIBOX_OM.pdf

[Leo_Gnardo]

What's the symptom Stan? Back in the days of TAPCO, DI boxes were generally pretty simple. Cheap little transformer, ground lift switch, maybe a pad switch with a resistor or two, input jacks & XLR out. I have a bunch of old Kelsey DI's like this, and a couple I made myself.

If it's active, all bets are off. So many designs but they still "should" boil down to simple, you would think. I got some Countryman 85 DI's and they're good - tough as hell - but even one of them quit working on phantom but will work on battery. The circuit is potted so no fixing it.

[J M Fahey]

Just curious, what´s it which does not make sense?

[km6xz]

It is a basket case where someone modified it when trying to repair it after it got zapped and burned by a hot ground and I wanted to get it back to stock for a local school. Having the schematic just would have made my task a but easier.

It is a DI in name only, since it has no isolation, just 8 opamp stages.
I made a lot of DIs in the past, plus had many from a local company, Countryman, back when they got started. I still have a few in storage back in California that must be 30 years old and still working like new despite rough handling with daily use for years.

[Leo_Gnardo]

Eight (!?!) op amp stages . . . in a DI? That's insane - oh well leave it to Tapco in the caffeine-soaked Seattle zone, they must have had their espresso machine going all day & night to design that.

Why not just whack together a couple good ol' cheepo transformer DI's for the school. Just not worth the brain power even if you had the Tapco schemo. No batteries, no phantom, no scissors nor glue. Well maybe some glue. To keep the transformer stuck where it's s'posed to be. Just keep away from AC fields.

And yes, Countryman Type 85, beside my own, done lots of Clair Bros. tours equipped with dozens - never a failure. Just make sure there's no battery inside when running off phantom, that'll make 'em sound crappy. Thanks Tom Foehlinger & Cathy Sander @ Clair for teaching me that back in 1987! You must have had a pile of them at Studio Stan back in the day.

[km6xz]

I did not want to deal with figuring out the original circuit and the missing parts and traces so I gutted it and put a 2 IC Vector board circuit in it. I am using a LF353 FET input opamp for the guitar input and the last SSM2142 balanced line driver I had as the output, using phantom power only. I am sure it worked a lot better than the Mackie circuit.